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Chemistry
FOR OUR TIMES
Courtesy o/ Hercules Powder Co.
Chemistry
FOR OUR TIMES
ELBERT COOK WEAVER, M.A.
Instructor, Phillips Academy, Andover, Massachusetts
Formerly Chairman of Science Department
Bulkeley High School, Hartford, Connecticut
AND
LAURENCE STANDLEY FOSTER, Ph.D.
Formerly Assistant Professor of Chemistry, Brown University
Chief, Powder Metallurgy Branch, Waterioivn
Arsenal Laboratory, Waterioivn, Massachusetts
McGRAW-HILL BOOK COMPANY, INC.
New York and London
CHEMISTRY FOR OUR TIMES
COPYRIGHT, 1947, BY THK
BOOK COMPANY, INC.
PRINTED IN THE UNITED STATES OF AMERICA.
All riyhts reserved. This book, or
parts f hereof \ may not be reproduced
in any form without permission of
the publishers.
ii
The quality of the materials used in the manufacture
of this book is governed by continued postwar shortages*
THE MAPLE PRESS COMPANY, YORK, PA.
PREFACE
AN ATOMIC age calls for a new approach to chemistry. Hence, we are
presenting an entirely new elementary .chemistry textbook. Chemistry
for Our Times describes chemistry of tod&y #s it affects the citizen.
In it we have interpreted advances in theoretical/'physical, and organic
chemistry, as far as they affect the elementary level. By keeping in close
agreement with experimental facts, we have eliminated many errors
that cling to chemistry textbooks by tradition. We have also tried
to strike a balance between chemistry principles and applications of
chemistry.
Understanding the environment, the method of science, and the
applications of chemistry to the life activities of the average citizen is an
important aim in this book. The workaday world of chemistry is never
far away, however, and hundreds of industrial plants and laboratories
were visited in order to incorporate the practical viewpoint.
This book centers about the individual pupil and his activities. It
starts with his immediate environment — air and breathing, water and
solutions — and then swings through the gamut of chemical actions,
progressing gradually from familiar to less familiar experiences. After
the principles have been established, the book concludes with a unit
on the applications of those principles to human problems of food, health,
and peace.
The basis of 'chemical progress has always been experimental evidence.
This book is organized around this fundamental principle rather than
theory, such as atomic structure, periodic classification, replacement
activity grouping, or some other basis. All these deductions are included
in their appropriate places, however.
References to books, periodical literature, visual aids, and other
materials used ordinarily only by the teacher are contained in a Teachers'
Manual, available from the publishers.
Weight-weight and weight-volume problems are postponed until
pupils have sufficient practice in using balanced equations and until
the need for solving problems using equations as a tool becomes evident.
At first there is a thorough grounding in percentage, density, molecular
volume, and other simple mathematical operations.
The questions that accompany each chapter are chiefly of the thought-
stimulating type rather than tests of rote memory. The number of
numerical problems is doubled by a simple device, making possible a
wider range of assignments.
vii
viii PREFACE
This book contains enough chemistry to be serviceable as a first
book, in case a student decides on chemistry as a profession, yet it is not
designed specifically for the training of future chemists. Thus, it is suited
to either college preparatory or general chemistry classes.
In keeping with the practical approach, titles such ^s safety, beauty,
and cleanliness will be found among the chapters. Also, more emphasis
is placed upon the metals themselves than upon compounds of the metals
and properties of the metallic ions. We agree with the findings of com-
mittees that have studied the matter and offer a broad, life-interest
content, at the same time meeting the requirements of recognized
syllabuses.
Within the last generation a new industry has sprung up in the
United States. This is chemistry as big business. Because of its research
program, the chemical industry is bound to develop rapidly. A shift
in emphasis in popular thinking is needed in order to appreciate this
fact. A new set of jobs is open; a new frontier appears for original thinkers.
Moreover, products of chemical laboratories require educated consumers.
A fact about chemistry seldom appreciated is its international aspect.
Ideas that have aided man's progress have come from all sections of
the world. Truth is not the special heritage of the United States, Germany,
China, England, or any other country. For example, although atomic
(nucleonic) bombs were developed for military purposes in the United
States, all the fundamental scientific discoveries on which this develop-
ment was based were made in other countries. Nature yields her secrets
to all persons who seek them in the proper way.
Further, the location on the earth of natural materials and ores
that are useful to man is without the slightest regard to accessibility
or to political boundaries. The general need for raw materials constitutes
a fundamental reason for preserving international peace and for the
free exchange of goods on a global basis. These thoughts are woven
into the fabric of the text.
The development of this book started with suggestions and conferences
with Dr. John A. Timm, now head of sciences at Simmons College,
Boston, Massachusetts. To him the authors are greatly indebted. Dr.
Hanor A. Webb of George Peabody College for Teachers, Nashville,
Tennessee and Dr. Pauline Beery Mack, Director of the Ellen H. Richards
Institute, Pennsylvania State College, State College, Pennsylvania,
have also contributed valuable suggestions.
The authors wish to express their appreciation to the many industrial
concerns that have cooperated in producing this book. Pictures were
furnished graciously by companies in every section of the United States,
and these have added greatly to the interest and understanding of the
text. Many industrial people were very helpful on the manuscript itself.
PREFACE ix
Notable additions to the sections on iron and steel, aluminum, mag-
nesium, petroleum, paper, and safety were made by technical men to
whom the satisfaction of presenting an accurate picture to students
and other readers is ample reward.
Thanks are due also to our colleagues on high-school and college
faculties who have given many helpful suggestions.
Finally, the authors are indebted to their many students who, by
their helpful questions, have guided the development of this book to
meet their requirements and needs.
ELBERT COOK WEAVER
LAURENCE STANDLEY FOBTLK
CONTENTS
INTRODUCTION
i. Chemistry as a Science 1
n. Substances Called Matter 11
UNIT ONE: OUR ESSENTIAL ENVIRONMENT
in. The Air 35
iv. Burning, Breathing, Rusting 53
v. Hydrogen, the Lightest Gas 81
vi. Water 101
vii. The Nature of Gases, Liquids, Solids 117
UNIT TWO: CHEMISTRY'S BUSINESS OFFICE
vin. The Inventory — Atoms and Molecules . 139
ix. Shorthand and Transcription — Writing and Naming Formulas. . 153
x. Balanced Accounts — Equations 171
xi. The Stock Room — Particles and Structure of the Atom 179
UNIT THREE: DISPERSIONS OF MATTER
xn. Solutions 201
xin. Acid and Alkaline Solutions: Neutralization 215
xiv. Electricity and Chemistry 239
xv. Colloids 259
UNIT FOUR: CHEMISTRY OF THE EARTH'S CRUST
xvi. The Earth and Its Ores 273
xvn. The Earth and Its Soil 285
xvin. Chemistry of the Sea— the Halogen Salts 297
xix. Crystals of Commerce 313
xx. The Great Classification 321
UNIT FIVE: CHEMICAL INDUSTRIES
xxi. The Acid Heavy Chemicals 343
xxii. The Basic Heavy Chemicals 373
xxin. The Silicate Industries 395
xxiv. Chemical Calculations 417
UNIT SIX: THE METALS
xxv. Iron and Steel 429
xxvi. The Light Metals 449
xxvu. The Denser Metals 467
xxvin. Corrosion — Harmful or Helpful 491
xi
xii
CONTENTS
UNIT SEVEN: THE CHEMISTRY OF CARBON COMPOUNDS
xxix. The Nature of Carbon Compounds 509
xxx. Our Fuels 525
xxxi. Plant and Animal Chemistry 553
xxxii. Cellulose and Plastics 565
xxxiii. Coal-tar Chemistry 581
UNIT EIGHT: CHEMISTRY AND HUMAN PROBLEMS
xxxiv. Food and Clothing 591
xxxv. Chemistry for Cleanliness, Health, and Beauty 603
xxxvi. Chemistry for Safety, Peace, and War 617
UNIT NINE: ADDITIONAL TOPICS
xxxvu. Radioactivity 639
xxxvin. Chemistry and Radiant Energy 653
xxxix. The Noble Metals and Some Less Familiar Elements 663
XL. What Lies Ahead 675
Review Equations and Questions 679
Glossary 685
Appendix 697
Index 725
INTRODUCTION CHAPTER I
CHEMISTRY AS A SCIENCE
The Chemists are a strange class of mortals im-
pelled by an almost insane impulse to seek their
pleasure among smoke and vapour, soot and flame,
poisons and poverty; yet among all these evils I
seem to live so sweetly that may I die if I would
change places with the Persian King.
— JOHANN JOACHIM BECKER, 1669.
Science in Action. A quiet woman, simply dressed, is ushered into
the White House at Washington. She is greeted heartily by the President
and First Lady of the United States, entertained at dinner, and presented
with an order for fifty thousand dollars with which to buy radium. Why
should this honor come to a chemist? Why is it that neither France nor
the United States could do enough to honor Marie Curie, who had spent
much of her youth washing bottles in a laboratory for a bare existence
while studying in a Paris university?
A knock is heard at an office door in Cambridge, Massachusetts. A
student, notebook in hand, enters and approaches Prof. Theodore
Richards of Harvard University. Together they go over notes and figures
that represent the results of experiments. A slight error is discovered.
The professor is distressed; the student more so. Why should these
people be concerned about a small fraction of 1 per cent?
The scene changes to the laboratory of a large brass factory. Aproned
men and women are busily engaged at different tasks. One is reading
electrical meters and making notes. Another is comparing the colors of
liquids in test tubes. A third is busy with a set of figures, part of a report.
The chemist completes the report and carries it to the factory manager.
They confer briefly. Both seem in agreement. The manager now gives
orders that the copper recently received is suitable material for his
company to use in making brass. Why is it that the manager can rely
on the work of the chemist?
The well-known story of Marie Curie shows chemistry in service. By
using radium, which she and Pierre Curie discovered, doctors have done
much to check dreaded diseases. Although the chief purpose of the Curies'
work was to find out, to investigate, or to discover, the knowledge they
gained and gave to the world has had direct practical benefit.
1
CHEMISTRY FOR OUR TIMES
Prof. Richards' work helped all chemists. His was another search into
the unknown, pushing back ignorance. His determination of the atomic
weights was just a little more accurate than that of any other chemist
at the time. Such work as his was a big step forward. Each scientist builds
on the work of others, an endless chain of progress.
science service
Madame Marie Sklodowska Curie (1867-1934), the only person to receive twice
the Nobel prize in chemistry, was distinguished for her discovery of radium, for her
unusual skill and perseverence, and for being the mother of two distinguished daugh-
ters, one of whom has herself shared with her husband in a Nobel prize.
The chemist in industry has the task of finding out new things — such
things as making threads for hosiery from coal, air, and water or making
suds without soap. Another part of his job is the control of processes,
checking products, and stopping waste. A paint company relies on its
chemists to control the color and quality of its paints. Chemical control
puts better steels in automobiles and railroad cars. Chemical control
produces better gasoline to run cars and airplanes.
Benefits from Science Research. Beautiful colors for clothing,
paper, and leather are now obtained from evil-smelling coal tar as a result
CHEMISTRY AS A SCIENCE
of science research. Music and entertainment by radio in homes have
been made possible by scientific research on electromagnetic waves n,nd
electrons. Lustrous fabrics of rayon have been the outcome of research
on the nature of woody fibers. The rapid rise of comfortable living during
the past 100 years has been the result of rapid strides in science; many
advantages that we now enjoy are the fruit of scientific investigation.
A dentist injects a little novocain into the gum of a patient. A tooth
now can be pulled without much pain. After a few whiffs of gas a child
Courtesy of Journal of Chemical Education
Theodore William Richards (1868-1929) was the first American to receive the
Nobel prize in chemistry. He was the top-ranking authority in the world on atomic,
weights of elements. In recognition of his outstanding achievements, 13 colleges
awarded degrees to him.
becomes unconscious so that tonsils can be removed or other troubles
corrected. The doctor places a drop of diluted silver nitrate solution in
the eyes of a newborn child, and thereby infection and loss of sight are
prevented. A visiting nurse changes the food of a child who has weak
legs. Soon the child gains strength, and the weak legs are straightened
as vitamin D goes to work. Novocain, nitrous oxide gas, silver nitrate
solution, and vitamin D are all being studied in chemical laboratories.
Through chemical research suitable metals for radio tubes have been
found; metals for stronger, lighter trains and trucks have been developed.
Even the sea has become a commercial source of the valuable light
metal, magnesium.
CHEMISTRY FOR OUR TIMES
The Aim of the Scientist. The person who is scientifically trained
seeks, first of all, to learn the truth about the deep secrets of nature.
He seeks to find out the sort of material world in which people live. He
discovers facts and interprets them. No prejudice or personal feeling is
allowed to enter the work of a true scientist. To the engineer is left the
invention of machines that make use of theories and facts discovered
by the scientist, and to the artist is left the expression of the spirit of the
age in terms of music, painting, or poetry.
Courtesy of Commercial Solvents Corporation and Martin n Photo Shop
FIG. 1-1. — These women are not from Mars but are workers in a penicillin factory.
Much of the work in preparing this modern medicine is done under ultraviolet light in
perfectly sterile air.
9
A story is told about a scientist and an unpracticed observer strolling
through the fields. " There," remarked the observer, "goes a white sheep."
"Yes," agreed the scientist, "there goes a sheep that is white on this
side."
The Scientific Method. Common to all branches of science is the
method of study that is used. This scientific method of solving problems
need not be limited to science alone. Indeed, many problems of business,
law, and government can be solved by methods that are as scientific as
those which led Pierre and Marie Curie to the discovery of radium.
Many persons are working on the problem of the cause and the cure
of the disease cancer. Some workers seek a solution to this baffling prob-
lem through biology; others through chemistry. The final solution will
be pieced together from the results of many different workers.
CHEMISTRY AS A SCIENCE
While the application of the scientific method will depend upon the
situation at hand, certain general and fundamental steps are followed.
The first step consists in collecting the facts, which may be done in dif-
ferent ways. If the methods of measurement of two scientists differ and
yet the results are identical, we are more certain of the accuracy of the
facts.
In the development of science, the early investigators discovered
many general trends. Later and more careful work in the same field,
Courtesy of E. I. du Pont de Nemours & Company, Inc.
FIG. 1-2. — One of the most significant steps in the protection of passengers against
broken glass has been the development of a satisfactory and efficient safety glass for
automobiles. Chemists have found an improved material for the interlayer between the
sandwich safety glass. This is a modern plastic, "Butacite," which is a type of resin.
The picture above shows the continuous Butacite sheeting passing through an air-cool-
ing process.
sometimes with improved tools, has revealed facts obscured or over-
looked at first. A notable example is found in the story of the discovery
of argon. Lord Rayleigh, an English investigator, was checking the
density of nitrogen with great accuracy. He found that the density of
nitrogen prepared from air differed from the density of nitrogen pre-
pared by heating ammonium nitrite by one-half of 1 per cent (0.5 per
cent). The accuracy of his measurements permitted no difference greater
than two-hundredths of 1 per cent (0.02 per cent). From these facts he
later proved that the gas from air was not entirely nitrogen and that
argon as well as some other gases were present in it.
In the city post office a postman has dumped on a table a pile of
CHEMISTRY FOR OUR TIMES
letters for the people who live in his territory. This postman's first job
is to sort these letters. In this way his load of mail is organized system-
atically, and he saves much time in delivering the letters. Thus, by sort-
ing and organizing the mail, the postman travels a route rather than
going on a ramble. Likewise, a scientist sorts and organizes facts. This is
the second step in the scientific method, organizing the facts. When the
facts are studied, many will be found similar. The similar facts are
classified and organized.
Robert Boyle (1627-1691) studied the effect of changing pressure on
the volume of a given amount of gas. He found that when the tempera-
ture is unchanged (constant) and the pressure is doubled, the volume of
a gas is halved; when the temperature is constant and the pressure is
trebled, the volume becomes one-third of the original volume; and so on.
This relationship he found to be true for all gases, pure substances and
mixtures alike, provided that they were in gaseous form. Organizing the
facts enabled Boyle to glean a general truth: The volume of a certain
amount of dry gas is inversely proportional to the pressure on it, provided
that the temperature is unchanged (Boyle's law).
After the facts had been collected and organized, Boyle came to the
third step in the scientific method, stating the law. A law depends upon
the facts collected and organized. A scientific law is a sentence describing
the general truth that has become evident by a study of the organized
facts. This statement describes the facts as known at the time, but it
should not be regarded in the same sense as a civil law. If our knowledge
of the facts becomes more complete, it is sometimes necessary to change
the statement of the law.
Scientists explain a law by a theory. This is the fourth step in the
scientific method. Of course, the theory is based on known facts, but all
the details of situations become clearer as the theory points out the way.
Later, it will be shown that Boyle's law was important in the growth of
a theory. The theory of the nature of all gases is called the molecular
theory of gases. This theory explains Boyle's law in addition to other
laws dealing with gases. "A collection of facts is no more science than a
pile of stones is a house." This saying illustrates the need of organizing
facts and developing a theory to fit them.
Now we come to the fifth step* Suppose we study the method of
numbering rooms in a certain high school. The rooms numbered 100
to 199 are on the first floor, those numbered 200 to 299j on the second
floor, and on both floors 101 and 201 are near the main entrance. We may
now make a good estimate of the location of a room numbered 321. We
have studied the organization of the room numbering, have reached
conclusions, and have used the conclusions for predicting new facts. Just
so in science, keen minds study the theory, and new outcomes are sug-
CHEMISTRY AS A SCIENCE
gested. Then comes the critical test of the theory. Are the new facts
found to be as predicted, or are different facts discovered? In the first
case, the theory is strengthened. If not, the theory is shown to need
repair, and repairing it will get. This ability to predict is one of the
remarkable things about science. It gives us more than satisfaction. It
shows us that, by the reasoning processes of the human mind, knowledge
of this universe can be obtained.
A great Russian chemist, Mende-
leyev, once stated in effect,
"Some day you will find element
X, which will be quite like the
description I have predicted for it.
The results of the study of my law
and theory tell me so." Later
events proved that he was right.
Element X was discovered, and it
was found to be remarkably like
the description predicted (page
325).
Thomas Midgley, Jr.r (1889-
1944), discoverer of Freon for
refrigerators and of Ethyl fluid for
gasoline, wrote concerning the
scientific method, "What is this
scientific process? ... To my
mind the basis of the scientific
process is the reproducible experi-
ment. Facts are still and probably
always will be determined by
vote ; ... in science we require a
practically unanimous vote for
establishing a fact. . . . The only fundamental tool at our command for
extending (our) knowledge is the reproducible experiment. This is the
accepted scientific method. . . . "L
The Value of Chemistry Study. So mucU chemistry enters our
daily lives that no really educated person can afford to be entirely
ignorant of it. It can mean more to us than a dread of atomic bombs and
of high explosives, more than "magic" tricks from a child's Chem-set.
The study of chemistry is necessary to the work of doctors, dentists,
nurses, pharmacists, and engineers. A knowledge of some of the funda-
mentals of chemistry enables us to do better in almost any business.
The farmer is directly concerned with chemical changes in plants and
1 Chemical and Engineering News, vol. 22, p. 1756, October, 1944.
Courtesy of Ethyl Corporation
FIG. 1-3.— Thomas Midgley, Jr. (1889-
1944) was a pioneer in the application of
chemical knowledge to problems relating
to automobiles. He was a leader in research
and the inventor of Ethyl gasoline and
of a nontoxic, nonflammable refrigerant.
"Science is power."
8
CHEMISTRY FOR OUR TIMES
animals. In addition, there are many jobs that deal with chemistry
entirely.
But what of the future housewife? Need she feel that studying
chemistry is a waste of time? The modern housewife is acknowledging
chemistry as one of her most efficient household aids. It helps her to cook
intelligently, to give her family good food and a balanced diet, to wash
clothes effectively, to understand clothing fabrics of all sorts, and to
keep her home free from insects. Even in selecting cosmetics, her knowl-
Courtesy of Armour Hesearch Foundation
FIG. 1-4. — Here a worker is carrying on research in a bacteriological laboratory.
Chemical training is essential for work of this sort, which helps in the conquest of
disease.
edge of chemical terms and of ingredients guides her in buying healthful
and avoiding harmful products.
How to Obtain More Information. Articles on many chemical sub-
jects appear in the Journal of Chemical Education, School Science and
Mathematics, Chemistry, School Science Review, and other magazines.
Many commercial companies issue illustrated pamphlets describing their
products and processes, often including a historical account of the in-
dustry in which they are engaged. When our curiosity is aroused, we
shall want to know more about the world in which we live. This curiosity
can be satisfied by the use of references such as those mentioned.
CHEMISTRY AS A SCIENCE
Chemistry Deals with Matter. It is fitting that we start our explora-
tion of chemistry with a study of matter. As a guide, let us take the
words of the great Chinese philosopher, Confucius (551-478 B.C.):
The ancients who wished to illustrate the highest virtues throughout the
empire first ordered well their own states. Wishing to order well their own
* states, they first regulated their families. Wishing to regulate their families,
they first cultivated their own selves. Wishing to cultivate their own selves,
they first rectified their hearts. Wishing to rectify their hearts, they first
sought to be sincere in their thoughts. Wishing to be sincere in their thoughts,
they first extended to the utmost their knowledge. Such extension of knowledge
lay in the investigation of things. Things being investigated, their knowledge
became complete. Their knowledge being complete, their thoughts were sincere.
Their thoughts being sincere, their hearts were then rectified. Their hearts being
rectified, their own selves were cultivated. Their own selves being cultivated,
their families were regulated. Their families being regulated, their states were
rightly governed. Their states being rightly governed, the whole empire was
made tranquil and happy.
SUMMARY
New products, processes, drugs, and most of the knowledge of healthful
living are the result of science investigation. Science study has made possible the
use of machines, new means of communication, travel, and many other advan-
tages that we may enjoy.
The scientific investigator seeks to find the actual facts about nature and to
interpret them. He allows no personal prejudice to enter into his work.
The scientific method is a method of approach to problems. It involves five
steps :
1. Collection of facts
2. Organization of the facts
3. Statement of a law
4. Explanation of the law by a theory
5. Prediction of new facts from the theory
The study of chemistry will give us a fund of information about materials
and processes that will be useful in our everyday life.
The student of chemistry should use the public and school libraries to obtain
further information on any subject in which he is particularly interested. The
Journal of Chemical Education and other magazines contain articles on chemical
subjects. Some commercial companies supply upon request pamphlet* describing
their products and processes.
QUESTIONS
1. State two important characteristics of a scientist.
2. The first step in most investigations is a thorough study of previous work
in the field. Point out the advantage of starting an investigation in this manner.
3. List three items of equipment in your home that could not have been
obtained 100 years ago.
10 CHEMISTRY FOR OUR TIMES
4. List three fabrics that were unknown a century ago.
5. Point out two examples of the application of science to relieving pain.
6. State a characteristic that should be lacking among truly scientific
investigators.
7. Give an important objective of the study of science.
8. List the five steps in the scientific method.
9. In Lord Rayleigh's experiment on the density of nitrogen, how many
times was the experimental difference in density greater than the accuracy of his
measurements?
10. Point out the value of organized classification to a lumberyard.
11. Does nature obey scientific laws, or do scientific laws describe generalities
in nature?
12. Do the statements of scientific laws ever change?
13. What is a theory? How does a theory in science differ from an ordinary
guess?
14. Point out the relationship between a fact, a law, and a theory.
15. Give an example of an abstract word; a concrete term.
16. Make a step-by-step diagram, V-shaped, of the items in Confucius'
saying.
HINT: In answering a question, make a complete sentence that has meaning
without referring to the question. It should not be necessary for the reader to
look back to the question in order to understand the answer. For example,
answers to question 1 could be:
Poor: Interest in truth and no prejudice.
Good: Two important characteristics of scientists are (I) an interest in truth and
(2) freedom from prejudice.
MORE CHALLENGING QUESTIONS
17. Show how the scientific method of approach can be applied to the solution
of some problem in school life.
18. Show how the scientific method of approach can be or has been applied
to some problem that affects your town or city. Examples might be water supply,
sewage treatment, and disposal of rubbish or garbage.
19. Write an essay on Confucius.
20. Point out examples of superstitions that have no scientific foundation.
INTRODUCTION CHAPTER II
CHEMISTRY A STUDY OF MATTER
The science of chemistry is the study of all the materials of the uni-
verse; especially, it is the study of the processes by which materials can
be changed into more useful ones. Fat is useful for food or fuel as we find
it in nature, but it can also be made into that practical substance, soap.
Coal may be burned as a fuel, or it may be changed into coke, gas, and
valuable by-products. All materials, substances, stuffs can be called more
accurately matter, the subject of our study.
"What is matter?" we ask. Here we must hesitate before answering
this simple question.
In order to give a satisfactory definition of a word, we must describe
or explain it in terms that are simpler and more fundamental than the
word itself. If the word for which a meaning is sought is simple and
fundamental, then it may not be easy to find a satisfactory definition.
If, for example, we try to express a clear meaning of the word time, we
soon discover that, the wider our experience, the more difficult it is to
define.
The same problem faces the chemist who attempts to define matter
and the physicist who tries to define energy, mainly because in physical
sciences the ideas of matter and energy are fundamental. The definitions
which we shall now give may be considered as working definitions, some-
thing like a scaffolding from which a more substantial structure can be
built.
Energy comes from a Greek word meaning active and is defined as
capacity for performing work or ability to do work. Matter is something
New Terms
On the first page of each chapter we shall list terms that may be new to you.
If, after studying the text, the meaning of any of these is not clear, (1) consult
the Glossary, (2) refer to a dictionary, or (3) ask your instructor for further
explanation.
matter element alloy
energy compound solid solution
alchemy mixture chemical properties
metal synthesis physical properties
nonmetal
11
12
CHEMISTRY FOR OUR TIMES
that has weight. Matter may be invisible; for example, air is invisible
and is known to have weight. Matter may be a gas, a liquid, or a solid,
and it may be dense or scattered. It has weight because of the pull of
the earth on it, usually called the pull of gravity. A steam shovel weighs
more than a hairpin because there is more matter, steel, in the shovel
than in the hairpin. Radiations, such as light and radio waves, are not
called matter. They are not subject to the pull of gravity. They are forms
of energy.
Matter and Energy. Matter has mass (weight), and for ordinary
purposes energy does not possess mass (weight). A piece of metal, such
32,000 FT.
To *tor» th« Mm* amount of
a *prlng would weigh 250
times mot* than a battery; and
comprttted air and tank*. S
timts more than a battery.
•<-lM':
_!«:-J>
Courtesy of Exide Battery
FIG. 2-1. — A storage battery is a reservoir of dependable power. Enough energy
can be stored in a good storage battery to lift its own weight well over 32,000 ft, or
over 6 miles. This tremendous power is used to perform more than 250 different jobs
for modern industry.
as a sewing needle, is matter. The needle has weight, and it has the same
amount of matter whether it is hot or cold, whether it is in a high or in a
low position, whether it is used as a part of an electric circuit or for sew-
ing. When, however, the needle is hot, is at a high position, or is in an
electric circuit, it has more energy than it has under the other conditions
mentioned because it can do more work. The amount of energy that a
needle possesses does not change the amount of material or matter in it.
The explanation of the needle as a piece of steel, of how the iron for the
steel was obtained from a rusty rock, and of how the " springiness "
(elasticity) is produced belongs in the realm of chemistry — a study of
matter. On the other hand, the explanation of how the needle may be
CHEMISTRY A STUDY OF MATTER
13
made to float on water or of how it may be separated from a haystack
belongs in the realm of physics — a study of energy.
The storage battery in the family automobile is another illustration
that shows clearly the difference between matter and energy and also
the different points of view of chemistry and physics. If we consider
the materials of the battery plates (lead and lead oxide), the rubber-
case, the wooden separators, the
liquid (water and sulfuric acid),
and the changes in the lead, the
lead oxide, and the sulfuric acid
when the battery is charged or
discharged, then the study of these
materials is called chemistry; but
if we consider the voltage^ and cur-
rent used in charging the battery,
measuring the density of the sul-
furic acid and the efficiency of the;
battery as a source of electrical
energy, then our study is called
physics. (See Fig. 2-tl.)
The division of physical sci-
ences into physics, the study of
energy, and chemistry, the study
of matter, is for convenience. This
division is an artificial one because
chemical changes are always
accompanied by energy changes.
CWr/e*;/ of Wadau-urth Anttifnt'um
FIG. 2-2. — This wistful cat was cast in
bronze in the second century B.C. in
Egypt. Notice the clearness of the details
that have been preserved for more than
2000 years. (From the J. P. Morgan
collection.)
Primitive Man and His
Knowledge of Matter. Primitive
people took from their natural
resources those substances which
were useful to them. At first these
natural materials consisted of
wood, stones, animals, and plants that helped meet the fundamental needs
for food, clothing, and shelter. Later, tools and weapons were sought from
natural materials, also clay for pottery, and fats and oils for fuels. A great
forward step in mankind's development was made when the first streak
of red-colored iron oxide was used to decorate a pottery jar or to orna-
ment a crude sketch on the walls of a cave. Later the noble metals,
silver and gold, which may be found lying about on the ground if one
looks in the right place, were used for ornamentation.
Still later, people discovered how to obtain useful metals from ores
in which the metals are combined chemically with other substances.
14
CHEMISTRY FOR OUR TIMES
Records and remains of 5000 years ago show that copper, lead, tin,
mercury, zinc, and iron were obtained from ores and that useful mixtures
of metals called alloys were made by melting two or more metals together.
Brass (copper and zinc) and bronze (copper and tin) are examples of such
early alloys. (See Fig. 2-2.) Swords and tools of fine steel were made in
the ancient Syrian city of Damascus about 350 B.C. Today many primitive
tribes in Africa are forgers of iron, an art they have inherited from
antiquity without aid from outside civilization.
In Egypt in very early times there were many experts in practical
skills. In Egyptian temples were found articles and carvings that show
Courtesy of General Ceramics Company
FIG. 2-3. — Byzantine chemical apparatus of the third century A.D. shows some resem-
blance to the apparatus of today. This equipment was used for distilling.
that the priests were skilled craftsmen. They tanned leather, made glass,
pottery, and enamels, colored the surface of metals to imitate gold, and
made dyes and drugs from vegetable materials. These forerunners of
chemists, however, were not much concerned with the question, "What
is matter?" They worked with matter and developed highly technical
processes, but ideas on its composition were not brought forth until many
years later.
The Greeks. For a few centuries Greece was the cultural center of
the ancient world. The Greeks, however, were not primarily workers or
doers. Once a problem had been solved by thinking it through, it seemed
to them unnecessary to test the solution by actual trial.
The ideas about the fundamental nature of matter that the Greeks
developed came in part to them from the country that is today called
CHEMISTRY A STUDY OF MATTER
15
HOT
Syria and also from the Far East, India and China. Some Greek thinkers
believed that all matter was made of a single fundamental material, or
materia prima. Several such prime materials were suggested, and four
were generally accepted: earth, air, fire, and water, the " elements" of
those ancient days. (See Fig. 2-4.) Such a view seemed reasonable; for
if wood is burned, earth remains in the ashes, smoke goes into the air,
fire is seen, and drops of water appear for a short while at the ends of the
sticks of wood.
One of the greatest of the Greek thinkers, or philosophers, was
Aristotle (384-322 B.C.). He was a
collector of all the information known
to the ancient world. Since his writings
were the only extensive source of
knowledge available to many people,
they were considered absolutely
reliable for centuries. Many arguments
were settled by the words ipse dixit
(he himself said it) ; for if a statement
was found in the writings of Aristotle,
it was considered true without further
question.
Among the teachings of Aristotle
we find one that considered earth, air,
fire, and water connected to the
qualities of heat (hotness), coldness,
wetness, and dryness. Earth was cold
COLD
FIG. 2-4. — The ancients considered
the world to be composed of just four
" elements/' Today we can count
92 from nature and can synthesize a
few more.
and dry; air, hot and wet; fire, hot and dry; and water, cold and wet. No
one for 2000 years took serious exception to these descriptions, although
air at times may be cold and dry and water hot or cold.
QUESTIONS
1. With what does the subject of chemistry deal?
2. Define matter; energy; substance.
3. Give an example of changing the amount of energy in a watch; in a mill-
pond behind a dam; in a baseball.
4. Define chemistry; physics.
5. List three chemical changes with which primitive man was familiar.
6. What is an alloy f Give an example.
7* List five metals known in ancient times.
8. Name the most prominent person in Greek science.
16 CHEMISTRY FOR OUR TIMES
9. What was the important general contribution of the early Egyptians to
the progress of science? Of the early Greeks?
10. When the word elements is used in one of Shakespeare's plays, to what
does the term refer?
The Alchemists. About 25Q B.C. the city of Alexandria, Egypt, re-
placed Athens, Greece, as the cultural center of the ancient world. Here
the famous library of 400,000 volumes was located. Here Ptolemy devel-
Courtesy of Fisher Scientific Company'
FIG. 2-5. — Alchemists arc; the subjects of many famous paintings. These paintings
are especially interesting because they reveal the same features that are found in a
modern laboratory: production department, sales department, and public press
(peering through the window) . Note also that the apparatus is somewhat like that used
today.
oped astronomy; Herophilus made the first important study of the human
body, and Euclid developed geometry, with which many students have
had a passing acquaintance. Here also was evolved a false logic called
alchemy, practiced by alchemists, men who by a curious combination
of witchcraft, magic, and experimentation tried to turn lead and other
metals into gold and to find the secret of perpetual life or of renewed
youth. (See Fig. 2-5.)
In other countries, too, notably China, the ideas of the alchemists
had taken root independently. Is there a means of changing base metals
into gold? Will anything restore youth? Is there a substance that will
CHEMISTRY A STUDY OF MATTER V7
dissolve all others? What is the formula for immortality in this world?
Such questions captivate the imagination, spur on investigation, and
allure financial supporters, for would not eternal fame come to him who
was able to answer even one of these questions?
Much valuable chemical information was discovered by the early
alchemists, but each alchemist kept secret what he had discovered. Usu-
ally an alchemist recorded his discoveries in a mystical language full of
signs and symbols so that the meaning was entirely hidden from anyone
else, and after a few years even from the writer himself.
It is surprising to realize that only a century ago many people main-
tained alchemists as an expensive luxury, somewhat as they might main-
tain a stable of fine racing horses — a gamble, but one with possibilities
of winning great wealth if ever the way was found of changing base
metals into gold. Queen P^lizabeth (1533-1603) in the time of Shakespeare
took her royal lessons in alchemy from John Doe. Ponce de Leon (1460-
1521) explored Florida in quest of the Fountain of Youth, thought by the
Indians to possess rejuvenating powers. Kaiser William II of Germany
(1859-1941) had dealings with alchemists. Craftiness, greed, and much
ordinary "bunk" often entered into the works of the alchemists, for they
had to maintain the appearance of making progress whether they were
progressing or not. Otherwise, their rich patrons would withdraw support.
Alchemy, from which chemistry drew much information, was a source
that we cannot always admire, although many bright spots shine out
like beacons in a sea of fraud.
The Decline of Alchemy. The hold of alchemy on the imagination
of the world was broken when its ideas were shown to be false. Again
we find clear thinking leading the way to progress. The chief upset came
when Robert Boyle (1627-1691) gave a clear definition of elements.
Boyle daimed that elements are simple substances that cannot be broken
down into anything simpler, are " incapable of decomposition by any
means with which we are at present acquainted." His views were con-
vincingly stated in his famous book The Sceptical Chymist; or Chemical-
Physical Doubts and Paradoxes Touching the Experiments Whereby vulgar
Spargyrists are wont to Endeavour to Evince their Salt, Sulphur and Mercury
to be the True Principles of Things. He further stated that, if this defini-
tion is accepted, then the goal of the alchemists to change one element
into another by chemical means is unlikely to be attained. After Boyle
had published his book, the true nature of elements became known to
all scientists. Boyle is often called "the father of chemistry."
Another blow to alchemy was the establishment of the law of the
conservation of matter. This law claims that matter cannot be created
or destroyed. Matter is eternal, never disappearing from the universe,
although it may change its form. In other words, we cannot by chemical
18 CHEMISTRY FOR OUR TIMES
means .get something for nothing or make something disappear into
nothing at all. The law of conservation of matter also upset the ideas of
Aristotle and lifted alchemy, an art, to chemistry, a science. The classic
elements, earth, fire, air, and water, were replaced by the chemical ele-
ments of today — elements that had earned their right to their names by
withstanding all chemical attempts to decompose them.
The Effect of an Idea. Technical knowledge continued to advance
slowly, and 18 centuries after the Greek philosophers came another
important forward step in man's conquest of matter. Before people can
act intelligently they must have ideas; the world's great thinkers have
ever been the source of ideas about fundamental truths. In the latter part
of the sixteenth century, Francis Bacon (1561-1626) gave to the world
a method for gathering more facts about matter. Bacon's directions
sound simple today because they are so obvious; but at the time he lived
they were quite new. He said that, if we wish to find out more about the
ways of nature, we must carry on experiments; he maintained that this
is the way to gather facts with which we can reason. Because of this
contribution to science study, Bacon has been called the "herald of
modern science." For about 150 years little was done with this thought
of Bacon's but it gave good results promptly when put into practice.
QUESTIONS
11. State clearly the contribution of Francis Bacon to the progress of science.
12. Name two possible places where the early study of alchemy may have
originated.
13. What were some of the aims of the alchemists?
14. Did the alchemists make any real contributions to the development of
chemistry?
15. Did any alchemist succeed in making gold from lead?
16. Who is called the herald of science? The father of chemistry'/
17. What definition of an element was given by Boyle?
18. State the law of conservation of matter.
19. List two factors in the decline of alchemy.
20. Did alchemy develop into chemistry, or are alchemy and chemistry two
separate developments?
MORE CHALLENGING QUESTIONS
21. Distinguish matter from energy.
22. Distinguish matter from weight.
CHEMISTRY A STUDY OF MATTER
19
23. What factors in the problem of deep-sea diving would be considered from
the standpoint of chemistry? From the standpoint of physics?
24. Point out why the possibility of changing base metals into gold seemed
reasonable to the alchemists.
Elements. The entire world is composed of elements, 92 of which are
known to exist naturally. No other natural elements have yet been dis-
covered anywhere in the universe. Each consists of 100 per cent of that
element, and that element only. Each one is a distinct kind of matter.
For convenience the elements may be sorted into two main groups,
metals and nonmetals. We all know of copper, tin, aluminum, silver, iron,
'->"
Courtesy of TCJCUS Gulf Sulphur Company
FIG. 2-6. — An enormous block of a single element, sulfur, dwarfs a railroad train
and workmen. It is almost 100 per cent pure. Most of it will be made into sulfuric
acid.
and other metals. These substances, if pure, are elements. Metals possess
a bright, metallic luster and are good conductors of electricity. Sulfur, a
yellow material, and phosphorus, of which the red coating on safety
matchboxes is composed, are well-known nonmetals. (See Fig. 2-6.) Other
common nonmetals are helium, neon, chlorine, oxygen, and carbon
(diamond). Nonmetals do not have a silvery luster, and they do not
conduct electricity.
These 92 elements, primary substances, are foundation materials —
building units — for more complicated substances. Like bricks that make
up a building, they can be examined in detail, but they are essential parts
of the whole. The science of chemistry is devoted to the study of the
elements and their interactions.
20 CHEMISTRY FOR OUR TIMES
We find out which elements are present in a given substance by
analyzing it. The attitude of the chemist toward matter is somewhat like
that of a small boy toward a watch; he wants to take it apart to see
what makes it tick, or, more technically, to analyze it.
The elements in the outer portion of the earth, usually referred to as
the "earth's crust " but including the sea and air, are estimated to be
present in the percentages given in the following table.
ELEMENTS PRESENT IN THE EARTH'S CRUST
Per Cent Per Cent
Oxygen 49 . 2 Potassium 2.4
Silicon 25 . 7 Magnesium 1.9
Aluminum 7.5 Hydrogen 0.9
Iron 4.7 Titanium 0.6
Calcium 3.4 Chlorine 0.2
Sodium 2.6 Phosphorus 0.1
9972
A complete list of the elements is found in the Appendix. The 80
remaining elements taken together make up the residue of the 0.8 per
cent not accounted for by the table above. The relative abundance of an
element, however, does not determine its usefulness. Carbon makes up
about 0.04 per cent of the whole earth, as shown in the table below, and
less than 0.1 per cent of the earth's crust; yet were it not for this element
it is likely that no life could have developed on the earth, since carbon is
an essential element in all living matter.
H. S. Washington of the Geophysical laboratory, Washington, D.C.,
made the following estimate of the composition of the entire earth:
COMPOSITION OF THE WHOLE EARTH
Iron .
Per Cent
39 76
Sodium
Per Cent
0 39
Oxygen
27 71
Cobalt
0 23
Silicon
14 53
Chromium
0 20
Magnesium
8 69
Potassium
0 14
Nickel ... . . . .
3.16
Phosphorus
0.11
Calcium
2 52
Manganese
0.07
Aluminum
.. . 1.79
Carbon
0.04
Sulfur
0.64
Titanium
0.02
100.00
How Elements Are Found. We should not assume that all elements
are found free, or uncombined, under natural conditions. A few are
(although they may be part of mixtures), but most of the elements are
in compounds, chemically combined with other elements. We see the
bricks in a brick house joined to other bricks of the same or a different
kind. Sometimes, however, we see a pile of individual bricks not part of
any structure. Similarly, the elements are most often found joined with
CHEMISTRY A STUDY OF MATTER
21
others in compounds; only occasionally do we run across an element
uncombined or free. From certain rocks near Lake Superior a person may
dig out chunks of fairly pure, free, or native copper, a common metallic
mineral. More often, as in Montana and in South America, we find
compounds containing copper combined with another element (oxygen
or sulfur), forming dazzling bits of purple or soft green-colored rocks.
Compounds. Table sugar is a compound. As anyone knows who has
spilled sugar on a hot stove, the compound decomposes when heated, A
black substance, the element carbon, remains. Some of the carbon and
the other elements — hydrogen and oxygen — in the sugar have been driven
off by the heat into the air in the form of water vapor and flammable
compounds.
As has been previously stated, elements are usually found in union
with other elements. Substances composed of elements joined together
chemically are known as compounds.
Constant Composition of Compounds. Furthermore, chemists
have discovered that the elements in a compound are not joined together
HYDROGEN
64%
COMMON TABLE SALT, NaCI
FIG. 2-7. — Every compound has a definite composition by weight. Common
salt contains 39.4 per cent of sodium and 60.6 per cent of chlorine; table sugar con-
tains 42.1 per cent of carbon, 6.4 per cent hydrogen, and 51.5 per cent oxygen.
in haphazard amounts. The amount of carbon in table sugar is always
42.1 per cent by weight, the same for every pure sample of sugar. This
percentage by weight of the elements in a compound we cannot change
by any known means. Salt, another compound, always contains 39.4 per
cent of the metal sodium and 60.6 per cent of the nonmetal chlorine. (See
Fig. 2-7.) In other words, the composition of a compound, if pure, always
contains a definite percentage of each element. In a given chemical com-
pound the elements are always present in the same proportion by weight.
This statement is known as the law of constant composition.
Certainly sugar is not like carbon, for sugar is comprised of white
crystals, while the carbon that is left when sugar is heated is a black solid
22
CHEMISTRY FOR OUR TIMES
of irregular shape. Water is not like oxygen, for water is a liquid that puts
out fires, while oxygen, an element in the compound water, is a gas that
makes fires burn better. A compound is a distinct substance. It is like
itself only; that is, it has its own properties. A given compound is the
same substance regardless of its source, provided that it is pure.
How Compounds Are Made. Making a compound may be demon-
strated by a simple experiment.
Let us put a thin sheet of copper foil, an element, into a jar of pale-green
chlorine gas, another element. The copper glows brightly, and it may become hot
enough to melt as it joins chemically with
the chlorine. (See Fig. 2-8.) Bits of a
brownish-white solid, the compound cop-
per chloride, are seen around the jar.
When water is added a blue color develops
as the copper chloride dissolves. The color
is intensified by the addition of ammonia
water.
When sulfur is rubbed on a cleaned
silver coin (90 per cent silver), a black
compound, silver sulfide, forms. Silvery
mercury warmed in a test tube with steel-
gray iodine forms red or yellow mercury
iodide.
Cover Plate
Warmed Copper
Jar of Chlorine
FIG. 2-8. — Copper burns in chlo-
rine, forming copper chloride. This is
an example of the direct union of two
elements to form a compound.
Many thousands of compounds are
known. A few can be made directly
from the elements by causing them to
combine, as in the examples above.
In the study of chemistry we may be inclined to emphasize these simple
cases. However, we should not forget two facts: (1) Not all elements
combine to form compounds directly. (2) Compounds are often obtained
from other compounds.
The creating of new compounds, some of which may be of the greatest
service to mankind, is one of the most interesting responsibilities of
chemists. Sometimes, indeed, compounds that exist in nature may be
prepared more cheaply in the chemical laboratory than they can be pre-
pared from natural resources. Indigo produced in a dye factory can be
sold for 12 cents a pound; but before this artificial product was put on
the market, natural indigo was selling for $4 a pound. In 1897 a million
acres of land in India produced a crop of indigo worth 20 million dollars.
Twenty years later India's production had shrunk about 99 per cent.
While this may be unfortunate temporarily from the point of view of
some of India, it is a triumph for chemistry.
We call the manufactured indigo dye just mentioned synthetic indigo
CHEMISTRY A STUDY OF MATTER 23
as compared with natural indigo. This distinction tells something about
the different sources of the materials. The materials themselves are
identical. We often read into the word synthetic a meaning that it does
not have. Many vegetable shortenings that are sold in cans or jars at
grocery stores are synthetic. Synthetic substances are made by putting
together simpler substances. Synthetic is not the same as substitute, and
neither word, synthetic or natural, means inferior. Often synthetic prod-
ucts are of greater purity than the natural products. Synthesis is a
putting-together process; it is the opposite of analysis.
QUESTIONS
25. Name a metal that is an element in addition to those mentioned in the
text; a gaseous nonmetal that is an element.
26. Define analysis; synthesis.
27. What four elements are most abundant in the earth's crust?
28. What percentage of the earth's crust is composed of metals?
29. Fluorine is the most active nonmetallic element. Is it found in nature
free or combined? Explain.
30. What percentage of table sugar is not carbon?
31. A few elements are mentioned in the Bible. Are these more likely to be
found free or combined in nature?
32. When 32.5 pounds of zinc is heated with 16 pounds of sulfur, a compound
forms. What percentage of metal does it contain?
33. Pure marble (calcium carbonate) contains 12 per cent carbon, 48 per cent
oxygen. What percentage of calcium is present?
34. List some characteristics of metals; of nonmetals.
Names of Simple Compounds. Compounds contain two or more
elements. Water contains two, hydrogen and oxygen. We name many
compounds of two elements by stating the name of the metal or the
element corresponding to the metal first. The ending of the name of the
other element is changed to -ide. Water is dihydrogen oxide.
What elements are present in common salt (sodium chloride)? In
silver sulfide? In mercury iodide?
Many compounds that have three elements are given the ending -ate.
Such compounds are composed of a metal, a nonmetal, and oxygen. An
examination of the name of the compound will tell what two elements
are present in addition to oxygen. Potassium nitrate contains potassium,
nitrogen, and oxygen.
What elements might one expect to be present in sodium carbonate
(washing soda)? In copper sulfate (blue vitriol)? In potassium chlorate?
24
CHEMISTRY FOR OUR TIMES
Mixtures. Nature provides us with elements and compounds, but
seldom are these elements and compounds found pure. Rocks, for example,
are usually streaked with impurities; plants consist of many parts —
roots, stems, flowers, leaves. Nature as we find it is seldom uniform to
any great extent.
The soil under our feet is not one definite substance but is made up
of several sorts of matter — clay, sand, water, and assorted bits of decayed
Stirring
Rod
.Water
Filter Paper
Glass Funnel
Sand and
Salt
Salt Water
Solution
FIG. 2-9. — The^ properties of salt are different from the properties of sand. This enables
us to separate a mixture of the two.
vegetable matter called humus. Soil is a mixture composed of particles
of different sorts. Such a material, made of particles unlike each other,
is called a nonuniform mixture. Salad, hash, and almost all our foods are
mixtures. Each substance in a mixture retains the properties that it had
before it became part of the mixture. The substances mixed are not
chemically combined; they are just scrambled.
We can make a mixture by stirring dry sand and salt together. This mixture
can be separated by placing it in a funnel in which a filter paper is inserted.
(See Fig. 2-9.) When water is poured through the filter, the salt dissolves, leaving
the sand on the paper. The salt may be obtained in the dry condition by evapo-
rating the water from the filtrate. The salt and sand together form a nonuniform
CHEMISTRY A STUDY OF MATTER J5
mixture, and the salt water is a uniform mixture. Both mixtures may have vary-
ing composition.
In addition to nonuniform mixtures, there are mixtures that are
entirely the same throughout. These are called uniform mixtures.
If we stir a little sugar in water until it is dissolved, we have made a sugar
solution. This solution is perfectly uniform; every drop is like every other drop,
even when examined under a microscope. We can mix together 1 per cent of sugar
and 99 per cent of water, 2 per cent of sugar and the rest water, and so on, up to
the limit of the dissolving ability of water for sugar at the temperature at which
the experiment is being performed. The uniform mixture will pass through filter
paper without separation of the sugar from the water.
Mixtures, such as sugar and water, have the appearance of compounds
because of their uniformity throughout. The distinguishing feature, how-
ever, is the fact that the percentage composition by weight of mixtures
is not fixed. The composition of a solution may be varied by the person
who makes up the 'solution. Brine for making pickles, sirup with canned
fruit, and the contents of a bottle of a carbonated beverage are other
examples of solutions that may have varying composition.
Another sort of uniform solution is interesting. When metals are
melted and thus become liquid, some dissolve ^quite well in one another.
When such a solution is cooled and hardened, frequently no separation
occurs and we have a mixture of metals called a solid solution. Brass,
composed of copper and zinc, is a familiar example. When these two
metals are melted together and cooled, an alloy is produced that is com-
posed of copper and zinc not chemically combined, yet with uniform
color and properties throughout the piece as far as the eye or microscope
can tell. The composition of brass, however, may be varied, depending
upon the purpose for which the material is made. Brass, therefore, is a
mixture, a solid solution, not a true compound. All the alloys used in the
United States coins contain usually two, sometimes three, metals in solid
solution.
What Are the Properties of Matter? Let us recall the fundamental
nature of matter. It has weight. Yet when we know the weight of a bit
of matter, much more remains to be told in order to give a complete
description of it. For example, matter occupies space; it may exist in any
of three states, solid, liquid, or gaseous; it may be colored or colorless,
transparent or opaque; and it may or may not possess odor. It is said
that Thomas Alva Edison (1847-1931), the famous inventor, knew more
about substances than any other person. He knew the physical properties
of color, odor, taste, density, solubility in water, boiling and melting
temperatures, and many others that are used in describing different sorts
26
CHEMISTRY FOR OUR TIMES
of matter. He also knew how substances act in chemical changes. These
are the reactions described under the heading of chemical properties.
Classification of Matter as Solid, Liquid, or Gas, Most people
know iron as a solid; yet at foundries workers are familiar with the liquid
iron that is poured into molds to make iron castings. We also know that
iron exists in gaseous form, for astronomers have detected this element
on the sun. Water, usually liquid,
quite often freezes to form solid
ice and may easily be boiled to
form water vapor, a gas. Water is
one of the most familiar examples
of a substance that may exist in all
three states of matter, and it may
exist in these three states simul-
taneously at a single temperature,
0 degrees centigrade (°C).
Not every substance is known
to exist in all three states of
matter, however. Mercury oxide
decomposes before it can be
changed into the gaseous state.
Matter can be thus classified
according to physical state as
solid, liquid, or gas. In spite of the
fact that the state of matter is
entirely dependent upon the con-
ditions of temperature (see Fig.
2-10) or pressure, we consider
that the state in which a sub-
stance exists at room temperature
and atmospheric pressure is the
Courtesy of Anaconda Copper Mining Company
FIG. 2-10. — Lead, a metallic element,
becomes liquid when heated and can be
cast into ingot molds. Each ingot shown
here weighs 4 tons.
usual one.
Changes in Matter. Children grow, leaves change color, wood rots,
food digests, milk sours, and many other examples show that even the
complicated processes of life itself involve chemical changes. We are
familiar with the fact that matter is everywhere in the process of building
up or tearing down, uniting, separating, or transforming. This process
of change that matter undergoes is a part of chemistry, of equal impor-
tance with the study of the composition of matter.
Two sorts of changes in matter may be noted: (1) those which are
accompanied by a change in the composition of matter and (2) those in
which no change in composition occurs. In the former, new substances
CHEMISTRY A STUDY OF MATTER 27
are produced, while in the latter no new ones are formed. Changes in
matter that are accompanied by a change in composition are called
chemical changes: other changes are called physical changes.
When water boils or ice melts, no new products are formed, since ice,
water, and steam are each composed of hydrogen and oxygen in the same
proportions by weight. If silver is heated to redness, no change in compo-
sition occurs: only silver remains after it has cooled. These changes are
therefore physical changes. On the other hand, when sugar is heated on
a hot stove, carbon is formed as well as water vapor and flammable gases.
Here a change in composition has taken place. Also, when iron rusts, it
combines with oxygen in the air, forming the product iron rust. Again a
change in composition has taken place. These are chemical changes. A
chemical change involves the disappearance of the original substances
and the appearance of new substances, different in composition and in
properties: the same elements are present after a chemical change, but
they have been rearranged to form new substances.
It is interesting to note that changing the physical condition of tem-
perature changes all the physical properties of a substance to a smaller
or greater extent.
Conservation of Matter. Let us place a small test tube containing lead
nitrate solution and another test tube containing potassium chromate solution
FIG. 2-11. — The weight of all the substances taking part in a chemical change is
precisely the same as the weight of the products of that change.
in a flask in such a manner that the solutions do not mix while the tubes are
nearly upright. (See Fig. 2-11.) Then let us set the apparatus on one pan of a
balance and carefully weigh it by placing the necessary weights on the other pan.
We now remove the flask and tip it so that the solutions in the two tubes run
together, allowing, however, nothing to leave the apparatus. A bright-yellow,
fluffy solid, lead chromate, forms in the liquid. A new substance has appeared,
showing that a chemical change has taken place. When replaced on the balance
CHEMISTRY FOR Ot)R TIMES
Courtesy of University of California
FIG. 2-12.— The upper picture shows a general view of a cyclotron, an apparatus in
which tiny positively charged particles are accelerated to very high velocities. The
speeding particles smash into atoms and break a few of them. By examining
the wreckage, scientists learn about the structure of the atom. Lower view shows the
active beam of particles emerging from the machine.
CHEMISTRY A STUDY OF MATTER
29
pan, the apparatus is found to weigh exactly the same as previously. Nothing has
been gained or lost. The weight of the substances that entered the chemical
change is the same as that of the substances produced by the change.
Antoine Laurent Lavoisier (1743-1794), one of France's greatest
scientists, was quick to realize the importance of the balance in chemical
experiments. In his experiments he used the best balances t® be found
at the time in all Europe and relied on the results he obtained by their
aid. Lavoisier concluded, " One may take it for granted that in every reac-
tion there is an equal quantity of matter before and after the operation."
Since Lavoisier's time a great many chemical chaifges have been
studied, some of them taking place entirely on the pan of a balance.
The weight of the substances entering into the change and the weight
of the products formed have been carefully determined. In each case a
remarkable agreement exists: the total weight of the products is exactly
equal to the total weight of the substances entering into the change.
Although its form may be altered, matter cannot be created or destroyed
in chemical reactions. This is known as the law of conservation of matter.
Very careful experiments in physics and chemistry give evidence that
this law may not describe the conditions on the sun and other stars
where matter is believed to be destroyed to produce energy. Energy,
once matter, is thrown out from the sun into space as heat, light, and
other radiations. The opposite change, the creation of matter from
energy, is assumed to exist somewhere in the universe, according to
the observations of astronomers. When atom-smashing machines like the
cyclotron are used, neither the law of conservation of matter nor the
law of conservation of energy alone holds strictly true; but when they
are combined under the law of conservation of mass-energy, the principle
holds true exactly. Matter and energy in extreme cases may thus be
connected one with the other. (See Fig. 2-12.)
Classification of Matter According to Composition. The classifi-
cation of matter according to composition can be summarized by this
table :
ALL MATTER
Nonuniform samples of matter
Uniform samples of matter
MIXTURES
(Composition not
definite)
Hash
Some alloys, such
as Steel
MIXTURES
(Composition vari-
able)
(1) Liquid solutions
Bottled soda water
(2) Solid solutions
Sterling silver (an
alloy)
COMPOUNDS
(Composition
fixed) Can be de-
composed
Pure water
of
ELEMENTS
(Simplest form
matter)
Have not been de-
composed by chem-
ical means
Aluminum
30 CHEMISTRY FOR OUR TIMES
SUMMARY
Chemistry is the study of matter, especially a study of changes in the com-
position of matter. Matter is something that has weight (mass). Physics is the
study of energy. Energy is capacity for performing work.
As early as 3000 B.C. man could obtain copper, lead, tin, mercury, zinc, and
iron from their ores and mix them to form alloys. Early Egyptians were especially
skilled as craftsmen. The arts of tanning leather, of coloring the surface of metals,
of obtaining vegetable drugs and dyestuffs, and of making glass, pottery, and
enamels were known by them. The ancient Greeks were interested in determining
the nature of the fundamental substances. Aristotle conceived of only four
" elements"- — earth, air, fire, and water.
Alchemy, a false logic, arose in Alexandria in the third century B.C. and
independently in China. Its aim was to discover a means of converting base
metals into gold and to find the secret of perpetual life. Alchemy declined in the
seventeenth century upon the acceptance of two discoveries:
1. Robert Boyle defined an element as a simple substance that cannot be
broken down into anything simpler.
2. The law of conservation of matter stated that matter cannot be created
or destroyed.
In the late sixteenth century Francis Bacon proposed experimentation to
determine facts about nature.
All materials in the entire world are composed of elements. Ninety-two ele-
ments are known to exist naturally. Elements may be classified as metals and
nonmetals. Most elements are found in compounds, although a few are found
free.
Compounds are substances composed of two or more elements joined together
chemically. The determination of the composition of compounds is aided by the
process of analysis as well as by synthesis. In a given chemical compound the same
elements are always present in the same proportions by weight. Compounds are
distinct substances, each with its own properties. Thousands of compounds are
known: some may be made by direct synthesis, that is, putting together elements
or simpler compounds. The name of a compound composed of two elements ends
in -ide, for example, silver sulfifle, composed of silver and sulfur. Some simple
compounds composed of three elements end in -ate, for example, potassium
chlorate, composed of potassium, chlorine, and oxygen.
A mixture is a combination of substances in which each retains for the most
part its individual properties. No chemical change takes place when a mixture
forms. A nonuniform mixture is one in which are found several kinds of particles,
unlike each other, for example, soil. A uniform mixture is entirely the same
throughout. A solid, uniform mixture is called a solid solution. Alloys may be
either uniform or nonuniform.
Physical properties of matter include color, odor, taste, solubility in water,
density, and melting and boiling points. Chemical properties are the behavior
in chemical reactions called chemical changes.
Chemical changes are those which are accompanied by a change in com-
position. New substances are formed. Relatively large amounts of energy are
involved. Physical changes do not involve a difference in composition. No new
CHEMISTRY A STUDY OF MATTER 31
substance is formed. The amount of energy required to cause a physical change
to occur is small. Although its form may be altered, matter can neither be created
nor destroyed, and no change in total weight occurs in a chemical change. (Law
of conservation of matter.)
Matter may be classified according to physical state as solid, liquid, or gas.
Matter may be classified according to composition as nonuniform mixtures, and
uniform mixtures, compounds, and elements.
QUESTIONS
35. What elements are present in the following compounds: iron sulfide, cal-
cium phosphide, sodium bromide, magnesium nitride, lead chloride?
36. Give a name to a compound composed only of (a) potassium and chlorine,
(6) magnesium and bromine, (c) copper and chlorine, (d) lead and oxygen, (e)
sodium and iodine.
37. What elements are present in each of the following compounds: potassium
sulfate, copper nitrate^ zinc sulfate, lead carbonate, tin oxide?
38. Define element; compound; mixture.
39. Classify as element, compound, or mixture, using three columns: soup,
potassium chloride, zinc; bronze, lead, bread, sugar, salt, hydrogen, calcium
hydroxide.
40. What facts about a substance are listed as physical properties? As chem-
ical properties? *
41. Name three states of matter. May all substances exist in all three states?
Explain.
42. Give an example of a .chemical change not mentioned in the text.
43. Distinguish a chemical from a physical change.
44. Are changes of ice to water, to steam, chemical or physical?
MORE CHALLENGING QUESTIONS
45. A certain ore is 50 per cent zinc oxide. Zinc oxide contains 67 per cent
zinc. The process of recovery of metal from the oxide is 80 per cent efficient.
What percentage of metal is obtainable when based on the weight of the original
ore?
46. Carefully define: synthetic; inferior; substitute; alternate; natural; ersatz.
47. What elements are present in the following compounds : silver chromate,
sodium zincate, potassium aluminate, calcium tungstate, lead arsenate, sodium
vanadate?
48. Classify the following as element, compound, or mixture, using three
columns: a dime, sterling silver, aluminum, yeast cake, baking powder, baking
soda, cake, soap, sea water, iron. Use a dictionary or the wrapper of the product,
if available, for needed information.
CHEMISTRY FOR OUR TIMES
49. When a stick of wood burns, it undergoes an extensive change. The ashes
weigh much less than the original wood. Is this observation contrary to the princi-
ple of conservation of matter? Explain.
50. Classify as physical or chemical changes:
burning a candle
glowing of a tungsten filament
boiling water
decaying of fruit
glowing of a neon sign
rotting of eggs
souring of milk
tarnishing of silver
licking a postage stamp
drying of clothes
exploding a bomb
61. Figure 2-13 illustrates an apparatus that may be used for showing the
principle of conservation of matter. Explain its operation.
burning gasoline
flowing of water in a brook
making fudge
soaking up ink with a blotter
glowing of phosphorus
decomposing water by an electric current
making caramel candy
drying of house paint
action of sunlight on a light-intensity
meter
Sodium Carbonte
(NajCOjl
Solution
Courtesy of Hermann Bernhardt
FIG. 2-13. — A closed system is suspended on the pan of a balance and counter-
poised. The two solutions are allowed to run together and react. After the chemical
change, has a change in weight taken place?
UNIT
ONE
Courtesy of Caterpillar Tractor Company
OUR ESSENTIAL ENVIRONMENT
OUR environment, or surroundings, consists of air, various
solids, more or less water, and living creatures. It is the
purpose of this unit to describe environment from the standpoint
of chemistry. Thus we may become better acquainted with the
sort of planet we inhabit.
Curiosity impels scientists to find out more about our sur-
roundings. Amazing voyages are made high into the stratosphere.
Drillings, at enormous expense, reach 3 miles below the surface of
the earth. Both geographical poles have been reached. The bathy-
sphere penetrates deep under the sea. The snow cruiser trudges its
path over the frozen antarctic wastes. Self-recording instruments
parachute from observation balloons. Few unexplored wildernesses
remain on earth. A challenge, however, still remains in the field of
science. Here we know a little, but our knowledge ends abruptly.
It is safe to predict that the greatest discoveries in science are yet
to be made.
Many ways have been devised to study
our surroundings. The above photograph
shows how our electric environment is
studied by putting enormous electrostatic
charges on hollow metal globes. The charge
is shown leaking to the metal frame of the
building that surrounds the apparatus. Some
of the oxygen of the air is changed into ozone
by the electrical energy.
Courtesy of Port of New York Authority
A chemist of the Port of New York
Authority is checking the accuracy of the
The fruits of scientific curi'
osity have been put to various
uses. Two atomic bombs
stopped a war. The sea has
become an inexhaustible mine
of chemical treasure. The air^
ways have become travel
routes now that strong,
tough, light metals can be
produced.
A generation ago no one
knew the healing powers of
penicillin. Two generations ago
color photography was not
practical. Three generations ago
there was no rayon, much less
nylon or vinyon, silicone
("bouncing putty11), or insulin.
Almost a century ago the first
coal-tar dye brightened the
colors of a cotton dress. No one
who sat around a campfire dur-
ing the American Revolution
could explain just what sort of
chemical change was going on
in that fire.
Whether we make a fire or
cook with one, dye cotton cloth
analyzing instruments used to measure the or Wear dyed rayon, enjoy the
concentration of poisonous carbon monoxide
gas in the Holland Tunnel. If the concentra- healing of a Sulfa drug Or aspirin,
tion of carbon monoxide rises above a safety i • j r
margin, the analyzers should operate in such We are taking advantage Of a
a manner that a warning bell rings. controlled chemical change.
Controlled chemical change is the theme of chemistry for our
times.
UNIT ONE CHAPTER
THE AIR
Living creatures as we know them exist on the earth because condi-
tions favorable to them are present. That the mysterious spark of life
may exist, warmth and light from the sun, food, air, and an orderliness
in nature are necessary. Without food, but with plenty of water and air,
a person may live for about 30 days. With no water whatever, but with
air, a person may live a few days. But without air a person suffocates in
10 minutes or less. Air, therefore, is one of the essentials of the environ-
ment of human beings. It is thus fitting that a study of air should form
the starting point of our introduction to chemistry.
Breathing. All the higher animals (including ourselves) need air.
Air surrounds the animal and penetrates his body to some extent. By
the breathing motions air is alternately pumped into the lungs and forced
out again. The animal uses from the air part of the oxygen (about 5 per
cent), a bit of the carbon dioxide, which seems to act as a stimulus to the
breathing process, but none of the nitrogen. The air breathed out contains
considerably more carbon dioxide and moisture than that taken into the
lungs and, as a rule, is warmer.
Air is a mixture of gases. About 78 per cent by volume of dry air is
nitrogen; 21 per cent by volume is oxygen; 0.9 per cent is argon and a
few other argonlike gases; and 0.03 to 0.04 per cent is carbon dioxide.
The air also contains water vapor in varying amounts. *
We may be surprised to learn that plants breathe, also. Oxygen is
taken in, and some of this gas is changed and sent out again as carbon
dioxide. Plants have another process of gas exchange in which the oppo-
site action takes place; carbon dioxide is taken in, and oxygen is given
out. In sunlight this second process goes on more rapidly than the first;
New Terms
oxygen ammonium nitrite radioactive
carbon dioxide fixation of nitrogen neon
nitrogen argon krypton
stratosphere helium xenon
catalyst spectrum radon
inert
35
36
CHEMISTRY FOR OUR TIMES
therefore, plants on the whole take in more carbon dioxide and breathe
out more oxygen than they absorb. This process continually renews the
supply of oxygen in the air and furnishes carbon for the plants to build
their tissues.
If we place a quantity of water in a flask and seal it with a stopper, air remains
above the water. (See Fig. 3-la.) Vigorous shaking causes some of the air to
disappear into the water. Such air is said to be dissolved in water. If we allow the
flask to stand or heat it slightly, bubbles of air leave the water and collect on the
inside of the glass below the surface of the water. (See Fig. 3-16.)
Water
Bubbles
of Air
Wire
Gauze
Tripod
FIG. 3-1.-
Distilled
Water
.
-(a) Air can be dissolved in water by shaking the two together. (6) Dissolved
air leaves water when heated.
Some of the oxygen in the air dissolves in water. Fish and other
aquatic creatures use this dissolved oxygen for their breathing. Fish will
die of suffocation if the water contains no dissolved oxygen.
Air Around the Earth. Air penetrates the earth to some extent.
Tiny cracks in rocks allow it to penetrate deep into the underlying rock
layers. It also penetrates the soil and furnishes oxygen necessary for the
roots of plants. The need of plants for air is one of the reasons for
plowing and harrowing the soil.
The air surrounds the earth and revolves with it. The height to which
it extends upward is limited: we know that about one-half of the air is
below a height of 3.6 miles (5.8 kilometers).1 We live at the bottom of
1 See Appendix for explanation of metric system of measurement.
THE AIR 37
the layer of air and in that part which has the greatest weight for a
given volume — that is, in the densest part. Above 6 miles (10 km) the
air is very thin (of low density), intensely cold [ — 55° Centigrade (C)
or —67° Fahrenheit (F)], and unable to support human life. This layer
of air is called the stratosphere. It has been investigated by daring
explorers, especially the Piccards of Belgium and the United States and
Capt. Stevens and others of the United States. As high as the stratosphere
is above the earth, evidence shows that life exists even there, for bacteria
and spores have been found at this great altitude. The air gets thinner
and thinner as one ascends, but the composition remains nearly the same
as at the surface of the earth.
Air Has Weight. Although we cannot see air, it nevertheless has
weight; it is matter in gaseous form. Because it is matter and has weight,
the air exerts pressure on everything in it. At sea level this pressure
amounts to 14.7 pounds per square inch (Ib per sq in.), but it becomes
less as one rises to higher altitudes.
Air moves from places of high to places of low pressure. This accounts
for the escape of air from a punctured tire, for the rush of air into a
vacuum cleaner, and for the tremendous motions of the winds.
The fact that air is an actual material becomes more evident when
one moves swiftly through it. A bicyclist going downhill is well aware of
the backward push of the air. A hand held out from a fast-moving auto-
mobile receives a strong backward push. Engineers take account of these
facts in designing streamlined airplanes, trains, and automobiles. Stream-
lining reduces the surfaces that obstruct the flow of air. The faster an
object moves through the air, the greater becomes the pressure of the
air on it and the greater the benefit gained by streamlining. This is
easily understood if we assume that the air is made up of a multitude of
tiny particles with spaces between them. This idea, true of all gases, will
be developed later.
The Nature of Air. Air is a mixture of elements and compounds.
Nitrogen, oxygen, and argon are elements found in the air in the free
state, which means that they are chemically uncombined with any other
element. Oxygen is also found in the air in compounds. Compounds
always present in the air include water, carbon dioxide, and many others
in smaller amounts.
All three states of matter are represented in atmospheric changes.
Air is chiefly gaseous; but, as everyone knows, water vapor in it is quite
often condensed into liquid form as rain or mist. If the weather is cold,
the water condensed from the air may solidify, forming beautiful crystals
of snow or occasionally hail.
There are always particles of dust, other solids, in the air. Dust tints
38 CHEMISTRY FOR OUR TIMES
sunsets, hinders cleanliness, and pollutes city air. Soot and ashes from
fires, fragments from volcanoes and meteors (shooting stars), and other
bits of solid material are found in dust. In fact, several tons of solid
material fall on the earth as dust each day. Ways have been found to
measure the amount of dust in the air. Information gained from these
measurements has been valuable in protecting workmen in shops where
dangerous dusts may be present in the surrounding atmosphere. In an
ordinary room near the ceiling a quart-bottle sample of air may contain
as many as 5 billion dust particles.
This air in which we live is a vast storehouse of oxygen and nitrogen,
serving as a reservoir of these gases. Tons of various gases are removed
from the atmosphere daily by burning, breathing, and manufacturing
processes. Also, tons of different gases and solids are daily put into the
air. Yet the total amount of air is so great that these changes are on the
whole of very little account. Also, the winds keep the air well stirred so
that no local change is effective for a long period of time.
Composition of Air. It has been stated that air is a mixture and not
a compound. We may well ask, "What proof is there that air is a mix-
ture?" Air, purified of dust, moisture, and carbon dioxide, is made up as
rollows :
COMPOSITION OF AIR
By weight, %
By volume, %
Nitrogen
Oxygen
Argon and other inert gases . ...
75.5
23.2
1.3
78.06
20.99
0.94
Proofs That Air Is a Mixture. 1. The composition of air, although
always consisting of essentially the same elements, does vary a little
from time to time; that is, the most accurate experiments show dif-
ferences which must be due to slight variations in the composition. A
true compound always has exactly the same composition by weight.
2. Air can be made into a liquid. A liquid compound has one boiling
point at a fixed pressure. Liquid air, however, does not have one definite
boiling point, since liquid nitrogen boils off first at a lower temperature
range than liquid oxygen.
3. When a compound is dissolved in water and then taken out again,
its composition is not changed. This certainly is true of table salt (a
compound, sodium chloride), which contains 60.7 per cent chlorine and
39.3 per cent sodium regardless of how many times it has been dissolved
in water. Air, on the other hand, dissolved in water and then recovered
shows a greatly increased percentage of oxygen because oxygen is more
THE AIR 39
soluble in water than nitrogen. The "air" bubbles that collect on the
side of a drinking glass left standing contain 35 per cent oxygen by
volume, 14 per cent richer in oxygen than the air in the room (21 per
cent). Such a condition is possible because air is a mixture and not a
compound.
4. If air is allowed to penetrate (diffuse) through a porous porcelain
tube, the lighter gases in the air pass through more rapidly and the
composition is changed. If a compound is treated the same way, no
change of composition takes place.
QUESTIONS
1. What exchange of gases takes place in animal breathing?
2. From what original source in the body does the carbon in exhaled carbon
dioxide come? The oxygen?
3. What is the effect on marine life of a coating of oil over water?
4. List three characteristics of air 6 miles above the earth's surface.
6. Give evidence that air is matter.
6. Name the two most abundant elements in the air.
7. In what state of matter are the elements in the air? Are they free or
chemically combined with each other? Are they pure or mixed?
8. How many cubic feet of oxygen is contained in 100 cubic feet of air? In
a room 20 by 10 by 10 feet?
9. How many pounds of nitrogen is contained in 100 pounds of air?
10. Prove conclusively that air is a mixture.
Oxygen. Oxygen is the most important element in the air. Our bodies,
to a large extent, are composed of compounds of oxygen. In the natural
world oxygen takes part in burning, rusting of metals, and decay of
vegetation.
Even a thousand years ago the Chinese recognized an active part of
the air and called it "yin." The writings of Leonardo da Vinci (1452-
1519), the famous Italian artist, mention the presence of two gases in the
air. The amount of the active portion of the air and its part in burning,
rusting, fermentation, and breathing were discussed at some length by
Mayow (1643-1679) in 1669. While Mayow did not prepare a sample of
oxygen, we believe that 62 years later Hales (1677-1761) made the gas
by heating saltpeter. Hales, however, did not recognize that the gas he
had prepared was also found in the air. During the years 1771 and 1772,
a Swedish druggist of great experimental ability, Karl Wilhelm Scheele
(1742-1786), mad4 oxygen from at least seven different substances.
40
CHEMISTRY FOR OUR TIMES
^y^;ij;7'''!/!^'" ',,, j n, \ ' ,, "
is|f |7^^if ''V^1^- f ' ^ ', i''!1- ' ; V"! ti n" , ' - ''i.' i
' ' l
Courtesy of Waller Tagyart and Frank C. Wkitmore
FIG. 3-2. — Joseph Priestley (1733-1804) lived in Northumberland, Pennsylvania,
during the latter part of his life. He is noted for his pioneer investigations of the process
of burning. The portrait of Priestley above to the left was painted by the well-known
artist, Gilbert Stuart. To the right above is some of Priestley's laboratory apparatus.
Below is Priestley's residence, now preserved by the Pennsylvania State College, and
a memorial built by the American Chemical Society,
THE AIR 41
Joseph Priestley, Chemical Experimenter. Although oxygen was
suspected, predicted, described, and even prepared by several investi-
gators in advance of his time, the discovery of oxygen is usually credited
to Joseph Priestley (1733-1804), a clergyman of Birmingham, England.
(See Fig. 3-2.) He not only prepared and described the gas but also
published an account of his experiments. His most famous experiment
took place on Aug. 1, 1774. He inverted a test tube filled with mercury
oxide, a red powder, over a pan of mercury, with the mouth of the tube
below the level of the mercury in the pan in such a fashion that the red
powder floated above the mercury. Then he heated the mercury oxide
with the sun's rays, focusing them by a large burning glass. In this
process a gas was released, leaving a heavy silver-white metallic liquid.
When Priestley put a burning candle in the gas, he noticed that the flame
burned with increased brilliance. He caught a mouse in his laboratory
and confined the animal within a jar of oxygen. The mouse did not
suffocate but scampered about excitedly. Then Priestley tried breathing
some of the gas himself. "The feeling of it to my lungs was not sensibly
different from that of common air; but I fancied that my breath felt pe-
culiarly light and easy for some time afterwards," he reported. Priestley's
choice of mercuric oxide was fortunate, for mercuric oxide is one of the
few oxides that decompose when heated at the temperature of an
ordinary gas burner.
Priestley's life outside the laboratory was tempestuous, for he was a
man of radical views. He sympathized with the French Revolution, and
his religious views were not popular. A mob rose against him and burned
his house and laboratory on July 14, 1791. The clergyman barely escaped
with his life. In his later years, he came to America and lived with some
of his children in Northumberland, Pennsylvania. (See Fig. 3-2.) He died
there in 1804. Because of his contribution to science, the American
Chemical Society purchased his house and made it into a museum.
Oxygen for Sale. Oxygen of commerce is prepared chiefly from liquid
air, but sometimes it is made by passing an electric current through
water. In many high-school laboratories this element is produced by
heating some compound rich in oxygen that decomposes readily. Potas-
sium chlorate is frequently used. This colorless crystalline compound
contains 39.2 per cent oxygen; when it is heated, oxygen is released as a
gas and solid potassium chloride, another colorless crystalline compound,
remains.
The apparatus used in this experiment is a flask or a hard glass test
tube mounted in such a manner that it can be heated by a Bunsen
burner. (See Fig. 3-3.) Usually some manganese dioxide, a material that
takes no part in the chemical reaction but that hastens the decomposi-
tion of potassium chlorate, is added to the potassium chlorate within
42
CHEMISTRY FOR OUR TIMES
the vessel being heated. Such a helper in a chemical change is called a
catalyst. The gas escapes from the generator (apparatus in which a gas
is liberated) through a rubber tube, and it is collected by displacing the
water in an inverted jar of water that rests in a pan of water. Such an
Potassium
Chlorate
(with Vs
manganese
dioxide,
catalyst)
..Vertical Support
One-holed
Clamp
Delivery Tube
Glass and Rubber
Oxygen
Inverted Bottle
Full of Water
Test Tube
(hard glass)
Used as a
Generator
Preparation of Oxygen
in the Laboratory
Collection of Oxygen Bottle of
by Displacing Water Oxygen
FIG. 3-3. — An apparatus for preparing oxygen in the laboratory by heating potas-
sium chlorate, with manganese dioxide as a catalyst, until the chlorate decomposes.
Note that the oxygen is liberated in the generator which is heated, that the gas is
conducted from the generator by the delivery tube, and that it is collected in jars
by displacing water in the pneumatic trough.
arrangement for collecting gases is sometimes called a pneumatic sink or
pneumatic trough.
Properties of Oxygen. Oxygen is a colorless gas, quite like air in
appearance. When pure, it has no odor or taste. Twenty-five quart
Courtesy of Journal of Chemical Education
FIG. 3-4. — Iron burning in oxygen.
bottles of water would absorb 1 quart (qt) of oxygen gas. We say, there-
fore, oxygen dissolves about 4 volumes in 100 volumes of water. A liter
volume at 0°C and a pressure of 1 atmosphere (atm) [760 millimeters
THE AIR 43
(mm)]1 weighs 1.429 grams, compared with 1.29 grams for a liter of air.
Substances burn better in pure oxygen than in air, but the oxygen itself
does not catch fire. At a very low temperature ( — 190°C) oxygen can
be changed to a pale-blue, magnetic liquid that is sometimes used as an
explosive.
Let us place successively in jars of oxygen (1) a wooden splinter with a glowing
spark on the end, (2) sulfur burning in a metal spoon that has a, long wire handle
(deflagrating spoon), (3) glowing charcoal suspended on a stout wire, (4) phos-
phorus burning in a deflagrating spoon, and (5) fine iron wire with a gob of
burning sulfur on the lower end. In each case the burning is noticeably more
brilliant than in air, dazzingly bright in the case of phosphorus. The iron burns
with bright sparks. (See Fig. 3-4.)
QUESTIONS
11. Who is given credit for discovering oxygen? When was it discovered?
12. What products are formed when mercury oxide is heated? Is a chemical
or a physical change illustrated? By what properties can we recognize the
products?
13. What products are formed when potassium chlorate is heated? What
properties do each of the products exhibit?
14. List five physical properties of oxygen. »
16. What is the relationship of oxygen to burning?
16. Is water present in liquid oxygen?
17. When 100 pounds of potassium chlorate is heated, what weight of oxygen
may be released?
18. Under the same conditions, how many times heavier is a liter of oxygen
than a liter of air?
19. How much does 1 liter of oxygen weigh at 0 degrees centigrade and 760
millimeters? 100 liters of oxygen?
20. If pure liquid oxygen is confined and allowed to warm up and explode
the container, what becomes of the liquid oxygen?
MORE CHALLENGING QUESTIONS
21. What weight of potassium chloride is left when 200 pounds of potassium
chlorate is heated?
22. What weight of oxygen can be made by heating 600 grams of potassium
chlorate?
1 These conditions of measurement, called standard conditions and abbreviated
STP, may be assumed unless other conditions are given.
44
CHEMISTRY FOR OUR TIMES
23. What volume (liters) of oxygen does 142.9 grains occupy (STP) ?
24. List four general properties of compounds, and opposite them list the
contrasting properties of mixtures.
25. What percentage increase in oxygen, based on original percentage of
oxygen in air, is effected by dissolving air in water and then recovering it?
Nitrogen. Nitrogen was discovered in 1772 by a Scottish professor
of botany named Rutherford and independently in the same year by
Scheele, the experimenter who is credited with the discovery of oxygen,
also. Rutherford prepared nitrogen by enclosing some air in a jar that
was inverted over water and then burning carbon within the jar. The
carbon dioxide formed was removed by dissolving it in the water, leaving
chiefly fairly pure nitrogen.
Four-fifths of the air by volume is nitrogen. Over each square mile
of the earth's surface are 20 million tons of gaseous nitrogen. We may
say safely that we have an ample supply of nitrogen as a raw material
for chemical manufacturing.
Properties and Some Uses of Nitrogen. Nitrogen is made com-
mercially, along with oxygen, by boiling liquid air. Cylinders containing
gaseous nitrogen at 2000 Ib per sq in. pressure are available.
White Smoke
(phosphorus oxide)
Crucible
Burning
Phosphorus
Water
Nitrogen Gas
• Inverted
Cylinder
Ring of Cork or
Balsa Wood
Phosphorus Oxide
Dissolves
in the Water
FIG. 3-5. — Impure nitrogen may be prepared by burning phosphorus within a
jar inverted in water. The phosphorus oxide formed dissolves in the water and leaves
impure nitrogen in the jar.
Nitrogen is a little lighter (1.25 grams per liter) than an equal volume
of air. It dissolves in water to a less extent than oxygen. It is seldom
used in the laboratory (see Fig. 3-5) except to supply an inert (inactive)
atmosphere, but if needed it can be made by heating ammonium nitrite
(a compound of nitrogen, hydrogen, arid oxygen). (See Fig. 3-6.) This
compound decomposes easily, releasing 43.75 per cent of its weight as
nitrogen and also forming water.
THE AIR
45
Ammonium
Chloride and
Sodium Nitrite
Solutions
Collection of Nitrogen
Bottle of
Nitrogen
Pressure
Gauge
FIG. 3-6. — Ammonium nitrite, an unstable compound, can bo prepared when
needed by warming a mixture of ammonium chloride and sodium nitrite solutions.
When these are warmed, nitrogen gas is liberated and collected by the displacement
of water.
Nitrogen as it occurs in the atmosphere is an inactive element; that
is, it is difficult to cause the nitrogen of the air to combine chemically
with other elements. Compounds of
nitrogen are rich in stored energy
and are very reactive (reaction
takes place at a rapid rate). Practi-
cally all explosives are nitrogen com-
pounds. Always difficult to got into
combination with other elements,
nitrogen gas readily re-forms. Be-
cause of its inertness, that is, lack
of chemical activity, nitrogen in the
free state is used to fill electric light
bulbs and the space above the mer-
cury in high-grade thermometers.
Nitrogen from the air is a raw
material of importance in many
chemical processes. Processes in
which atmospheric nitrogen enters
chemical combinations are referred
to as fixation of nitrogen. Later
references to food, fertilizers, dyes,
Steel
Cylinder of
Compressed
Nitrogen
Fio. 3-7. — One use of nitrogen. What
properties of nitrogen make it suitable
for keeping moisture out of telephone
cables? Would oxygen serve as well?
How does the lineman know when the
cable sheath becomes broken?
and explosives will show the importance of nitrogen compounds.
46 CHEMISTRY FOR OUR TIMES
QUESTIONS
26. Who discovered nitrogen and at what date?
27. How many cubic feet of nitrogen, approximately, are contained in
100 cubic feet of air?
28. List five physical properties of nitrogen.
29. What adjective describes the chemical activity of nitrogen?
30. Define inert.
31. When ammonium nitrite is carefully warmed, what two products are
formed?
32. What is meant by the term fixation of nitrogen?
33. Hot magnesium joins nitrogen chemically. What compound is formed?
34. List two uses of free nitrogen.
35. List three classes of compounds that are nitrogen-containing.
The Inert Gases. The story of the inert gases starts in London, Eng-
land, with some experiments performed by Henry Cavendish (1731-
„ , 1810). a nobleman who had a
Spark . ''
Jumps Here^ r u d scientific hobby. He was an eccen-
Experiment trie bachelor, shy, rich, and very
cautious in the presence of ladies.
Cavendish experimented with an
L-shaped piece of bent glass tub-
Wires inp . Two wires were placed within
Connected & \
to Sparking the tube, extending to the top of
Machine the bend where their ends were a
small distance apart, and were
FIG. 3-8.-Cavendish used an apparatus connected ^^ a sonrce of elec_
similar to the one shown here. . .
tricity. The lower open ends of
the tube were placed in goblets that contained water. (See Fig. 3-8.)
Gases or a mixture of gases could be placed within the glass tube.
When Cavendish placed air in such a tube and caused a spark to
jump across the ends of the wires within the tubing, nitrogen of the air
joined oxygen and formed nitrogen dioxide. The nitrogen dioxide then
dissolved in the water contained in the goblets, and water rose in the
tube to take the place of the gas used up in the experiment. After con-
tinued sparking, all the oxygen of the air was used up, and no further
action took place. Cavendish then added more oxygen and continued the
experiment, but he found after several trials that always a small part of
the air would not combine with oxygen when a spark was passed through
THE AIR 47
the mixture. He writes: " ... If there be any part of the ... air
[oxygen] of our atmosphere which differs from the rest, and cannot be
reduced to nitrous acid [or oxide], we may safely conclude that it is not
more than ^20 part of the whole."
About a century later that small part of the air became important.
John William Strutt (1842-1919), who later became Lord Rayleigh, was
performing experiments to find very accurately the density of nitrogen
gas. To his surprise he found that nitrogen prepared by heating ammo-
nium nitrite differed in density by 1 part in 200 from nitrogen prepared
by removing all the oxygen from dry air. He could not solve this problem
alone and discussed the question with Sir James Dewar, a fellow pro-
fessor at the Royal Institution. Dewar suggested that the two samples
could not be exactly alike and that possibly some other gas, hitherto
undiscovered, might be present in the air. Together these men looked
up the report that Cavendish had made years before, and both read the
words quoted above. Then they saw clearly that the search was a chal-
lenge. The very air we breathe had become a frontier. Only the two most
obvious elements had been found in it. They enlisted the aid of Sir
William Ramsay (1852-1916), a chemistry professor at University
College, London, and five more elements were found eventually among
the gases in the air.
Argon. Ramsay took an enclosed sample of dry air and passed it over
hot copper until all the oxygen was removed by combining with copper
to form copper oxide. Then he passed the remaining oxygen-free gas over
hot magnesium until all the nitrogen was removed by combining with
the magnesium to form magnesium nitride. The remainder, small in
volume, was chiefly argon.
Argon is found in air 0.94 per cent by volume and a little over 1 per
cent by weight. This colorless, odorless, and tasteless gas is a little more
dense than either nitrogen or oxygen, a fact that accounts for the small
difference noticed by Rayleigh. The outstanding characteristic of argon
is its complete chemical inactivity. It has not been made to combine
with any other element, a fact that is very important in the develop-
ment of a chemical theory that we shall study later. Argon's name, well
deserved, comes from a Greek word meaning "lazy." We obtain the gas
as a by-product of liquefying air. Oxygen and nitrogen are made into a
liquid, and the part of the air that resists being changed into a liquid
is chiefly argon.
Because argon will not combine chemically with any other substance,
even a red-hot metal, and because the gas is now readily available, it is
used to fill electric light bulbs to prevent too rapid evaporation of the
hot filament. In fact, most incandescent light bulbs between the 50- and
1000-watt sizes are now filled with this gas at about atmospheric pres-
48
CHEMISTRY FOR OUR TIMES
sure. Just as the nitrogen-filled electric light bulb was better than the
older evacuated type from which the air was removed as completely as
possible, so the argon-filled bulb is an improvement over the nitrogen-
filled bulb. Argon is also used inside the fluorescent tubes. Argoh is
shipped compressed in -steel cylinders, much more expensive than similar
cylinders of oxygen or nitrogen.
Inert Helium, the Sun Element. In 1868 Prof. Janssen studied
the sun by observing it through an instrument called the spectroscope,
in which the light of the sun is spread out into a " rainbow/ ' or spectrum.
In this spectrum the presence of an element in the sun's atmosphere is
indicated by a set of black lines, the position of which is definite for that
element. This had been proved by observing in the laboratory the light
emitted or absorbed by the various elements, by means of the spectro-
scope. (See Fig. 3-9.) As he was investigating the ruddy gaseous layer
surrounding the sun, known as the chromosphere, he discovered a black
Courtesy of E. Harold Coburn
FIG. 3-9. — The sun's spectrum (light with dark bands) is compared here with the
spectrum of iron made by a spark between two spikes (bright lines). Notice that the
position of the lines coincides. This proves that iron is on the sun.
line in the yellow portion of the spectrum that belonged to no element
then known upon the earth. This element was called helium, or the sun
element. In 1890 the American chemist Hillebrand found that a gas
which he thought to be nitrogen was liberated when samples of certain
rofcklike substances obtained from the earth, called minerals, were
immersed in dilute acid. After hearing of Hillebrand's experiments,
Ramsay promptly bought all those minerals which he could obtain.
From them, in 1894, he found the gas helium, the second inert gas to
be discovered. It gave the same line in the spectroscope that Prof.
Janssen had observed.
A year later helium was also found in the air, but in an exceedingly
small amount. It is a gas that comes from certain minerals that contain
radioactive elements. These elements give out radiations of both matter
and energy. More will be said about such minerals in a later chapter
(page 641). Some natural gases, particularly in Texas, contain helium.
Helium is next to the lightest gas, the first being hydrogen. Like argon,
it shows no chemical activity whatever. Helium is the most difficult of
all gases to liquefy, because for liquefaction to take place it must be
THE AIR
49
Courtesy of Goodyear News Service
FIG. 3-10. — Here are side
and rear views of a six-lobe six-
iiu Strato Sentinel barrage bal-
loon for high altitude protection
against bombing attacks. This
balloon has 68,000 cu ft helium
capacity and can ascend to
15,000 ft.
50
CHEMISTRY FOR OUR TIMES
cooled to an exceedingly low temperature, — 268°C. Helium is also the
least soluble gas. It boils at — 268. 9°C at atmospheric pressure. Solidified
helium melts at — 272.3°C at a pressure of 26 atmospheres (atm).
Helium is present in many natural gases in the United States, and
these have proved to be ample sources of this gas for filling airships.
(See Fig. 3-10.) The gas from certain wells near Fort Worth, Texas,
contains 0.97 per cent helium. Helium is obtained by liquefying all the
o.ther elements of a natural gas and in this way separating them from
the helium, which is the most difficult to liquefy. In 1925 a plant in
Texas was able to isolate helium at a cost of 3 cents per cubic foot. With
improved methods of separating it, helium now costs about 2 cents per
cubic foot.
In addition to being used as a lifting gas in balloons in place of
hydrogen, helium mixed with oxygen is used to make an artificial atmos-
phere for deep-sea divers. Helium is teas soluble in the blood than is
nitrogen. The use of the helium-containing mixture for respiration
lessens the likelihood of painful " bends," due to bubbles in the veins
and arteries, experienced by men who have to work in caissons and
elsewhere under great pressure. Nonflammable helium-hydrogen mix-
tures (20 to 80 parts by volume) are used in some balloons.
Neon, Krypton, Xenon, and Radon. After argon and helium had
been discovered in the air, interest in finding new elements was awak-
ened. Ramsay immediately continued the search. Exceedingly skillful
methods of analysis were devised, and in 1898 the discovery of three
new elements, krypton, xenon, and neon, was announced. Another
gaseous inert element, radon, was later discovered to be liberated when
radium disintegrates. All these gases, like argon and helium, do not act
chemically on any other element. Radon has been used in the treatment
of the disease cancer, but krypton and xenon do not exist in sufficient
amounts in the air to make use of them. Neon, however, forces itself
upon our attention. This is because at a low pressure in a closed tube
it conducts electricity well and gives forth an attractive red glow. Hence,
TYPICAL ANALYSIS OF A NATURAL GAS
FROM A WELL NEAR FORT WORTH, TEXAS
Substance
Formula
Per Cent
Methane
CH4
56 85
Nitrogen
N2
31.13
Ethane and other hydrocarbons
C2H6
10.30
Helium
He
0 93
Oxygen
02
0.54
Carbon dioxide
CO*
0.25
THE AIR 51^
it is used for advertising signs, for filling spark-plug testers, and for
filling a type of glow lamp frequently used for pilot lights because the
power demand is as low as J^ watt.
SUMMARY
Breathing is a process by which living creatures obtain oxygen. Animals
absorb oxygen and breathe out carbon dioxide. Plants in sunlight absorb carbon
dioxide and give out oxygen — a type of breathing. Marine life uses oxygen and
carbon dioxide dissolved in water.
Air is matter. It has weight, exerts pressure, and dissolves slightly in water.
Air surrounds and to some extent penetrates the earth. It consists of a large
reservoir of chemical raw material. Although many changes go on in it, the com-
position is almost constant; by volume, 21 per cent oxygen arid 78 per cent
nitrogen, and by weight mainly 23 per cent oxygen and 76 per cent nitrogen, to-
gether with 1 per cent of other gases. The following are proofs that air is a mixture
and not a compound:
1. The composition of air varies slightly. A compound does not vary in
composition.
2. Liquid air boils at several temperatures. A compound has a constant boiling
point at a given pressure.
3. Dissolving air in water increases the percentage of oxygen because the
oxygen is more soluble in water than the nitrogen. Dissolving a true compound in
water has no effect on the composition of the compound (provided that the com-
pound does not react with water).
4. Air passed through a porous porcelain tube shows a change in composition.
A true compound so treated shows no change in composition unless it decomposes.
Oxyge/n is found free in air and combined in water; it is also found combined
in many other oxides and in other types of compounds. It is the most abundant
element. Credit for its discovery is usually given to Joseph Priestley, an English
clergyman, who prepared and identified the gas in 1774 by heating mercuric
oxide and thus obtaining mercury and oxygen. The gas is commercially prepared
by passing an electric current through water and thus obtaining hydrogen and
oxygen or by allowing liquid air to evaporate, whereupon the nitrogen escapes,
leaving liquid oxygen. In the laboratory, oxygen is prepared by heating potassium
chlorate and thus obtaining potassium chloride and oxygen. Oxygen is colorless,
odorless, tasteless, a little more dense than air, and slightly soluble in water. It
can be liquefied. Ordinary burning is the combining of oxygen with some other
element; ordinary burning goes on more rapidly in pure oxygen than in air,
forming oxides in either case.
Nitrogen was discovered by Rutherford in 1772 and independently by Scheele
at about the same time. It is found free in air and is combined in many living
tissues. It is found in relatively few other compounds in nature. Nitrogen is pre-
pared commercially by boiling liquid air and collecting the gas that escapes first.
In the laboratory it can be obtained by removing oxygen from air by means of hot
phosphorus, or purer samples can be obtained by the careful heating of ammo-
nium nitrite. Nitrogen is colorless, odorless, tasteless, a little less dense than air,
and very slightly soluble in water. The gas does not burn, nor will ordinary burn-
52 CHEMISTRY FOR OUR TIMES
ing go on in nitrogen. At elevated temperatures nitrogen combines with a few
very active elements, forming nitrides of these elements. Magnesium is such an
element.
The inert gases comprise less than 1 per cent of the air. Each has its history of
discovery, but in general their discovery came as a result of very careful work.
They are all colorless, odorless, tasteless, and insoluble in water and do not burn
or support burning. In fact, they form no ordinary chemical compounds. The
uses of the inert gases depend upon their inactivity. Argon and neon are used in
electric light bulbs and signs. Helium is used as a lifting gas in airships because
it is very light and nonflammable. Krypton and xenon are found in only very
tiny amounts.
QUESTIONS
\£UMliJ M. JLV^l
36. Name the five inert gases of the air.
37. Name one property that is common to all the inert gases.
38. How many cubic feet of argon are contained in 100 cubic feet of air?
39. Name a use of argon; of neon; of helium.
40. Compare hydrogen with helium as a lifting gas for balloons.
41. What advantage is secured when liquid oxygen is used for an explosive
in a coal mine? >
UNIT ONE CHAPTER IV
BURNING, BREATHING, RUSTING
"Sir, last Christmastide four of my sturdy men dragged an immense
yule log into the fireplace in my great room. For five days and nights
this log burned while the household made merry celebrating Christmas.
Afterward one of the kitchen servants cleaned out the fireplace, carry-
ing off the ashes, scarcely more than a basketful. There is no doubt in
my mind, sir, that things lose weight when they burn."
"I agree with you, my lord, that the reports which come to us from
this Frenchman Lavoisier seem unreasonable. How can one be expected
to believe that which goes against reason? Any child can see that burning
makes for loss of weight. Surely charcoaFVeighs less than wood. This
fellow Lavoisier, who claims that substances gain weight when they
burn, is a little queer."
In this manner was the news of the experiments earned on by Lavoisier
in Paris received by the people of about 175 years ago. Many warm
arguments were taking place in Europe at that time. The political dis-
agreements were extensive, but the scientific wrangle centered chiefly
about the question, " What is burning?" The saddlebags of the postriders
and the mail pouches of 'the stagecoaches carried letters between noted
people who argued this point. Some thought that burning was a process
by which weight was lost, but a few ventured the opposite view that
weight was gained. Many supporters of the first idea clung to the fantastic
theory that a fiery principle phlogiston escaped in the flame, leaving a
calx, or ash; substances that burned leaving very little ash, like wood,
were thought to be composed of nearly pure phlogiston. This theory,
founded by Stahl and Becher in Germany (about 1690), soon led to
absurd ideas. Yet these ideas were believed by learned poeple. Even
Priestley, who did such fine work with oxygen and certainly understood
something about the nature of burning, died (1804) still believing this
New Terms
physical properties igniMon effervescent
chemical properties oxide sublimation
spontaneous photosynthesis reduce
53
54
CHEMISTRY FOR OUR TIMES
older but incorrect phlogiston theory. One writer summarizes the transi-
tion in thinking about burning as follows:1
This alchemistic notion that combustible substances contained the ponder-
able principle phlogiston, which on rapid escape caused the appearance of fire,
was doomed by the discovery of various pure gases. In 1775 Black discovered
carbon dioxide (C02) and showed that it was present in small amounts in the
air. Between 1767 and 1777 Priestley and Scheele discovered several new gases,
each having properties different from air, and laid the foundation for modern
gas chemistry > incidentally providing Lavoisier with material to disprove the
phlogiston theory ajid enabling him to substitute therefor the oxygen theory
of combustion, which has since been amply verified.
The argument about "What is burning?" was settled conclusively
by Lavoisier. Not only did this famous French experimenter reason
Neck of
Retort
Final Level
of Mercury
Where Red
Oxide Collects
Mercury-
Fire Door,
of Furnace
Ash Pit _
of Furnace
FIG. 4-1. — With this apparatus, Antoine Laurent Lavoisier performed his classic ex-
periments on burning.
correctly, but unlike his less scientific opponents he secured facts to
support his reasoning. Lavoisier obtained such excellent results because
he made use of accurate balances and weights. (See Fig. 4-1.) He weighed,
reweighed, organized his data, and formed conclusions from the results.
In 1772 he wrote:
About eight days ago I discovered that sulfur in burning, far from losing
weight, .rather gains it; that is to say that from a pound of sulfur may be ob-
tained more than a pound of vitriolic acid, allowance being made for the moisture
of the air. It is the same in the case of phosphorus. The gain in weight comes
from the prodigious quantity of air ...
Two years later Lavoisier experimented with tin and mercury, heat-
ing each with air in a closed vessel. Both these metals he found to unite
with a portion of the air, about one-fifth. The "air" that remained after
oxygen had been removed would not allow substances to burn in it.
1 FIOCH, E. F., Scientific Monthly, Vol. 52, pp. 216, 349, March, 1941.
BURNING, BREATHING, RUSTING
55
The metals took on a new appearajnce, since they had combined with
the oxygen of the air, and in every case he found that they had gained
weight. By these experiments the old theory was overthrown and a
chemical revolution started.
A political upheaval, the French Revolution, was in progress at the
time when Lavoisier was conducting his famous experiments. Unfortu-
nately, Lavoisier had made many enemies through his activities in public
life as a member of the board of Farmers-General. He was brought before
the Revolutionary Tribunal and accused of putting water in tobacco
intended for soldiers' use. For this unproved and supposedly serious crime
he was sentenced to be beheaded with these infamous words: "The
Republic does not need scholars. Justice must take its course."
Prof. C. S. Minot has said of this event:
Compared with the growth of science, the shiftings of government are minor
events. . . . Until it is clearly realized that the gravest crime of the French
Revolution was, not the execution of the King, but the execution of Lavoisier,
there is no right measure of values: for Lavoisier was one of the three or four
greatest men France has produced.
How to Make a Fire. If we wish to make a fire, we procure some-
thing to burn and a match. The substances to be burned, fuel, may be
a solid (coal, wood, coke, or charcoal), a liquid
(kerosene or alcohol), or a gas (natural gas,
bottled fuel gas, or the gas supplied by city
gas companies). One characteristic is common
to these fuels: they are all capable of combining
with oxygen. Rock (except coal) is not selected
as a fuel because it does not combine with
oxygen.
The match is used because, when lighted
and applied to the fuel, it raises the temperature
of the substance high enough to cause it to burn.
Flammable substances will burn when they
become warm enough; we say that they have
reached their igniting or kindling temperature.
The kindling temperature is not the same for
overy substance or for every condition of the
same substance. However, some substances can,
in general, be classified as having low kindling temperatures — paper,
leaves, hay, match heads — and these are used to start fires.
Who has not heard of kindling wood? Why will a large stick not serve
as well to start a fire? Let us try an experiment.
Suppose we apply a lighted match to a large stick of wood; it
scorched spot but does not ignite the wood. We then try wood sha
FIG. 4-2.— If a burn-
ing candle is placed in an
inverted closed jar of air,
it is soon extinguished be-
cause the supply of oxy-
gen is consumed.
56
CHEMISTRY FOR OUR TIMES
Courtesy of Travelers Insurance Company
FIG. 4-3.-r-Notice that three methods of fighting a forest fire are illustrated here.
BURNING, BREATHING, RUSTING
57
same conditions; they catch fire quickly. The difference is explained by the fact
that a solid stick conducts heat away from the burning match much better than
do shavings. So we may say that the time required for a substance to reach its
kindling temperature depends upon its ability to conduct heat.
We have said that to make a fire we must raise the temperature of
fuel to the kindling point, but one more condition is required if a sub-
stance is to burn. Oxygen or air containing oxygen
must be present in adequate amount. If a piece of
lighted paper is placed under an inverted drinking
glass, it goes out before all the paper is consumed
because the supply of oxygen in the glass is soon used
up. (See Fig. 4-2.)
If any one of the three conditions — fuel, temper-
ature above the kindling point, and oxygen — is
lacking, the common chemical change called burning
cannot take place.
How to Put Out a Fire. The fire siren sounds.
The firemen anive quickly at the burning building
and pump water on it. A temperature race is on! If
the firemen can cool the building below7 the kindling
point by sufficient cold water, the building is saved.
If the heat of the fire can keep the building above
the kindling temperature in spite of the efforts to cool
it, the building is doomed. If a substance is kept cool
enough, it will not burn.
After a skating party we join friends around an
open fire. Its welcome warmth is inviting. One of the
girls, busily talking while standing too close to the
flame, finds to her horror that her clothing has caught
fire. Quickly she rolls on the ground. Sweaters and
blankets are thrown over the burning garments. The
fire goes out for lack of oxygen. The fire is smothered,
we say.
Other ways to smother a fire are sometimes used.
Sand or dirt may be thrown on the fire. Water also
helps, although the chief purpose of using water is to
lower the temperature of the burning substance. A
heavy gas that does not burn can be directed over the
fire to act as a gaseous blanket, shutting out the air.
(See Fig. 4-3.) Carbon dioxide serves well for this
purpose but is hazardous because it suffocates people and animals. A
liquid that turns to a heavy vapor in the heat of the fire may also be
used. Carbon tetrachloride (CC14; tetra means "four") is such a liquid.
Courtesy of Pyretic
Manufacturing Com-
pany
FIG. 4-4.— This
fire extinguisher
contains carbon
tetrachloride. The
operator us.es the
handle as a pump
and directs a
stream of liquid at
the base of the
flames. The evap-
orating liquid
smothers the flame
with a dense gas.
58
CHEMISTRY FOR OUR TIMES
This is the chief substance contained in one kind of fire extinguisher
(see Fig. 4-4) in which the liquid is pumped onto the fire. Since the vapor
formed is injurious to human beings, ventilation after use is important.
To put out the fire in a gas burner we remove the fuel, that is, shut
off the gas. Removing the fuel is sometimes accomplished by dynamiting,
as is done in the cases of oil-well fires and fires involving flimsy beach
buildings in a high wind. Setting " backfires " and trenching to stop a
forest fire are ways to remove the fuel.
Some Properties of Oxygen and Air. A bottle of air and a bottle of
oxygen are alike in many ways. Both oxygen and air are gases at ordinary
temperatures, without color or odor. One liter of air weighs 1.29 grams,
while a liter of oxygen weighs 1.43 grams.
Oxygen dissolves in water only a little
better than air.
These facts about oxygen and air
describe their physical properties. They
do not describe any change, involving
chemical action. Their chemical nature
or properties can be investigated by
testing to find out the chemical changes
they undergo under certain conditions.
Oxygen
Does Not
Catch Fire
A Lighted Stick
Burns Brightly
in Oxygen
FIG. 4-5. — A test for oxygen.
One of the simplest tests for oxygen is to
place a burning splinter in the gas. (See Fig.
4-5.) We then discover that the splinter burns
much better in oxygen than in air. In fact, even a tiny spark will glow so
brightly in oxygen that soon the splinter will catch fire. In this way we can test
to distinguish oxygen from air or many other gases.
Breathing Is Like Burning. In a hospital or dentist's office one may
notice cylinders of oxygen; the strong steel bottles hold the gas compressed
until it is ready to be used. When a patient " takes gas," the oxygen is
mixed with nitrous oxide (N20). When a person is ill with certain lung
difficulties, the air used for breathing is enriched with pure oxygen;
thereby the lungs are well supplied with this gas so that a sufficient
amount of it dissolves in the blood.
Let us consider what happens to the oxygen after it is dissolved in
the blood. The blood carries the oxygen to the tissues where it is needed.
Here the oxygen combines with the food material in the same manner as
oxygen combines with fuel in burning, but at a much slower rate; energy
for action and heat in the body are released, at the same time producing
waste products, which are carried off by the blood on its way back to the
lungs for another load of oxygen. This process goes on whether we are
sick or well. If breathing is carried on with difficulty, as at high altitudes
BURNING, BREATHING, RUSTING 59
or in closed spaces as in submarine work, the oxygen of the air may be
supplemented by oxygen from tanks.
In a similar manner, oxygen from cylinders is used to make fires burn
better. Frequently we see the oxyacetylene flame used in welding metals.
The torch that produces this intensely hot flame develops enough heat
to melt steel even under water. When the steel is hot enough, it will burn
with a brilliant shower of sparks as pure oxygen is supplied.
QUESTIONS
1. When sulfur burns, what change in weight, if any, takes place?
2. When tin burns, what change in weight, if any, takes place?
3. The wood in an ordinary chair is good fuel, and it is surrounded by air.
What condition for burning is lacking?
4. Define kindling temperature.
5. A burning candle is covered by an inverted bottle. What happens? Ex-
plain the answer.
6. A crumpled newspaper burns more quickly than a stack of folded news-
papers. Explain.
7. Describe the action of carbon tetrachloride when it is used to extinguish
a fire. *•
8. A very shallow layer of kerosene is placed in a dish. A lighted match is
placed so that it is only partly submerged. The match continues to burn. The
dish is now tilted quickly so that the kerosene covers the match. What happens?
Explain this experiment.
9. What is an oxygen tent?
10. Compare the relative amounts of carbon dioxide and oxygen in the blood
of the arteries and in the blood of the veins.
What Are the Products of Burning? Ordinary burning consists in
joining a fuel with oxygen, producing simple chemical products. The
physical result of the chemical change is the liberating of heat and light
energy. We buy fuel oil, coal, coke, or gasoline because of the heat energy
they will produce when burned. This part of the story is interesting to
the chemist, but chemists also deal with substances formed by the process
of burning.
We are now ready to illustrate chemical changes by a shorthand
method called an equation. We need not be concerned for the present
about the small numbers before the formulas or subscripts (written
beneath) in the formulas. Their meaning will be brought out later. For
the present it is good practice to write the names of the substances
below the chemical formulas.
60
CHEMISTRY FOR OUR TIMES
When an element combines with oxygen, the substance formed is
called an oxide of that element. Examples are:
c + oa — >
Carbon and oxygen form
Sulfur and oxygen form
4P + 5O2 >
Phosphorus and oxygen form
2HS + 02 . >
Hydrogen and oxygen form
CO2
carbon dioxide (di - two)
SO,
aulfur dioxide
2P206
phosphorus pentoxide (pent — five)
2H?0
hydrogen oxide (water)
Many metals readily unite with oxygen. Examples are :
4AI + 3O2 >
Aluminum and oxygen form
2Zn + O2 »
Zino and oxygen form
3Fe -f 2O2 ^
Iron and oxygen form
2Cu -f O2 ^
Copper and oxygen form
2AI2O3
aluminum oxide
2ZnO
zino oxide
Fe3O4
iron oxide
2CuO
copper oxide
In general :
Element + oxygen — » element oxide
form
Zinc and Sulfur
Asbestos
Sheet
Carbon dioxide and sulfur dioxide are gases under ordinary condi-
tions, and hydrogen oxide (water) is a
liquid. The heat developed in the process
of burning, however, changes water to a
vapor or gas. Phosphorus pentoxide and
all the oxides of metals listed above are
solids.
Some fuels, for example oil and
natural gas, are chiefly carbon combined
with hydrogen; these burn to form car-
bon dioxide and water. Other fuels, such
as wood, fat, and alcohol, have oxygen
in combination in the substances; this
oxygen present in the compound means
that less is needed from the air than
would be required otherwise for complete
burning.
Now we have the explanation of
why a piece of wood actually gains
weight when it burns. The ashes are
largely the part of the wood that for the most part did not burn. The
substances formed that weigh more than the original wood are the gases,
Fia. 4-6. — When a mixture of
small amounts of powdered zinc
and sulfur are heated, a lively
burning results; the zina joins the
sulfur, forming zinc sulfide.
Zn -I- S -» ZnS
BURNING, BREATHING, RUSTING
61
and they usually pass off into the air or up the chimney. Small wonder
that they were overlooked by the pompous country gentleman who is
represented as speaking at the beginning of this chapter.
We are also ready to give an explanation of how metals tarnish or
corrode. Iron rusts chiefly by combining with oxygen, forming a brown
flaky scale, principally iron oxide. Moisture helps the process. Zinc and
aluminum when joining with oxygen form white oxides, -while copper
forms two oxides, one black and the other red.
Joining with oxygen is a common chemical change. Ordinary house
paint hardens because linseed oil adds oxygen; rubber becomes hard and
brittle when it has joined with oxygen; lacquers on cars become dull by
this sort of corrosion; fresh-cut fruit darkens because of oxidation; and
blood clots in part because the scab of oxidized blood temporarily closes
the wound.
Other elements behave like oxygen in that they unite with the same
elements as oxygen. It is possible to have burning that resembles ordinary
burning go on in a chemical laboratory without using oxygen. Note how
similar in action to oxygen are the elements chlorine and sulfur. (See Fig.
4-6.)
C
Carbon
+ 28
and sulfur
4P + 3S
Phosphorus and sulfur
H2 + S
Hydrogen and sulfur
Fe + S
Iron and sulfur
2Cu + S
Copper and sulfur
2Ag + S
Silver and sulfur
form
form
form
form
form
form
CSi
carbon disulflde
phosphorus sulfide
H2S
hydrogen sulfide
FeS
iron sulfide
Cu«S
copper sulfid*
Ag2S
silver sulfide
28
Sulfur
and chlorine
2P + 3CI2
Phosphorus and chlorine
H2 + Cl,
Hydrogen and chlorine
2Na + Cl«
Sodium and chlorine
Cu + CI2
Copper and chlorine
form
form
form
form
form
S2CI2
sulfur chloride
2PCI3
phosphorus chloride
2HCI
hydrogen chloride
2NaCI
sodium chloride
CuCIt
oopper chloride
In one of the above cases, that of the union of hydrogen with chlorine,
both the uniting substances are gases. They burn together with a pale,
weird flame, which gives off a feeble, flickering light. A mixture of chlorine
and hydrogen when illuminated with sunlight explodes with great
violence.
62 CHEMISTRY FOR OUR TIMES
Special Cases of Burning. Many fuels contain both hydrogen and
carbon. When they burn, water vapor and carbon dioxide are formed,
provided that enough air is present. If the supply of , air is insufficient or
the flame cools, the burning is incomplete. Instead of carbon dioxide,
carbon monoxide or even black carbon (soot) may be formed. There is
always some incomplete burning inside the cylinder of a running auto-
mobile engine. The flame of burning gasoline vapor and air strikes the
water-jacketed or air-cooled metal wall of the cylinder. Poisonous carbon
monoxide is always present (3 to 12 per cent) in the exhaust gas of an
automobile engine. As little as 0.04 per cent of carbon monoxide (CO)
is definitely poisonous to breathe. In fact, harm may come from but a
few parts per million (ppm) of this deadly gas.
If burning is still more hampered, water and carbon are formed. The
carbon is formed as smoke or soot, black and dirty, a waste of fuel. A
candle flame is sooty if cooled by a draft.
The following equations represent different degrees of burning :
Complete burning:
CH4 4- 2O2 > CO2 + 2H2O
Methane and oxygen (abundant) form carbon dioxide and water
Partial burning:
2CH4 4- 3O2 > 2CO 4 4H2O
Methane and oxygen (limited) form carbon monoxide and water
Burning with difficulty :
CH4 4 O2 > C 4- 2H2O
Methane and oxygen (scarce) form carbon and water
Here are some examples of substances, already oxides, that can be
made into higher or more complete oxides:
2CO 4 O2 > 2CO2
Carbon monoxide and oxygen form carbon dioxide
2SO2 4- 02 1 2SO3
Sulfur dioxide and oxygen form sulfur trioxide (tri = three)
2Cu2O 4 O2 > 4CuO
Cuprous oxide and oxygen form cupric oxide
4FeO 4 O2 > 2Fe2Oi
Ferrous oxide and oxygen form ferric oxide
Chlorine has a similar action. For example:
2FeCI2 4 Cl? >• 2FeCI3
Ferrous chloride and chlorine form ferric chloride
PCI3 4 Cl? — > PCU
Phosphorus trichloride and chlorine form phosphorus pentachloride
Each chemical change represented here is one of the simplest sorts of
chemical action, that of joining together. Each product is a distinct and
separate substance having its own properties.
BURNING, BREATHING, RUSTING 63
All the chemical changes given previously in this chapter can be
performed in the laboratory. Some, indeed, require a high temperature
and some are aided by the presence of a catalyst, but all will form the
products shown, provided that the conditions are correct. On the other
hand, the reverse actions usually do not work.
C -f O2 » CO?
Carbon and oxygen form carbon dioxide
represents a reaction. The reverse,
CO? » C + O2
carbon dioxide forms carbon and oxygen
does not work under any ordinary set of conditions. We should not
assume chemical actions beyond the reach of our chemical experience.
QUESTIONS
11. Define oxide.
12. What is burning?
13. Complete these chemical statements (do not write in this book):
tin + oxygen — > ; sulfur + oxygen — > ; selenium + oxygen — >
lead + oxygen — >
14. Name the elements present in each of the following compounds: carbon
dioxide, sulfur dioxide, ferric oxide. What element is common to them all?
16. What element is present in all oxides?
16. Explain how the law of conservation of matter applies to the burning of a
piece of wood.
17. Some freshly cut fruit, such as bananas, darken rapidly when exposed to
air. Suggest one possible cause for the change.
18. Does a change in weight take place when a metal corrodes?
19. What evidence do we have of similarity between the chemical actions
of oxygen and of sulfur?
20. When 1 ton of coke, 95 per cent carbon, burns, approximately 2.5 tons of
gaseous products go up the chimney. Explain the increase in weight.
MORE CHALLENGING QUESTIONS
21. Why does soot accumulate in a chimney?
22. A hand-fed boiler sends smoke up the chimney chiefly when fresh fuel is
supplied to the fire. Explain.
23. Calculate the weight of unchanged gas that went up the chimney in
question 20.
64 CHEMISTRY FOR OUR TIMES
24. Describe how Lavoisier applied the scientific method in his studies of the
process of burning.
25. Investigate the Stahl-Becher theory of phlogiston, and explain it con-
vincingly.
26. What products are formed when kerosene burns?
27. For what reason does the flame on a lighted candle go out when
(a) The wick is pinched with the fingers?
(b) A person blows on it?
(c) The candle is suddenly dropped?
(d) The candle is thrown?
(e) The wick is inserted between the nearly closed jaws of a monkey wrench?
The Rate of Burning. 1. Iffect of Temperature. Experiments
show that, the hotter a fuel, the better it burns. Many chemical actions
take place more easily when the substances reacting are warm rather
than when they are cold. In fact, many reactions that proceed nicely at
high temperatures apparently do not take place at all at ordinary tem-
peratures. An automobile engine is designed so that the pipe carrying the
mixture of fuel and air to the engine passes over the pipe carrying the
hot exhaust gases from the engine. This arrangement preheats the gaso-
line vapor, making more efficient use of the fuel. Throwing cold fuel
on top of a hot fire is a wasteful process, although it is often the only
practicable way to feed a fire. A temperature rise, then, increases
the rate at which fires burn or, in general, increases the rate of oxide
formation.
2. Effect of Surface. A crumpled newspaper burns better than a
flat one; shavings burn better than a log of wood.
A "fuzz stick " (see Fig. 4-7) is used to start a
fire. Finely divided iron burns in air, as evidenced
by the sparks seen when a knife is sharpened on a
grinding wheel.
Chemical action takes place between particles
Attached °f reacting substances. Just as two boxers who are
to Stick close together have a better chance to " mix it up "
than when they are far apart, so it follows that,
the more closely or intimately mixed the different
particles are, the better the chance for chemical
IG. - .— uzz stick. ac^jon jf pure oxygen is used in place of air for
burning, the chance of the fuel and the oxygen coming together is
increased fivefold. Pure oxygen is seldom used for ordinary fires because
of the expense of gas. Another method, however, is commonly used if
rapid burning and a very hot fire are desired, namely, that in which the
BURNING, BREATHING, RUSTING
65
fuel is powdered and sprayed into the air. Powdered coal packs and burns
slowly, and an open vessel of oil burns poorly. But if particles of coal or
droplets of oil are mixed well with air and carried along by an air or
steam jet and thrown into a firebox, then burning takes place so
quickly that it is almost explosive.
We can illustrate this reaction by opening up a firecracker, spreading the
black gunpowder out on a metal pan, and carefully applying a lighted match to
the powder. The resulting flash shows that the carbon and sulfur in the gun-
Lighted Candle
FIG. 4-8. — A homemade dust explosion apparatus produces impressive results.
powder have united with oxygen, but in this case compacted oxygen comes from a
compound, potassium nitrate, which readily gives up that element.
Iron in Form of Burning
Spikes None
Steel wool Slowly if heated strongty
Dust Well if blown into air and ignited
" Pyrophoric " * iron (atom-fine dust) Catches fire by itself
* Pyrophoric iron may be made by heating ferrous oxalate carefully. Beware of the carbon monoxide
produced at the same time.
The effect on burning of the amount of surface exposed to the air is well
illustrated by the oxidation of iron. As we know, a common nail or spike will rust
(oxidize slowly), but we cannot light it with a match and make it burn. Fine steel
wool, on the other hand, burns a bit in air if heated in the flame of a Bunsen
burner, and the shredded metal burns brilliantly if heated and plunged into
pure oxygen. If the iron is powdered, it burns readily when warm enough, as is
66
CHEMISTRY FOR OUR TIMES
the case when fireworks " sparklers" are burned. Still further, if the iron is in a
very finely divided condition, as it is when it is made by heating ferrous oxalate,
it catches on fire when sprinkled into the air. We may observe that the nail is the
best conductor of heat in the group and that the fine dust, separated by air spaces,
is the poorest.
Dust Explosions. Sometimes the large amount of surface of a fuel
exposed to air is the cause of a serious disaster. Dust of flour, starch,
paper, or other substances that
will burn readily may become
suspended in the air of a mill.
While the mixture does not burn
under ordinary conditions for lack
of a kindling temperature, a
lighted match or cigarette or any
spark will set the entire mass to
burning. What was once dust
floating in air in a twinkling
becomes a raging inferno of heated
gas; we say that a dust explosion
has taken place. Thousands of
dollars' worth of property are
destroyed and lives are lost each
year in such explosions. Dust
from spices, cork, hard rubber,
and even dry milk has been re-
ported as causing dust explosions.
Courtesy of The Travelers Insurance Company
FIG. 4-9.— Will the dust in a factory
explode? Insurance companies find out by
using this apparatus. Once a hazard is dis-
covered, measures are taken to avoid an
explosion.
We can make a laboratory-size
dust explosion by using some flamma-
ble dust and a "press-on" covered
can, funnel, rubber tubing, and
candle arranged as shown in the dia-
gram. (See Fig. 4-8.) Using a tea-
spoon, let us put the dust in the funnel, then light the candle, press the cover
on, give a sharp puff through the rubber tubing to distribute the dust inside
the can, and (important) immediately pinch the tube to prevent backfire. A
miniature dust explosion should occur instantly. Lycopodium powder works
well in this experiment, although starch, wood dust, and other powders might
be tried. An electric sparking device may be substituted for the candle.
3. Effect of Catalysts. All of us have at some time attended a party
that "fell flat." Perhaps the right person did not come. Some persons
seem to ensure the success of a social event: they may not do anything in
particular, but by merely being present they "make things go." In like
manner some chemical actions "do not go well" unless another substance
BURNING, BREATHING, RUSTING 67
is present. This substance merely by its presence seems to control the
rate at which the chemical change proceeds. Strangely enough, the sub-
stance is not changed in nature or amount and may be recovered un-
changed after the chemical action. For example, dry phosphorus burns
hardly at all, but if the phosphorus is moist the burning will proceed
easily. Also, extremely dry ammonia and hydrogen chloride are reported
not to react, but when only slightly moist they form a white cloud of
ammonium chloride. Apparently in many cases a little moisture acts as
a helper of burning.
Let us illustrate the action of a catalyst by a competitive experiment. Two
pupils are given test tubes containing identical weights of potassium chlorate,
but one has a little manganese dioxide mixed in with the potassium chlorate. At
a given signal both pupils begin to heat their tubes at the same rate and to test
by inserting glowing splinters into the tubes to see which produces oxygen
sooner. The pupil in whose tube the catalyst (manganese dioxide) is placed
wins the contest easily, but the other will also get just as much oxygen although
a longer time and higher temperature are required.
Many other helpers might be mentioned. For example, sulfur dioxide
unites with oxygen in the presence of platinum; and platinum causes a
mixture of hydrogen and oxygen to explode. The chemists call these
helpers — substances that change the rate 01 chemical actions — catalysts.
A large measure of the success of the present-day chemist depends upon
his finding suitable catalysts to act as regulators for his chemical reac-
tions. A rubber tire contains catalysts that aid its curing and others
(antioxidants) that delay its hardening. Prepared house paint has a
"drier," a catalyst that helps it harden. A black substance, manganese
dioxide, speeds the decomposition of potassium chlorate when the latter
is heated to release oxygen. The same catalyst will make hydrogen
peroxide solution decompose rapidly. This solution sold at drugstores
usually contains an inhibitor (acetanilide), a sort of negative catalyst, to
prevent decomposition.
QUESTIONS
28. Certain types of stokers feed coal to a fire slowly from below the fire bed.
What advantage has this method of supplying fuel?
29. A certain type of stove has coal supplied to it from a hopper that is
placed directly above the center of the fire. What advantage has this method of
supplying fuel?
30. Describe and explain the burning of fireworks " sparklers."
31. Why does a nail not catch fire in the flame of a burning match?
32. Suggest a way to make sawdust burn well.
68 CHEMISTRY FOR OUR TIMES
33. When oil is sprayed into the firebox of a boiler by a steam jet, what be-
comes of the steam?
34. Describe the conditions that cause a dust explosion,
36. What can be done in a starch factory to avoid a dust explosion?
36. Define and give an example of a catalyst.
37. Manganese dioxide hastens the decomposition of potassium chlorate.
Does manganese dioxide hasten other decompositions?
MORE CHALLENGING QUESTIONS
38. What conditions are needed to produce spontaneous ignition?
39. The term flammable is now preferred to the word inflammable, both having
the same meaning. What advantage has the first-mentioned term?
40. Oily rags used about a garage do not catch fire as easily as rags used by
painters. Compare the rate of oxidation of motor crankcase oil with that of linseed
oil.
41. How does a flowing stream of water purify itself?
42. Do "fireproof" buildings ever burn?
Spontaneous Ignition, Commonly Called Spontaneous Com-
bustion. Burning may go on rapidly or slowly, as we found when we
considered the three factors — temperature, amount of surface, and the
presence of a catalyst — that influence the rate of this process. The burn-
ing of a match is quite rapid; the explosion of a firecracker is still more
rapid. The combining of a substance with oxygen, on the other hand,
may be exceedingly slow. The rusting of iron, the decay of wood, the
"drying" of paint are all examples of slow oxidation. Even when they
are cold, coal and sulfur both join slowly with oxygen.
Some painters who were working on a house used cloths to wipe off
excess paint. When the job was finished, they threw the cloths together
in a metal can, as was proper, although spreading them out would have
been a better way to avoid fire. The cloths were soaked with paint, which
is mixed with linseed oil, the oil from flaxseed (linen seed). This oil has
the ability to unite slowly with oxygen, liberating heat. If the heat energy
is not conducted away by air currents, thus cooling the cloths, the rise
in temperature will hasten the rate of oxidation. Faster oxidation means
heat generated at a still faster rate. The cloths mentioned above became
warmer and warmer until finally the temperature was reached at which
they began to burn actively. They had reached their kindling tempera-
ture by their own slow but rapidly accelerating oxidation and had begun
to bum of their own accord. This process is called spontaneous ignition.
Moist hay, coal, and other substances sometimes set themselves afire
BURNING, BREATHING, RUSTING 69
this way. In order to prevent spontaneous ignition, ventilating shafts
are put in piles of coal, in the holds of ships carrying grain, and in other
closed spaces where flammable materials are kept, to allow the hot air
to escape before the temperature rises to dangerously high values.
We can illustrate spontaneous ignition by wetting some paper with a solution
of phosphorus in carbon disulfide and allowing the carbon disulfide to evaporate.
This leaves the phosphorus in finely divided condition. Oxidation will be rapid,
and the paper soon catches fire. (See Fig. 4-10.)
Filter Paper
.Supported by a Beaker
r
Solution of
, White Phosphorus
in Carbon Disulfide
FIG. 4-10. — Spontaneous ignition of phosphorus in air.
Fireproof Substances. If a building is to be absolutely fireproof, the
construction materials must consist of fireproof substances, such as
bricks, concrete, plaster, glass, and asbestos. These substances do not
burn because they cannot; they already hold in combination all the
oxygen that they can. Structural steel is also used; it is fireproof, but for
a different reason. Unlike brick, the iron can combine with oxygen; but
a girder exposes so little surface compared with the total amount of iron
particles in it that oxidation takes place at a very slow rate. Also, heat is
conducted away rapidly by the girder. Of course, we know from experi-
ence which materials are fireproof and which are not, but we may expect
to find out from our study of chemistry the reason why some substances
burn and others do not.
The Great Scavenger. The earth is a much pleasanter place in which
to live because of decay. Were it not for this process, the earth's surface
would be littered with dead plants and animals. By the help of oxygen
this dead matter is changed into soil and other products, which in turn
furnish nutriment for living matter.
After a stream has traveled for several miles over rocks and water-
falls, it purifies itself of waste matter that may have been put into it.
The problem of waste matter disposal needs attention in many communi-
ties. Some people take great liberties with nature by turning rivers and
70
CHEMISTRY FOR OUR TIMES
lakes into open sewers. A farsighted city located on a river or lake first
treats its sewage before discharging it into the water. The great harm that
waste matter does in a stream is to consume the life-giving oxygen. If no
fish or plants can live in the stream because of lack of dissolved oxygen
in the water, then the stream becomes foul. Harmful bacteria that may
cause disease can be killed by spraying sewage or drinking water into the
air and sunshine. This enables the oxygen of the air to destroy the bacteria.
Of course, the effect of spraying is to increase the available surface for
the action of the oxygen. For the same reason a storm on inland or coastal
waters has a sanitary effect.
Thus we see the element oxygen playing two parts on the stage of
life. Its role as a necessary, humble, life-giving servant, healer of the sick,
and preventer of disease is one that we all appreciate. Oxygen also plays
the part of the villain when out of control, destroying our homes and
forests with its terrible chemical action, burning.
Plaiit-life-Animal-life Balance. The woody part of plants con-
sists chiefly of compounds containing three elements — carbon, hydrogen,
PHOTOSYNTHESIS
IN SUNLIGHT
BREATHING
FIG. 4-11. — Carbon dioxide-oxygen cycle.
and oxygen. These elements must be obtained by the plant from its sur-
roundings, the soil and the air. The soil furnishes water, the air carbon
dioxide, With sunlight, the leaves of a plant are able to carry on changes
in these materials, converting them into starches, sugars, and woody
tissues — wonderful changes that no person has yet been able to duplicate
BURNING, BREATHING, RUSTING
71
in the best chemical laboratory. Photosynthesis, as this process is called,
essential for animal life on the earth, uses the carbon dioxide from the
air and restores oxygen to it. A green coloring matter, chlorophyll, in
the leaf is the catalyst.
We have seen that carbon dioxide may be formed by burning in air
anything containing carbon. This gas also enters the air from the
natural processes of decay, breathing, and fermentation. It is apparent,
therefore, that the same carbon does duty again and again, going through
the plant-animal cycle from time to time. It is also apparent that energy
from the sun is necessary to keep carbon, essential to both plant and
animal life, moving in this cycle. Possibly all the oxygen in the air is
there as a result of photosynthesis. (See Fig. 4-11.)
Making Carbon Dioxide. At certain places on the earth gas wells
send forth enormous supplies of carbon dioxide gas. An old well, cistern,
^Hydrochloric
Acid (HCI)
Carbon Dioxide
Warm Water
,COo
Preparation Collection of Collection of A Bottle of
of Carbon Carbon Dioxide Carbon Dioxide by Carbon Dioxid<
Dioxide by Displacing Air Displacing Warm Water
FIG. 4-12. — Carbon dioxide is prepared in the laboratory by the use of a carbonate
and an acid — in this case, marble and hydrochloric acid.
cave, or similar cavity where decay is going on may have a layer of this
gas near the bottom where it is being produced faster than it diffuses into
the air above. One instance of this is a certain Italian cave, where any
small animal, such as a dog, becomes suffocated in the lower layer of gas,
whereas a larger animal or adult human being may wade through it
unharmed.
Carbon dioxide was discovered and shown to be a distinct gas by a
Scotch chemist, Joseph Black (1728-1799) , in 1775. All complete burning of
carbon or its compounds in air produces carbon dioxide, C + 02 — > C02.
This reaction and the process of fermentation are both used industrially
as a source of this gas. Commercial sources of carbon dioxide also include
some natural gas and carbonates and bicarbonates, which are heated to
obtain the gas.
72
CHEMISTRY FOR OUR TIMES
We generate carbon dioxide in the home when we make bread. The
yeast plant acts on the sugar to produce this gas, which in turn makes
bubbles in the dough to leaven (lighten) it. The porous nature of most
baked foods is due to bubbles of this gas. All baking powders make
carbon dioxide when added to water or heated. Effervescent tablets or
powders, sometimes used medicinally, generate carbon dioxide in a
manner similar to the action of baking powders.
In the laboratory it is customary to select the method for making a
gas that proceeds at a moderate rate, is convenient, and uses cheap and
Courtesy of Pure Carbonic, Incorporated
FIG. 4-13. — Every 7 minutes a 220-pound block of solid carbon dioxide drops out of
this huge machine. Solid carbon dioxide has extensive use as a refrigerant because it
sublimes.
readily obtainable materials. These conditions for making carbon dioxide
are all met by putting acid on marble in a gas generator bottle. (See Fig.
4-12.) Marble is almost pure calcium carbonate (CaC03), the source of
the carbon dioxide in this case. Hydrochloric acid (HC1), a compound of
hydrogen and chlorine in water solution, is added through a funnel or
safety tube, and the gas escapes through the delivery tube into a vessel
made ready to receive it. The action is thought to go on in two steps,
the carbonic acid first formed being quite unstable and therefore decom-
posing at room temperature.
CaCO3 + 2HCI : — > CaCl2 + H2CO3
Calcium carbonate + hydrochloric acid — * calcium chloride -f- carbonic acid
H2CO8 > H2O 4- CO?
Carbonic acid decomposes to form water and carbon dioxide
BURNING, BREATHING, RUSTING
73
This action is quite general; any strong acid and any caifmnate will give
similar results.
If carbon dioxide is present in large amounts in the air, there is usually
a lack of oxygen. For example, in Chungking, China, in 1941, 4000
Chinese died in an air-raid shelter, not from bombs, but from suffocation
and panic caused by lack of sufficient oxygen in the air.
Properties and Uses of Carbon Dioxide. The gas carbon dioxide,
since we breathe it out through our nostrils, obviously has no odor, color,
or marked taste. One liter weighs 1.98 grams, compared with 1.29 grams
for a liter of air. Water dissolves a moderately large volume of carbon
dioxide, especially when the water is cold and the gas under pressure.
Carbon
Dioxide
Christmas
Candles
FIG. 4-14. — The effect of carbon dioxide on burning can be demonstrated by this ex-
periment. As carbon dioxide reaches each candle, the flame is extinguished.
Seltzer or soda water contains dissolved carbon dioxide, and tastes slightly
sour. Sufficient pressure on the gas alone changes it into a liquid, "liquid
carbonic acid gas," which is supplied to drugstores for soda-fountain use.
Solid carbon dioxide, called Dry Ice, is well known. (See Fig. 4-13.) This
substance may be formed by rapid expansion of the compressed gas from
a small opening. It is useful for refrigeration purposes because of its low
temperature, about — 78°C, and the fact that it evaporates into a gas
at room conditions of temperature and pressure without going through a
liquid state, a process known as sublimation.
Dry Ice generators make effective fire-fighting devices. One notices a
funnel or cone-shaped end on the hose leading from the cylinder of liquid
carbon dioxide on this type of fire-fighting equipment. (See Fig. 4-15.) The
funnel-shaped opening directs the shower of carbon dioxide snow formed
when the valve is opened. Since ordinary burning will not occur in carbon
74
CHEMISTRY FOR OUR TIMES
dioxide, nor will the gas catch fire and burn, this dense, cold gas makes
an effective substance to use to put out fires.
The turnover type of fire extinguisher contains a bottle of acid that
when inverted mixes with a bicarbonate solution, generating carbon
dioxid^ gas.
H2SO4 + 2NaHCO3 -> Na2SO4 + 2H2O + 2CO2|
(See Fig. 4-16.)
Other types of fire extinguishers generate the gas by a similar action
but enclose it in a stiff foam. This is a much more effective way to use
the gas, especially for fighting oil fires. (See Fig.
4-17.) Still another sort of fire extinguisher contains
a capsule of compressed liquid carbon dioxide similar
to that used for inflating life rafts. When the capsule
is broken by inverting the extinguisher and striking
it against a hard surface, the gas forces itself and
water, which is also in the extinguisher, out the
nozzle.
Liquid carbon dioxide is used extensively as an
explosive in mining coal.
Sparkling beverages containing carbonic acid are
great thirst quenchers. Soda water in all its tasteful
flavors is sweetened carbonic acid solution. The
beverage is prepared by the addition of a little
flavored sirup to a carbon dioxide-water mixture
under pressure.
CO2 + H20 -> H2C03
Taken into the mouth where the temperature is
warm, the carbonic acid decomposes into water and
carbon dioxide again, the gas bubbles causing a
sensation on the tongue that "tastes like your foot's
asleep." Beverages like homemade root beer have
carbon dioxide produced in them by fermentation.
Carbon dioxide reaches our lungs and is dis-
charged as a waste product of the body after it is
separated from the blood. Experiments show that
some carbon dioxide dissolved in the blood is
essential for normal breathing. In cases of attempts
to revive a person after gas poisoning, Prof.
Henderson of Yale University found that 3 per cent carbon dioxide mixed
with oxygen is more effective than pure oxygen. The carbon dioxide
stimulates the " breathing centers" in the brain.
Courtesy Pyrene Manu-
facturing Company
FIG. 4-15.— This
fire extinguisher con-
tains liquid carbon
dioxide. When the
valve is opened, the
escaping liquid evap-
orates, forming car-
bon dioxide snow,
thus showering the
fire with a very cold
blanket of nonflam-
mable gas.
BURNING, BREATHING, RUSTING
75
READY
IN USE
Loose Lead
Stopper
Baking Soda
in Water,
Filled to Mark
NaHC03
H2S04
FIG. 4-16. — When the extinguisher is inverted, the contents
of the acid bottle mixes with the bicarbonate solution. Carbon
dioxide is formed under pressure, and the contents of the ex-
tinguisher is forced out of the nozzle.
Courtesy of Pyrene Manufacturing Company
4
, 4 ;;
FIG. 4-17. — A typical industrial lire involving flammable liquids is short lived when
a foam-type carbon dioxide extinguisher is used. A stream of water would be useless
for such a fire.
One way in which an engineer tests his steam boilers for operating
efficiency is to measure the percentage of carbon dioxide in the gas t hat
goes up the chimney. Frequently a "stack CO2 recorder" is part of the
76
CHEMISTRY FOR OUR TIMES
equipment of a large boiler. (See graph, Fig. 4-18.) One type of recorder
depends for its success on one of the important properties of carbon
dioxide — its ability to combine with a solution of a hydroxide. Probably
the carbonic acid is first formed.
FIG. 4-18. — At what time did the fireman start the boiler for heating the school
building? At what time was the oil fire shut off? The record on the stack carbon
dioxide recorder tells the story. It also indicates how effectively the fuel was burned.
H2O + CO2 -4 H2CO3
Then the acid acts on the hydroxide.
H2CO3 + 2NaOH
Carbonic acid + sodium hydroxide (lye)
Na2CO3 -f 2H2O
sodium carbonate -}- water
When a solution of calcium hydroxide is used for this action, the
calcium carbonate that is produced is insoluble in water. It is seen as a
white powder in the liquid, giving an appearance of milkiness. Small,
solid, insoluble particles formed in this manner are called a precipitate.
When their density is greater than that of the liquid, they usually settle
to the bottom of the container.
H2CO3 + Ca(OH)2
Carbonic acid -f- calcium hydroxide
(limewater)
CaC03 + H20
calcium carbonate -f water
Since no other gas acts in just this way, this action is used as a test
to identify the gas carbon dioxide. (See Fig. 4-19.)
BURNING, BREATHING, RUSTING
77
Clear Limewater
(calcium hydroxide solution)
Becomes Cloudy
FIG. 4-19. — The presence of carbon dioxide can be proved by the milky precipitate it
forms in lime water.
Secondary
Air
FIG. 4-20. — A number of chemical changes go on in an ordinary coal fire. When the
stove is operating properly, the dangerous carbon monoxide is completely burned.
The Household Stove. Another chemical action of carbon dioxide
is illustrated by the changes that take place in the firebox of a household
78 CHEMISTRY FOR OUR TIMES
stove that burns charcoal, coal, or coke — all considered to be pure carbon
in this discussion. (See Fig. 4-20.) Air enters the stove through the bottom
door. The oxygen unites with the hot carbon in the lower part of the fire.
C + O2 -> CO2
As the carbon dioxide formed rises, it meets more hot carbon, which
shares the oxygen with it, forming carbon monoxide.
CO2 + C -+ 2CO
In this action we say that the carbon dioxide was reduced, that is,
had oxygen taken from it. Cai'bon monoxide reaches the top of the bed of
coals, where it receives more air through the upper door and burns with
the blue flame seen playing over a coal fire, again forming carbon dioxide.
2CO + O2 -> 2CO2
Compared with oxygen, carbon dioxide often exhibits an opposite
character.
Oxygen aids burning. Carbon dioxide stops burning.
Oxygen aids breathing. Carbon dioxide suffocates.
Oxygen combines with burning substances. Carbon dioxide is a product of burning
SUMMARY
In ordinary burning a flammable substance unites with oxygen of the air,
a change that gives out light and heat; the products formed are oxides. This
process was not always understood correctly. The phlogiston theory (about 1 700)
gave an incorrect explanation that was disproved by careful experimentation on
burning carried out by Antoine Laurent Lavoisier, a great French scientist.
The requirements for burning are
1. A flammable fuel
2. An adequate supply of air or oxygen
3. Temperature up to the kindling or ignition point
Methods of extinguishing a fire include removal of any one of the three con-
ditions necessary for burning. More specifically, we may
1. Cool the burning material below its kindling point
2. Shut off the air or oxygen
3. Remove the fuel
Physical properties: Oxygen is colorless, tasteless, odorless, and slightly
soluble in water and has a density of 1.29 grains per liter at standard conditions.
Chemical properties: Oxygen aids burning and does not catch fire, and it forms
oxides when it combines with both metals and nonmetals.
Oxygen is identified by the fact that a glowing wooden splinter will burst into
flame in the gas.
Oxygen is used to aid breathing under difficulties such as in sickness, in sub-
marine work, and at high altitudes. It is also used to produce intensely hot fires
as in the oxyacetylene torch. The gas comes to the market compressed in strong
steel cylinders.
When an element joins oxygen, an oxide is formed. The oxide weighs more
BURNING, BREATHING, RUSTING 79
than the original element, but the weight of the element plus the weight of the
oxygen used just equals the weight of the oxide formed. The elements sulfur and
chlorine both act chemically in supporting burning in a manner similar to oxygen,
but they form sulfides and chlorides, respectively, as products of burning.
Incomplete burning of carbon or its compounds may produce carbon mon-
oxide, a very poisonous gas. Hence attention to the exhaust fumes from a running
motor and to other sources of this deadly gas is advisable from a health stand-
point. Oxidation may be complete or partial, depending upon the conditions of
burning.
Increased temperature hastens the rate of burning, and the closer the contact
between the fuel and air the more rapid the burning. A dust explosion is an ex-
treme case of rapid burning. Conditions necessary for a dust explosion include the
distribution of a flammable dust in the air of a closed space and a means of igniting
the mixture. An extremely rapid oxidation takes place.
Substances acting as catalysts hasten the rate of combining with oxygen.
Their action is specific to a given situation. An example of the use of a catalyst is
the adding of manganese dioxide to hasten the decomposition of potassium chlor-
ate in the preparation of oxygen.
Spontaneous ignition is sometimes called spontaneous combustion. To undergo
spontaneous ignition, a substance must be capable of slow oxidation, and the heat
resulting from the oxidation must accumulate. The rising temperature increases
the rate of oxidation, and this in turn increases the temperature until the kindling
temperature is reached.
Oxygen enters in the natural processes of decay and fermentation of waste
materials. Oxygen purifies natural water, and it is used for burning and breathing.
Carbon dioxide is found in the air (about 0.03 per cent) and in places where
decay and fermentation are occurring. Some natural gas wells are rich in this gas.
A little of the gas is needed to stimulate the breathing of animals, and plants use
the gas extensively in photosynthesis. Impure carbon dioxide is made by burning
carbon or carbon compounds. It can also be collected from tanks in which fermen-
tation is proceeding and from certain natural gas wells.
In the laboratory, carbon dioxide is prepared by the action of an acid on a
carbonate or a bicarbonate. Marble, consisting chiefly of calcium carbonate, is
usually used as the source of the gas. The gas may be collected by displacement of
either water or air.
. Physical properties: Carbon dioxide is colorless, odorless, almost tasteless,
moderately soluble in water, and more soluble with increased pressure. Its density
(1.98 grams per liter) is greater than that of air, and it is rather readily changed
to" a liquid or to a solid (Dry Ice).
Chemical properties: Carbon dioxide not only does not burn, but also it ex-
tinguishes ordinary fires. It combines with water, forming carbonic acid, and it
forms a carbonate with any soluble hydroxide. The test to identify the gas is
made by passing some of it into lime water (calcium hydroxide solution). If a white
precipitate forms, the presence of carbon dioxide is shown.
Carbon dioxide is used in carbonated beverages because it is moderately
soluble and forms a weak acid with water. It is used extensively as in fire extin-
guishers and as a refrigerant, especially in the form of Dry Ice.
80 CHEMISTRY FOR OUR TIMES
QUESTIONS
43. Suggest a practical way to find out whether carbon dioxide is present in a
well; in a silo.
44. Explain the holes in baked cake dough.
46. List five natural sources of carbon dioxide.
46. Tell how to make impure carbon dioxide from paper.
47. Describe a laboratory method of preparing carbon dioxide from marble.
Include a labeled sketch of the apparatus.
48. Complete these statements of chemical changes (do not write in this book) :
(a) Magnesium carbonate + hydrochloric acid — >
(6) Strontium carbonate + hydrochloric acid — >
(c) Barium carbonate + hydrochloric acid — >
(d). Sodium carbonate + hydrochloric acid — »
49. List at least four physical properties of carbon dioxide.
60. Dry Ice is sometimes placed inside closed automobiles crossing the desert.
Point out a possible danger from refrigerating a car in this manner.
51. Point out a use of carbon dioxide in 'connection with rubber life rafts.
62. Complete these statements of chemical changes (do not write in this book) :
(a) Carbonic acid + sodium hydroxide — »
(b) Carbonic acid + potassium hydroxide — »
(c) Carbonic acid + calcium hydroxide — »
(d) Carbonic acid + barium hydroxide — >
MORE CHALLENGING QUESTIONS
53. Distinguish carbon dioxide from oxygen by practical laboratory testing.
64. Compare the methods of storing and distributing ice cream using mechan-
ical refrigeration and Dry Ice with methods of doing the same job without these
conveniences.
65. Give a description of conditions that can cause a parlor stove to become a
death-dealing device.
68. Make a labeled diagram of a furnace burning coal, pointing out all chem-
ical changes occurring.
67. A stack COz recorder shows an abnormally high amount of the gas. What
are the cause and remedy of this condition? If the CO 2 indicator shows too low a
percentage of the gas under full load, why is fuel being wasted?
UNIT ONE CHAPTER1 V
HYDROGEN, THE LIGHTEST GAS
On May 6, 1937, the dirigible Hindenburg, pride of Germany's air-
craft, was nosing her way toward a mooring mast at Lakehurst, New
International News Service
FIG. 5-1. — One of the greatest disasters in air history took place in 1937. Many
lives were lost in this tragedy. The burning of hydrogen from the gas cells of the
Hindenburg is clearly shown here.
Jersey. Suddenly the hydrogen-filled bag, which buoyed the ship up,
burst into an inferno of blazing gas. (See Fig. 5-1.) The intense heat from
decomposition
electrolysis
reducing agent
New Terms
reduction
oxidized
oxidizing agent
deuterium
81
heavy hydrogen
kinetic
molecule
82 CHEMISTRY FOR OUR TIMES
the fire melted much of the metal framework as the ship fell to the ground,
a complete disaster. The cause of this tragedy is thought to have been a
spark due to static electricity resulting from friction. Afterward a small
local rainstorm occurred; the burned hydrogen formed steam, and the
steam condensed to water which soon followed the framework of the ship
to the ground.
Early History of Hydrogen. Hydrogen was discovered in 1766 by
Henry Cavendish, a wealthy Englishman who studied science as an all-
absorbing hobby. He called the gas " inflammable air/7 The name
hydrogen, meaning "water producer," was given to the gas by Lavoisier
(see page 54) in 1783, when he proved that water is the only product
formed by burning hydrogen.
Soon its lightness was noticed, and hydrogen-filled balloons were
making ascents over Paris. Pilatre de
Rozier (1754-1785), who made the first
notable flight in 1783, also tried breathing
the gas. (See Fig. 5-2.) No immediate effect
was noticed until an additional experiment
was tried. The experimenter filled his lungs
with hydrogen. On exhaling, he applied a
FIG. 5-2. Pilatre de Ho- lighted torch to his breath. The result was
zier's famous balloon flights startling. Not only did his exhaled breath
are commemorated on this b jyi the effect of human torch
French postage stamp. i i i • 111
but the hydrogen mixed with air exploded
in his mouth, throat, and lungs. "I thought that my teeth would jar
loose from their sockets," he writes, after barely surviving the explosion.
Where Is Hydrogen Found? The element hydrogen is seldom found
free. Free hydrogen does occur among the gases coming from certain gas
wells, but only to a small extent. Although this gas exists so rarely in the
free state on earth, astronomers report that free hydrogen is abundant in
the exceedingly hot gases on the sun and other stars.
Compounds of hydrogen, on the other hand, are abundant. For
example, all living tissues contain compounds of hydrogen. Also, water,
fats, oils of every sort, starch, sugar, alcohol, acids, wood, cotton, paper,
gasoline, and natural gas all contain hydrogen in combination, that
is, in compounds.
In many manufacturing processes hydrogen is a product. Water gas,
coal gas, and producer gas are three commonly manufactured fuel gases
that contain hydrogen. Water gas, a mixture of hydrogen and carbon
monoxide, contains about 48 per cent hydrogen, coal gas almost 50 per
cent, and producer gas 14 per cent by volume. Many processes involve
electrolysis, or the passage of an electric current through a solution, and
HYDROGEN, THE LIGHTEST GAS
83
hydrogen is usually a product. When, for example, a storage battery is
charged, bubbles of hydrogen come up through the liquid (sulfuric acid
solution) inside the battery. When these bubbles mix with air, they may
explode if ignited. Electroplating and other processes in industry, such
as the electrolysis of salt water, may evolve hydrogen.
Decomposing Water into Its Elements. Water is such a common
compound that for many centuries it was thought an element. Water is
stable; that is, it is extremely difficult to decompose by heating. When
steam in a closed vessel is heated to the extremely high temperature of
2000°C, about 1 per cent of the water decomposes into hydrogen and
Hydrogen
Oxygen
Pencil Leads or other
Carbon Rods
Copper
Wire
3 Dry Cells in Series
FIG. 5-3. — The electrolysis of water can be carried out with a relatively simple
apparatus. Two metal strips, preferably platinum, are inserted in separate test tubes
that are inverted in a vessel of dilute acid. When the metal strips, or electrodes, are
connected to a battery, decomposition proceeds readily.
oxygen. As the mixture cools the two elements rejoin to form water.
Heating to a high temperature, therefore, is not a satisfactory way to
decompose water, but it is readily decomposed by means of electrical
energy.
Pure water is a poor conductor of electricity. The addition of sulfuric acid or
sodium hydroxide (lye) to water improves its conducting ability. A suitable
apparatus in which we can carry out this important experiment consists of two
connected vertical tubes. (See Figs. 5-3, 5-4.) Each tube is equipped with a metal
plate at the bottom, one providing a surface for the electrical energy to enter the
solution and the other for the electricity to leave. A stopcock at the top of each
tube is convenient for removing the gases collected. When we turn the current on,
bubbles of gas arise from the two plates, or electrodes, and collect at the top of
the tubes. After the chemical change has gone on for a short while, we notice that
gas is collecting faster in one tube than in the other. Let us stop the current after
84
CHEMISTRY FOR OUR TIMES
Na2S04
Solution
:- Electrode
Courtesy of Buffalo Museum of Science
FIG. 5-4. — Hoffman's apparatus for
electrolysis of water. Water yields two
volumes of hydrogen and one of oxygen
when sulfuric acid is added and an elec-
tric current is passed through the
solution.
a few minutes and measure the amount of gas found in each tube. We find, for
example, that 18.4 ml has collected in one tube while a little less than 9.2 ml has
collected in the other.1
What are these gases? Both are colorless like air. The larger volume of gas
catches fire when a lighted match is applied; this will serve for the present as a
1 The volumes of hydrogen to oxygen gas are not exactly in the ratio 2: 1 because of
the differences in solubility of the gases in water.
HYDROGEN, THE LIGHTEST GAS 85
test for hydrogen. The smaller volume of gas makes a glowing splinter catch fire ;
it is oxygen.
This chemical change can be summed up in the statement that
Water forms hydrogen (18.2 ml) and oxygen (9.2 ml)
or, in general, that
Water forms hydrogen (2 parts by volume) and oxygen (1 part by volume)
Still more concisely:
2H2O -f 2H2 + O2
This experiment is called the decomposition of water. Since it is a
chemical change brought about by electrical energy, it is also called the
electrolysis of water.
How to Prepare Hydrogen. Hydrogen gas is readily liberated from
its compounds. Let us conduct some experiments in its preparation.
1. From Water, a. We have just seen (above) that passing an electric
current through water that contains some sulfuric acid liberates hydrogen as well
as oxygen. This experiment is identical with the preparation of oxygen by this
method. The volume of hydrogen formed is twice that of the oxygen.
The change that takes place may be represented by the statement
(sulfuric acid)
2H2O » 2H2| + O,T
Water > hydrogen -j- oxygen
b. Active metals — calcium, sodium, or potassium — replace hydrogen from
cold water, forming the hydroxides of the metals at the same time.
Chips of metallic calcium are allowed to sink in a bottle of water. (See Fig.
5-5.) The bottle is immediately covered with a glass plate and inverted, mouth
downward, in a tank of water. The glass plate is then removed. The liberated
hydrogen rises through the water to the top of the bottle, and the slightly soluble
calcium hydroxide [Ca(OH)2], or slaked lime, may be seen as a white suspension
in the water.
Ca +2HOH -4 Ca(OH)2 + H2|
Calcium -f- water — * calcium hydroxide + hydrogen
Apparently more rapid action takes place when sodium is used instead of
calcium, so that a different experimental method (technique) is used. A piece of
sodium the size of a small pea is cut from a larger chunk with a dry knife. The
soft, bright, silvery metal is placed in a wire-screen cage at the end of a long wire
handle and cautiously but quickly lowered under an inverted bottle full of water,
which is resting in a pan of water. (See Fig. 5-6.) CAUTION: The experimenter
should be protected by goggles and by working at arm's length, for the action is
86
CHEMISTRY FOR OUR TIMES
rapid, and the resulting solution of hot sodium hydroxide (NaOH) is corrosive to
the flesh.
2Na + 2HOH*> 2NaOH -f H2T
Sodium + water — > sodium hydroxide -j- hydrogen
Even more vigorous action takes place when a tiny chip of metallic potassium
is dropped into a large pan of water. In this case the hydrogen is formed at a tern-
Hydrogen
Calcium
<» (ID
FIG. 5-5. — Active calcium replaces part of the hydrogen in water, liberating the ga*.
Hydrogen
Sodium Tongs
Water
Sodium Hydroxide
Solution
FIG. 5-6. — Extreme care must be used when sodium is placed in water. The
energy of the reaction may cause steam to spatter the Aiemicals. The use of sodium
tongs, shown above, keeps the experimenter somewhat removed from this danger.
perature above its kindling point ; thus the gas will catch fire and burn as fast as
it is produced if the action takes place in the open air. The caustic potash solution
— potassium hydroxide (KOH) — formed at the same time is also dangerous. The
experiment, therefore, must be performed with extreme care, only small bits of
potassium being used at one time.
This last experiment is not practical for a laboratory preparation of
hydrogen; but, if considered with the other two experiments, it shows
the relative activity of the metals used. We may arrange these metals in
a list on the basis of the vigor of their action with water.
Most active
Potassium
K
Less active
Calcium
Sodium
Ca
Na
HYDROGEN, THE LIGHTEST GAS
87
Other experiments show that the problem of determining the relative activity
of a metal is not quite so simple, for surface tarnish may interfere.
c. Steam produces hydrogen when it is passed over hot coke, iron, or zinc.
In the first case the hydrogen is mixed with carbon monoxide, a gas that might
Hydrogen
FIG. 5-7. — Heated iron will replace the hydrogen in steam. A convenient method
of performing this experiment is shown above. Any unchanged steam passes through
the tube and is condensed in the water over which hydrogen is collected.
interfere with the laboratory use of hydrogen but that usually does not interfere
with its commercial use.
H2O 4- C
steam coke
CO -
carbon
monoxide
Hz
hydrogen
water gas
For several reasons, this experiment is not easily adapted to demon-
stration on a small scale, but there is no trouble in using a ton of hot coke
in a generator to prepare water gas on a large scale.
To pass steam over iron, an iron pipe is stuffed loosely with steel wool and
placed in position to be heated. The steam is then passed into one end, and a mix-
ture of hydrogen and steam emerges from the other. The steam is condensed by
passing the products through water, and the hydrogen is collected as shown in
the figure. (See Fig. 5-7.)
3Fe + 4H20 <=t Fe3O4 + .4H2
iron steam magnetic hydrogen
iron oxide
After a while the iron in the pipe becomes changed into magnetic iron oxide.
It is interesting to note that the process can be reversed by passing hydrogen
through the tube containing heated iron oxide. Then the iron oxide changes back
to iron and the hydrogen to steam. Such a chemical action is called reversible.
88
CHEMISTRY FOR OUR TIMES
2. From Acids. All strong acids contain hydrogen that can readily be re-
placed by a metal. A plumber "cuts" muriatic acid (hydrochloric acid) by adding
bits of scrap zinc. The resulting solution of zinc chloride is useful as a flux in
soldering metals together.
Hydrogen is usually prepared by the replacement method in the laboratory.
If we wish to examine the gas formed, we use a generator similar to that shown for
Acid
Water
Zn
Hydrogen
Generator
Collection of Hydrogen
by Displacing Water
A Bottle of
Hydrogen
FIG. 5-8. — The common method of preparing hydrogen. A moderately active
metal, such as zinc, is used to replace the hydrogen in a dilute acid. The gas is col-
lected in the same manner as is oxygen,
the preparation of carbon dioxide (see Fig. 5-8) and collect the hydrogen by dis-
placing water. The chemical action that takes place is represented by the equations
Zn -f 2HCI
Zinc -f hydrochloric
acid solution
Hit + ZnCI2
hydrogen gas + zinc chloride
(left in solution)
With dilute sulfuric acid the statement is
Zn -f H2S04 -4 Hs| + ZnS04
Zinc -j- sulfuric acid — » hydrogen gas -f zinc sulfate
(solution) (left in solution)
An action of this kind is rather general. Aluminum, magnesium, or
tin may be used instead of zinc. Each metal produces hydrogen at a
different rate. Dilute sulfuric acid, phosphoric acid, or acetic acid may
also be used in place of hydrochloric (muriatic) acid. Aluminum and tin
do not liberate hydrogen from nitric acid because of a protective oxide
coating. Copper and the precious metals are not active enough to replace
the hydrogen from acids.
HYDROGEN, THE LIGHTEST GAS
89
By comparing the activity of metals in acids, as we did in the case of
potassium, calcium, and sodium in water, we can list all the metals in the
order of their activity. (See Fig. 5-9.) It is customary to place the most
ft
Calcium Magnesium Aluminum
ft\
s^
Zinc
Tin
Copper
No Action
FIG. 5-9. — The metal that dissolves in the acid first is the most active chemically
(provided all other conditions are equal).
active metal first and the least active last and to include hydrogen in
the list. Any metal above hydrogen will replace it from an acid, but any
metal below hydrogen will not.
T ., . * i u MI THE REPLACEMENT SERIES OF
Likewise, any metal above will METAIS*
replace one below it from a com- R * ...../. Potassium
pound of the less active metal. For
example, an iron nail placed in a
solution of copper sulfate soon
forms a pink coating of copper on
the nail.
Fe
Nail
CuSO4 -
copper sulfate
solution
FeSO4 4- Cu
iron sulfate copper
solution
. Calcium
Sodium
Magnesium
Aluminum
Zinc
. Iron
. Nickel
. . . Tin
Lead
HYDROGEN
Copper
. Mercury
. Silver
Platinum
Gold
B, that Zinc is beloW magne- * The first part of the list is easily memorized
Our list* and Since it is ^y referring to the synthetic name of the " Russian
7. chemist," P. C. S. Mazintl.
thus a less active metal than
magnesium, we expect no chemical action to take place.
3. From Solutions of Alkalies. Zinc, aluminum, or silicon will act with a
solution of lye (NaOH) or caustic potash (KOH) to liberate hydrogen vigorously.
Yet a solution of Epsom
(magnesium sulfate) can be carried
in a zinc pail without any chemical
change taking place. We notice, of
Na..
Mg.
Al...
Zn..
Fe...
Ni..
Sn...
Pb..
H...
Cu..
Hg..
Ag..
Pt..
Au...
90
CHEMISTRY FOR OUR TIMES
The action may be represented thus:
2AI + 2KOH + 2H2O
2KAIO2
potassium
aluminate
3H2T
Pure Hydrogen. When hydrogen is prepared by the reaction of an
acid and iron or zinc, the gas has a disagreeable odor due to impurities
in the commercial metal. Most of the impurities may be removed by pass-
ing the impure gas through solutions that absorb and react with the
impurities but do not affect the hydrogen. Moisture is removed by passing
the gas through a tube that contains a drying agent. We then have pure,
dry hydrogen, which has no odor or taste.
Apparatus for obtaining pure and dry hydrogen by such a method is
shown in the figure. (See Fig. 5-10.) The solution of sodium hydroxide
Impure
Hydrogen
,Pure Dry
Hydrogen
Water-
FIG. 5-10. — When pure hydrogen is required, the gas may be passed through a purify-
ing train such as the one above.
(NaOH) removes any acid impurities, and the potassium permanganate
solution (KMn04) oxidizes others. The drying agent, commercial Drierite
(anhydrous CaS04) or calcium chloride (CaCl2) in small lumps, removes
any moisture.
QUESTIONS
1. By whom and when was hydrogen discovered?
2. What does the name hydrogen mean? Who gave this name to the gas?
3. If a bottle of hydrogen is broken on a mountaintop, which way will the
hydrogen tend to move?
4. Point out the danger in bringing a lighted match near a storage battery
that is being charged.
5. Name the gases formed in the decomposition of water by electrolysis.
6. Complete the word equations for the action of the following active metals
on water (do not write in this book) :
Potassium -f water — *
Lithium •+• water — >
HYDROGEN, THE LIGHTEST GAS 91
7. What experimental evidence have we for arranging the elements potas-
sium, calcium, and sodium in this order?
8. In World War I hydrogen for balloons was prepared by the action of a
hot solution of sodium hydroxide on ferro-silicon, acting according to the equation
Si + 2NaOH + H2O -+ Na2SiO3 + 2H2f
Copy the equation, and under each formula write the name of the substance.
From what original substances might the hydrogen come?
9. (a) When zinc is placed in hydrochloric acid, what is the source of the
hydrogen evolved? (6) After the zinc has disappeared and the resulting solution
evaporated to dryness, a white solid remains. Name this compound.
10. Complete the word equations for the actions of zinc, magnesium, and alu-
minum, each, on hydrochloric acid, sulfuric acid, and phosphoric acid, respectively.
MORE CHALLENGING QUESTIONS
11. Name the products formed when metallic calcium acts on each of the
following acids: hydrochloric, nitric, sulfuric, phosphoric.
12. In each case below tell whether or not a chemical action of replacement
takes place. Name the products in case there is a chemical reaction.
(a) Zinc -+• magnesium chloride solution
Zinc + silver nitrate solution
Zinc + zinc sulfate solution
(6) Copper plus each of the same three solutions
13. Tell several possible ways in which a hydrogen-air mixture around the
gas cells of a dirigible might become ignited.
14. A pupil prepared hydrogen in the laboratory and then smelled the gas.
The unpleasant odor seemed to disagree with the description given in the book,
that " hydrogen has no odor." Account for the disagreement.
15. Prepare pieces of different metals, each having approximately the same
amount of surface. Place each in a test tube, and add equal portions of hydro-
chloric acid. By noting the differences in the rate of reaction, arrange the metals
in order of their chemical activity. Look up more information about metals; can
you explain any seeming disagreement with the replacement series given in this
chapter?
Physical Properties of Hydrogen. Hydrogen is a gas at room tem-
perature. It can be changed to a liquid, but only with great difficulty.
The gas is colorless and without odor or taste. We can collect the gas by
displacing water from a container because hydrogen dissolves in water
even less than does oxygen. One liter of hydrogen at standard conditions
weighs approximately 0.09 g. It is the lightest gas known, a fact that can
be demonstrated
92
CHEMISTRY FOR OUR TIMES
1. By pouring hydrogen gas from one bottle to another upward. (See
Fig. 5-11.)
2. By catching some hydrogen in an inverted beaker that has been
balanced on a scale. (See Fig. 5-12.) The pan
holding the beaker will rise after hydrogen has
been caught in it.
3. By filling soap bubbles (use Drene or
Dreft solution and two generators connected
to a Y tube) with hydrogen. The bubbles rise
readily and explode when brushed with a
lighted taper.
4. By filling a toy paper or rubber balloon
with hydrogen from a cylinder. Either will rise
and carry a small load.
Hydrogen is the readiest of all gases to
diffuse, that is, to pass through small openings.
Air
FIG. 5-11. — Hydrogen gas
pours up.
If a porous clay jar is covered with a glass bell jar full of hydrogen, so much
more hydrogen will pass into the clay jar than air will pass out that the pressure
rises inside the jar. This pressure may be used to squirt water. (See Fig. 5-13.)
Chemical Actions of Hydrogen. The most marked chemical action
of hydrogen is its ability to burn in air, a fact we have already noted.
FIG. 5-12. — When hydrogen is poured upward into the inverted beaker on the balance,
what happens to that side of the balance beam?
When it does so, water is the only product. When this experiment, illus-
trated by Fig. 5-15, is performed, the hydrogen is dried in order to prove
that the moisture that collects has not been carried over from the gen-
erator to the beaker that acts as a condenser.
HYDROGEN, THE LIGHTEST GAS
93
Beaker
FIG. 5-13. — This shows how to water
flowers the hard way. Diffusion rates vary
inversely as the square roots of the
densities. Hydrogen (density 1) diffuses
four times as fast as oxygen (density 16).
FIG. 5-14. — Here is an experiment
to try: light a jet of flammable gas J
by first catching a test tube full,
carrying it to lighted burner B, and
then returning it lighted to /.
Moisture
FIG. 5-15. — When this apparatus is
used, we know conclusively that the water
formed must be a product of the burning at
the jet.
Hydrogen
Wax Taper
FIG. 5-16.— A lighted
wax taper inserted into an
inverted bottle of hydrogen
ignites the gas at the mouth
M where it meets the air.
The gas burns at the mouth
of the bottle and melts the
wax. The taper goes out in
the hydrogen but reignites
on being withdrawn slowly.
94
CHEMISTRY FOR OUR TIMES
In the above experiment hydrogen burns quietly in air. (See Fig. 5-16
for another illustration of the same point.) But when a bottle of mixed
hydrogen and air is ignited, it explodes. This has been known to cause
serious accidents to beginners in chemistry. A safe rule to follow is to
keep hydrogen generators away from flames and to take them apart
as soon as the necessary amount of gas has been delivered. If a test
tube full of the gas burns quietly, air is not present.
A stout bottle is filled two-thirds with hydrogen and one-third with oxygen.
It is then wrapped with a cloth and held at arm's length. A lighted taper applied
to the mouth of the bottle containing this mixture produces a report like a pistol
shot. The slight amount of steam formed with all this noise is unnoticeable.
Hydrogen will also burn in chlorine and in an atmosphere of sulfur
vapor. As we recall, when hydrogen combines with oxygen, ordinary
burning takes place. The combining of hydrogen with chlorine or with
sulfur is a similar chemical action accompanied by the evolution of light
and heat. These three burnings may be represented thus :
2H2 + 02
H2 + CI2
H2 4- S
2H2O
2HCI
H2S
The second marked chemical action of hydrogen is its ability to
remove oxygen from oxides; this action is said to be a replacement
(see page 89).
For example, some black copper oxide is heated in a tube and dry hydrogen
passed over it. (See Fig. 5-1 7.) Moisture collects on the cool part of the walls of
the tube, and the copper oxide be-
comes copper. Hydrogen replaces the
copper, forming the oxide of hydro-
Moisture,
Dry
Hydrogen
Hard Glass
Test Tube
~&f$ ^ Black Copper
v / Oxide (wire form)
gen, namely, water.
CuO + H2 -> H2O
Cu
FIG. 5-17. — Hydrogen changes black
copper oxide to pink copper. The copper
oxide is reduced and the hydrogen
oxidized.
Under some conditions this sort
of chemical change may be made
to take place with oxides of
metals more active than hydro-
gen. An example has been given
in the case of iron oxide and
hydrogen forming iron and steam
(see page 87).
In this action we may say that the hydrogen is a reducing agent, for
it has liberated a metal from its compound. The copper oxide was re-
duced to copper, the product of reduction. At the same time the hydrogen
HYDROGEN, THE LIGHTEST GAS 95
was oxidized to water, the product of oxidation. The copper oxide served
as the oxidizing agent.
The third chemical characteristic of hydrogen is its ability to attach
itself to other elements or compounds. We have already seen how hydro-
gen can join with oxygen, chlorine, or sulfur.
Under proper conditions
1. hydrogen adds to nitrogen to form ammonia;
2. hydrogen adds to active metals to form hydrides;
3. hydrogen adds to vegetable oils to form semi-solid fats, which are
called vegetable shortenings and are sold at grocery stores;
4. hydrogen adds to coal to form synthetic petroleum;
5. hydrogen adds to petroleum, or certain oils from it, extending the
supply of gasoline and improving the product.
%
Uses of Hydrogen. The colored toy balloons at the circus or fair were
probably filled with hydrogen, especially if they floated away when not
held tightly. Military observation and barrage balloons are filled with
this gas, as are the weather-observation balloons. Hydrogen has proved
to be too hazardous for filling dirigibles except for military necessity.
Hydrogen is very useful as a fuel gas, for it burns with an almost
colorless blue flame and gives a high heat. As we have previously stated,
it is found in several fuel-gas mixtures, especially water gas and coal gas.
Hydrogen alone is used as a fuel in torches, the oxyhydrogen torch that
is used in constructing X-ray tubes, for example. The hottest of all
torches is the atomic hydrogen torch, in which a stream of hydrogen
passes over an electric arc. Immediately 'thereafter the hydrogen burns,
liberating the heat taken from the energy of the electric arc as well as
the heat of burning. This makes an intensely hot spot (4000 to 5000°C),
hot enough to melt quartz (Si02, 1710°C) or tungsten (W, 3370°C) or to
boil iron (Fe, 3000°C).
In addition to being very hot, the atomic hydrogen flame is a reducing
flame. Metallic oxides react with hydrogen and form the metal. A metal-
to-metal bond with no oxide film between makes a strong and satis-
factory welding job.
Large amounts of hydrogen are used to make ammonia, to " harden "
fish and vegetable oils, and especially for the hydrogenation of petroleum.
Kinetic Molecular Theory. In order to explain the rush of air when
one moves through it rapidly, the fact that hydrogen passes through
porous porcelain easily, and the fact that hydrogen can be heated by an
electric arc, producing extreme heat immediately thereafter, let us extend
the suggestion that all gases are composed of unit particles called mole-
cules. This useful explanation is called the kinetic molecular theory. It
consists of the following points:
96 CHEMISTRY FOR OUR TIMES
1. Gases are made up of tiny particles called molecules. The mole-
cules are extremely small, and in a given sample of gas the millions of
molecules are relatively far apart. A liter of oxygen at standard condi-
tions contains 3 X 1022 (3 followed by 22 zeros) molecules, but the actual
space that these molecules occupy is only a small fraction (about one-
thousandth) of the liter volume the gas occupies.
2. The molecules of each substance are alike but are different from
those of other substances. The molecule is the smallest particle of a
compound that can exist. The molecules of carbon dioxide are different
in composition from those of water or oxygen, but the molecules of
carbon dioxide are essentially all like each other. If the molecule is broken
up, the compound no longer exists as such but new substances are formed
from it.
3. Molecules of a gas are always in motion. They move with extreme
rapidity in straight lines until they collide with neighbors or with the
walls of the container. After the collisions each molecule moves off in a
different direction. We can imagine them to be something like balls
moving rapidly and incessantly on a billiard table. The number of colli-
sions occurring each second in a liter of gas at standard conditions is
astonishingly large. The collisions are perfectly elastic, and no loss of
energy occurs. The pressure exerted by a gas on the walls of the container
is due to the ceaseless bombardment by the molecules. Another way to
enable us to visualize the motion of molecules is to imagine a swarm of
insane insects in a jar, darting about in all directions, each having un-
tiring energy to keep it in perpetual motion.
Diffusion of perfume in the air of a room occurs because of the motion
of the molecules. The particles bounce off each other and off the molecules
in the air and gradually get farther away from the source of the odor.
Soon the odor is noticeable everywhere in the room.
4. Changing the temperature of a gas changes the rate of motion of
its particles. If the temperature of a gas sample is lowered, the velocity
of its molecules becomes less; the molecules have less kinetic, or motion,
energy. If the temperature of a gas sample is raised, the velocity of its
molecules rises and they collide with each other more often and with
greater force. The molecules thus have a greater amount of kinetic
energy.
The four properties of molecules listed above are not facts; they are
assumptions used to explain the properties of gases. If they explain \vell
the facts that we know about gases, then they are good assumptions and
we may believe them to be true, as we do in this case. If they did not
explain the behavior of gases, we should reject them. If later we should
find facts about gases that are not explained by the kinetic molecular
theory, we should have to change the assumptions. This has actually
HYDROGEN, THE LIGHTEST GAS 97
been necessary in the case of the second assumption, that the molecules
of a given gas are exactly alike. We know now that some molecules of
hydrogen are twice as heavy as others. The new discovery does not make
us distrust the kinetic molecular theory, but it does make it necessary
for us to modify it slightly. A theory is not a/ac£ or a law; it is an explana-
tion of facts and laws.
Hydrogen Molecules. Several facts about hydrogen molecules are
peculiar to the element. First, hydrogen molecules are the smallest mole-
cules known and the lightest. Hence at a certain temperature, 20°C for
example, they are moving faster than the molecules of any other gas at
FIG. 5-18. — Dr. Harold Urey, while at Columbia University, was a Nobel Prize winner
and a codiscoverer of heavy hydrogen.
this same temperature. Further, they always come in packages of two:
When they pass through an electric arc in. the atomic hydrogen torch,
each hydrogen molecule takes in energy and becomes for an instant two
separate particles called atoms. When the atoms form molecules again,
heat is liberated.
Hydrogen diffuses more readily than any other gas. It passes through
porous porcelain or through a sheet of metallic palladium at 500°C as
easily as water passes through a filter paper; no other gas will do this
so readily. Also, hydrogen is absorbed by platinum very readily; platinum
and palladium catalyze many chemical actions of hydrogen.
Finally, there are abnormal hydrogen molecules called deuterium.
These have twice the weight of ordinary hydrogen molecules, but the
same size. They correspond somewhat to a double-yolked egg, and they
98 CHEMISTRY FOR OUR TIMES
are just about as rare. Hydrogen made up of such molecules is called
heavy hydrogen. Its chemical conduct is just the same as that of normal
hydrogen. When it burns, it forms heavy water. An explanation of these
abnormal hydrogen molecules will be given later.
Heavy water apparently acts the same as any other water in plant
and animal tissues. To prove this we can make a compound containing
heavy hydrogen or heavy nitrogen and follow its course throughout the
body. This can be done by analyzing parts of the body to see where the
compound is located. This experiment is equivalent to feeding an
animal tagged molecules.
SUMMARY
Hydrogen was discovered by Henry Cavendish in 1766 and was named " water
producer " by Lavoisier 17 years later. Soon afterward it was used as a lifting gas
for filling balloons.
Hydrogen is very seldom found free on the earth, although free hydrogen
occurs on the sun. Compounds of hydrogen are abundant in nature. Oils, fats,
living tissues, water, and ammonia are among them.
Hydrogen may be prepared (1) by the decomposition of water by electrolysis;
(2) by the reaction between an active metal, such as sodium, and water (in this
case sodium hydroxide is another product) ; and (3) by the action of hot coke or
hot iron on steam. The customary laboratory method of preparation consists in
reacting a strong acid with a moderately active metal, such as zinc. Strong alkalies,
sodium hydroxide solution for example, will act on aluminum, zinc, or silicon and
release hydrogen.
Hydrogen is collected in the laboratory by displacing water from an inverted
bottle. It is colorless, odorless, and tasteless, very slightly soluble in water, and
the lightest known gas. Also, it diffuses, or spreads out, very rapidly, for its mole-
cules at a given temperature are moving faster than those of any other element
or compound.
Hydrogen burns quietly at a jet, forming water as the only product. When
mixed with air or oxygen and ignited, it explodes violently. Its action with
chlorine is similar to that with oxygen.
Hydrogen is known as a reducing (or oxygen-removing) agent. It reacts with
hot metallic oxides of relatively inactive metals, replacing the metal, that is,
taking the oxygen from the metal. Hydrogen also adds to active metals, nitrogen,
and to certain vegetable oils under proper conditions, a reaction of direct com-
bination. Many shortenings sold at grocery stores today are made by adding
hydrogen to vegetable oils, a process called hydrogenation. Hydrogen is also used
as a lifting gas in balloons and as a fuel.
The kinetic molecular theory includes the following points: (1) All gases are
composed of a multitude of particles called molecules. (2) All molecules of the
same gas are alike and different from those of another gas. (3) Molecules are
continually moving rapidly in straight lines and colliding. (4) Increased temper-
ature increases the rate of molecular motion.
HYDROGEN, THE LIGHTEST GAS 99
In hydrogen molecules the atoms are paired, that is, the molecule is thought
to be composed of two atoms. A few hydrogen molecules are extra heavy because
they contain a variety of hydrogen atoms called deuterium that is heavier than
ordinary hydrogen atoms.
The replacement (or electromotive) series is a list of the metals and hydrogen
in order of chemical activity. Any element in the list will replace those below it
from solutions of their compounds. In general, the greater the spacing in the table,
the more vigorous the reaction.
QUESTIONS
16. List five physical properties of hydrogen.
17. Under pressure at red heat, hydrogen passes readily through steel, (a)
Name the phenomenon, (b) What conclusion may be drawn about the size of
hydrogen molecules?
18. With what gas does hydrogen combine when it burns in air? Name the
product. Why is this product not visible when a jet of hydrogen burns?
19. Why is hydrogen dried in the experiment in which hydrogen burns in
air? (See Fig. 5-15.)
20. Describe a safe way to light a jet of hydrogen.
21. List three important chemical properties of hydrogen.
22. Give an example to illustrate each of the three important chemical prop-
erties of hydrogen.
23. What products are formed when heated hydrogen is passed over silver
oxide?
24. In the chemical action of hydrogen on hot copper oxide name (a) the
reducing agent, (b) the oxidizing agent, (c) the product of reduction, (d) the
product of oxidation, (e) the substance oxidized, and (/) the substance reduced.
25. Examine a can or jar of vegetable shortening at home or in a store, and
report what the label tells about its method of manufacture.
MORE CHALLENGING QUESTIONS
26. In which of the following cases does chemical action take place more
readily?
(a) Mercury oxide + hydrogen — >
(6) Magnesium oxide + hydrogen — >
27. In the action of steam on iron oxide, answer the items given in question
24. Does this action seem to agree with the replacement series?
28. A solution of hydrochloric acid contains 30 per cent hydrogen chloride
(HC1). Hydrogen chloride is 2.8 per cent hydrogen. What weight of hydrogen
can be evolved from j ... grams of the hydrochloric acid?1
1 The instructor may wish to assign one of these figures to one group of pupils,
the other figure to another group.
100 CHEMISTRY FOR OUR TIMES
/200 *
29. What is the weight of JQKQ liters of hydrogen at standard conditions?
{90
27Q grams of hydrogen at standard
conditions ?
31. Why is hydrogen sometimes used in balloons for sounding the "ceiling"
over airports?
32. When hydrogen is used as a fuel in a torch, what change does it make in
metallic oxides?
33. How can we show experimentally that city fuel gas contains hydrogen
(or compounds of hydrogen) ?
34. Suggest a reason for representing hydrogen by the formula H2, not H, in
chemical writing.
35. Tell how to keep hydrogen in a bottle with the least loss of gas.
36. What two conclusions can be drawn from the experiment of putting a
lighted taper into an inverted bottle of hydrogen? (See Fig. 5-16.)
37. Write a paragraph on hydrogenation of oils, using and underlining the
following terms: cottonseed oil, hydrogen, vegetable shortening, lard, substitute,
price.
UNIT ONE CHAPTER VI
WATER
A dry well means trouble, but even nlore serious is the loss of water
to a whole community. Crops wilt, livestock suffers, and people go with-
out a necessity for life and its comforts. The parched soil, lacking a binder,
is blown by the wind into dust storms. Living in such a place becomes
troublesome if not impossible. Then is felt the force of the ancient meta-
phor, "A dry and thirsty land, where no water is." (Psalm 63.)
With plenty of water comfortable living is possible. For not only does
water supply life's needs, but it also furnishes sport and recreation for
thousands.
An ordinary glass 'of water is in many respects most amazing. It
contains millions upon millions of separate particles of water, called
molecules, milling about in it. Some are leaving the surface and others
returning, a few million per second each way. Living creatures are
present too, some large enough to be seen readily under a microscope,
others so small that we have difficulty in seeing them even with the aid
of the best microscope under the most favorable conditions. Some of
these living plants and animals may be harmful if we drink water that con-
tains them. Usually, however, if the body is in good health, they are not.
We have just begun to list the contents of this " museum." Dissolved
in the water are several gases, oxygen chiefly, but also carbon dioxide,
nitrogen, and frequently smaller amounts of other gases. Dissolved
solids also make up a long list. Small traces of many chemical compounds
are found in a glass of drinking water. Even some of the drinking glass
itself is dissolved by the water — not much, to be sure, but some. Finally
there are many small particles floating on or suspended in the water.
Often a number of small, dustlike particles can be seen when a glass of
apparently clear water is held up to the light. Nevertheless, in spite of
its many shortcomings from the standard of absolute purity, we must
New Terms
deliquescent chlorination hydroxide
suspended volumetric water of crystallization
filtration gravimetric anhydrous
distillation efflorescent
101
102 CHEMISTRY FOR OUR TIMES
have water to drink. Without it we perish. One of the duties of chemists
in public-health service is to see to it that the drinking water is suffi-
ciently pure.
Properties* of Water. Among all chemical substances, water is
unique. It is the outstanding solvent, dissolving more types of sub-
stance than any other liquid, although some are dissolved only slightly.
Water exists in three states on the earth, and it can be readily changed
from one state to another by altering the temperature. The ordinary
boiling point of water is 100°C, and the freezing point is 0°C. For a rise
of temperature of 1°C, a gram of liquid water must absorb one calorie
(cal) of heat energy. This amount of energy is larger than the amount
required to raise the temperature 1°C for an equal weight of any other
substance. This is one reason why water is an excellent liquid to use in
the cooling systems of motors.
Importance of Water to Life. All living things require much water.
Jellyfish and tomatoes are almost all water. About 9 per cent of the
weight of the known outer portion of the earth is water. A pessimist
describes the human body as "twelve pounds of ashes and eight buckete
of water. " Because water is present in all forms of life and because water
requires a large heat change to raise or lower its temperature, living
things warm up or cool off more slowly than if any other liquid were
present in their bodies.
Food is of no use to the body unless it can.be dissolved in water
during the process of digestion. We eliminate those portions of the food
that cannot be dissolved and absorbed through the walls of the digestive
system. Water is the principal fluid in the blood by which food is carried
to our tissues and waste matter removed. We excrete about 3 kilograms
(kg) of water a day in the urine, lose other large amounts through the
pores of our skin by evaporation, and still other large amounts in our
breath.
The manner in which water freezes is most considerate to fish and
to people who enjoy skating. We all recognize that a pond freezes from
the top downward. Ice, therefore, must be a little less dense than the
water on which it is floating. This property of having its solid less dense
than its liquid is characteristic of only a few substances. As water cools,
it contracts, which is the way most other liquids behave — mercury in a
thermometer, for example. This contraction of water, however, comes to
a halt at 4°C, and from that temperature downward to 0°C water expands
as it cools. Water has its greatest density at 4°C; at that temperature
the water is most closely compacted. One milliliter (ml) (almost a cubic
centimeter) of water at 4°C weighs exactly 1 g, but at 0°C it weighs a
little less; that is, 0.999841 g. One milliliter of ice at 0°C weighs 0.916 g.
WATER
103
Water at 4°C is left under the ice at the bottom of a pond; frozen milk
rises out of milk bottles because water expands upon freezing; and vessels
or pipes holding water often break when the water in them freezes. All
are results of the abnormal way in which water behaves when it freezes.
Water freezing and expanding in cracks of rocks causes small bits to break
off. This, combined with the well-known scouring effect of water on rocks,
is important in forming soil.
Courtesy of National Park Service, Photo by Ralph Anderson
FIG. 6-1. — The Merced River flows past stately El Capitan (7,564 ft elevation)
in Yosemite National Park, California. From the raw materials represented in this
picture — air, water, minerals, plants — chemists build "better things for better
living."
Sometimes ice freezes from the bottom up. For example, in extremely
cold weather running streams do not allow the water to form ice crystals
on the surface. In such cases a mush of ice crystals may form throughout
the water where it slows up, the crystals pack, and an ice dam results.
The makers of artificial ice take advantage of ihis knowledge and keep
water that is being frozen in motion by bubbling air through it. Then
the ice forms from the outside of the cans toward the center, and in clear
crystals. The central V-shaped piece of snow ice that we notice in a large
cake of artificial ice was frozen without stirring.
104
CHEMISTRY FOR OUR TIMES
When pure, water appears faintly blue. Large amounts of water seem
to be colored blue or green as we may notice in a swimming pool, lake,
river, or ocean.
Since water is essential to life, astronomers think that life is more
likely to exist on those planets where there is evidence of the presence of
water than on those where no evidence of water is seen. The conditions
appear to be most favorable upon the earth.
QUESTIONS
1. The human body is approximately 66 per cent water. What is the weight
of water in your own body?
f50
2. How many calories are needed to change |~- grams of water 2°C?
3. Rabbits seldom drink water. From what source do these animals obtain
their water?
4. What changes in volume take place when the temperature of water rises
from 0°C to 100°C?
I
6. What changes in density take place when water cools from 100 to 0°C?
From 20 to -20°C?
6. What is the weight in grams of 50 milliliters of water? Of 5000 liters?
7. What damage may be caused by freezing the water in an automobile
cooling system?
8. Many roads in temperate climates " heave" in the springtime. Suggest
a cause of this trouble.
9. Describe the freezing of a pond, giving definite temperatures.
10. One liter of ice (0°C) melts. What weight in kilograms of water forms?
What volume in milliliters does this water occupy at 4°C?
Why Does Salt Get Lumpy on Moist Days? On a foggy, humid
day everything is covered with a
thin layer of water. The salt in a
salt shaker accumulates so much
moisture that the crystals will not
shake out easily. Chemists find
that bottles containing certain
compounds used in the laboratory
must be kept well closed or the
compounds will absorb so much
FIG. 6-2. — A region of perfectly dry air moisture from the air that they
is maintained within a desiccator. become a sirupy solution of the
substance. Calcium chloride is an example of these deliquescent
Drying Agent
WATER
105
(becoming fluid) substances. Calcium chloride is often one of the impuri-
ties in common salt (sodium chloride) that makes it clog in muggy
weather. Because of its water-accumulating nature, calcium chloride is
sometimes used to keep dust down on tennis courts or gravel roads.
Some types of hard candy are deliquescent, also.
Impurities in Water. As soon as water starts to fall as rain, it begins
to accumulate impurities. First, gases dissolve in the rain. Then, as soon
as the rain touches the earth, it becomes more impure by dissolving solids.
The amount of solid dissolved increases until the water finally reaches
the sea. The dissolved compounds in sea water do not settle out. It is
thus evident that the sea is becoming saltier.
FIG. 6-3. — What properties of water determine its selection as the collection medium
for gases, such as oxygen and hydrogen?
Dissolved materials in water are not to be confused with suspended
matter, which consists of solids mixed in a liquid but not dissolved.
Muddy water contains many solid particles suspended in it. The color
of the clay suspended in a river may tint the water brOwn, gray, or
yellow.
Chemists usually consider bacteria as a separate class of suspended
materials in water. Dissolved substances are rarely harmful ; on the con-
trary, they are often beneficial to health. Bacteria are also generally
harmless, but occasionally they are dangerous. Typhoid fever and dys-
entery bacteria are among the harmful types that are carried in water.
" Is this sample of water good to drink?" is a question many people
want to have answered, for chemists are often asked it. To answer this
question completely involves a long and expensive process, requiring
much equipment, experience, and skill. A satisfactory test of drinking
106
CHEMISTRY FOR OUR TIMES
water is to find out whether or not harmful bacteria are present. The
finding of Bacillus coli from the intestines is sufficient to condemn water.
Also, if common salt is found in water, sewage is suspected, but not
proved, because, although a little is found in drinking water, salt in larger
amounts is always present in sewage. In case of doubt it is always best
to boil the water before using it.
How to Purify Water. Just as window screens keep out flies and
mosquitoes but allow tiny gnats to go through the meshes, so a piece of
uncoated paper, like newspaper,
or a layer of sand offers free
passage for water but acts as a
strainer, so that particles sus-
pended in the water are removed.
This process of separating a sus-
pended solid from a liquid by
straining out the suspended par-
ticles is called filtration. Filtration
is a process much used, both in
the laboratory and in industry.
Filtering through paper is com-
mon in the laboratory, but com-
mercial filters may use sand or
cloth. Filtering does not remove
suspended particles that are small
enough to pass through the pores
of the filtering material. It is
Courtesy of The Travelers Insurance Company therefore not Certain to remOVC
FIG. 6-4.-The process of filtering is a all bacteria f rom water umess the
common laboratory operation. Here the
chemist is directing a fine stream of dis-
tilled water from the wash bottle into the
beaker so the contents will all drain into
the filter paper in the funnel.
niter is exceedingly line.
Filtering may be more effec-
tiye Jn removing bacteria if it is
° . ...
done through some jelly like sub-
stance, such as that formed by adding alum to water, to which the
bacteria tend to stick. One city reduced the death rate from typhoid
fever from 114 to 25 per 100,000 population by merely filtering its drink-
ing water. The experience of Columbus, Ohio, and that of many other
places shows that typhoid fever can be controlled and may some day be
wiped out. In fact, all cases of typhoid fever are due to carelessness
or neglect.
Complete purification of water removes both suspended and dis-
solved impurities. The process of removing the dissolved matter, although
expensive to carry out on a large scale, is simple in principle. Water is
boiled to form steam. The steam is then condensed back to water by
WATER
107
cooling it below the boiling point. The process of changing a liquid to a
gas and condensing the gas to a liquid again is called distillation. In gen-
eral, if the impurities have boiling points above the boiling point of water,
they will remain behind in the vessel in which the water was boiled. In
order to carry out the process of distillation, an important process for other
liquids as well as water, one uses a boiler and a condenser. The boiler
changes the liquid to a vapor; the condenser changes the vapor back to
a liquid. As much heat is carried away by the cooling Avater in the con-
denser as is supplied by the flame to the liquid in the boiler. (See Fig.
6-5.) If, in distilling water, some steam is first allowed to escape from the
end of condenser tube, the dissolved gases are eliminated and nearly
Thermometer
FKJ. 6-5.— A simple method of purifying water is boiling it and then condensing the
steam. Liebig's apparatus is a device for carrying on both processes continuously.
chemically pure water results. The product of the distillation of water is
called distilled water. Distilled water is used in storage batteries, in
making solutions in laboratories, and for other purposes.
The Ancient Mariner, who had " Water, water, everywhere, Nor any
drop to drink, " made his readers suffer unnecessarily because of his lack
of resourcefulness. A slight knowledge of chemistry would ruin this part
of the poem completely. Any practical mariner could make steam by
boiling sea water in a teakettle obtained in the galley. The steam will
condense on a sloping board held above the kettle into many a "drop
to drink. "
To kill bacteria in water, many methods are used. Boiling water kills
most germs. This method of purifying water is used by many Chinese
who live on boats. Thousands of families discharge all their wastes into
the stream and yet drink the water, after it is boiled.
108 CHEMISTRY FOR OUR TIMES
The element oxygen attacks bacteria and kills them. The element
chlorine is also used for the same purpose. The amount of chlorine used
in purifying water for drinking [0.7 gallons (gal) of chlorine per million
gallons of water] is sufficient to kill most of the bacteria, but not to harm
the users of the water. Experience has shown that chlorination of water
is safe and economical and a reliable way to make water fit to drink.
Often ammonia is used with chlorine. Swimming pools, which are con-
taminated by constant use, must obviously be chlorinated more highly
than reservoir water. In times of flood when river water may unexpectedly
"back up " into city water mains the amount of chlorine used is increased
to ensure safe drinking water.
Photo by Joe Roller
FIG. 6-6. — Sugar beets are shown here growing under irrigation. This is the Belle
Fourche Project in South Dakota.
Through many experiments the preparation and properties of the
element chlorine have been worked out. Its effects on other elements,
on bacteria, and on the human body are all recorded in scientific writings.
This knowledge may be used to save human lives, as it is when chlorine
is used to purify drinking water; or the knowledge may be abused, as
it was when chlorine was used as a poison gas in World War I to
destroy human beings. This contrast forms a good example of one of
the limitations of science, for the scientific investigator is content to find
knowledge and thus far cannot control its use.
City Water Supplies. Fortunate indeed is that city which has avail-
able an adequate supply of pure, soft, clear, uncolored drinking water
with no taste or odor. Some cities are located without much regard to
available sources of water supply, so that water must be brought to them
WATER 109
in pipes over hundreds of miles at enormous expense. Los Angeles, Cali-
fornia, for example, brings water from the mountains 223 miles away.
A city that needs an unusually large water supply buys a suitable
stream that can be dammed up. A watershed is cleared, a dam built, and a
lake created. By doing this, in some cases a large community may benefit
to the disadvantage of smaller ones. Boston draws some of its water from
streams that are located near the center of the commonwealth of Massa-
chusetts. The neighboring state of Connecticut felt aggrieved because
it was deprived of this water, which normally flowed southward through
the Connecticut River Valley. A lawsuit between the states was brought
in the United States Supreme Court. The right of Boston to direct the
water eastward was maintained.
QUESTIONS
11. Define deliquescence.
12. What causes salt to cake in a salt shaker in damp weather? Suggest a
practical way of preventing this inconvenience.
13. Free-running salt is often sold in cardboard cartons. What substance is
added to the salt? HINT: See the carton.
14. (a) List the harmful impurities in natural water, (b) List the harmless
ones.
*
15. Distinguish between pure water for drinking (potable water) and chemi-
cally pure water.
16. Thousands of families live on boats in the Yangtze River in China. All
their waste is discharged into the water. The same water is used for drinking.
What home purification method is used to make the water fit for drinking?
17. Tell how the process of filtering is used in jelly-making.
18. African explorers are sometimes forced to use ill-smelling water, green
with assorted vegetation. What method is used to purify such water?
19. What methods are economical to use for purifying water on a large scale?
What methods may an army adopt?
20. Distinguish: water, ice, steam, water vapor, fog.
Hard and Soft Water. Water that does not contain a great amount
of dissolved mineral matter (elements or compounds of inorganic sub-
stances) is called soft water. Those who use soft water do not know what
a convenience it is until they are confronted with hard water. Hard water
contains dissolved compounds of the elements calcium and magnesium.
These compounds react with soap to form a curdy solid to such an extent
that washing with hard water becomes a test of patience. This curdy
material deposits in cloth, making streaks.
110
CHEMISTRY FOR OUR TIMES
Much trouble results from using hard water in boilers because a scale
forms on the inside. This scale, which forms from hard water when it
is heated, is a hard, crusty layer, often mixed with rust.
In order to make hard water suitable for most uses, it must be soft-
ened. The process of softening will be explained later. Sea water is very
hard water and except with special suds-making substances is not at all
satisfactory for washing clothes. Hard water is discussed in more detail
later.
Producing Water from the Elements. We have already pointed
out (page 83) that water is a stable compound and that it can be decom-
posed into its elements when an electric current is passed through it.
2H2O
Water
2H2|
hydrogen
(2 parts by volume)
oxygen
(1 part by volume)
A remarkable 2-to-l volume relationship exists between the hydrogen
and oxygen gas volumes, respectively. The questions naturally arise,
"Can this be reversed? Do hydrogen and
,. . , ,„,,
oxygen combine in any special amount ?"
Spark Jumps Here
To answer these questions let us use a
long glass tube that has measuring marks on
the side (see Fig. 6-7) and two wires sealed in
through the glass almost touching inside at the
closed end. We then fill the tube with mercury
and invert it in a dish of mercury. For a start,
let us select by chance equal amounts of the
gases, say, 10 mi of pure hydrogen and 10 ml
of pure oxygen (20 ml of mixed gas), and intro-
duce them into the tube; we now connect the
two wires to an electric sparking machine and
make a spark jump across between the wires
through the mixed gases inside the tube. The
hydrogen burns rapidly — indeed, a mild explo-
sion takes place. The mercury absorbs the
shock of the explosion to some extent but
immediately rises inside the tube. Measuring
shows that 5 ml of gas is left, and also a small
volume of liquid water is seen floating on the
mercury. The gas may be hydrogen, oxygen, a mixture of both, or perhaps
some new substance. A glowing splinter inserted into the gas burns brightly,
showing that the gas is oxygen.
10 ml hydrogen + 10 ml oxygen — » liquid water and leaves 5 ml oxygen
Now we repeat the experiment, leaving out the extra 5 mi of oxygen that was
found to be unused; thus 10 ml of hydrogen and 5 ml of oxygen are put into the
tube.
- Gases to be Exploded
Mercury
FIG. 6-7. — The eudiometer is
a stout- walled glass tube within
which chemists carry on small
gas explosions.
WATER
111
After sparking, we see this time that mercury fills the tube except for the small
volume of liquid water formed. No gas remains.
10 ml hydrogen + 5 ml oxygen
(tube cold)
liquid water (and no gas)1
For a third experiment the entire apparatus is enclosed in a jacket heated with
vapor of some liquid so that the temperature at which all the measurements are
made is over 100°C. The previous experiment is repeated: 10 ml of hydrogen and
5 ml of oxygen are put into the tube, and a spark is sent across the gap between
the wires. This time after the explosion the volume of gas has shrunk two-thirds,
10 ml of gas remaining. What can this gas fee? If tested, we find that it does not
burn, nor does it cause a spark on the end of a splinter to burst into flame. When
the gas is cooled, it changes to a liquid that freezes at 0°C and boils at 100°C at
760 mm pressure. This is proof positive that the liquid is water and, therefore,
that the gas is steam.
The experiment can be summarized as
10 ml hydrogen + 5 ml oxygen
10 ml water vapor
(tube heated)
or, in general, since the amounts of gas in the first place were selected by chance,
2 volumes hydrogen + 1 volume oxygen
(tube heated)
2 volumes water vapor
This experiment shows the formation of water (steam) from the
gases hydrogen and oxygen and the measurement of the volume of the
gases formed in the experiment. Sometimes it is called the volumetric
(measured by volume) synthesis (putting together) of water.
What Is the Percentage of Hydrogen and Oxygen in Water?
W. A. Noyes (1857-1942), an American experimenter, repeating more accurately
^Copper
Oxide
Pure Dry
Hydrogen '
FIG. 6-8. — This apparatus is used to determine the approximate composition of water
by weight.
the method of J6ns Jakob Berzelius (1779-1848) of Sweden and of Jean Baptiste
Andre* Dumas (1800-1884) of France many years before, passed carefully purified
hydrogen over a weighed amount of pure copper oxide in a heated tube (1). (See
1 This experiment is not practical for demonstration in most elementary labora-
tories.
112 _ CHEMISTRY FOR OUR TIMES _
Fig. 6-8.) The chemical change that took place is expressed
H2 4- CuO -» Cu -f H2O
Hydrogen 4- copper oxide — * copper + water
The copper oxide gave up its oxygen to the hydrogen to form water. The
water was collected in another tube (2) attached to the first and containing
a weighed amount of a substance, such as calcium chloride, that would absorb
water. In this reaction, the tube (1) containing copper oxide lost weight because
it lost oxygen, while the absorption tube (2) containing calcium chloride gained
weight because it gained water. By using the measurements of weight changes,
the percentage of oxygen in water could be found by the following:
Loss of weight in tube (1) (0) ^, +„* ^ • ± A
TT-- — = - . u. , . , 'v /TT ' X 100 = % oxygen in water. Ans.
Gam in weight of tube (2) (H20) e
The answer is 88.81 per cent. The percentage of hydrogen is found by subtracting
88.81 from 100, the result being 11.19 per cent. This experiment is sometimes
called the gravimetric (measured by weight) synthesis of water.
The Chemical Nature of Water. Water enters into many chemical
changes, although it is a stable substance. So important are chemical
• • changes in water solution as a medium that
• f~\ • ' "~end we s^a^ cons^er ^em later. All growth of
^ • \^/ • plants and animals takes place in cells a
V • • large part of which is water. Sometimes
^ water is one of the substances in a chemical
FIG. 6-9.— The water mole- «hange; more often it is the medium in
cule is composed of two sorts which the change takes place.
of atoms. Many substances that act chemically on
water can be considered in two groups: (1) elements; (2) oxides.
1. We have seen from experiments that water, the formula for which
is H20, has two parts of hydrogen. Active metals take the place of one
part and leave the other part in a new compound, called a hydroxide,
which is made of the metal, hydrogen, and oxygen. For example,
2K -f 2HOH -4 H2 -f 2KOH
Potassium -j- water — > hydrogen -j- potassium hydroxide
2Na + 2HOH -> H2 + 2NaOH
Sodium + water —» hydrogen -j- sodium hydroxide
Ca +2HOH -» H2 + Ca(OH)2
Calcium -f- water -* hydrogen -f calcium hydroxide
Other less active elements act on water when they are strongly heated,
driving out the hydrogen and forming an oxide of the element. Another
way to consider this reaction is that the element has substituted itself
for the hydrogen of water. The exchange is similar to the ballroom custom
according to which a young gentleman leaves the "stag line" and "cuts
WATER 113
in" on a couple dancing on the floor. In this comparison the part of the
young lady is played by oxygen.
Zn -f H2O -> H2 + ZnO
Zinc 4- steam (hydrogen oxide) — > hydrogen 4- zinc oxide
C -f H20 -4 H2 4- CO
Carbon + steam (hydrogen oxide) —» hydrogen -j- carbon monoxide
3Fe -f- 4H2O -» 4H2 + Fe3O4
Iron 4- steam (hydrogen oxide) — » hydrogen -f iron oxide
2. Some oxides of nonmetals unite with water. The chemical change
is one of simple addition, one product being formed.
CO2 -f H2O -f H2CO3
Carbon dioxide + water — * hydrogen carbonate (carbonic acid)
502 -f H2O -» H2SO3
Sulfur dioxide + water — > hydrogen sulfite (sulfurous acid)
503 4- H2O -4 H2SO4
Sulfur trioxide -f water -r* hydrogen sulfate (sulfuric acid;
P2O* +3H2O -4 2H3PO4
Phosphorus + water — > hydrogen phosphate (phosphoric acid)
pentoxide
Oxides of a few metals combine with water to form hydroxides. The
most important one is
CaO 4- H2O -4 Ca(OH)2
Calcium oxide -j- water — * calcium hydroxide
Water in Crystals. Most solids found in nature and those made in
the laboratory are crystalline. When heated, a great many crystalline
solids crumble to a powder, lose weight, and sometimes change their
color. Investigation shows that in such cases when the crystal is heated
water is lost. Such a substance is gypsum, sometimes represented by
CaSO4'2H20 (the dot is read " combined with"). Great masses of solid
rock are made of gypsum; an examination of its formula shows that
with each particle of gypsum two particles of water are associated. When
this substance is heated, water is lost and plaster of Paris is formed. As
anyone knows who has ever broken a bone and worn a cast, plaster of
Paris takes this water back to form a mass of hard crystals. It "sets"
to a rigid mass and is used to support the bone structure while it heals.
Washing soda crystals (sodium carbonate), alum crystals (potassium
aluminum sulfate), and blue vitriol crystals (copper sulfate) are all
examples of crystalline solids that contain water. When they form from
solution, they take some water of crystallization with them. Such sub-
stances are called hydrates. All hydrates have water chemically held in
the crystal. Common salt and sugar are crystals that have no combined
water with them and are therefore not hydrates.
114
CHEMISTRY FOR OUR TIMES
Some hydrates lose their water of crystallization without being heated,
merely on being exposed to air. Washing soda (Na2C03*10H20) turns to
a dry powder and becomes Na2CO3, anhydrous (without water) powder,
when it is exposed to the air.
Na2CO3-10H2O
Washing soda
Na2CO8
soda ash
10H2O
water
A package of washing soda loses weight while it stands on a grocer's
shelf unless it is packed in a carton from which moisture cannot escape.
Crystals of this sort are said to be efflorescent (flowering out or blooming)
because the powder formed on the surface of the crystal resembles the
blooming of a flower.
(.'ourtfisy of E. T. da Pont de Nemours A' Company
FIG. 6-10. — One chemical change makes way for others. The pictures show a drainage
ditch being blasted and the ditch after the blast.
SUMMARY
Water is important as a solvent for plant and animal food, as the chief con-
stituent of living tissues, as a temperature regulator for life processes, as a
catalyst in chemical actions, and as the solvent in which many chemical actions
take place quickly.
Water most closely approaches the " universal solvent." It boils at 100°C at
760 mm pressure (standard) and freezes at 0°C. One calorie is required to change
the temperature of a gram of water 1°C. Its approximate density is 1 g per ml,
and its maximum density occurs at 4°C.
Some substances, calcium chloride for example, have the property of absorb-
ing water from the air and dissolving in it. Such substances are called deliquescent.
Dissolved impurities in water include gases and mineral compounds called
salts, of which common salt is one. Suspended impurities are abundant in muddy
water. Harmful bacteria may be present. Some suspended matter may be invisi-
ble, but the larger particles are readily removed by the process of filtration.
WATER 115
Methods of purifying water include
1. Filtration, a process of straining water through cloth, paper, sand, or soil
2. Distillation, which consists in boiling and condensing the vapors
3. Boiling, which removes dissolved gases and kills most of the bacteria
4. Mixing with air (aeration), to kill bacteria and to oxidize organic matter
5. Chemical treatment with chlorine, often plus ammonia, to kill germs
Hard water is difficult to use for laundry purposes and for making steam in
boilers. It contains dissolved inorganic compounds that act on soap and also
produce a scale deposit in boilers. Soft water has relatively little dissolved mineral
salts and is better than hard water for almost all purposes.
Water is relatively stable, being difficult to decompose. Essentially, water is
decomposed by passing an electric current through dilute sulfuric acid solution.
The processes called electrolysis of water, and the products are two volumes of
hydrogen and one volume of oxygen.
Water is synthesized and the results determined by weight in the experiment
of passing dry hydrogen over heated copper oxide. The results show 88.81 per
cent oxygen and 11.19 per cent hydrogen. Water is synthesized by exploding
measured volumes of hydrogen and oxygen in a strong glass tube. The results
by volume show that two volumes of hydrogen join one volume of oxygen to
form two volumes of steam, all gases being measured at the same temperature
and pressure.
Chemical actions of water include
(1) Water + active metal -> metallic hydroxide + hydrogen
(2) Water + moderately active metal — > metallic oxide + hydrogen
(3) Water + nonmetal oxide — > acid % ~
(4) Water + metallic oxide —> metallic hydroxide
(5) Water is a catalyst in many chemical actions '
Certain crystals include definite (molecular) amounts of solvent chemically
combined when they form. They are called hydrates. For example, washing soda
has the formula Na2C03*10H20. Some hydrates lose water when exposed to air,
thus becoming anhydrous, leaving a dry powder. Washing soda loses water when
exposed to air.
QUESTIONS
21. Distinguish hard water from soft water.
22. State two disadvantages of hard water.
23. What is the meaning of the term unstable?
24. In the decomposition of water,
(a) Energy in what form is used?
(6) What substance is added to improve the electrical conductivity of the
wajier?
(c) What gaseous products are formed?
(d) Compare the volumes of the products.
{50
,~ liters of hydrogen is made by electrolysis of water, what volume
of oxygen is formed at the same time?
1j6 CHEMISTRY FOR OUR TIMES
{124
«s milliliters
of oxygen are collected from the electrolysis of water?
(50 (25
4P milliliters of hydrogen and i or* nil of oxygen is ex-
ploded in a hot tube, what volume in milliliters of steam is formed?
[27
28. When j , - milliliters of oxygen is used, how much hydrogen can be burned
and how much steam is formed?
NOTE: Assume all temperatures arid pressures at which volumes of gases are
measured remain the same in each question.
MOKE CHALLENGING QUESTIONS
(150
29. When |OOK liters of hydrogen forms from the electrolysis of water, what
volume of oxygen can be recovered at the same time if 4 per cent dissolves in the
water?
(50 (40
30. When |-^ milliliters of hydrogen and | . - milliliters of oxygen are mixed in
a tube, warmed above 100°C, and exploded, what gases remain, and what is the
volume in milliliters of each?
31. When jor milliliters of hydrogen and i .« milliliters of oxygen are mixed
and exploded as in question 30, what volume of gases remain?
32. In a pupil's experiment for synthesizing water the copper oxide tube
{45 2 (44 5
c7' grams before and i „„ ' grams after the experiment. The drying
(38 7 (39 5
tube weighed 1~c "~ grams before and {-„ 'A grams after. From these figures find
I /O.O l/O.^x
the percentage of oxygen in water.
33. What weight of oxygen is present in a ton of water? Oxygen helps fires
burn. In view of these two facts account for the seeming contradictory use of
water as a fire extinguisher.
34. How can shipwrecked sailors get drinking water from fish?
35. Why do not engineers design an automobile that utilizes the burning of
hydrogen and oxygen for automotive power? Could the decomposition of water
by electrolysis be carried out in such an automobile from the energy produced J3y
the combustion?
UNIT ONE CHAPTER VII
THE NATURE OF GASES, LIQUIDS,
SOLIDS
Galileo Galilei (1564-1642) of Italy will always be remembered as a
man who did not rely on the teachings of Aristotle but who sought truth
while carrying out his experiments with objects falling from the leaning
tower of Pisa. Besides these famous experiments, he was the first person
to weigh air.
People, to be sure, had always recognized the tremendous force of
the wind and feared it. Then, too, other "airs" were known. At various
spots on the earth evil-smelling or poisonous gases made their presence
known; birds were killed by flying into such regions. It became recog-
nized, therefore, that all gases, or "airs," are not the same.
Scientific experiments take nothing for granted; and the fact that a
gas is invisible neither proves that it does not exist nor that it is the same
substance as air. Today many different gases are known, many of which
are of great service to mankind. Natural gas is piped to houses and
factories in many cities. Trucks use tanks of compressed gas for fuel.
"Laughing gas" puts patients to sleep for minor operations. Fumigating
gas destroys vermin. Gases are used extensively for refrigeration.
In order to distinguish one kind of gas from another, we describe
each by answering the questions, "What is its composition? What is its
name? How much does a liter weigh at a given temperature and
pressure?"
Automobile tires lose air easily on a hot day; the air expands when
warm, forcing its way through the somewhat porous wall. If the wall is
weak, a "blowout" may occur. A milk bottle is washed in warm soapsuds
and placed mouth downward to drain. If a soap 'film forms across the
mouth of the bottle, which way will the film move as the bottle cools?
Upward, of course, for the air in the bottle contracts when it becomes
New Terms
Kelvin, or absolute, degrees condensation boiling point
attractive force evaporation melting point
cohesion vapor pressure crystal
117
118 CHEMISTRY FOR OUR TIMES
cooler. Most of us have noticed that gases expand when heated and con-
tract when cooled. Gases likewise contract when put under increased
pressure and expand again when the pressure is reduced.
Blueprint of a Gas. Let us consider a cubic foot of air. Let us assume
that the volume of this gas is measured when the barometric pressure is
760 mm of mercury and the temperature is 0°C, or 273°K (Kelvin degrees,
sometimes called absolute degrees). These conditions are called standard
conditions, often referred to as STP. Now let the pressure on the air be
doubled, namely, increased to 1520 mm, the temperature remaining con-
stant. The volume of the air now measures only % cu ft. When the pres-
sure is doubled, the volume of the gas becomes one-half if the temperature
is constant. Experiments of this sort are summed up in Boyle's law: The
volume of a definite amount of dry gas is inversely proportional to the
pressure on it, provided that the temperature is not changed. (See
Fig. 7-1.)
FIG. 7-1. — A mechanical model of this type may be used to illustrate the mathe-
matical principle of Boyle's law.
If the ^2 cu & °f air is now warmed to 273 °C, or 546°K, with the pres-
sure remaining unchanged, its Kelvin temperature is doubled and its
volume again becomes 1 cu ft. That is, at constant pressure, doubling
the temperature (in Kelvin degrees) of a sample of a gas doubles the
volume the gas occupies. Experiments of this sort are summed up by
Gay-Lussac's (Charles') law: The volume of a definite amount of dry
gas is directly proportional to its Kelvin temperature, provided that the
pressure is not changed.1
The next step in the scientific method is to develop a theory about
the nature of gases. Items to be taken into account in building this theory,
or mind picture, include the fact that
1. Boyle's and Gay-Lussac's (Charles') laws hold true for all ele-
ments, mixtures, and compounds alike, provided only that they are in
the gaseous state. Some similarity of all gases is suggested.
2. The fragrance of perfume penetrates a space that already contains
air. The fact that empty spaces exist in gases is evident from this obser-
vation. One gas may spread into the space already occupied by another,
an action called diffusion. Gases tend to fill the entire container in which
they are placed.
1 The application of Boyle's and Gay-Lussac's (Charles') laws is given in the
Appendix.
THE NATURE OF GASES, LIQUIDS, SOLIDS 119
3. If no leaks interfere and the temperature is kept constant, the
pressure of a gas is maintained eternally. Once an automobile tire is
blown up, it will stay that way, keeping the air at the original pressure,
provided that there is no loss of air from chemical action with the rubber
or from leaks. Actually, for reasons suggested here, automobile tires
"go down/' and more air must be supplied if the same pressure is to be
maintained.
4. A rubber toy balloon whose walls are uniformly thick will tend to
form a sphere when blown up because the gas inside exerts equal pressure
in all directions. The behavior is the same with hydrogen, illuminating
gas, carbon dioxide, or any other gas.
These properties of gases are explained in the molecular theory of
gases, often called the kinetic (motion) molecular theory. The different
statements in the theory are assumptions used to explain the observed
behavior.
The student will recall
1. Gases are made up of tiny particles called molecules. A liter of
oxygen gas at STP, for example, is made up of an enormous number of
these molecules.
2. Molecules of oxygen are alike on the average, as are molecules of
any given kind of gas; different kinds of molecules of gases are, however,
unlike. For example, carbon dioxide molecules are different from oxygen
molecules.
3. Molecules of a gas are always moving rapidly in a straight line
for a short distance. Then they hit something, bounce off, and move in
another direction with the same speed.
4. Changing the temperature of a gas changes the rate of motion of
its molecules. If a gas is cooled, the motion of the molecules becomes
slower. If a gas is heated, the molecules set about their haphazard, tireless
colliding at an increased rate.
Effect of Temperature Change. If a certain amount of oxygen is
heated to twice its present temperature on the Kelvin (absolute temper-
ature) scale (see page 118), say from 300 to 600°K, the energy of molecular
motion is doubled. Each molecule on the average has twice the motion
energy it had previously and hits the walls more often and harder.
Consequently, 1 cu ft of oxygen tends to occupy 2 cu ft, or just twice the
original volume, if the pressure is to remain the same. Each molecule
doubles its energy, quadruples its speed. (K.E. = )^mv2.) If the gas is
held within a container so that it cannot expand and the temperature is
doubled, then the pressure will also be doubled. This means that the
molecules will hit the wall of the vessel that holds the gas with twice
the former energy, tending to push the wall back with greater total force.
120
CHEMISTRY FOR OUR TIMES
Effect of Pressure Change. If a gas is compressed, its particles are
moved closer together. With a larger crowd in a given space, the pressure
is increased since the number of collisions with the walls will be increased.
This explains Boyle's law, according to which the pressure of a gas
increases as the volume becomes less. (See Fig. 7-2.)
Molecular Motion Explained. A cool gas has slow-moving mole-
cules, and the same gas when warm has faster moving molecules. The
temperature of a gas is a measure of the energy due to the motion of its
molecules. Absolute zero, 0°K, which is 273° below 0°C, is the condition
that would be reached if molecular motion stopped.
When a tennis ball is dropped on a hard floor, it bounces several
times; but gradually the energy of the fall is reduced, owing to friction,
and it finally comes to rest. Molecules, however, lose none of their energy
:v
FIG. 7-2. — When the pressure of a gas is increased, the distance between the mole-
cules becomes less.
in friction; for friction produces heat, and heat is molecular motion. No
loss of motion energy takes place, as no change in temperature is ob-
served. The collisions of gas molecules with each other, and with the
walls of the container, if at the same temperature as the gas, are perfectly
frictionless.
If the motion of gas molecules is haphazard and the number of
particles greater than the upper stretches of our imagination, then we
can understand the reason why gases exert their pressure equally in all
directions. It is important to realize that the size of the individual gas
molecule is small compared with the distance between any two molecules
and that the velocity of these tiny projectiles at room temperature is
about 1 mile per sec.
Using the Gas Theory. The theory that gases are made up of mole-
cules is so well established that no one doubts its truth. As our knowledge
becomes more complete, a few details may be altered, but the picture as a
whole is essentially correct.
THE NATURE OF GASES, LIQUIDS, SOLIDS 181
This theory will be useful in explaining changes of state of matter.
As an illustration, we want to see how it is possible to change a substance
from the gaseous into the liquid state. Molecules are present in liquids,
but they are closer together than they are in gases. In order to change a
gas into a liquid, the problem is one of making the molecules come closer
together. Frequently all that we need to do to accomplish this change
is to increase the pressure and to remove the heat produced. Usually,
however, we lower the temperature (remove heat) and keep the pressure
at atmospheric. By applying sufficiently high pressure and by sufficiently
lowering the temperature, all known gases have been changed to liquids,
and even to solids. Helium, the most difficult gas to change to a liquid,
has now been liquefied in several laboratories.
An illustration of the fact that the molecules are farther apart in a
gas than in liquids is that 1 ml of water becomes about 1700 ml of steam,
even though both are at the same pressure, 760 mm, and temperature,
100°C.
QUESTIONS
1. What two conditions of a gas are called standard conditions?
2. State Boyle's law. (This question means to give the sentence or statement
that is the law.)
3. Name the two most important conditions thdt affect the volume occupied
by a given weight of gas.
4. What is the effect on the volume of 1 liter of gas at 300°K when the tem-
/ i fxQ
perature becomes | <rc°K with no pressure change?
5. The pungent odor from an open bottle of household ammonia can soon be
smelled anywhere in a room. Explain.
6. State Gay-Lussac's (Charles') law.
7. Explain the ball-like shape of soap bubbles.
8. Summarize the four main points of the kinetic molecular theory.
9. When a confined gas has its pressure doubled and its temperature as
measured on the Kelvin scale halved, what changes take place in the condition
of the molecules? What is the observed change in the volume of the gas?
10. What happens to the volume of 1 cubic foot of oxygen when its tempera-
ture on the Kelvin scale is doubled and at the same time its pressure is halved?
MORE CHALLENGING QUESTIONS
11. When a gas is compressed to one-fourth its original volume and the tem-
perature is restored to1 the starting temperature, what change, if any, takes place
in.
122 CHEMISTRY FOR OUR TIMES
(a) The size of the molecules?
(6) The average distance between any two molecules?
(c) The average velocity of the molecules?
(d) The pressure the gas exerts?
12. Prove that at a given temperature the velocity of hydrogen molecules
(mass = 2) must be four times that of oxygen molecules (mass = 32). Kinetic;
energy is proportional to mv2.
13. What two conditions must be altered to change a gas to a liquid?
14. What force holds together (a) glue and wood, (b) glue and glue, (c) chewing
gum and hair, (d) two flat steel gauge blocks?
15. Some desert cactus plants are shaped like a ball. What advantage is this
shape to the plant in its struggle for existence in a hot, dry climate?
16. Concentrated sulfuric acid usually runs down the outside of the bottle
when it is poured. Explain this observation in terms of cohesion and adhesion.
17. A stirring rod is sometimes used to transfer liquids from one vessel to
another. (See Fig. 2-9.) Try the experiment, or one like it, and explain the result.
Observe Dropping Water. As we have said, a liquid differs from a
gas chiefly because the molecules, in general, are closer together in a
liquid than in a gas.1 When molecules are close together, the attractive
force between them becomes apparent, a force that can be illustrated by
observing a drop of water fall from a water faucet. We notice that the
water takes a shape resembling a sphere. This is because the molecules
of water are pulling each other together, causing the water to take the
form that has the least surface for a given volume, a sphere. Mercury
droplets show this effect even more strikingly than water droplets. The
forces holding the molecules together in the case of a liquid are not enough
to keep it from flowing. In the case of a solid, the molecules are held
together even more firmly, and a more or less rigid structure results.
An oil film on water shows this cohesion of oil molecules for one
another, because the film spreads out until it sometimes becomes only
one molecule thick. Afterward it ceases to spread because of the cohesive
force among the oil molecules. Again, at a pressure of 100 times
atmospheric, the contraction of carbon dioxide due to cohesive forces
alone can be shown to be over 4.5 times the contraction due to pressure
increase.
How Cases, Liquids, and Solids Compare. A gas has no definite
shape. It fills whatever container holds it, the molecules being dis-
tributed evenly in the space allowed. A liquid is also shapeless but differs
1 Substances that are gases at room temperature are called by the name gas. The
term vapor is sometimes applied to the gas from substances that are normally liquid
or solid at room temperature.
THE NATURE OF GASES, LIQUIDS, SOLIDS 123
from a gas in that it has a surface; this means that it has a definite
volume. A liquid takes the shape of the container; its surface remains at
right angles to the force acting upon the liquid. A drinking glass full of
water has an upper surface parallel to the floor of the room, at right
angles to the downward force of the earth's pull that acts on the water.
A solid^has surfaces and shapes of its own.
A gas can be compressed readily; but the effect of pressure in de-
creasing the volume of a liquid is slight. A gas expands when heated,
but, as a rule, a heated liquid changes in size much less than a gas, and a
solid still less. A liquid tends to evaporate (become a vapor or a gas) at its
free surface. Some solids evaporate, but much more slowly than liquids.
Moth crystals (naphthalene or paradichloro-benzene), camphor, and
Dry Ice all evaporate. Even snow evaporates, but at an exceedingly
slow rate.
Condensation. Steam readily changes back to water. The changing
of any gas to a liquid is called condensation. This is a physical change,
and it is the opposite of evaporation. When a gas or vapor is cooled
sufficiently, the gas becomes liquid. The molecules move less rapidly
when the gas is cooled. The attractive force, or their cohesion for one
another, becomes relatively strong enough for them to form a liquid.
On the other hand, increasing the pressure on carbon dioxide causes
it to become liquid, and it is marketed in this*form in steel tanks. Am-
monia, sulfur dioxide, water vapor, and many other gases liquefy when
their pressure is increased. The heat generated during the process of
liquefaction by increasing the pressure is considerable. It is removed by
some cooling device.
Molecular Motion. Consider a closed room the size of a small gymna-
sium. If people are packed in tightly, the capacity is about 500. Motion
is possible, but extremely limited. The people "mill about " but do not
progress far from their starting places. If the people are to move, as in
dancing, the hall will hold only 100. The same area will hold 10 basketball
players, leisurely "warming up." All may be in motion at the same rate,
but the distance through which any one person travels is limited by the
nearness of his neighbor. Such is a partial picture of a solid, liquid, and
gas of a given substance, all at the same temperature. The molecules are
all moving with the same speed, on the average, although some molecules,
because of a fortunate combination of collisions, will be moving faster
than their neighbors. Others will be moving somewhat more slowly. The
distance a molecule can move is determined by the free space about it.
The molecules of a liquid (or a solid) are in motion just as they are in a
gas, but the distance they go before colliding is more limited in a liquid,
and still more limited in a solid, because the molecules are closer together.
124
CHEMISTRY FOR OUR TIMES
- — Water
Our comparison would be better if people could move naturally in every
direction like birds, for molecules do not stay on one level. Thus mole-
cules of water vapor, ice, and liquid water all at
0°C have the same average velocity.
Evaporation. The layer of molecules on the
surface of a liquid is different from the molecules
elsewhere in the liquid. Inside the liquid all the
molecules are subjected to the attractive force of
their neighbors, which is equal in all directions;
but on the surface there is no cohesive force
acting on the molecules from above. A film is
formed on the surface of water because this outer
layer of molecules has only downward cohesive
forces acting on it. (See Fig. 7-3.) Water insects
skate about the surface of a pond on this film;
this layer of surface molecules is even strong
enough to keep a razor blade from sinking.
Not only are there no cohesive forces pulling the molecules in the
surface film upward, but also there are no collisions from molecules of
FIG. 7-3.— The sur-
face layer of a liquid
has no upward co-
hesive force acting on
it, a unique situation
since all other mole-
cules in the liquid are
covered.
Courtesy of General Ceramics Company
FIG. 7-4. — An Egyptian is here evaporating the moisture from the surface of a
porous earthenware jug filled with water. By this means he will be able to serve a
cool drink.
the liquid from above. Occasionally some of the especially energetic
molecules of the liquid are moving fast enough to "take off" from the
THE NATURE OF GASES, LIQUIDS, SOLIDS 125
surface of the liquid into the space above. For this reason we always
find some of the molecules of the liquid above its surface.
We may ask, "How can the molecules of the liquid escape into the
space above if that space is already filled with air?" The answer is that
any space which contains air is far from " filled." Plenty of room is left
between the molecules in the air for the molecules that come from the
liquid. Thus the space above a liquid contains air molecules and molecules
of the vapor of the liquid.
This tendency of molecules at the surface of a liquid to escape or to
form vapor, called evaporation, increases when the temperature of the
liquid is raised. Warm water evaporates more quickly than cold water.
This is because the molecules of the liquid are moving faster when the
liquid is heated, and thus more molecules have sufficient energy to leave
the liquid. Fanning a liquid or causing a draft of air to blow over it
will also hasten the rate of evaporation. (See
Fig. 7-4.) Let us see why this is true.
Cooling by Evaporation. As we have dis-
covered, above the surface of every liquid are
molecules from the liquid. These are constantly
moving about so that they collide with one
another. Some of them hit the liquid again, and
then they are close enough to the molecules of
the liquid to allow the force of cohesion to act.
They join the liquid again and hence condense.
(See Fig. 7-5.) If, instead, a draft of air takes these
vapor molecules away, they cannot reach the
liquid to become part of it again. The liquid cools
because the molecules, moving away from the
surface, take excess energy along with them. A
Molecules of Water Vapor
Leaving Surface of Liquid
and some returning
Water
' FIG. 7-5.— The mol-
ecules constantly "take
off" and return to the
surface of a liquid dur-
ing evaporation.
windy day favors the drying of clothes, and damp clothes are cooler
than dry clothes hanging on the same line.
Vapor Pressure. A balance of molecular action, or equilibrium, as
it is often called, can be illustrated by considering the surface of gasoline
in a partly filled closed tank. The air in the space above the gasoline
is saturated with gasoline vapor. The gasoline vapor is continually
forming liquid gasoline again and just as rapidly evaporating. (See
Fig. 7-6.)
It is interesting to consider what happens in general when evaporation
of a liquid goes on in an enclosed space at a constant temperature. The
molecules from the liquid hop out and mix with the vapor in the space
above. The air molecules are relatively few and act as spectators for this
procession of acrobatic molecules from the liquid. Some of these molecules
126
CHEMISTRY FOR OUR TIMES
rejoin the liquid, while others continue to escape from it. The rate of
return grows as the vapor molecules increase in number. The temperature
of the liquid layer becomes the same as that of the vapor, and the rate of
molecules leaving and returning becomes the same. The two actions are
equal in rate, but exactly opposite in their effect.
Gasoline Tank v
. o o/o*
* '
°'° o.'o'.o-.o-o -o o-
°«? °-'o -° 'o ° o' o
->•*«„ r<r'5^tr°.-bTcro-<3-o-
K_O__. oj^0^ O^ __. O_. O^ i_°_._ O_j jO '_ O^ .jO ^O,
i -zj~_t- JT; -ZL "Gasoline"- ~— "~- — ~f^~-
_ 3- — _ ~-T=_ — — ~~~ — iri. :_"— '•— ~
o Gasoline Vapor • Air Molecules
FIG. 7-6. — An equilibrium between the rate of "take-off" of molecules and their
return is set up within a closed tank partially filled with liquid.
The vapor molecules of a liquid exert a constant pressure under the
conditions just described because the number of vapor molecules is
fixed. This pressure of the vapor is called the vapor pressure. Vapor
pressure is defined as the pressure at any temperature of the vapor
molecules in equilibrium with the liquid. It increases as the temperature
is raised.
ur
U-Tube
Alcohol
(C2H5OH)
Bell
Jar
Liquid
Blown
Out
Carbon Tetrachloride
(CCI4)
Ether
(C2H5)20
FlG. 7-7. — The extent to which liquid in the U-tube is pushed down from its closed end
is a measure of the vapor pressure of the volatile liquid enclosed by the bell jar.
Boiling. Let us observe an open flask of water as it is heated to the
boiling point. We notice first the escape of bubbles of air that were dis-
solved in the water. At the surface, a mist forms that is often considered
steam but is actually comprised of little droplets of water condensing
from the evaporated liquid. Next, little bubbles of water vapor form on
the bottom of the vessel, rise part way up the liquid, but collapse and
THE NATURE OF GASES, LIQUIDS, SOLIDS 127
condense again before they reach the surface. Finally, these bubbles
of vapor do rise out of the liquid, growing larger as they rise nearer the
surface of the liquid, where the (hydrostatic) pressure on them is less.
These bubbles contain water vapor at sufficient pressure to prevent
collapse. Since the vapor is now at the boiling temperature of water, it is
called steam. We say that the liquid is boiling and that a temperature
has been reached called the boiling point. More heat applied makes the
evaporation faster, but the temperature does not rise because more heat
merely increases the rate of evaporation. At the boiling point the average
velocity of the molecules of the liquid and of the vapor is the same. In
Solution to
Evaporated
.Cool Water
in Beaker
Air
Bubbles
£ i Steam
Boiling
Water
Condensed
Moisture
Outside
Fuel
Gas
Burning
I 2 3
FIG. 7-8. — 1. Moisture condenses on the cool outside walls of the beaker. The
moisture is a product of burning the hydrogen in the fuel gas. 2. The moisture on
the outside walls evaporates as the temperature rises. Small bubbles of air that were
dissolved in the water appear around the sides of the beaker. 3. Bubbles of steam
form within the water during the boiling. The steam heats the underside of the
evaporating dish and condenses, warming the dish and hastening evaporation of the
liquid within it.
fact, the molecules of liquid, solid, and gas of the same substance are
moving at the same average velocity if they are at the same temperature,
no matter what the temperature may be.
Obviously, the boiling point is not a definite temperature but depends
upon the pressure on the surface of the liquid. That is, the vapor in the
bubbles must have enough pressure to prevent their collapse. If the
liquid with which a chemist is working happens to be one that is chemi-
cally decomposed at a temperature below its normal boiling point under
atmospheric pressure, it may nevertheless be boiled by reducing the
pressure at its surface. Vitamin A can be distilled and purified, and orange
juice can be concentrated in this way. Boiling-point temperatures are
usually stated at standard pressure, 760 mm.
The boiling point may be defined as the temperature at which the
vapor pressure becomes equal to the pressure at the surface of the liquid.
128
CHEMISTRY FOR OUR TIMES
A demonstration to show that the boiling point may be changed is worth
following.
A strong, round-bottomed flask is selected, filled partly with water, and
heated until the contents boil vigorously. (See Fig. 7-9.) A thermometer inserted
reads about 100°C. The space above the boiling water in the flask contains steam
but no air. The flask is closed tightly with a rubber stopper through which a
thermometer has been inserted. The flask is then removed from the heat, inverted,
and placed under running cold water. The steam in the flask changes to liquid
water, occupying about H?oo of its former volume. The pressure on the water in
the flask becomes less than it was previously. Vigorous boiling takes place inside
Steam
Condensing
Steam
Boiling
Water
Stopper with
Thermometer
FIG. 7-9. — This experiment must be seen to be appreciated. Vigorously boiling
(but lukewarm) water in a flask can actually be carried in the bare hands. That is,
boiling depends upon pressure as much as upon temperature.
the flask. In fact, finally the flask of boiling water can be comfortably held in the
bare hands. The thermometer now shows a temperature very much lower than
100°C.
Energy Changes. If a person holds his hand in a stream of air escap-
ing from a tire, he finds that the expanding air is cool (I).
Every time a person washes his hands and face, the slight cooling of
the skin as it dries is noticeable. The same effect of cooling by evaporation
is noted when gasoline, ether, or dry-cleaning fluid gets on the hands and
evaporates. An alcohol rub is useful in cooling the surface of the body
because the alcohol evaporates (II).
The opposite effect is evident when we pump up a tire, using a hand
pump of the plunger type. Of course motor-driven pumps show the same
effect to a greater degree. Both get warm (III).
THE NATURE OF GASES, LIQUIDS, SOLIDS 129
In order to explain these three effects, let us consider that one of us is holding
a tennis ball in his hands. The ball is pulled toward the earth. The two objects
(the earth and the ball) have a force of gravity acting between them. If the ball
is allowed to drop to the earth, the rate of motion becomes faster and faster.
On the rebound, as the ball moves away from the earth, the rate of motion be-
comes slower. From this illustration we get the idea that as two bodies that have
a mutual attraction move toward each other their speed increases, potential
energy is changed to motion, or kinetic, energy; and as the objects separate their
speed is retarded, kinetic energy is stored as position, or potential, energy.
Compressing a gas means reducing the space between the molecules.
The molecules move toward each other; the molecules attract each other
also. As molecules approach, their speed increases owing to forces of
attraction. Hence the average motion energy has become greater, and
the gases are raised to a higher temperature (III).
Following the same reasoning for evaporation (II) or an expanding
gas (I), in each case the molecules move apart, against forces of attrac-
tion. A slowing up of their rate of motion is caused, and the temperature
is thus lowered.
Practical Applications. Steam heating and mechanical refrigeration
both use these simple principles, that evaporation causes cooling and
condensation causes heating. In steam heating the water takes energy
from the chemical change of oxidation going on in the fire under the
boiler. Evaporating the water requires energy to drive the molecules
apart. The steam formed travels to radiators, where it strikes a large
surface of cooler metal. The steam now condenses to water. The molecules
come closer together. Heat is evolved.
Steam burns are especially painful, for in addition to the high temper-
ature of the steam the extra heat from its condensation is liberated on
the unfortunate victim.
Measurement of Heat Energy. Heat intensity is measured by a
thermometer. The thermometer tells the temperature at the position
where it is located, but it does not tell how much material is heated to
that temperature. In order to measure the amount of heat, the amount
of material must be included with that of the temperature. The con-
venient standard amount of material for heat measurements in the
laboratory is 1 g of water. When the temperature of 1 g of water is
changed 1°C, 1 cat of heat is required. The Calorie used for measuring
the energy value of foods is 1000 times larger, and is the large or kilo-
calorie. To heat 1 g of water 10°C requires 10 cal; to heat 10 g of water
1°C requires 10 cal; to heat 10 g of water 10°C requires 100 cal.
The calorie is the unit used to express the energy change accompanying
a change of state of a substance, to measure the heat of combustion of
130
CHEMISTRY FOR OUR TIMES
fuels, and to measure the heat absorbed or liberated in chemical actions
generally.
Amount of Heat in Change of State. When ice melts, it remains at
the temperature called the melting point (0°C) until it has all melted.
Adding more heat will hasten the melting but will not raise the temper-
ature until all the ice has melted. The molecules of ice at 0°C and of
water at 0°C move with the same average velocity, since they are at the
same temperature. After all the ice has melted, the water will rise in
temperature as the molecules move more rapidly, absorbing 1 cal per
Beaker Containing
Cone. Sulfuric Acid
Bell Jar
Water Vapor
Ice, Boiling Water
Watch Glass
FIG. 7-10. — Under reduced pressure it is possible to have ice, liquid water, and
water vapor all in equilibrium at the same temperature. This diagram illustrates the
so-called " triple point. "
g per deg in so doing, until it reaches its boiling point, 100°C (standard
pressure is assumed). Now the water boils. As we have previously stated,
adding more heat now will hasten the boiling but will not raise the
temperature while any water is left. Molecules in the liquid and vapor
are now moving with the same average velocity. Steam can be separately
heated to any higher temperature desired, or superheated. Molecules
of superheated steam are moving at a much higher velocity than those in
ordinary steam at 100°C.
In terms of molecules, those of the solid ice become freer to move
about when ice is changed into liquid water (although slightly closer
together). Heat is required to overcome the cohesion that the molecules
have for one another in the solid and to give them the greater liberty of
motion that they have in a liquid. After this change, the molecules in
THE NATURE OF GASES, LIQUIDS, SOLIDS 131
the liquid condition move faster and faster as the temperature is raised.
When finally the boiling point is reached, enough heat energy is absorbed
to free each molecule from the forces of attraction of its neighbors.
The amount of heat energy required for these changes, in terms of
1 g of water, gives some measure of the force of cohesion that is overcome
by the water molecules. To change 1 g of ice to 1 g of water without
changing the temperature, both ice and water staying at 0°C, 80 cal is
necessary. The amount of heat required to change 1 g of a solid to 1 g
of liquid without raising the temperature is called the heat of fusion.
In the case of water the heat of fusion is 80 cal.
^Paraffin
Courtesy of Journal of Chemical Education
FIG. 7-11. — An interesting way to grow crystals. Saturated solutions of barium
chloride and sodium thiosulfate in beakers are covered carefully with distilled water
and the whole covered. Large crystals of barium thiosulfate form slowly. Other pairs
of solutions that can be used are lead nitrate and potassium iodide, silver nitrate and
sodium nitrite.
Still with respect to 1 g of water, the amount of heat needed to raise
its temperature from 0 to 100°C is 100 cal. The temperature now stays
at 100°C, while 540 cal of heat, a relatively large quantity, is absorbed.
This shows the great amount of energy that is needed to free the mole-
cules from the cohesive forces that they have for each other in liquid
water. The number of calories needed to change 1 g of a liquid to 1 gram
of a gas of the same substance at the same temperature is called the heat
of vaporization. The heat of vaporization of water is 540 cal.
Solids. We are now ready to consider the most familiar form of mat-
ter— solids. Strange as it seems, only recently has much been learned
about the structure of solids. Rocks of a peculiar coloring or formation
have always attracted people. One of the rocks that people often pick up
because of its attractive appearance is quartz. Some quartz has six-sided
and pointed crystals, often clear, but sometimes tinted in delicate colors,
purple as in amethyst, for example. Quartz is an oxide, silicon dioxide
132 CHEMISTRY FOR OUR TIMES
(SiOe). At this point we are not so much interested in its chemical nature
as in its form. Quartz and other solids that have regular form, flat sur-
faces, and edges are called crystalline. Salt and sugar are common ex-
amples of crystalline solids. Large crystals are frequently found in
nature. But most rocks consist of small crystals, matted together. Solid
metals are crystalline, usually masses of tiny crystals. Since we consider
even very minute solid particles as crystalline, every true solid is
crystalline.
Materials evidently not crystalline are called amorphous (without
shape). Glue, glass, and flesh are examples of amorphous materials. The
dividing line between amorphous materials and crystalline substances is
not sharp; the classification is a general one, but quite useful.
Crystalline substances have a definite melting point and, like ice,
remain at that temperature until all the solid has melted. Amorphous
substances gradually become softer with no change of state and hence
have no definite melting point. As the temperature is raised, they finally
flow so readily that anyone would recognize them as liquid.
The fact that crystals of a given substance are perfectly regular is
interesting. Any given substance always forms the same kind of crystals
under like conditions. There must be something quite regular about the
way in which the molecules or other building stones are arranged in these
crystals. X-ray examination of crystals shows this to be the case.
Refrigeration. When ice is used for cooling, its success as a cooling
agent is due chiefly to its melting. In melting 1 g of ice to 1 g of water,
both at 0°C, 80 cal of heat is absorbed. This heat is absorbed from what-
ever is near the ice. If the ice is in a refrigerator, then the heat is taken
from the contents of the refrigerator. The change of state from solid to
liquid is the active process in producing cooling, for the molecules take
in heat to overcome the cohesive forces in a cake of crystalline ice.
Unless ice is melting in a refrigerator, there can be but limited cooling
effect.
Household refrigeration of the mechanical type may be of the sort
which for its success depends upon another change of state, that from
liquid to gas. In many mechanical refrigerators electricity supplies
energy, which runs a motor, which in turn drives a pump. This pump
compresses a vapor. For small models the vapor is often sulfur dioxide
(SO2) or one of several other vapors that easily change into a liquid, such
as Freon (CF^d*). For larger installations, as for a cold storage ware-
house, ammonia (NH3) is most commonly used, although carbon dioxide
(CO2) may be used on ships. The compressed vapor from the pump is sent
to a coil (a long pipe wound in a spiral so that there is much pipe in a
small space), where it is cooled, for during compression the vapor be-
comes heated. The cooling may be brought about by forcing air or water
THE NATURE OF GASES, LIQUIDS, SOLIDS 133
across the pipe or by simply allowing air to go over it naturally, since
the warmer air near the coil will rise. All this goes on outside the refrig-
erator. The cooling changes the compressed vapor to a liquid, which runs
through a tube into the "unit" inside the refrigerator. The liquid passes
an expansion valve, which is equivalent to letting it enter a larger pipe.
High Pressure
Gas
I Low Pressure
I Liquid
Refrigerator Oil
High Pressure l::.M:::'fe:| Low Pressure
Liquid l.v-::V:'-:':V.-..i Gas
Courtesy of Temperature Research Foundation of Kelvinator Corporation
FIG. 7-12. — The heart of a household refrigerator is a pump run by an electric motor.
The pump compresses a gas that becomes a liquid when it is cooled in air. The liquid
evaporates within the "unit," producing the desired cooling within the box.
Here the liquid rapidly evaporates, forming the vapor again. Heat
energy is absorbed in this process of evaporation. The entire system is
closed so that the gas does not escape but is taken back to the pump,
compressed again, cooled, condensed, and then allowed to evaporate for
another cycle. (See Fig. 7-12.) The cooling process is not continuous but is
1j4 CHEMISTRY FOR OUR TIMES
controlled by a thermoregulator (temperature regulator) so that it goes
into action only when the temperature inside the refrigerator rises to a
certain point. On modern refrigerators this temperature can be adjusted
by the temperature-control knob.
SUMMARY
The volume that a given amount of gas occupies is influenced by the condi-
tions of temperature and pressure on it. The effect of pressure alone is described
by Boyle's law: The volume of a given quantity of gas is inversely proportional
to the pressure, provided that the temperature is unchanged. The effect of tem-
perature alone is described by Gay-Lussac's (Charles') law: The volume of a
given quantity of gas is directly proportional to the Kelvin or absolute tempera-
ture, provided that the pressure is unchanged. Kelvin, or absolute, temperature
is based on the centigrade scale. Absolute zero is — 273°C, and 0°C is 273°K.
(C + 273 = K.)
Evidence for the correctness of the kinetic molecular theory includes
1. Boyle's and Gay-Lussac's (Charles') laws apply to all gases (within
limits).
2. The phenonemon of diffusion, or continual spreading of a gas by its own
motion.
3. The pressure exerted by a gas is continual.
4. A gas exerts its pressure equally in all directions.
The kinetic molecular theory is reaffirmed and used to explain many phe-
nomena.
There is a relatively large space between molecules in the gaseous condition.
The force of attraction between like molecules is called cohesion; the force of
attraction between unlike molecules is called adhesion. When molecules move
apart, energy must be supplied. When molecules come closer together, energy is
liberated.
When a gas changes to a liquid, the process is called condensation. The opposite
process of changing a liquid to a gas is called evaporation. The process of evapora-
tion may be hastened by heating, lowering the pressure above the evaporating
liquid, stirring the liquid, and increasing the circulation of air over the liquid.
The process of evaporation in the open produces cooling. When the rates of
escape and return of molecules at the surface of a liquid in a closed vessel are
the same, the liquid and vapor layers are in equilibrium. We may measure the
vapor pressure of a liquid; and it rises with the temperature. Boiling takes place
at such a temperature that the vapor pressure is equal to the pressure of the
atmosphere above the liquid. Then evaporation can take place at any point in a
liquid. The boiling temperature is usually given at standard pressure (760 mm of
mercury), but boiling points may be changed by altering the pressure.
The unit of heat quantity is the calorie, the amount of heat needed to change
the temperature of 1 g of water 1°C. To change 1 g of ice at 0°C to water at 0°C
requires 80 cal, and to change 1 g of water at 100°C to steam at 100°C requires
540 cal. The fact that energy changes accompany changes of state has many
practical applications, as in refrigeration and in steam heating.
THE NATURE OF GASES, LIQUIDS, SOLIDS 135
Solids may be classed as amorphous or crystalline. Amorphous solids like glue
have no definite shape, but crystalline solids like common salt have smooth flat
surfaces, sharp edges, and definite angles between surfaces.
TEMPERATURE SCALES
Kelvin
or absolu
Centigrade Fahrenheit
373°
Boiling F
100° 212°
K)int of water
273°
Freezing
0° 32°
point of water
0°
Absolute
-273° -459.4°
zero
Helpful
conversion
formulas
C 5
F - 32. 9
K = C + 273
QUESTIONS
18. A glass of water held at arm's length can be whirled over one's head
and back to the original position. If this is done rapidly and skillfully, no water
spills. Explain.
19. List four factors that change the rate of evaporation. How should each be
altered to hasten evaporation?
20. Portions of a gasoline-engine carburetor may become so cold when the
engine is running that ice may form. How is this effect explained?
21. What is the vapor pressure of water at its boiling point under standard
pressure?
22. Pipes made of plastic material can stretch considerably without breaking.
Suggest conditions under which plastic plumbing could be used advantageously.
23. (a) In temperature measurement, distinguish between a degree and a
calorie, (b) What is specific heat?
136 CHEMISTRY FOR OUR TIMES
<nf\ /
.Q grams of water from |
o f\
25. How many calories are needed to melt 8 gram(s) of ice and to raise the'
{20
OQ°C?
26. How many calories are needed to change l~ gram of water at ]oQ°C
to 100°C and to boil away the resulting hot water?
27. Water on a stove in an open pan is boiling gently. The heat is now sud-
denly increased. What is the effect on (a) the temperature of the water and (6) the
rate of boiling?
28. Certain home-heating systems include a boiler that boils water under
reduced pressure. What is the effect of such an arrangement on the boiling point of
water?
29. Define and give an example of crystallization.
30. How many prominent axes has a snow crystal?
31. Describe the changes that a raindrop undergoes on its way back to rejoin
a cloud.
32. Trace the course of a refrigerant in a mechanical refrigerator.
MORE CHALLENGING QUESTIONS
(20
33. How many calories are needed to change | ™ grams of ice at 0°C to steam
at 100°C?
34. Do locomotives use steam at a temperature of 100°C?
.36. Can a person cool a kitchen on a hot day by opening the door of a mechan-
ical refrigerator in the kitchen?
36. List the properties of an ideal refrigerant.
UNIT
TWO
Gay-Lussac and Biot made a balloon ascension for
scientific observations in 1804.
CHEMISTRY'S BUSINESS OFFICE
A CERTAIN pupil, who had become intensely interested in the
subject of chemistry during his high-school years, reached
college with even more intense curiosity about this branch of
science. There he consulted the dean in regard to planning his
courses so that he might prepare wisely for the chemical profession.
"It is advisable to be able to read either French or German," said
the dean.
The freshman was surprised; but later when he learned from a
senior that many reports of chemical work have never been trans-
lated from the language in which they were written, the reason
became clearer. "My chemistry professor/1 said the senior, "is now
studying Russian in order that he may find out the information dis-
covered in that country about his pet research field."
"Are the symbols and equations different in other languages?"
asked the freshman.
"No. They are substantially the same in every language, even in
Chinese books on chemistry," was the comforting reply.
A group of chemistry pupils was once being guided through an
industrial plant. The chemist who was conducting the party
stopped near a gasmaking machine and explained the process by
which it worked. "In the generator of the water-gas machine, we
heat coke by burning it in a forced draft of air. Then the air is shut
off and steam forced through the deep bed of hot coke. A chemical
reaction takes place, as your instructor has probably shown you, as
follows :
c + H2o -4 co -h H2
In this process heat energy is absorbed, and the coke is thus
cooled."
In these two instances we see that symbols play an important
role in chemistry study and industrial processes. While all chemists
do not have the same mother tongue, it is an enormous advantage
that all use the same scientific language, the same symbols and
formulas, and understand all common abbreviations.
This sketch shows chemistry's business office in action in Paris in 1760. Some
of the work consisted of the preparation of medicines. Can you notice any similarity
between these apparatus and those common today?
Courtesy of General Ceramics Company
UNIT TWO CHAPTER VIII
THE INVENTORY— ATOMS
AND MOLECULES
Once again it is profitable to go behind the scenes. In our previous
trip to the backstage of chemistry we found out something about mole-
cules. These little particles are useful in explaining many things. Perhaps
asking a few more questions about molecules will lead somewhere. Are
they the smallest particles? How do molecules of elements and compounds
differ?
Avogadro's Reasoning. In the early nineteenth century Amadeo
Avogadro (1776-1856), who did not claim to be a chemist and who is little
known for his laboratory investigations, hit upon a simple idea that has
greatly aided the progress of science. In 1811, while England and the
youthful United States were warming up for their second war, this pro-
fessor of physics at the University of Turin, Italy, wrote an article. In it he
claimed that equal volumes of all gases have the same number of mole-
cules, if the gases are measured under the same conditions of temperature
and pressure. This holds true whether the gas is a mixture, an element, or
a compound. One liter of air, oxygen, or carbon dioxide each contains
the same number of molecules. Avogadro did not state what the number
was ; nor is the number important for our present purpose.
In arriving at his conclusions the imagination of Avogadro had been
fired by some facts that were found to be true about all gases. Robert
Boyle, over 100 years before, had shown that the volume of any given
amount of gas changes inversely with the pressure at constant tempera-
ture (Boyle's law). Charles' law (1787) that the volume of a given amount
of gas at constant pressure changes directly with the absolute temperature
also applied to all gases was given exact expression in 1802 by Gay-Lussac
(1778-1850), a French investigator.
A few years before Avogadro reached his conclusions, Gay-Lussac
had carried out extensive experiments with gases. In this work he studied
New Terms
atom liter density
molecular weight atomic weight
139
140
CHEMISTRY FOR OUR TIMES
the chemical reaction between the gases hydrogen and oxygen, measuring
the volumes used. He was impressed by the simplicity of his results,
namely, that 2 liters of hydrogen combines with 1 liter of oxygen. Study-
ing the combining volumes of other gases he found that the volumes which
combined completely were all whole-number volumes. For example 1 liter
of chlorine joins with 1 liter of hydrogen exactly to form 2 liters of hydro-
gen chloride. Also, 1 liter of nitrogen joins with 3 liters of hydrogen to
form 2 liters of ammonia. In general, he concluded that gases take part in
a chemical change in simple volume ratios, J£, J^, and the like. The state-
ment in boldface italics is called Gay-Lussac's law of combining volumes.
O 0 0 0
o o o o
0 O O 0
O O 0 0
0000
0 O 0 O
o o o o
O 0 0 O
f>°°
o'°
Ao°
& 8- £ &
8- 8- 8- 8*
8' 8- 8- 8-
8- 8- 8- &
8* 8*
8- 8*
fr 8-
8r
2 Volumes
Hydrogen
1 Volume
Oxygen
(a)
2 Volumes Steam
(water vapor)
00 0
°° o°«o°0
0 ° °
o o o o
b o °o
00 0
°° ° 0
00°
o°o0°
0 0 0
0°
• •
3 Volumes Hydrogen
2 Volumes Ammonia
1 Volume Nitrogen
(&)
FIG. 8-1. — In (a) and (6) the molecules are represented as circles. The diagrams
suggest the actual volumes of gases that combine in a chemical change. Gay-Lussac's
law points out that these volumes are small whole numbers.
Avogadro was greatly impressed by Gay-Lussac's law. He reasoned in
terms of molecules that, in the union of hydrogen and oxygen, two mole-
cules of hydrogen joined with one molecule of oxygen to form two mole-
cules of steam (see Fig. 8-la), while, in the union of hydrogen and nitrogen,
one molecule of nitrogen joined with three molecules of hydrogen to form
two molecules of ammonia. (See Fig. 8-16.) He concluded that the reason
why two molecules of hydrogen and one molecule of oxygen did not form
three molecules of steam and one molecule of nitrogen and three molecules
of hydrogen did not form four molecules of ammonia was because the
steam molecule and the ammonia molecule were made up of parts. The
number of parts (atoms) present in the molecules of steam and of am-
monia was not the same as in the molecules of the elements that formed
the compounds.
Let us translate the excellent reasoning of Avogadro into terms of a
chemical change. From the laboratory we find that
2 volumes of hydrogen + 1 volume of oxygen -» 2 volumes of steam
THE INVENTORY-ATOMS AND MOLECULES 141
The one volume (any definite number of liters, milliliters, cubic feet, or
other volume measure) of oxygen contains a certain number of molecules.
The two volumes of hydrogen or of steam contain just twice that number
of molecules.
Molecules of Compounds. Compounds are made up of two or more
elements joined together in definite proportion by weight. Some com-
pounds can be decomposed easily into
their elements; water, for example, can be
decomposed into parts. Probably these
parts are smaller than the molecules.
What are they called? The name atoms
(not divisible) has been given to them.
For our explanation, let us carry our
thought back to England just a few years
before the time of Avogadro's work at
Turin.
The Atomic Theory. When he was
not too busy making notes about the
weather in his collection of notebooks,
John Dalton (176&-1844), an English
schoolteacher, relaxed and thought. His
mind was of the sort that generalizes,
sees fundamental ideas clearly in spite of
many confusing situations. His thoughts
were often about the structure of matter,
a subject that had been considered from
the earliest times. The result was Dalton's
atomic theory.
In this theory an atom is defined as
the smallest particle of an element that
can exist in a molecule. It is the smallest
particle of an element that has all the
chemical properties of larger amounts of
that element. Since 92 natural elements
are now known, 92 sorts of natural atoms
FIG. 8-2.— "While at Kendal
employed his leisure in studying
Latin, Greek, French, and the
Mathematics with Natural Phi-
losophy, removed thence to Man-
chester in 1793, as Tutor in
Mathematics and Natural Phi-
losophy in the New College, was
six years in that engagement, and
afterwards was employed as pri-
vate and sometimes public
Instructor in various branches of
Mathematics, Natural Philos-
ophy and Chemistry chiefly in
Manchester, but occasionally by
invitation in other places, namely
London, Edinburgh, Glasgow,
Birmingham, & Leeds." So
writes John Dalton of his career.
must exist — 1 for each kind of element.
An atom is a fundamental building stone of matter. All molecules are
made of 1 or more atoms.
Each sort of atom is different from every other sort of atom in weight
and properties. All atoms of the same element are alike in weight and
properties.1 When elements combine, atoms of the elements are combin-
1 Subject to later developments.
142
CHEMISTRY FOR OUR TIMES
ing. When compounds are decomposed, new molecules are formed in
which the original atoms are rearranged. The entire world is built up of
atoms, so small that they are invisible to us. (See Fig. 8-3.)
These, Dalton's ideas, were accepted slowly by the people of his day.
The atomic theory has won its place in science because it is successful in
explaining facts as we know them. We may wonder at believing that which
cannot be definitely proved by direct evidence or that which cannot be
seen. We can, however, see effects caused by a single particle of atomic
size in the Wilson cloud chamber. The theory is accepted today to the
ELEMENTS
Ow*« ^w^
Hydrogen / £* Strontian
CarHun
Oxygen J
U^ Phosphorus
SulpKur
Magnesia ?
Lime %
Sodd <2
Potash ^
J) Iron **
z} Zinc Jtf
Copper sf
$) Stiver ,
^ Gold
**&
1h Platma
Courtesy of Fisher Scientific Company
FIG. 8-3. — This lecture diagram was used by John Dalton to illustrate his famous
atomic theory in 1803. It is a reproduction from the original chart by the Science
Museum, London.
extent that one dictionary defines chemistry as a science that considers
matter to be composed of atoms.
Applications of the Atomic Theory. The test of a theory is its
value in explaining the situations to which it refers. The atomic theory
enables us to explain the law of constant composition. The composition of
nitric oxide is always 46.67 per cent nitrogen and 53.33 per cent oxygen,
no more and no less. This is one illustration of the law of constant com-
position. A certain number of nitrogen atoms (one) combined with a cer-
tain number of oxygen atoms (one) is a molecule of nitric oxide. Since the
weight of each element in the compound does not change, the percentage
of each in the molecule is constant..
THE INVENTORY— ATOMS AND MOLECULES 143
A second application of the atomic theory is its explanation of the law
of multiple proportions.1 In numerous cases two or more compounds are
made of the same two elements. Both water and hydrogen peroxide are
made of hydrogen and oxygen. There are two oxides of carbon, namely,
carbon monoxide and carbon dioxide. Many compounds of hydrogen and
carbon exist, among them ethane, ethylene, and acetylene. Laboratory
experiments give the following figures (columns A and B in the table
below) for the composition of these compounds:
Compounds
Percentages
Parts by weight
A
B
C
D
Case I:
Oxygen
Hydrogen
Oxygen
Hydrogen
Water
88.81
94.07
11.19
5.93
7.94
15.86
1
1
Hydrogen peroxide . .
Case II:
Oxygen
Carbon
Oxygen
Carbon
Carbon monoxide ....
57.14
72.73
42.86
27.27
1.33
2.67
1
1
Carbon dioxide ....
Case III:
Hydrogen
*
Carbon
Hydrogen
Carbon
Ethane
Ethylene . ...
20.00
14.29
7.69
80.00
85.71
92.31
0.25
0.17
0.08
1
1
1
Acetylene
The figures in column C are obtained by dividing the percentages in
column A by those in column B. The two sets of columns of figures (per-
centages and parts by weight) are therefore equivalent. Column D is
1 in each case, since it represents the element in column B expressed as one
part by weight. When the hydrogen is expressed as one part by weight in
case I, then the parts of oxygen are 7.94 and 15.86, a ratio of 7.94/15.86, or
practically J^. In case III, three compounds are considered, each com-
posed of hydrogen and carbon. The carbon is represented as one part by
weight; the hydrogen has the ratio 0.25/0.17/0.08, or approximately
3/2/1. In each example one element has been represented as one part by
weight. Also, the weights of the other elements can be represented by a
small fraction made up of whole numbers. This is found to be true every
time two or more compounds composed of the same elements are studied.
These facts can be summarized as follows: // two or more compounds are
made of the same two elements and the weight of one of the elements be
1 The law of multiple proportions may be omitted in a general study of chemistry.
144 CHEMISTRY FOR OUR TIMES
represented by one part, then the weights of the second element are
related as a simple fraction. This statement is called the law of multiple
proportions.
The explanation of the law just stated is based on the existence of
atoms. The one part by weight represents one or more atoms (often one)
of a certain element in each of two compounds. Both these compounds
also contain another element in common. The numbers of atoms of the
other element are related as 1 to 2, 2 to 3, or a like group of small numbers.
In case I both water and hydrogen peroxide have two atoms of hydro-
gen in each molecule (one part by weight) ; and both have the element
oxygen in common. There is one atom of oxygen in a molecule of water,
and two oxygen atoms in a molecule of hydrogen peroxide (per means
" extra "). The weights of the oxygen in these two compounds are related
in the ratio of ^, a simple fraction.
In case II both oxides of carbon have one atom of carbon, one part.
The one oxygen atom in carbon monoxide and the two oxygen atoms in
carbon dioxide have a ratio of %> a fraction of small whole numbers. This
fact is shown by the ratio of the weights of oxygen, 1.33/2.67, which
reduces to approximately J^.
The law of multiple proportions was first stated by John Dalton. It
was undoubtedly very influential in establishing in his mind the truth
of the atomic nature of matter.
Atoms and Molecules. To summarize, the smallest part of a com-
pound is a molecule. The molecule of a compound is made up of atoms of
two or more different sorts; the molecule of an element is made of one,
two, or more atoms, all of the same sort. Thus elements differ from com-
pounds in that the atoms present in the molecule of an element are all of
the same kind, while those in the compound molecule are of two or more
different kinds.
If the element is normally a gas, like oxygen, or can be changed into
a gas readily, we can find out how many atoms are present in its molecule.
For example, let us seek an answer to the question, " How many atoms are
present in a molecule of oxygen?"
Chemical Geometry. Whatever our feelings about the subject of
geometry, we all admire the method it uses in establishing truths. Once
demonstrated, the conclusions of geometry cannot be denied. Let us use
the method of geometry, to show that the molecule of oxygen has two
atoms.
Proposition: The oxygen molecule has two atoms.
Given: Avogadro's law; laboratory equipment.
To prove: The molecule of oxygen has two atoms.
THE INVENTORY-ATOMS AND MOLECULES t45
Statements Reasons
(1) 2 volumes hydrogen + 1 vol- (1) Laboratory measurement
ume oxygen — > 2 volumes
steam (water)
(2) Let 1 volume of gas hold 1000 (2) NOTE: Any number may be
molecules assumed
(3) 2000 molecules hydrogen + (3) Avogadro's law
1000 molecules oxygen — *
2000 molecules steam
(4) Each molecule of steam (water) (4) Water can be decomposed into
contains at least 1 atom of elements in the laboratory. The
oxygen least amount of an element is 1
atom
(5) 2000 molecules of water con- (5) From statements (3) and (4)
tains 2000 atoms of oxygen
(6) 1000 molecules of oxygen have (6) Statements (3) and (5)
accounted for 2000 atoms of
oxygen
(7) Therefore 1 molecule of oxygen (7) Dividing by 1000 (or whatever
has 2 atoms number was assumed)
More strictly, the conclusion of this proposition is as follows: One
molecule of oxygen has at least two atoms. However, since we have no
evidence that more than two atoms are present in a molecule of ordinary
oxygen, the "at least" may be omitted. By using a similar method, we
can prove that the molecules of chlorine, hydrogen, and nitrogen also
contain two atoms.
Not all elements have two atoms per molecule when in the gaseous
state. For example, phosphorus vapor has four, arsenic vapor four, and
sulfur vapor eight. The inert gases of the air have only one atom per
molecule.
Weight of an Atom. By very careful calculations, it is possible to
obtain the actual gram weight of one atom of oxygen. This weight is
exceedingly small, 0.000,000,000,000,000,000,000,026,39 g. It can be seen
that so small a weight has no practical meaning; in fact, no balances in
the laboratory can weigh one atom. An ounce or a gram weight from a
set of weights is so large compared with the weight of an atom that the
comparison is like telling the weight of a grain of sand in terms of the
weight of the earth.
This perplexing situation was solved by selecting an atom of the
element oxygen as a standard of weight. Experience has shown it wise
to assign it the weight 16. This is because the lightest substance, hydro-
gen, would then have a relative weight of at least 1, Oxygen was originally
146 CHEMISTRY FOR OUR TIMES
selected as a standard because it is able to combine with so many other
elements. Since two atoms are present in a molecule of oxygen, the weight
that represents the oxygen molecule is 32. The weights of the other atom
are represented in terms of the oxygen atom. Sulfur has atomic weight
32; this means that the sulfur atom is twice as heavy as the oxygen
atom. Copper with atomic weight 64 (approximately) is four times as
heavy as oxygen, atom for atom. The atom of carbon to which is assigned
the weight 12 compares in weight with the oxygen atom as 12 to 16,
or«.
We must be sure to realize that the relative weights do not tell how
much atoms actually weigh. However, careful laboratory experiments
were performed in finding the relative atomic weights. Moreover, the
work is revised when necessary by an international committee of dis-
tinguished scientists.
International Atomic-weight Table. At the end of this book is a
list of all known elements and their atomic weights. This table summarizes
the work of chemists in many countries; it is a clearing-house for
scientific information of this nature. The table is used by chemists and
students of chemistry in every country. The information is the best
available on the relative atomic weights of the known elements. It may,
of course, be slightly in error in some details; thus we may expect small
revisions as our knowledge becomes more complete and our methods of
performing accurate experiments become better. Yet in this table as it
now stands chemical accuracy has risen to a great height. It is a common
meeting ground for chemists all over the world.
History of Atomic- weight Determination. Dalton's atomic theory
had been presented in 1808, closely followed by Avogadro's law in 1811.
These ideas were not fully accepted at once; in fact, the first real apprecia-
tion of Avogadro's work came as late as 1860 from his pupil, Stanislao
Cannizzaro (1826-1910), a brilliant Italian professor of chemistry. The
actual laboratory work needed to translate these theories into use was
carried out by Berzelius. He is known as the " organizer of science," for he
purified and analyzed over 2000 compounds and determined the atomic
weights of over 50 elements. It will encourage many readers of this book
to learn that this distinguished chemist did not have a happy time in his
school days. He was graduated with a diploma which stated that his work
"justified only doubtful hopes." He almost "flunked" his regular course
in chemistry, but after his school days he worked along chemical lines
with steady persistence. The facts presented in his article, "An Attempt
to Determine the Definite and Simple Proportions in Which the Con-
stituents of the Inorganic World Are Combined with Each Other," are
famous for their accuracy. His results are remarkable when we consider
THE INVENTORY— ATOMS AND MOLECULES 147
that at this time the science of chemistry was no more than a husky
youngster cutting its first teeth. This work of Berzelius gives proof of his
skill and thoroughness.
Elements
Atomic weights
Berzelius
(1826)
International Table
(1945)
Nitrogen ....
14.05
32.18
35.41
39.19
108.12
207.12
14.008
32.06
35.457
39.096
107.880
207.21
Sulfur . .
Chlorine ....
Potassium.
Silver
Lead
The challenge to obtain more accurate atomic weights was accepted
by a Belgian, Jean Servais Stas (1813-1891), who showed remarkable
genius for the task, "making his weighings on balances of hitherto un-
equaled precision, and exercising extraordinary care in his manipulations/'
The mantle more recently descended on the shoulders of Theodore
William Richards (1868-1928), of Harvard University. (See page 3.)
He found the atomic weights of no less than 22 elements. For his researches
in this field he was awarded many honors, among them the Nobel Prize
in chemistry in 1914.
Modern physics has developed new methods, including use of the
mass spectrograph, for finding atomic weights. These methods have been
used with fine results by Dr. F. W. Aston, Dr. K. T. Bainbridge, and
others — present-day successors to the heritage of Berzelius.
Laboratory Facts. The atomic weight of an element may be found
by using a combination/ of facts and theories already considered. For
example, let us learn how to determine the atomic weight of carbon.
We select several compounds that contain the element carbon and in
the laboratory find the percentage of carbon in each one. Several such
compounds with their percentage of carbon have been listed in the
table on page 143. Carbon' dioxide, containing 27.27 per cent carbon,
is found to weigh 1.98 g per liter. Carbon monoxide, containing 42.86 per
cent carbon, is found to have a density of 1.26 g per liter. Oxygen gas
weighs 1.43 g per liter.
Finding Molecular Weights. According to Avogadro's law, a liter
of any of these three gases contains the same number of molecules (under
the same conditions of temperature and pressure). Their densities and
also the weights of the molecules compare (oxygen to carbon dioxide to
148 CHEMISTRY FOR OUR TIMES
carbon monoxide) as the figures 1.43 to 1.98 to 1.26. The standard molec-
ular weight is that of oxygen, with the figure 32 selected to represent it.
To find the molecular weight of carbon dioxide a simple ratio is used.
densities molecular weights
Oxygen ^ 1.43 = 32
Carbon dioxide 1.98 "" x
1 98 X 32
Molecular weight carbon dioxide = ,» — > or 44
In the case of carbon monoxide,
Oxygen = 1.43 = 32
Carbon monoxide 1.26 x
1 26 X 32
Molecular weight of carbon monoxide = ,Q — > or 28
1 .4*5
Since 27.27 per cent of carbon dioxide is carbon, then
0.2727 X 44,
or 12 parts by weight of carbon dioxide's 44 is due to carbon.
Also, 42.86 per cent of carbon monoxide is carbon. Therefore,
0.4286 X 28,
or 12 parts by weight of carbon monoxide's 28 is due to carbon.
The smallest part of the molecular weight due to an element in any
of its compounds is selected as the atomic weight of that element. In all
compounds of carbon, at least 12 parts by weight are due to carbon. No
less a number has been found. Twelve is therefore accepted as the atomic
weight of carbon.
22.4 Liters at STP. Let us find out what volume of oxygen gas will
be needed to obtain a quantity that will represent its molecular weight
in grams, or 32 g. One liter of oxygen weighs about 1.43 g. The volume
that is needed to make up 32 g, 1.43 g for each liter, will be found by
dividing 32 by 1.43. The answer is 22.4 liters.
Nitrogen has a molecular weight of 28. One liter of the gas weighs
1.25 g. 28/1.25 = 22.4 liters, the volume that is required to include a
molecular weight in grams of nitrogen.
Methane gas, a compound, has a molecular weight of 16. Its density
is 0.72 g per liter. 16/0.72 = 22.2 liters, approximately 22.4 liters.
In a similar manner, other gases give the same approximate answer;
that is, 22.4 liters at standard conditions of any gas is the volume that
holds the molecular weight in grams. In general,
Molecular weight (g) rtrt A /Vx N
— rpr — ~. — , ,.., ^ = 22.4 (liters)
Density (g/hter) v '
THE INVENTORY-ATOMS AND MOLECULES 149
If we clear fractions by "cross-multiplying," this expression becomes
Molecular weight = 22.4 X density
Here is a simple way to find the molecular weight of a gas: Weigh
a given volume (find the density), and then calculate the weight of
22.4 liters. The molecular weight of any gas is the number that represents
the weight in grams of 22.4 liters of the gas. We have emphasized the
fact that atomic weights are relative weights; this is also true of molecular
weights; no unit, such as a gram, is expressed or meant.
Another Method of Finding Atomic Weights. The atomic weight
of nitrogen might be found this way. A liter weighs 1.25 g; 22.4 liters
weighs (22.4 X 1.25) 28.0 g. We have shown that each molecule of
nitrogen, like the molecule of oxygen, has two atoms. If the molecular
weight is 28, then the atomic weight (weight representing one atom) is
2^ = 14. The formula of nitrogen, thus, is N*.
SUGGESTION: In considering the new ideas of atoms, their rela-
tionship to the molecule, and their atomic weights, we should not assume
that we have completed our discussion. If the molecule is represented as
a bunch of grapes, then the atom will be represented as a single grape,
for that is the smallest unit that is like another. Each single grape is a
complex structure in itself, having skin, pulp, and seeds. We may think
of the atom in this way, a fundamental unit, but one that can be investi-
gated in more detail later.
SUMMARY
Statement of Avogadro's principle. Equal volumes of gases at the same tem-
perature and pressure have the same number of molecules; that is, the number of
molecules is proportional to the volume of a gas.
Avogadro's principle was based on the following laws about gases: Boyle's
law, Charles's law, Gay-Lussac's law of combining volumes. The statement of the
law of combining volumes is as follows: the volumes of gases used or produced
in a chemical change have the ratio of small whole numbers.
Dalton's Atomic Theory.
1. Matter is composed of atoms. Each atom is the smallest part of a molecule,
and every molecule contains one or more atoms.
2. All atoms of the same element are alike in weight and properties.
3. Atoms of one element differ from atoms of another element.
4. Compounds are formed by the combination of atoms.
The atomic theory explains (1) the law of definite composition (each com-
pound has a definite composition by weight) and (2) the law of multiple propor-
tions (if two or more compounds are made of the same two elements and the
weights of one of the elements are represented by one part, then the weights of
the second element are related as a simple fraction).
150 CHEMISTRY FOR OUR TIMES
Certain conclusions follow if Avogadro's principle is true. Among them are
the following:
(1) Molecules of hydrogen, oxygen, nitrogen, and chlorine have two atoms.
Hence we represent them as H2, 0*, N2, and C12, respectively.
(2) Molecular weights may be determined by comparing densities of gases.
For this work the oxygen molecule at 32 is standard,
(3) The gram-molecular weight of any gas at standard conditions occupies
22.4 liters. The expression
Molecular weight (g)
Density (g/iiter) ~ ^A Ulters)
summarizes this statement.
Atomic weights were determined by chemical methods by Berzelius, Stas,
Richards, and many others. More recent determinations by physical methods
have been carried out by Aston and others.
The smallest part of a molecular weight of a compound due to a single ele-
ment is its atomic weight. The standard of atomic weights is the oxygen atom
taken as 16. Ninety-two different natural elements are known.
QUESTIONS
NOTE : Assume all gases measured at standard conditions of temperature and
pressure.
1. State Avogadro's principle.
f 5
2. How does the number of molecules in \*. liters of oxygen at standard
f2
conditions compare with the number of molecules in jo liters of nitrogen?
f50
3. When i-- liters of hydrogen burns, how many liters of oxygen are used?
What is the ratio between the volume of hydrogen and the volume of oxygen?
4. Name and state the law illustrated in question 3.
5. How many cubic feet of hydrogen will combine with J^A cubic fee^ °f
nitrogen? What volume of ammonia is formed? Assume complete reaction.
6. When hydrogen chloride is formed, what volume ratio exists between its
elements?
7. Distinguish a molecule of an element from a molecule of a compound.
8. Define atom.
9. What is the original (Greek) meaning of the word atom?
10. Name two theories that are firmly established, and name one that has
been rejected.
THE INVENTORY— ATOMS AND MOLECULES 151
11. What is the percentage composition of water by weight?
12. State the law illustrated in the answer to question 11.
13. Sulfur dioxide is 50 per cent sulfur and 50 per cent oxygen. Sulfur trioxide
is 40 per cent sulfur and 60 per cent oxygen. Show that this is a case of multiple
proportions.
14. Show that the three compounds in the following group illustrate the law
of multiple proportions :
Percentage
nitrogen
Percentage
oxygen
Nitrous oxide
63.6
36.4
Nitric oxide.
46.7
53.3
Nitrogen dioxide.
30.5
69.5
15. State the law of multiple proportions.
16. Using the synthesis of hydrogen chloride from its elements, prove that
a. The hydrogen molecule has two atoms.
6. The chlorine molecule has two atoms.
17. Using the synthesis of ammonia from its elements, prove that the nitrogen
molecule has two atoms.
18. The atomic weight of magnesium is 24. How does the weight of a mag-
nesium atom compare with the weight of (a) an oxygen atom; (6) an oxygen
molecule?
19. What was the percentage of error in Berzelius's determination of the
atomic weight of sulfur?
20. Sulfur dioxide has a molecular weight T>f 64 and a density of 2.93 grams
per liter. What volume does a gram-molecular weight of this gas occupy at stand-
ard conditions?
21. Acetylene (C2H2) has a molecular weight of 26 and a density of 1.17
grams per liter. What volume does a gram-molecular weight of this gas occupy
at standard conditions?
22. Find the density in grams per liter of a gas that has a molecular weight
of (a) 17; (6) 2; (c) 44; (d) 160.
23. What are the molecular weights of gases having the following densities in
grams per liter: (a) 1.43; (6) 1.98; (c) 0.178; (d) 5.45?
MORE CHALLENGING QUESTIONS
24. Two oxides of lead have percentages of oxygen of 7.18 and 13.4, respec-
tively. Show that these two oxides illustrate the law of multiple proportions.
152
CHEMISTRY FOR OUR TIMES
25. Complete this table (do not write in this book):
Molecular weight, g
Density, g/liter
Molecular volume,
liters
2
28
?
58
0.09
?
3.2
?
?
22.4
22.4
22.4
UNIT TWO CHAPTER IX
SHORTHAND AND TRANSCRIPTION
—WRITING AND NAMING
FORMULAS
In the writings of the alchemists many mysterious signs and figures
were used. The records of these "fire philosophers" were designed to con-
fuse outsiders and to keep secret whatever discoveries had been made.
In those days few people could read or write. For this reason the inn,
cobbler's shop, or tavern would be known by a symbol, such as a white
horse, rather than a printed sign. Some of the symbols used by the al-
chemists were so common that even today we are able to decipher them
and thus understand the meaning of parts of their writings. For example,
the symbols for the metals became associated with the heavenly bodies:
3 (lima, the moon) was the symbol for silvery© (sol, the sun), was the
symbol for gold; ? (Venus), copper; @x (Mars), iron; 3>x (Jupiter), tin;
5 (Saturn), lead; and $ (Mercury), quicksilver. These signs can be
found in some almanacs of the present day.
While the alchemists used symbols to keep their discoveries secret,
modern chemists use symbols to understand one another. Another impor-
tant reason for the use of symbols in -chemistry is that time is saved.
If we were required to write down information in which the word oxygen
occurred often, we should soon begin to write 0, an abbreviation, to
represent the word. But chemical symbols are more than abbreviations.
One of their great advantages lies in the fact that they express so much
in so small a space.
Many false starts were made in selecting chemical symbols. John
Dalton made little pictures to represent the atoms about which he built
his theory. A circle with a cross in it stood for sulfur; a large black dot
stood for carbon; and, equally sensibly, a large 0 stood for oxygen. (See
Fig. 9-1.) Lavoisier used symbols that resembled those of the alchemists.
The modern symbols were introduced by the great organizer, Berzelius.
New Terms
symbol radical percentage composition
formula combining number
153
154
CHEMISTRY FOR OUR TIMES
Chemical Symbols of Today. In the modern system of representing
elements the first letter of the name of the element is used as its symbol.
ATOMIC SYMBOLS
L EC T&ll RE
jw* tyfatto tk MEMBERS tffa
JKanctytrter
FIG. 9-1. — John Dalton's atomic symbols and his representation of certain compounds.
O is the symbol for oxygen, H for hydrogen, and N for nitrogen. Where the
names of two or more elements begin with the same first letter, two letters
are used for all but one: C is the symbol for carbon; Ca, that for calcium;
SHORTHAND AND TRANSCRIPTION 155
Cd, that for cadmium; Cr, that for chromium. Notice that the first letter
only is capitalized.
It should be remembered that English is not the only language which
has contributed names for elements. It is not surprising to find that Na is
the symbol for sodium (Latin natrium) and K for potassium (kalium).
Some elements were known in ancient times, and these have symbols
from the names by which they were known in ancient Rome. The symbol
Fe for iron is from the Latin ferrum. The symbol Cu for copper comes from
cuprum, and Pb for lead comes from plumbum.
The list of elements and their symbols included at the end of the book
need not be memorized. It is convenient, however, to know a few of the
most important symbols.
The Full Meaning of a Symbol. Symbols are abbreviations for
elements, but the entire meaning of a symbol includes (1) one atom of that
element and (2) one atomic weight of the element expressed in grams.
The symbol 0 stands for one atom of oxygen and 16 g of oxygen (a
gram-atomic weight). Zn means, not only one atom of zinc, but 65 g of
zinc.
Chemical Formulas. A symbol represents an 'atom; a formula
stands for a molecule. If a molecule has only one atom, the symbol and
the formula are the same. In most cases, however, this is not so. Molecules
that contain two atoms of the same element have a small 2 written below
the line, following the symbol for the element. The formula O2 means one
molecule of oxygen, two atoms in the molecule. In like manner another
number of the same atoms may be written. The formula O3 represents one
molecule of ozone, a variety of oxygen, and shows that the molecule
contains three atoms of oxygen.
Formulas for compounds contain the symbols for the several different
elements joined chemically in the compound. The symbols are written
side by side.
Where more than one atom of an element is contained in the compound,
a subscript number is placed following the symbol to designate the number
of atoms of that element in the compound. As everyone knows, H2O is a
formula for water. The entire meaning of H20, as everyone may not know,
is (1) one molecule of water; (2) two atoms of hydrogen and one atom
of oxygen; (3) two gram-atomic weights of hydrogen (2X1 = 2) and one
gram-atomic weight of oxygen (16); (4) 2 + 16 = 18 grams of water.
This last figure, 18, the sum of the weights of all the atoms in the molecule,
is called the gram-molecular weight, or the gram-formula weight.
Sometimes parentheses are used in formulas. The number outside the
parentheses is a multiplier and indicates the number of times that all
atoms in the parentheses are to be taken, ^Hs^O represents one mole-
156 CHEMISTRY FOR OUR TIMES
cule of ether. The molecular weight of this formula can be figured as out
follows:
Carbon 2X2= 4 atoms 4 X 12 = 48 parts by weight
Hydrogen 2 X 5 = 10 atoms 10 X 1 = 10 parts by weight
Oxygen 1X1= 1 atom 1 X 16 = H) parts by weight
One molecule of ether = 74 parts by weight
The gram-molecular weight of ether is 74 g.
If in a formula a symbol has no .subscript number, the number 1 is
understood. The formula HC1 for hydrogen chloride tells that one atom of
each element is present in the molecule. Also, 1 is understood before the
entire formula, meaning one molecule of the substance. If we wish to
represent some other number of molecules, that number appears before
the formula. Three molecules of hydrogen chloride are represented by
3HC1. If we write 5NH8, we mean five molecules of ammonia containing a
total of five atoms of nitrogen and 15 atoms of hydrogen.
Formulas do not tell how a compound is made. The formula for table
sugar is C^H^On. This does not mean that 12 atomic weights of carbon
mixed with 22 atomic weights of hydrogen and 11 of oxygen together with
the necessary energy will produce sugar. In some instances the elements
can be combined in this way, but in the case of sugar they cannot. In fact,
there is no way of telling from the formula alone how the compound may
be made. The methods of making compounds are a separate problem.
Chemical formulas for compounds and elements differ from
recipes. We can find in the proper books the recipes, commonly called
the "formulas," for iron rust remover, photographic developing solution,
and other useful mixtures. These, of course, are not formulas in the sense
in which the word is used in chemistry texts. In both senses, formulas tell
" what's in it and how much."
Developing a Formula. Like candidates being initiated into the
mysteries of a secret order, we have received instruction in the meaning
of our symbols and signs. We are now to learn how the correct formulas
came into existence, formulas that are not several meaningless letters and
figures put together. These chemical formulas represent the composition
of substances as created by nature (or synthetically), and they are true to
nature to the letter. To find a formula we turn to the place where nature
answers our questions, the laboratory.
From laboratory experiments we can find the percentage composition
of compounds. For example, ordinary water contains 11.19 per cent of
hydrogen and 88.81 per cent of oxygen. From these facts finding the
formula of water would be an easy matter if hydrogen and oxygen atoms
were of equal weight. Then about one part of hydrogen would go with
eight parts of oxygen, and we should write HiOs. But, if we think back
SHORTHAND AND TRANSCRIPTION
157
to our discussion of weights of atoms, we shall recall that the atomic
weights of the two elements are different. An oxygen atom is sixteen times
heavier than a hydrogen atom. If we divide the Cumbers of atoms in
Hi08 by their respective atomic weights, we get H^0^6 or HiO^. In order
to avoid the impossible one-half atom, we multiply by 2 and write H20.
A good way to understand the mathematics of percentages is to con-
sider an example from school life. Helen has the following grades for
her senior work: English 80, French 60, chemistry 90, trigonometry 80,
art 90. The first four are regular full-time subjects, studied once each
day for a full period; art, an extra subject, is studied twice a week. Art
counts as one credit, and the others count four credits each. In finding
Helen's final average we multiply the grades in each subject by its
number of credits, or weights, to obtain the total number of points on
which to base her average.
80 X4 =
60 X 4 =
90 X4 =
80 X 4 =
90 X 1 =
320
240
360
320
90
17)1330(78.2 Final average of all subjects
UL
"140
136
Sum 17 = 1330
40
34
In this case it would be unfair obviously to bmit the grade in art, for
the 90 raises her average. Likewise, it would be equally unfair to count the
grade in art on the same basis with her other subjects. As we figured
the average, the art grade counts one-fourth that of any other subject,
just what it is worth on the basis of the credits allowed.
In chemistry we deal with elements, not subjects, with different
weights, not credits. Sometimes we are given only the percentages, not the
final average, and are told to figure back to the value for each element. In
reversing the process we divide the percentages by the atomic weights
of the respective elements, rather than multiplying as was done in finding
the school average.
Below is given a table that we shall use to find the formula for water:
Elements of water
Percentage
composition
Atomic weight
of elements
Quotients
Ratio of
quotients
Hydrogen
11.19
1
=- 11 19
2
Oxygen
88.81
16
» 5 55
1
The numbers 11.19 and 5.55, if both are divided by the smaller, have
the ratio of approximately 2 to I.1 The simplest formula for water is
1 If the accurate atomic weight for hydrogen (1.008) is used, the ratio will come
158
CHEMISTRY FOR OUR TIMES
therefore H^O. Of course, H402, H608, and so forth, are equally correct
from the figures given. In many compounds the simplest formula is also
the correct one.
Another illustration will again show how the formula is obtained from
laboratory figures. Some white crystals are found to contain 32.37 per
cent of sodium, 22.58 per cent of sulfur, and 45.05 per cent of oxygen. The
simplest formula is to be found.
Elements in
compound
Percentage
composition
Atomic weight
of elements
Quotients
Simplest ratio
of quotients
Na
32.37 -*- 23 1.41
2
S
22.58 ^ 32 0.705
1
o
45.05 + 16 2.81
4
From the table above the simplest formula Na2SiO4, or, better, Na2SO4
is obtained.
The method of obtaining a simple formula illustrated by these exam-
ples is that of first finding in the laboratory the percentage weight due to
each element, then dividing these figures by the atomic weights of the
respective elements. The final answer, expressed as a simple ratio, is the
relative number of atoms of the elements in the compound. If no simple
ratio is evident when the quotients are divided by the smallest, divide
by one-half, one-third, etc., of the smallest quotient.
How to Derive Formula Weights from Formulas. If we know the
formula for a substance, it is possible to find the formula weight. Since the
formula weight is the sum of the weights representing all the atoms in
the compound, the process is one mainly of addition. The formula weight
of salt (NaCl) is 23 + 35.5, or 58.5. For the second example let us turn
back to the illustration of finding the molecular weight of ether (page 156).
Here is another illustration, one of the most complicated that we shall
meet. Beef suet (hard fat) is chiefly stearin [CsH^dsHssC^s]. Let us find
the formula weight of this substance.
(C)
(H)
(O)
(C)
(H)
18 X 12 = 216
35 X 1 = 35
2 X 16 = 32
The weight of the part in the parentheses is
found first, then multiplied by 3 and added to
the rest.
283 X 3 = 849
3 X 12 = 36
5X1= _5
890 formula weight
out more closely 2 to 1. In all examples the approximate figures will be given to center
the attention on the idea rather than on the arithmetic.
SHORTHAND AND TRANSCRIPTION 159
Percentage Composition from the Formula. If we know the value
of each part and the value of the whole, then we can find the relationship
each part bears to the whole. This process is the familiar one of finding the
percentage one quantity is of another. The percentage is equal to
The part X 100 -f- the whole
To find the percentage composition (percentage of each element in the
compound) of potassium nitrate (saltpeter) (KNO8), the formula weight
is first found.
(K) 1 X 39 = 39
(N) 1 X 14 = 14
(0) 3 X 16 = 48
101 formula weight
Part X 100 £ *heiuway to
— „,, , — find the per-
Whole centage.
The percentage of potassium in potassium nitrate is
39 X 100 4- 101 = 38.6 %
The percentage of nitrogen in potassium nitrate is
14 X 100 + 101 = 13.9 %
The percentage of oxygen in potassium nitrate fs
48 X 100 -f- 101 = 47.5 %
The sum of the percentages found should equal 100 per cent. This
check on the arithmetic does not tell whether the formula weight is
correct or not. Usually such calculations are sufficiently accurate if
expressed to the nearest tenth of 1 per cent.
Sometimes we wish to calculate the percentage of a part or group in
a formula. An illustration is the answer to the question, "What is the
percentage of water in the gypsum (CaS04-2H20)?"
Formula weight 40 + 32 + (4 X 16) + 2 X (2 + 16)
40 + 32 + 64 + 36 = 172
The water is represented by 36 parts of the 172. The percentage of
water in gypsum is
36 X 100 4- 172 = 20.9% Ans.
Let us carefully note that the formula weight of the entire substance is
first found, not merely the weight representing the CaSO4, for this, of
course, has no water in it.
Method of Finding the True Molecular Formula. The true
molecular formula of a compound is not necessarily the simplest formula.
160
CHEMISTRY FOR OUR TIMES
The molecular formula can be found if the molecular weight and per-
centage composition are both known.
The molecular weight of methyl chloride gas is found in the laboratory
to be 50.5. Analysis of the compound shows 23.8 per cent of carbon, 5.9 per
Courtesy of National Archives
RG. 9-2. — The chemical laboratory of the National Archives in Washington, D.C.,
is concerned, among other things, with the preservation of documents. Here, as in
all chemical laboratories, symbols, formulas, and equations are all a part of the
day's work.
cent of hydrogen, and 70.3 per cent of chlorine. Find the correct formula.
Of the total molecular weight, 50.5,
23.8 per cent is carbon, or 12 parts; one atomic weight (12) of C
5.9 per cent is hydrogen, or 3 parts; three atomic weights (1) of H
70.3 per cent is chlorine, or 35.5 parts; one atomic weight (35.5) of Cl
The correct molecular formula for methyl chloride is therefore, CH3C1.
How Is the Simplest Formula Related to the Molecular For-
mula? Ethylene gas has been used since 1926 as one means of changing
the color of oranges and other fruits to make their appearance more
attractive. Of this gas 85.7 per cent is carbon, and 14.3 per cent hydrogen.
One liter of the gas weighs 1.26 g. What is the correct formula?
Elements in
compound
Percentage
composition
Atomic weight
of elements
Quotients
Ratio
C
H
85.7 -J- 12 7.1
14.3 * 1 = 14.3
1
2
SHORTHAND AND TRANSCRIPTION 161
The simplest formula for the compound is then CH2. If the formula
is CH2, the formula weight of the compound is 12 + 2, or 14.
The molecular weight of any gas is the weight in grams of 22.4 liters
of that gas at standard conditions. One liter of ethylene weighs 1.26 g.
The weight of 22.4 liters (22.4 X 1.26) is 28.6 g, the true molecular
weight. This answer is about twice 14. This shows that the true molecular
formula has twice the weight of the simplest formula and that the true
formula is 2 X CH2, or C2H4. This molecular formula is the one accepted
for ethylene, and the compound has a molecular weight of 28.
In general, the way to tell whether or not the simplest formula is
also the molecular formula is to compare the weight found by adding
the weights of the elements in the simplest formula with the molecular
weight found experimentally by measuring the density or by some other
means.
When the formula weight of the simplest formula is the same as the
molecular weight found experimentally, then the simplest formula is the
correct molecular formula. Chemists have not always known how to
find correct formulas, nor have the figures from the experiments always
been accurate enough to give good results. This was particularly true in
the early days of chemistry. John Dalton's notebook shows that he con-
sidered water to be composed of one atom each of hydrogen and oxygen,
for he represents the formula for water as OO (HO).
QUESTIONS
1. What element is represented by each of the following symbols: C, Cl, Cu,
Zn, W, P, S, Na, K, A?
2. Tell the full meaning of each of these symbols : Fe, Ca, Sn, Mg, N.
3. What is the complete meaning of each of the following formulas: 862,
CH4, P4S3, N20, CHI3?
4. (a) How many different kinds of atoms are represented in the following
formulas and (6) what is the total number of atoms represented by each formula :
HN03; Ca(C,H,0,)»; C17H35COONa; H202; Fe3[Fe(CN)6]2?
5. What is the simplest formula of a compound that is composed of 40 per
cent calcium, 12 per cent carbon, 48 per cent oxygen?
6. Chemical analysis shows that a certain compound contains 67 per cent
zinc and the rest oxygen. What is the simplest formula of this oxide?
f27 3
7. An oxide of carbon contains « ' per cent carbon. What is its simplest
formula?
8. A compound is composed of 90.9 per cent carbon and 9.09 per cent hydro-
gen. Find its simplest formula.
162 CHEMISTRY FOR OUR TIMES
9. A professor, with a twinkle in his eye, likes to tease his class with this one:
"An inventor in New York claims to have discovered a green fluid that when
added to water, 1 teaspoonful to a gallon, produces a motor fuel equivalent to
high-test gasoline. We have analyzed the compound and find that it contains
3.6 per cent boron, 78.9 per cent uranium, 4.6 per cent nitrogen, 12.9 per cent
potassium." What is the formula of this compound?
10. Find the formula weight of (a) pearls (CaCOs); (6) zinc white (ZnO);
(c) milk of magnesia (Mg(OH)2); (d) silver tarnish (Ag2S); (e) Prussian blue
{Fe4[Fe(CN)6]3}; (/) soft soap (CnHasCOOK).
11. Find the percentage composition of the 1 -numbered compounds in
i even
question 10.
12. Find the percentage of water in
a. Plaster of Paris [2(CaS04)-l(H2O)]
b. Blue vitriol (CuS04-5H20)
c. Washing soda (Na2C08-10H20)
13. The simplest formula of a compound has a formula weight of 13. The
{OA
,_£. How many times should the simplest formula be
multiplied to give the molecular formula?
14. From experiments we find that ethyl alcohol has a molecular weight of 46.
It is composed of 52.2 per cent carbon, 13.0 per cent hydrogen, and 34.8 per cent
oxygen. Find its molecular formula.
16. Hydrogen peroxide consists of 5.9 per cent H and 94.1 per cent 0. Its
true molecular weight is 34. Find the molecular formula.
16. Hydrogen fluoride gas of a certain sort is composed of 5 per cent hydrogen
and 95 per cent fluorine. Its density is 5.4 grains per liter. Find the molecular
formula.
17. Cyanogen gas, 2.34 grams per liter, is composed of 46.1 per cent C and
53.9 per cent N. Find its molecular formula.
18. Chloroform (mol. wt. 119.5) consists of 10.05 per cent C, 0.83 per cent H,
and 89.12 per cent Cl. Find its molecular formula.
19. What is the percentage composition of Freon (CF2C12)?
Radicals. In politics the word " radical" has a far different meaning
from the sense in which the word is used in chemistry. A radical is a
small group of chemical elements that keeps its identity in many reac-
tions. A radical is a sort of synthetic element. These groups act as a whole
in many chemical changes, although a radical may be altered in more
drastic chemical changes. Such groups are sulfate (— S04), hydroxide,
( — OH), ammonium (NH4 — ), nitrate, (— N08), carbonate, ( — C08), and
SHORTHAND AND TRANSCRIPTION 163
many others. Each group is a part of a compound, but each acts as if it
were a single element. Vinegar contains the acetate radical, — C2H802.
Radicals are not at all uncommon in substances.
Compared with words, radicals are like syllables such as -ing, pre-,
or -tion, which alone have no meaning but often are found as part of a
word. Radicals are found as parts of compounds.
Combining Number (Valence). Let us carefully examine the for-
mulas of these compounds:
I II
HC1 Hydrogen chloride NaCl Sodium chloride
H2O Dihydrogen oxide (water) CaCl2 Calcium chloride
H3N Hydrogen nitride (ammonia) Aids Aluminum chloride
H4C Hydrogen carbide (methane) SnCl4 Tin chloride
We notice that in column I all the substances are compounds of
hydrogen and that the number of hydrogen atoms in each compound is
different. Chlorine has the ability to hold one hydrogen atom in a com-
pound; oxygen, two; nitrogen, three. In methane, carbon holds four
hydrogen atoms. The numbers of hydrogen atoms that an element can
hold in a compound is called its combining number (often called valence
number). Chlorine has a combining number of 1; oxygen, of 2; and so on.
What is the combining number of phosphorus if the formula for phos-
phine is PH3?
In column II all the substances are compounds of chlorine. What was
said about hydrogen in the preceding paragraph can be repeated about
chlorine. The combining number of any element is that number of chlorine
atoms which an element can hold in a compound. From column II calcium
has a combining number of 2 and aluminum has a combining number of
3. What is the combining number of carbon if its chloride has the formula
CC14?
In addition to elements, we must also consider radicals that act as
if they were elements. From the formula H2S04 we see that the combining
number of the radical — S04 is 2, because it holds two hydrogen atoms.
NH4C1 shows that the combining number of the ammonium radical
(NH4— ) is 1, for it holds one atom of chlorine in a compound. Both these
radicals happen to contain the figure 4, The subscript figures in a radical
do not tell the combining number. These figures show the number of
atoms of the elements that they contain. In the formula H3P04 the 4
tells us that four atoms of oxygen are present. The combining number of
the phosphate radical is learned from the fact that the group — P04 is
combined with three hydrogen atoms — a combining number of 3.
By definition, a combining number is the number of hydrogen or
chlorine atoms that an atom of an element or a radical can hold in a
compound.
164 CHEMISTRY FOR OUR TIMES
How to Write Chemical Formulas. In order to write formulas
correctly we should have for a start a knowledge of a few correct formulas.
If we know these well, it is a simple matter to write the formulas of other
compounds. In fact, it is something of a game,
CORRECT FORMULAS
Commit this list to memory.
1. HC1 Hydrogen chloride 9. Nad Sodium chloride
(hydrochloric acid)
2- HNQ* Hydrogen nitrate 10. AgNQ3. . . . Silver nitrate
(nitric add)
3. HClQa Hydrogen chlorate 11. KC10* Potassium chlorate
(chloric acid)
4. HaS Hydrogen sulfide 12. CuS Copper sulfide
(hydrosulfuric add) (cupric)
5. HsCOa Hydrogen carbonate 13. CaCQ3. . . . Calcium carbonate
(carbonic add)
6. H2§Q4 Hydrogen sulfate 14. MgSQ4. . . . Magnesium sulfate
(sulfuric add)
7. HiPO* Hydrogen phosphate 15. A1PQ* Aluminum phosphate
(phosphoric add)
8. HOH Hydrogen hydroxide 16. NH4OH. . . Ammonium hydroxide
or
HaO Hydrogen oxide 17. HgO Mercury oxide
(water) (mercuric)
The compounds in the first column are compounds of hydrogen; thus
in each compound the combining number of the part not hydrogen can
easily be ascertained by inspecting the number of hydrogen atoms present.
All the radicals are underlined to aid in selecting them. The combining
number of the chlorate radical is 1, for it joins with one hydrogen atom
in the formula HC1O3. SUGGESTION: Read down the list, finding the com-
bining number of each element or radical present.
The second column contains a list of compounds that can be related
to the first column by taking the hydrogen out and putting another ele-
ment (or radical) in the place of the hydrogen. For example, consider
HC1 and NaCl. The sodium atom in NaCl is in the place of the one hydro-
gen atom in HC1. Its combining number, therefore, is 1. Also, the fact that
the atom of sodium is found combined with one chlorine atom shows
that its combining number must be 1. Continuing this procedure, we
find that the combining number of Mg is 2; of Al, 3.
For practice, find the combining number of the first part of each
formula in the second column. The combining number of the second part
of each formula in the second column is the same as it is in the first
column.
Experience has shown that, if this list (quite short if we except those
formulas which are already known) is memorized perfectly, no trouble
will be encountered in writing correct formulas.
SHORTHAND AND TRANSCRIPTION
165
The formula for ammonium hydroxide is interesting, for this com-
pound is composed of two radicals.
The order of writing elements of radicals in a compound is chiefly
a matter of custom. Usually the metal element, hydrogen, or the radical
NH4— is placed first. A table of combining numbers of those elements or
radicals which are placed first in compounds is valuable.
Combining number
1
2
3
H
Most metals
Al
Ag
Sometimes Fe
Na
K
NH4-
A way of showing how atoms are put together in compounds is to
suppose that each element has a number of links, or bonds, equal to
its combining number. An element of combining number 1 has one link ;
of combining number 2, two; and so on. In ordinary compounds these
links are always connected, never dangling or unsatisfied. The formulas
of several compounds are shown pictured in this way.
Hydrogen chloride (HC1)
H -- Cl
Water (H20)
H - o - H
Ammonia (NH8)
Calcium chloride (CaCU)
/Cl
Ca
-Cl
Aluminum sulfate [A12(S04)3]
>S04
>SO4
Methane (CH4)
H
H
H-
-H
H
One of the most stimulating discoveries in modern chemistry is the
knowledge of the nature of the Unking of the atoms in a compound. We
166
CHEMISTRY FOR OUR TIMES
can now explain the combining number of 2 for calcium and 1 for hydro-
gen. Finding the explanation of combining numbers is a real adventure
into the nature of matter and its structure, a search into the very founda-
tion stones of the universe. A later chapter will carry this hunt further.
How is the correct formula for sodium carbonate written? Sodium
has a combining number of 1; the carbonate radical, of 2 [see carbonic
acid (H2CO3) in table, page 164]. The skeleton is Na C08. A "one" ele-
ment like sodium will have to be taken twice to furnish the two links to
join to a "two" radical, carbonate. Na2C03 is the right formula.
What is the formula for calcium oxide (lime) ? The combining number
of calcium is 2 (table, page 164), as is that of oxygen. The two imaginary
links on each element will just match, and they will satisfy each other,
nothing remaining. One unit of each element will give the formula CaO;
Ca2O2 might seem to be the correct formula at first, but this is a multiple
of the simplest formula, CaO, and unless experimental data give means of
obtaining the true formula the simplest formula is always taken.
In order to practice writing formulas for chemical compounds, let us
take a large sheet of paper, about twice the size of a page of this book, and
write across the top, as follows, the symbols for elements and radicals
that are written second in chemical compounds:
Ag-
Na—
K—
NH4—
Ca—
Mg-
Cu—
Zn—
Hg-
Fe—
(combining
number 3)
Al
-fYl
— Cl — N03 —OH — S — O — S04 — CO3 — P04
chloride nitrate hydrox- sulfide oxide sulfate car- phos-
ide bonate phate
Down the left-hand side let us write the symbols for
those parts of compounds usually written first, as is done
here on the left; then block in all the squares with a ruler,
and write the formula in the proper square. For example,
the upper left-hand square should contain the formula
for silver chloride; the lower right-hand square that for
aluminum phosphate. We should be sure to take account
of the combining number of each element or radical. No
harm will be done in writing a practice formula for am-
monium oxide and silver hydroxide, although these two
compounds are very unstable.
We should recall at this point that when the combining numbers are
both the same, both parts having the combining number of 1, 2, or 3, no
combining (subscript) numbers are necessary in the simplest formula. The
number of atoms in a radical is not changed in any of these formulas, but
the whole radical is taken the required number of times. Aluminum car-
bonate, for example, where aluminum has a combining number of 3 and
the carbonate radical a combining number of 2, is written Al2(COs)3. In
SHORTHAND AND TRANSCRIPTION 167
this formula we should notice that (1) the combining number of alu-
minum is written as the subscript of the carbonate radical and the com-
bining number of the carbonate radical is written as the subscript of
aluminum and that (2) the C08 radical is written unchanged.
While this practice list contains many of the formulas we shall need,
a few more should be mentioned. The name alone suggests the formula
in some cases. Carbon dioxide is C02; silicon tetrafluoride, SiF4; phos-
phorus pentoxide, P206.
We have proved that the elementary gases, oxygen, nitrogen, chlorine,
and hydrogen, have two atoms in each molecule. When alone and repre-
senting the gas, their formulas are written 02, N2, C12, and H2, respec-
tively. In compounds, these elements may have any required subscript
numbers as in NH3 (ammonia).
Elements of More than One Combining Number. Most of the
elements are fickle enough to have two or more combining numbers.
In carbon monoxide (CO), carbon has the unusual combining number of 2.
Usually carbon has the combining number of 4 as in carbon dioxide (CO2).
FeCl2 and FeCl3 are the formulas for two common chlorides of iron, fer-
rous chloride and ferric chloride. In the former the combining number of
iron is 2; in the latter, 3. In such cases the element's lower, combining
number is designated by -ous; the higher, as^-ic. HgCl is mercurous
chloride; HgCl2, mercuric chloride. For the beginner a general rule that
may be helpful is that with oxygen or its equivalent an element tends to
take its higher combining number, while hydrogen or its equivalent with
an element favors the formation of compounds of lower combining
number. With hydrogen, sulfur forms H2S, in which the combining num-
ber of sulfur is 2. With oxygen, S02 is formed, in which the combining
number of sulfur is 4. With more oxygen, SOa (sulfur trioxide) is formed,
in which sulfur has a combining number of 6.
Naming Compounds. After a stenographer has taken her dictation
in shorthand, she must transcribe her shorthand symbols. In similar
manner chemists write formulas of compounds in symbols but usually call
each compound by name. It is convenient to group compounds for the
purpose of naming them.
Hydroxides. We name the element or radical and add the word
hydroxide. NaOH (lye) is sodium hydroxide; Ca(OH)2 (lime water) is
calcium hydroxide. What is the chemical name of milk of magnesia
[Mg(OH)2]? Of caustic potash (KOH)?
Acids. It is customary to represent acids by formulas that start with
the element hydrogen. Two-element acids, compounds of hydrogen and
one other element, are named hydro ic. In the blank space most of
168
CHEMISTRY FOR OUR TIMES
the name of the element other than hydrogen is written. HC1 is hydro-
chloric acid; H2S, hydromlfuric. What is HBr?
Three-element acids — hydrogen, a second element, and oxygen — are
named on the basis of the second element present, with the ending -ic for
the most common one. H2S04 is sulfuric acid; HC1O3, chloric acid. What is
H8P04?
With one oxygen atom fewer, the ending is changed to -ous. H2SO3 is
sulfurous acid; HC102, chlorous acid. What is H3PO3?
With two fewer oxygen atoms, the prefix hypo- (under) is used with
the -ous ending. H2SO2 is hypomlfurous acid; HC10, hypochlorous acid.
With one oxygen atom more than the common -ic acid, the prefix per-
is used. HC1O4 is perchloric acid. HIO4 is periodic acid ; H2S06, however,
is peroxymono-sulfuric acid, named according to a different system.
Salts. These are crystalline compounds considered to have a metal
atom or radical in the place of the hydrogen atom of the acid.
Hydro- -ic acids form -ide salts. NaCl is sodium chloride; BaS,
barium sulficte. What is KBr?
-ic acids form -ate salts. Na2SO4 is sodium sulfate; KNOa, potassium
nitrate. What is Ca3(PO4)2?
-ous acids form -He salts. Na2SO3 is sodium sulfite; KNO2, potassium
nitrite. What is NH4C102?
The hypo- and per- prefixes are used as in the names of the acids.
NAMING COMPOUNDS
Acid
Potassium salt
Acid
Calcium salt
HC1 hydro-
KC1 -chloride
H2S hydrosul-
CaS -sulfide
chloric
furic
HC1O hypochlo-
KC1O -hypo-
H2SO2 hyposul-
CaSO2 -hypo-
rous
chlorite
furous
sulfite
HCiO2 chlorous
KC102 -chlorite
H2SO3 sulfurous
CaSOs -sulfite
HC103 chloric
KC103 -chlorate
H2SO4 sulfuric
CaSO4 -sulfate
HC104 perchloric
KC104 -perchlo-
rate
SUMMARY
The purpose of writing chemical symbols and formulas is to save time and to
aid understanding. Chemical symbols represent (1) an atom of an element and
(2) an atomic weight of the element.
The meaning of the formula of a compound may be illustrated as follows: H2O
means
1. One molecule of water
2. Two atoms of hydrogen and one of oxygen chemically combined
SHORTHAND AND TRANSCRIPTION 169
3. Two gram-atomic weights of hydrogen, plus 16 of oxygen
4. 18 g of water, the gram-molecular weight
Formulas are found from percentage composition, determined by laboratory
analysis. The formula weight is the sum of the atomic weights of the elements
represented by a given formula.
The true molecular formula is found from the simplest formula by comparison
of molecular weights.
Radicals are groups of elements that act as a unit in many chemical reactions.
An example is the sulfate radical, -S04. Each element or radical in a chemical
compound has a combining number that is used to write formulas of compounds.
Hydrogen and chlorine each have a combining number of 1 and may be con-
sidered the unit for comparison of the combining numbers of other elements in
simple compounds. Writing correct formulas takes into account the combining
number of each element or radical. Elements that have more than one combining
number usually show the lowest in combination with hydrogen and the highest
in combination with oxygen. Most radicals have just one combining number.
Compounds are named as follows:
Hydroxides — name of metallic element or radical and the word hydroxide
Acids — binary hydro ic
ternary, most common ending -ic
ternary, with one oxygen atom less than -ic ending -ous
Salts — of hydro ic acids -ide
of -ic acids -ate
of -ous acids -ite
QUESTIONS
NOTE: Do not write any part of these exercises in this book.
20. (a) Name the following radicals: -SO4; -CO3; -N03; -OH; NH4-; -PO4;
-SO8; -C2H3O2.
(6) What combining number does each exhibit?
21. Represent the following radicals by the use of symbols: sulfate, nitrate,
carbonate, phosphate, hydroxide.
22. Write the combining number above each element or radical in the fol-
lowing formulas: HC1, HaS, AsH8, NaH, Ca8P2, Ag2O, CuCl2, Li8N, Ca(OH)2,
KN08.
23. Correct the following formulas by supplying the needed subscript numbers
wherever necessary: NaCl, NaS, CaS, CaCi, A1C1, A1S, ZnS, MgCl, MgN,
MgOH.
24. Correct the following formulas by supplying parentheses where needed:
CaOH2; ZnNO82; A10H8; A12S048; Ca8P042.
25. Write formulas for each of the following compounds: silver chloride,
sodium nitrate, potassium sulfide, copper carbonate, calcium suifide, calcium
nitrate, magnesium carbonate, magnesium chloride, silver phosphate, sodium
phosphate.
170
CHEMISTRY FOR OUR TIMES
26. Underline each radical: NaOH, (NH4)2S04, CuO, Zn3(P04)2, K2CO3.
27. Name the following: SiO2, CC14, NO2, SiC, Mg8N2.
28. Write formulas for two chlorides of iron, two chlorides of copper, two
oxides of copper, two sulfates of iron, and two oxides of sulfur. Name each
compound.
29. Name the following: K2SO4; LiClO8; NaNO8; Zn8(PO4)2; A12(CO8)8
s; LiCl; NaNO2; Zn3(PO8)2; A14C3
30. Name the following: H^O,; H2SO8; H2S; HCi; HC1O; HCIO2; HCIO3;
KN02; CaS08; Fe(N03)2; Fe(N03)8; KC104.
31. Write formulas for
numbers) :
A
1. Zinc hydroxide
2. Copper chloride
3. Hydrosulfuric acid
4. Potassium sulfate
5. Aluminum sulfide
6. Ammonium chloride
7. Silver oxide
8. Magnesium phosphate
9. Calcium sulfite
10. Dihydrogen oxide
D
1. Aluminum chloride
2. Magnesium chlorate
3. Calcium sulfate
4. Ammonium hydroxide
5. Sulfur trioxide
6. Potassium carbonate
7. Tin chloride
8. Silver nitrate
9. Aluminum oxide
10. Sodium sulfate
the following (use Cu = 2, Sn = 4 for combining
B
Copper hydroxide
Zinc chloride
Chloric acid
Potassium sulfide
Aluminum sulfate
Silver chloride
Ammonium carbonate
Calcium phosphate
Magnesium nitrate
Carbon dioxide
E
Zinc chlorate
Magnesium chloride
Calcium hydroxide
Ammonium phosphate
Phosphorus pentoxide
Sodium sulfite
Potassium suifate
Tin nitrate
Silver sulfide
Aluminum carbonate
C
Magnesium hydroxide
Calcium chloride
Carbonic acid
Potassium nitrate
Sodium carbonate
Silver phosphate
Ammonium sulfate
Copper sulfide
Zinc sulfite
Sulfur dioxide
MORE CHALLENGING QUESTIONS
32. The cyanide radical ( — CN) has a combining number of 1. Write formulas
for sodium, calcium, potassium, silver, and gold cyanides and for the acid from
which these salts may be made.
33. Acetate radical ( — C2H302) has a combining number of 1; chromate
(— CrO4) of 2; oxaiate (— C204) of 2; vanadate (— VO4) of 3. Write the formula
for the salts of sodium, potassium, calcium, and aluminum with the acetate,
chromate, oxaiate, and vanadate radicals, respectively (16 different formulas).
UNIT TWO CHAPTER X
BALANCED ACCOUNTS-
EQUATIONS
Chemical formulas are helpful because they save time. They are
helpful also because they aid our understanding. By their use we can
visualize the changes that take place in molecules during chemical
changes — the chemical changes by which our power is generated, our
food grown, and our medicines made. Formulas are useful in representing
the composition of compounds. Formulas may be used to represent
molecules alone, but more often they are used in equations to show how
compounds have changed.
Chemical and Physical Changes. It is well to review here the dis-
tinction between chemical and physical changes. Physical changes
studied thus far include boiling, freezing, and evaporating as a result of
changing pressure and temperature. In each of these changes no new
substance forms, molecules remaining unaltered after the physical change.
The chemical formula representing water, steam, and ice is the same,
H2O. Since no changes that alter the composition of the molecule occur
during a physical change, the formula for the molecule in the different
states is identical.
On the other hand, a chemical change involves a change in the com-
position of molecules. One of the simplest of chemical changes is the
joining of atoms to make a compound. Zinc atoms join with sulfur atoms
to form zinc sulfide, a compound. Zn represents the metal, S represents
the nonmetal, sulfur; the solid formed by their union is represented by
ZnS, and it is a salt. Both elements have a combining number of 2. The
chemist writes Zn + S — » ZnS, an expression called an equation.
Symbols, Formulas, Equations. In order to understand clearly the
meaning of an equation as contrasted with that of a formula, let us
remember that an equation shows a chemical change, while a formula
represents the composition of a substance.
New Terms
equation molecular formula balancing an equation
171
17J CHEMISTRY FOR OUR TIMES
H2O is the molecular formula for water; 2H2 + Oa — > 2H20 is the
equation for the formation of water. The HjO represents a substance;
the 2H2 + 02 — > 2H20 represents a chemical change, or reaction.
The arrow in the equation, — >, is read "forms," "produces," "yields,"
or "gives." The substances written to the left of the arrow, joined by the
+ sign if more than one is present, are those that enter the change. To
the right of the arrow are written the substances formed during the
chemical change. These are different substances from those on the left-
hand side; otherwise, no chemical change would have taken place. The
substances on the right-hand side are joined by a + sign if more than
one product is formed.
Chemists are interested in the products of a chemical change. Some
of the new substances thus formed do not occur naturally. They can be
obtained only as a result of the chemist's work in the laboratory. Herein
lies a great measure of the charm and fascination of chemistry. We never
can foresee all the possibilities of new substances formed by chemical
changes.
At the start it should be emphasized that the chemical change comes
first and our representation of it in writing second. Each equation repre-
sents a change that occurs in the laboratory. Our information comes
from experiments. Equations may be written without laboratory experi-
ments having preceded them, but merely to suggest the experiments that
may be tried in the laboratory. Otherwise, an equation has no meaning.
We should remember that the arrow is directional. C + O2 — > CO2
tells us that an atom of carbon joins with a molecule of oxygen to form
a molecule of carbon dioxide. It does no* tell us that carbon dioxide
breaks down into carbon and oxygen; that is, C02 — » C + 02 is without
meaning unless we know from experience that the compound is one which
decomposes. Indeed, carbon dioxide is quite a stable compound, and it
does not decompose directly under any ordinary conditions. The "reverse"
equation just written is incorrect.
Statement
Example
*
A symbol represents an atom of an element
C
A formula (molecular) represents a molecule
of a compound or an element.
CO2 or 03
An equation represents a chemical change
C + Q2 -* CO2
Limitations of Chemical Equations. We have said that chemical
equations are a useful way of representing chemical changes. Their mean-
ing is understood by scientists of all countries, and the changes that
they represent can be carried out by anyone who has the proper direc-
BALANCED ACCOUNTS— EQUATIONS 173
tions, equipment, and skill. It is obvious, however, that a chemical
equation cannot represent all the facts. We often include notes with an
equation to tell the details that the equation does not show. The catalyst
used, if any, the temperature, and the pressure may be included in notes.
We cannot tell, for example, from an equation alone whether or not the
Courtesy of Corning Glass Works
FIG. 10-1. — Weighed batches of raw materials are used in industrial processes.
The sand in the cart is to be used in making glass. Notice how the worker protects
himself from dust.
reaction occurred in the medium of water or some other liquid, or whether
the substances were melted together, acted slowly, or exploded with
violence. Notes are also useful in telling whether the reaction required
heat to cause it take place or whether it proceeded easily and gave off
heat energy.
How to Write Equations. Equations involve formulas; therefore, in
writing equations it is well to master the writing of correct formulas. An
equation that contains an incorrect formula cannot represent a true
chemical change.
174 CHEMISTRY FOR OUR TIMES
In writing an equation a list is made of the substances (sometimes
there is only one substance) that enter into the chemical change. Correct
formulas for these compounds or elements are written down and con-
nected by a + sign. The order is not important. Then an arrow is placed
to the right of these formulas. After the arrow are written the formulas,
connected by a + sign, of the substances (sometimes there is only one
substance) formed in the chemical change. The order of writing these is
also not important.
When a chemical change takes place no atom is lost or gained; the
law of conservation of matter is found to apply in all cases. For this
reason an equation must be balanced; that is, the same number of atoms
of each element must be on both sides of the arrow. Balancing an equation
is the process of counting the atoms of each element on both sides of
the arrow and adjusting the number if necessary, so that the number is
the same.
Balancing Equations by Inspection. In order to obtain the neces-
sary number of atoms to balance an equation, we may take any number
of molecules of any reacting substance, without limit. The formulas
themselves, however, must not be altered. An illustration will make the
point clear. Ammonia is heated to produce hydrogen and nitrogen; we
should first write NH3 — » H2 + N2. In writing the right-hand side of
this equation we recalled (page 145) that both nitrogen and hydrogen
are typical gases which have two atoms to a molecule; therefore, their
correct formulas are H2 and N2. Also, NH3 is the correct formula for
ammonia. But, with three atoms of hydrogen in ammonia and two atoms
of hydrogen gas produced, one atom of hydrogen is left over. We must
have the same number of atoms on both sides of the arrow. The correct
adjustment of the equation is to take two molecules of ammonia, which
will give the two atoms of nitrogen needed. The number of atoms of
hydrogen is thus increased at the same time from three to six, and this
will call for adjustments of the hydrogen molecules, namely, to 3H2. The
equation becomes 2NH3 — > 3H2 + N2. It would be incorrect to write
NH2 or N2H or .N2H2 for ammonia. This would change the formula into
one that is incorrect.
A few more illustrations will be helpful in writing equations.
The decomposition of water by an electric current is represented thus:
H2O — ^ substance entering change
H2O — ^ H2 4- Oz reacting substance and products
The equation is not balanced, for one oxygen atom cannot produce two.
2H2O -» 2H2 + O2
The equation is balanced and completed.
BALANCED ACCOUNTS-EQUATIONS 175
Check:
Molecular formula for water H20
Molecular formulas for hydrogen and oxygen H2, O2
Hydrogen atoms on left and right 4
Oxygen atoms on left and right 2
When phosphorus burns it forms an oxide, usually with a higher
combining number of 5.
P 4- O2 -4 P2O8 reacting substances and prod-
ucts, all formulas correct
2P + O2 — > P2Os balancing phosphorus
2P + 5O2 -4 2P2O6 balancing oxygen
4P 4- 5O2 — ^ 2P2O5 rebalancing phosphorus
Final check:
Oxygen atoms on left and right . . . * 10
Phosphorus atoms on left and right 4
For decomposing potassium chlorate we write
KCIO3 -4 KCI + O2
and then balance the equation.
2KCIO3 -4 2KCI + 3O2
The equation is balanced.
We do not write KCIO3 -4 KCIO + O2 9
for the products would be incorrectly represented.
Examples of correct equations are
heated
2KCIO3 >> 2KCI 4- 3O2 T
MnO2, catalyst
2K 4- 2HOH -4 2KOH 4- H2|
2H2O 4- 2SO2 4- O2 > 2H2SO4
HNOi, catalyst
CaCIs -f 2AgNO3 -4 2AgCI | + Ca(NO3)2
SUMMARY
A symbol is a letter or group of letters standing for an atom of an element.
A formula is a group of symbols representing the composition of a compound ;
the simplest formula shows only the relative number of atoms, but the molecular
formula also shows the true molecular weight.
An equation is a connected group of formulas representing a chemical change.
In writing equations:
1. Show substances used and substances formed, and connect by an arrow.
2. Balance by adjusting if necessary so that the same number of atoms of each
element occurs on both sides of the equation.
Equations:
1. When balanced, show parts by weight of reacting substances and relative
volumes of gases taking part in the reaction.
t76 CHEMISTRY FOR OUR TIMES
2. Do not show temperature, pressure, catalyst, energy, or any other condi-
tions of the reaction unless especially noted.
QUESTIONS
1. Distinguish between a chemical and a physical change in terms of mole-
cules.
2. Distinguish among a symbol, a formula, and an equation. Give an exam-
ple of each.
3. What is the symbol for salt? The formula for salt? The equation for salt?
(Salt is sodium chloride.)
4. What does an equation show?
5. What does an equation not show?
6. From what source do we get the original information on which to base
equations?
7. Point out an error in this equation :
CO + O2 -4 CO2
8. Why should an equation be balanced?
9. Balance the following equations :
Mg + O2 -4 MgO
Mg + N2 -4 Mg3N2
Fe + H2O -4 Fe3O4 + H2
Na + H20 -4 NaOH + H2
N2 + O2 -4 NO
10. When zinc is heated intensely in air, it burns, forming a white powder.
(Burning in this case obviously means ordinary burning or combining with oxy-
gen.) Write an equation to represent the burning of zinc.
11. Complete and balance the following equations, using formulas throughout
(Do not write in this book.)
a. Potassium + oxygen — >
b. Nitrogen + oxygen — > nitrogen dioxide
c. Carbon + oxygen -»
d. Copper + oxygen -*
e. Lead + oxygen — >
12. Complete and balance, using formulas:
a. Copper + chlorine -» * d. Lead + chlorine — >
b. Zinc + chlorine — *• e. Mercury -f chlorine — >
c. Sodium + chlorine — >
13. Complete and balance, using formulas (assume that phosphorus takes
{3
. in each case) :
BALANCED ACCOUNTS-EQUATIONS 177
a. Phosphorus -f chlorine -> d. Phosphorus + bromine (like chlorine) -+
6. Phosphorus + oxygen -* e. Phosphorus + iodine (like bromine) —>
c. Calcium + phosphorus — *
14. Write equations to represent the following chemical changes;
a. The decomposition of water by electrolysis
6. The synthesis of water from its elements
c. The decomposition of mercuric oxide when heated
d. Mercury heated strongly in air
e. Mercury (combining number 2) rubbed with iodine
/. Decomposition of potassium chlorate when heated in the presence of
manganese dioxide
g. Action of sodium on water
h. Action of zinc on hydrochloric acid
i. Action of iron on dilute sulfuric acid
j. Reduction of hot copper oxide by hydrogen
MORE CHALLENGING QUESTIONS
15. Write the equations for the reaction of metallic calcium with each of the
following elements: oxygen, nitrogen, chlorine, sulfur, phosphorus.
16. Write equations for each of the following chemical changes:
a. Decomposition of hydrogen peroxide into water and oxygen
b. Decomposition of sodium chlorate when heated
c. Decomposition of potassium nitrate to form potassium nitrite and oxygen
d. Oxidation of sulfurous acid to form sulfuric acid
e. Calcium carbonate heated to form calcium oxide and carbon dioxide
/. Burning methane (CH4) to form carbon dioxide and steam
g. Zinc and hydrochloric acid — >
h. Aluminum + sulfuric acid — »
i. Copper + hydrochloric acid — >
j. Burning tin
REVIEW
1. Find the percentage composition of sulfur dioxide.
2. The molecular weight of a gas is 71. Find the weight of a liter. At what
conditions of measurement does the answer hold true?
3. A compound analyzed in a laboratory contains 27.1 per cent sodium, 16.5
per cent nitrogen, and 56.4 per cent oxygen. Find the simplest formula of this
compound.
4. A gaseous compound contains 30.4 per cent nitrogen and 69.6 per cent
oxygen. One liter is estimated to weigh 4.14 grams at STP. Find the molecular
' formula of the gas.
5. One silicate radical, called metasilicate, has combining number of 2 and is
written -SiO* Write the formulas for the metasilicates of silver, sodium, lead,
copper, and aluminum.
UNIT TWO CHAPTER XI
THE STOCKROOM— PARTICLES
AND STRUCTURE OF THE ATOM
The exciting new field of the structure of the atom is a common meet-
ing ground for both physics and chemistry. Gains in knowledge
from chemical study in this field are promptly put to use by physicists.
In turn the tools of the physicists — spectroscopes, fog-track chambers,
Geiger counters, and cyclotrons — are used by chemists. It is amazing
that enormous cyclotrons weighing many tons are being built to attack
something as small as an atom. Here, indeed, is much ado about almost
nothing — imagine using an instrument as large as a two-car garage to
find out about something that has never been seen !
Unfortunately, the instruments used to study the atom and the train-
ing required for their use are not available for students of elementary
chemistry. We must be content with a summary, of the results of experi-
ments and the ideas that the experiments suggest to skilled and highly
trained workers. We can be sure, however, that these experiments are
more precise by far than the taking of the census in a large city, more
precise than the determination of the weight of this book.
The Electron. If we turn on an electric light, we are putting electron*,
to work. An invisible swarm of tiny bits of electricity rushes through the
filament in the bulb and back on copper wire to the powerhouse with
nearly the velocity of light — and light travels at a speed of 186,000 miles
a second! Although electricity is in common use today, no one knows the
complete answer to the challenging question, " What is electricity ?" But
the picture of an electron stream serves for most practical purposes;
moreover, much is known about the behavior of electrons in motion.
The electron was discovered when electricity was passed through long
glass tubes from which the air had been withdrawn. It is a simple matter
New Terms
electron neutron heavy hydrogen
ion positron deuterium
proton planetary electrons ionic- or electro valence
nucleus isotopes covalence
orbit
179
180
CHEMISTRY FOR OUR TIMES
to show that the energy passing through such a highly evacuated tube
consists of a stream of electrically charged particles. We can experiment
with a narrow beam of electrons if by means of a slit all but a small part
of the negative end, or cathode, of the tube is shielded. When the elec-
trons strike an object in their path they produce a greenish-purple glow.
This streain can be deflected from its path by a magnet or by an elec-
trically charged object. (See Fig. 11-1.)
Such experiments show that the electrons are charged negatively
(— ), a fact first announced by Sir J. J. Thomson (1856-1940) at Cam-
bridge, England. He also announced that these electrons, separate par-
ticles, were extremely light.
Deflected
by Electrically
Charged Plates
Deflected
by a
Magnet
Glass
Glows
Beam of
Electrons
Cathode
To Vacuum Pump
' Anode
FIG. 11-1. — The deflection of cathode rays by a magnet is shown here. If the
magnet were moved nearer the slot, a greater deflection of the cathode rays would
be observed.
Later, the weight and the charge of the electron were found. If 1836
electrons are weighed together, their total weight equals that of one
hydrogen atom. An electron (er) is considered to be one unit of negative
electricity.
Simple Experiments with Electrons. If we wish to experiment with
electrons, one of the simplest ways is to rub a closed fountain pen on
woolen clothing. The pen accumulates electrons from the wool and be-
comes electrically charged ( — ), leaving the wool oppositely charged (+).
Bits of paper will be attracted to the pen. In a short time this condition
disappears, for the electrons readily leak off into the air. The swishing of
gasoline inside an oil-tank truck causes a similar charge, which may
result in a spark and an explosion. Consequently, oil-tank trucks drag a
chain or use filler in the tires to conduct this charge away to the ground.
Experiments show that opposite electric charges attract each other
and, conversely, that like charges repel each other. The paper that the
pen attracted must have become positively charged. We explain this by
saying that the electrons of the paper were repelled when the charged
THE STOCKROOM— PARTICLES OF THE ATOM 181
pen came near it, leaving the end nearer the pen positively charged.
(See Fig. 11-2.)
Other experiments show that the amount offeree between two charges
is proportional to the product of the strength of the two charges and
inversely proportional to the square of the distance between them
(Coulomb's law).
Electrons
Force of
Attraction*^ /\
*'* ountain Pen
Electrons — *-£**7 Rubbed on Fur
Repelled \/
to Far End Bit of Paper
FIG. 11-2. — This convincing and simple experiment with electrons should be per-
formed by everyone not familiar with it.
Electrical Neutrality. We have assumed one fact that does not seem
contrary to experience: All matter is, as a rule, electrically neutral, that
is, without electric charge. When, for example, we place a piece of copper
wire across the terminals of a delicate electric meter, the needle does not
move. We conclude that no electricity is flowing through the meter.
Any other object held to such an electric meter shows no evidence of an
electrical disturbance. This means that any object, element, or com-
pound is composed of an equal number of negative electric units and
positive electric units. Further, a positively charged object is, as a rule,
one from which negatively charged electrons have been lost.
Gas Ions. Let us now go back to the experiments with glass tubes
mentioned on page 180. Further investigation revealed the presence of
positively charged particles in these tubes. They are called positive ions.
They consist of atoms that have lost electrons.
The Hydrogen Atom and the Proton. Hydrogen is structurally
the simplest element. When hydrogen is placed in the apparatus
shown in Fig. 11-1 and an electric current sent through it, we interpret
the experiment that each hydrogen atom is composed of one unit of
negative and one of positive electricity. The positive particle is called a
proton. Experimenters have shown that the positive part of an atom is
located in the center, or nucleus, and that the electrons are located out-
side this center. The opposite signs of the electron and the proton imme-
diately suggest an attractive force of one for the other. They would bump
together if the electron were not moving. A pattern for the motion of the
CHEMISTRY FOR OUR TIMES
electron about the nucleus of an atom is seen in the rotation of the earth
and the other planets about the sun; for the sun attracts all the planets,
and our earth would surely fall into the sun if it did not continue to move
oti its orbit.
One proton as a center, with a single electron spinning about it, is
our simplest picture of the hydrogen atom. The nucleus is small and
dense and weighs almost as much as the neutral hydrogen atom. The
electron is relatively large and light, about 1/1850 the weight of the pro-
ton. The space between the two is tremendous compared with the size
of either. This is a space through which forces are exerted but is otherwise
quite empty. Dr. John A. Timm writes in his Introduction to Chemistry:1
If the hydrogen atom were magnified to such a size that the distance between
its electron and its proton would be the order of the distance between New York
and Philadelphia (about 90 miles), then on the same scale its electron would be
as large as a 20-ft balloon revolving about the proton nucleus the size of
buckshot.
The Ion. When a hydrogen atom loses its outer electron, only a
proton remains. Its electrical condition becomes changed also. As an
atom it is neutral electrically; for its proton had one unit of positive
electricity, and the electron balanced that with its one unit of negative
electricity. Without the electron, it is left positively charged, one unit.
We write this in our symbol language H+ and call it a hydrogen ion, or
just a proton, p+. Its diameter is only 1/100,000 that of a hydrogen atom.
Hence it exerts a relatively large attractive force on anything that comes
within range. This particle is strongly additive, joining many substances,
especially water.
H+ + H20 -4 (H30)+
Hydrogen ion + water — * hydronium ion
The hydrogen atom H and the hydrogen ion H+ present different
exteriors to the world. They are quite different chemi-
cally. The ion is much smaller and carries a unit of
positive electric charge.
FIG.- 11-3.— A The Neutron. In 1932 from the same laboratory
neutron is an eiec- in which Sir J. J. Thomson carried out his experiments
particle. on ^e e^ectron came the announcement that J. Chad-
wick had discovered a new particle. This newly dis-
covered fragment of matter carried no electric charge and hence had
escaped the attention of earlier experimenters. The name given to this
uncharged particle is the neutron. It may be considered to be a close
combination of a proton and an electron, a pair (see Fig. 11-3) or, better,
no _ p+ + e-
1 McGraw-Hill Book Comoanv. Inc.
THE STOCKROOM-PARTICLES OF THE ATOM 183
as a unit particle in itself. It is now thought that the neutron has approxi-
mately the same weight as the hydrogen atom, but with no charge.
The Positron. Science always expects the unexpected. In recent
years new developments in the field of subatomic chemistry have been
rapid and numerous. One of the most startling was the discovery by C. D.
Anderson at the California Institute of Technology in 1932 of a new
particle that is called the positron. This newly found atom fragment, as
a result of atom smashing by cosmic rays, is about the same weight as
an electron, extremely light, but it carries one unit of positive electric
charge. Its life is short. Later the positron was found elsewhere in entirely
different experiments. Eventually we shall know its proper place in the
structure of atoms. One suggestion is worth considering. There is evidence
that a proton can be formed from a positron and a neutron.
Positron (e+) + neutron (n°) = proton (H+) or (p+)
The Helium Atom. Next to the hydrogen atom in order of atomic
weight comes the helium atom. Its atomic weight is 4. It has two elec-
trons revolving about its nucleus, which has two positive charges.
Helium Atom (He)
(a)
Helium Ion (He"1"1")
or Alpha Particle (a)
(when ejected from a radioactive
element)
(6)
2p =
2n -
2e =
Helium atom
Weight
2
2
0
4
Charge
2 +
0
2-
0
2p -
2n =
Helium ion
Weight Charge
2 2
2 0
4 2
FIG. 11-4. — (a) The helium atom has two neutrons and two protons in the nucleus
and a filled shell of two electrons; (6) helium ion.
The outermost electrons of an atom are called the planetary electrons.
Within the nucleus of helium are two protons, which accounts for its
two positive charges. This is not enough, however, for the atomic weight
of helium is four times that of hydrogen. The rest of the weight must
be in the nucleus^the location of the heavyweight protons. But if helium
had four protons in the nucleus and two planetary electrons, we should
not have an electrically neutral condition. Actually, the helium atom
184 CHEMISTRY FOR OUR TIMES
is electrically neutral, like other atoms. The explanation lies in the
assumption that the nucleus of helium contains two protons and two
neutrons; the atomic weight of 4 is the sum of the weights of these four
particles, and the two positive charges are those of the two protons. The
structure of helium, then, is represented by two planetary electrons
revolving about a nucleus containing two protons and two neutrons.
(See Fig. 11-4.)
A fast-moving helium ion (He*"1") shot out from a radioactive element
is called an alpha particle.
The Nucleus. The nucleus is extremely dense. Unexpected support
for the idea of extremely dense matter comes from astronomy. Many
highly compact stars have been recorded. For example, the companion
star of the Dog Star, Sinus, has matter that according to calculations
must be much denser than any substance known upon earth; 1 cu in.
weighs 40 tons. Possibly this star is a peculiar collection of nuclei of atoms,
stripped of their planetary electrons.
Atomic Numbers. Our ideas of the structure of the hydrogen and
the helium atoms put a new light on the meaning of atomic numbers,
numbers that were assigned to atoms by H. J. Moseley (1887-1915).
Hydrogen has one proton in the nucleus and one outer, or planetary,
electron. Its atomic number is 1. Helium, with atomic number 2, has
two protons in the nucleus.
We can say in general that the atomic number is equal to the number
of positive charges on the nucleus of an atom or the number of protons
in the nucleus. It is balanced in a neutral atom by an equal number of
negative electrons. If we wish to find out the number of neutrons for any
simple element, we subtract its atomic number from its atomic weight.
Accordingly, carbon, which has an atomic weight of 12 and an atomic
number of 6, must have six neutrons in its nucleus.
QUESTIONS
1. Name the fundamental electric unit. How much electric charge does it
represent, and of what sort?
2. If two long ribbons of newspaper are held together at one end by one hand
and the dry fingers of the other hand are drawn through their length, the papers
tend to separate at the lower end. (Try it.) What happens when the fingers are
brought between the diverging ribbons?
3. An inflated toy balloon is suspended by a thread. Another similar balloon
is rubbed with wool and brought near the first. The two attract, touch, and then
repel each other. Explain, using diagrams.
4. A fountain pen is rubbed briskly with dry fur or wool. Then it is dipped
into fine cork dust. The dust forms bristling projections from which bits of the
dust are ejected from time to time. Explain these observations.
THE STOCKROOM— PARTICLES OF THE ATOM 185
6. Review the evidence for the statement that the ordinary atom is elec-
trically neutral.
6. When a molecule of carbon dioxide (in a gas at low pressure) loses an
electron(s), what is the remaining particle called? What sort of electric charge
does it possess?
7. Make a labeled diagram to show the structure of (a) a hydrogen atom;
(b) a hydrogen ion; (c) a helium atom; (d) a helium ion.
8. Make a table listing four fundamental particles of matter; the nature of
their electric charge ( + , — , or 0); the number of weight units in terms of the
weight of a hydrogen atom.
9. Contrast an electron with a proton; an alpha particle with a helium atom.
10. Define atomic number.
Isotopes. Three American workers, Harold C. Urey, George M.
Murphy, and Ferdinand G. Brick-
widde, showed in 1931 that ordinary
hydrogen contains some heavy hydro-
gen. Today this form of the element
is called deuterium and is known by
the symbol D. One out of 6,400 hy-
drogen atoms in ordinary hydrogen is
deuterium.
The atom of heavy hydrogen has
one planetary electron, just like ordi-
nary hydrogen, but its nucleus con-
tains a neutron. That is, the deuterium
nucleus contains one neutron and a single proton; hence, the weight of
deuterium is twice that of ordinary hydrogen. (See Fig. 11-5.)
Heavy Water contains one or two atoms of deuterium in place of ordi-
nary hydrogen. (See Fig. 11-5.) We can represent this by formulas as
follows :
H H
Ordinary
Hydrogen Atom
Heavy Hydrogen
or Deuterium
FIG. 11-5. — The nucleus of heavy
hydrogen has an extra neutron. Both
sorts of hydrogen present the same
exterior to the world.
O
H
ordinary
water (dihydrogen
oxide)
D
hydrogen-deuterium
oxide
D
heayy water
(dideuterium
oxide)
PHYSICAL PROPERTIES OF ORDINARY AND HEAVY WATER
Property
Value for H2O
Value for D2O
Density at 20CC .
0.9982g/ml
1 . 1059 g/ml
Freezing point
0°C
3.82°C
Boiling point
100°C
101.42°C
Temperature of maximum density
3.98°C
11.6°C
186
CHEMISTRY FOR OUR TIMES
Deuterium and hydrogen differ
in weight, but they do not differ
appreciably in their chemical ac-
tions. Such atoms of an element
that have identical chemical actions
but that differ in weight are called
isotopes. Isotopes of the same ele-
ment differ from each other in the
weight of the nucleus, but they
have the same number of planetary
electrons.
A few common elements includ-
ing some that have isotopes are
shown in the table.
F. W. Aston, who did outstand-
ing work on isotopes at the Caven-
dish Laboratory in England, was
able to separate the isotopes of an
element by an instrument called a
mass spectrograph, which uses
electric and magnetic fields. Al-
most all elements are comprised
of several isotopes — uranium has 3 and tin has 11 isotopes.
Courtesy of Journal of Chemical Education
FIG. 11-6.— F. W. Aston (1877-1945),
an English chemist, was famous for his
work on isotopes.
Plane-
Nucleus
Atomic
Atomic
Element
Symbol
tary
elec-
Ne
Atomic
number
weight
(mass
weight
natural
trons
trons
Protons
num-
ber)*
mixture
Hydrogen
H
1
0
1
1
1)
1.008
Deuterium ....
D
1
1
1
1
2J
Helium
He
2
2
2
2
4
4
Lithium
f «Li
I'Li
3
3
3
4
3
3
3
3
s
6.94
Carbon
C
6
6
6
6
12
12
Nitrogen . ...
fl4N
115N
7
7
7
8
7
7
7
7
a
14.008
I16Q
8
8
8
8
16]
Oxygen
170
8
9
8
8
17
16.000
18Q
8
10
8
8
18,
|35C1
17
18
17
17
35 '
Chlorine
37C1
17
20
17
17
37
35.457
39C1
17
22
17
17
39 ,
* The mass number is the nearest whole number to the atomic weight. The difference is slight.
THE STOCKROOM-PARTICLES OF THE ATOM 187
The atomic weight of chlorine, 35.457, is actually an average of the
weights of its isotopes. It represents 76 per cent of chlorine with atomic
weight 35, 24 per cent of isotope 37, and a trace of isotope 39. These
proportions are always the same for natural samples of chlorine.
FIG. 11-7.-
1 Lithium b Lithium
-Two sorts of lithium atoms are possible. Both have one electron in their
outermost orbits.
£05)2)8)
FIG. 11-8. — Electron structures of atoms.
2)8)1)
Arrangement of Electrons. Helium and the other inert gases are
key elements in one respect. Helium has no chemical action; nor have its
related elements. We assume, therefore, that two electrons in the outer
188 CHEMISTRY FOR OUR TIMES ^_
part of the helium atom make a complete and stable arrangement.
Elements of slightly higher atomic weight, which have more than two
electrons, have an additional shell. Lithium, with atomic number 3 and
therefore three planetary electrons, has the first, or helium, shell filled
with two electrons and just one electron left over for the next shell. (See
Fig. 11-7.) Carbon has a filled inner shell and four electrons left for the
next shell. Nitrogen has five, oxygen six, and fluorine seven electrons in
this second shell. The next element, neon, an inert gas, has no chemical
action. Its outer shell holds eight electrons, and here again evidence
suggests that the inertness of the gas is du.e to the fact that this second
shell is filled. (See Fig. 11-8.)
To summarize, the first shell of an atom can hold only 2 electrons.
The second shell can hold as many as 8. The third can hold as many as
18, although 8 forms a stable arrangement. The inner shells are always
filled for the 20 lightest elements before electrons are present in outer
shells. The fourth layer may hold even more electrons, but atoms with
such a complex structure are beyond our scope at present.
Atom Diagrams. We have gone far enough to enable us to make
diagrams of the 20 atoms of lower atomic weight. These are not true
pictures of atoms, but they help us understand chemical reactions. Take
chlorine for example. Its most abundant isotope has atomic number 17
and atomic weight 35. Consequently, there are 18 neutrons in the nucleus
and 17 protons. In the outer shells are 17 planetary electrons, arranged
as follows: 2 in the filled inner shell; 8 in the next shell, also filled; and 7
in the outermost shell.
The abundant oxygen isotope with atomic number 8 and atomic
weight 16 has 8 neutrons and 8 protons in the nucleus. The 8 planetary
electrons have filled the first shell with 2, and the other 6 are in the
outer shell.
SUGGESTION: Try making diagrams of a sodium atom (at. wt. 23,
at. no. 12) ; a magnesium atom (at. wt. 24, at. no. 12) ; an aluminum atom
(at. wt. 27, at. no. 13); and a phosphorus atom (at. wt. 31, at. no. 15).
Completed Shells. Eight is the magic number for atoms of light
elements! Somehow the atoms favor a shell full of electrons. The first
shell is filled when it holds 2, but the next two shells of electrons are
apparently filled when they hold 8 (unless electrons are present in a
fourth shell; in this case the third shell may hold up to 18 electrons).
Chemical inactivity is associated with a shell of 8 electrons, an arrange-
ment with staying power. Let us recall the complete inactivity of neon
and argon. Both these elements have their outermost shells filled with 8
electrons, a stable arrangement because neither of these gases unites
with any other substance. Let us also look ahead and note that the first
THE STOCKROOM-PARTICLES OF THE ATOM 189
period of the periodic table has two elements, the second eight, and the
third eight.
Salts. Common salt (NaCl) is a crystalline substance well known to
everyone. It has characteristic cubical crystals, which are worth investi-
gating with a magnifying glass. (See Fig. 11-9.) It has a high melting
point (801°C). When salt is a liquid, it is a conductor of electricity.
Further experiments show that liquids conduct electricity only if charged
particles (ions) are present. This with other evidence leads us to con-
clude that its building units are ions. Other similar salts include magne-
FIG. 11-9. — We believe that a crystal of common salt is a lattice of ions, or electrically
charged particles.
sium oxide (MgO — m.p. 2500°C), potassium sulfate (K2S04 — m.p.
1076°C), and sodium hydroxide (NaOH— m.p. 318°C). The arrangement
of the ions in the crystal can be revealed by studies with X rays.
On the other hand, many compounds like carbon dioxide (C02),
ammonia (NH3), hydrogen chloride (HC1), water (H20), and methane
(CH4) have low melting points and are readily changed to a gas. Indeed,
many are gases at room temperature. These compounds form true mole-
cules, quite different from salts. When liquefied, they do not conduct
electricity. X-ray examination of crystals of these compounds shows that
the building blocks are molecules.
It is reasonable to assume that the forces that hold the atoms in the
190 CHEMISTRY FOR OUR TIMES
two types of compounds are different. We call the first sort an ionic, or
electrovalent, bond and the second a covatent bond.
These can be explained by reference to atomic structure.
How Atoms Join. 1. Electrovalence. The third shell of sodium
contains just one electron, lip 2)8)l).1 If this electron should become
lost, the outer arrangement would resemble that of neon. The third
outer shell of chlorine, I7p 2)8)?), contains seven electrons. If its atom
should gain one electron, say the one sodium has to offer, its outer arrange-
ment would resemble that of the stably arranged element, argon, and
the sodium would resemble neon. These two atoms are suited to be
partners. Sodium gives up its electron, and chlorine gladly accepts it. To
celebrate the transfer some heat is given off, and common salt is formed.
Na + Cl -» Na+CI-
Now the sodium atom has lost an electron. Since the number of
protons is greater than the number of electrons, its charge must be
expressed in our sign language with a + sign (the sign of lack of elec-
trons), Na"1". The chlorine atom has gained an electron, and therefore
we add a — sign to it, Cl~. The total number of planetary electrons now
becomes 10 for sodium and 18 for chlorine. Their nuclei still have the
charges due to 11 and 17 protons, respectively. Each atom has become
an electrically charged ion with one unit of electricity, and of an opposite
sort. Hence they attract each other in common salt.
11p 2)8) + 17p 2)8)8)-
sodium ion chloride ion
Let us consider another example for the union between a metal and
a nonmetal, magnesium and sulfur. The magnesium loses its two outer-
most planetary electrons, and the sulfur fills its two spaces by complete
transfer of the electrons to its own outer shell. The magnesium now has
acquired a charge of + + and the sulfur a charge of . The two attract
each other.
Mg + S -4 Mg++S~-
Such joining of elements in which electrons are completely trans-
ferred from one element to another is called salt formation, since such
compounds have the properties of salts.
Let us recall that the combining number of both sodium and chlorine
is 1. For magnesium and sulfur the combining number of each element is
2. The combining number in these cases corresponds to the number of
electrons transferred. The combining number is the same as the ionic
1 The lip represents the number of positive charges, or protons, in the nucleus, and
2)8) l) represents the number of electrons in each shell.
THE STOCKROOM— PARTICLES OF THE ATOM 191
valence, or electrovalence, number. No molecules of an ionic compound
exist in solution, in the liquid state, or in the solid salt.
2. Co valence. Another type of bond between atoms is well illus-
trated if we consider the link that holds either chlorine atoms or
oxygen atoms together in a molecule. The chlorine atom has seven plane-
tary electrons, I7p 2)8)?). A pair of these atoms gets together in such a
way that one electron from each does double duty, that is, helps to com-
FIG. 11-10. — A chlorine molecule is composed of two atoms held together by the
force of a shared pair of electrons — a covalent bond.
plete the outer orbit of each atom. The sketch shows how this is possible.
(See Fig. 11-10.)
The curious fact that two like charges apparently attract each other
has been explained by assuming that
they are spinning on their axes in op-
posite directions. By experiment it has
been found that two like charges ro-
tating oppositely can attract each
other. This attraction between two
oppositely spinning electrons is one of
the most important forces in nature.
In the case of oxygen atoms, two
such pairs of shared electrons are the
active force in the formation of an
oxygen molecule, Oz- (See Fig. 11-11.) The combining number is the same
as the number of these pairs of electrons.
Such bonds are called covalent bonds (co- means "together")- It is
thought that every hydrogen compound is held together by this sort of
H
H:N:H
FIG. 11-11. — An oxygen molecule
is composed of two atoms, held to-
gether by two shared pairs of elec-
trons— covalent bonds.
bond. Ammonia may be represented as
; hydrogen chloride,
H:C1: . In these diagrams the dots represent electrons. Both types of
valence bonds, covalent and electrovalent, agree in number with the
combining number of the element.
198 CHEMISTRY FOR OUR TIMES
3. Coordinate Covalence. The compound ammonium chloride
(NEUCl) suggests a third possibility. Nitrogen joins three hydrogen atoms
with covalent bonds, forming ammonia. Hydrogen also joins chlorine
with a single covalent bond. When hydrogen chloride (HC1) and ammonia
(NH8) are brought together, a solid salt, ammonium chloride (NH4C1),
is formed.
This reaction is thought to occur through the pair of electrons on
the nitrogen atom to which no hydrogen is attached. The hydrogen ion
(proton) in the hydrogen chloride leaves the chloride ion and becomes
attached to the "lone" pair of electrons of the nitrogen atom, forming an
ammonium ion (NH^"1". The product, ammonium chloride, is a true
ionized salt.
NH3 + HCI -> NH4+ + Cl-
^ H
H:CI: -» H:N: H+ + :CI:~
" H
ammonia hydrogen ammonium ion chloride ion
chloride
Such a bond in which both electrons are furnished by one element
only is called a coordinate covalent bond. This type of bond is very
common.
To summarize, atoms may join by (1) transfer of one or more elec-
trons completely, (tonic valence, or electrovalence) ; by (2) sharing pairs
of electrons, each atom furnishing one of the pair (covalence); or by (3)
sharing a pair that was provided by one atom only (coordinate covalence).
QUESTIONS
11. Define isotope.
12. How does heavy water differ from ordinary water: (a) in density; (6) in
composition?
13. Ninety-two natural elements are known. Is it correct to say that only 92
different sorts of atoms exist?
14. What is the maximum number of electrons possible in the innermost shell
of an atom? In the next outermost shell? In the third shell?
15. Make atomic structure diagrams to represent: (a) lithium (at. wt. 7, at.
no. 3); (6) boron (at. wt, 11, at. no. 5); (c) nitrogen (at. wt. 14, at. no. 7).
16. How many electrons are in the outermost orbit of the neutral atoms of
the elements in group la, -Ila, -YI&, and -VII6? (See periodic table, page 329.)
17. No element in group 0 (periodic table) forms compounds. Account for
this in terms of electrons.
18. From the table in the Appendix, select three salts and list their melting
points.
THE STOCKROOM— PARTICLES OF THE ATOM 193
19. From the table of data about common gases (Appendix) select three
typical molecular compounds, and list their melting points.
20. Distinguish ionic valence, or electrovalence, from covalence. (live an example
of each.
cr
Chloride Ion
(17^ 2)8)8)
A
Argon Atom
(1802)8)8)
Potassium Ion
2)8)8)
Calcium Ion
2)8)8)
FIG. 11-12. — All three substances represented above have idcnt ical outer orbits. They
differ only in respect to nuclear arrangement.
Distinction between an Atom and an Ion. If a chlorine atom
gains an electron, it has an outer shell filled. It now has the stable arrange-
ment of a rare gas like argon.
Its electrical condition becomes
changed, also. The gained electron
gives it one extra unit of negative
electricity. We represent this in
our sign language writing as Cl~~
and call it a chloride ion. (See Fig.
11-12.)
chloride ion chlorine atom chlorine molecule
Chlorine atoms (see Fig. 11-13)
in molecular pairs comprise chlo-
rine gas, a green, poisonous sub-
stance, extremely active chemically.
Chloride ions are present in com-
mon salt. They are good to eat in
moderation. They are not espe-
Courtesy of Pennsylvania Salt Manufacturing
Company, Photo by Gladys Miiller
Fi<;. 11-K5. — This mode1! of the
chlorine atom is now on display at the
cially active chemically. Truly a Franklin Institute, Philadelphia. The
great difference is accomplished by model represents the structure of an atom
a single electron per atom. according to some of the best current
& * conceptions. It is based on the magmfi-
Radicals Form Ions. Not only cation of two and one-half thousand
do atoms form ions, but radicals mi lontimes-
may also have electric charges. The number of positive or negative charges
that is to be written above any given ion is the same as its combining
194
CHEMISTRY FOR OUR TIMES
number. Here are some examples that illustrate the ions present in some
common compounds:
Compound
Formula
Positive ion
Negative
ion
Sodium chloride
NaCl
Na*
Cl~
Potassium nitrate
KNO3
K+
NOr
Ammonium sulfate
(NH4)2S04
2NH|
so"
Calcium carbonate
CaCO3
Ca++
COr-
[Magnesium oxide
MgO
Mg++
O"-
Copper sulfate
CuSO4
Cu++
SO"
Aluminum sulfate
A12(S04)3
2A1+++
3SO"
Calcium phosphate
Ca3(PO4)2
3Ca++
2PO7-"
Electron Transfer. In many chemical chahges one or more electrons
per atom take part. The burning of magnesium is a familiar example.
Combining number
before change
2Mg 4- O2
magnesium oxygen
0 0
2MgO
magnesium oxide
ion 2-f" ion 2— Combining number
ufter change
12p 2)8)2) +8p 2)6) -4 12p
8p
In this case it is easy to see that the free elements with valence zero
have become part of a compound and hence have acquired ionic valence.
The change in charge is due to the transfer of electrons. The magnesium
has been oxidized, gaining in valence by two units positive. This means a
loss of two electrons per atom. The oxygen atoms, on the other hand,
have become negative in charge by two units, or, more definitely, they
have gained two electrons each.
lose 2 electrons each
gain 2 electrons each
2Mg (atoms)
2O (atoms)
-4 2Mg"l"H
2O~ ~
The oxygen atoms in this case have gained negative valence, or
gained electrons, and are said to have been reduced.
In the case of the chemical change,
2Na + MgBr2 -4 2NaBr + Mg
2Na° + Mg++ + 2Br~ -+ 2Na+ + 2Br~
Mg°
(formula equation)
(ionic equation)
or
2Na°
2Na+
Mg°
the valences are as marked in the ionic equation. The bromine atom
remains at valence — 1 and therefore has no real part in the change. The
magnesium atom changes from valence +2 to zero, a move in the nega-
tive direction. It has gained two electrons per atom. Hence it is reduced.
Mg++ + 20- — » Mg°. The sodium atoms have each lost one electron
THE STOCKROOM— PARTICLES OF THE ATOM 195
to become sodium ions, Na+, a gain in positive valence. Na° — > Na+ + er.
The sodium atoms are said to be oxidized. These are more general mean-
ings of the terms reduced and oxidized.
Other examples of electron transfer are seen in the chemical changes
Cu + 2AgNO3 -» 2Ag + Cu(NO3)2
or, more directly,
Cu° + 2Ag+ -» 2Ag° + 011++
The copper is oxidized, and the silver is reduced.
Common Salt, an Ionic Lattice. In forming salt (NaCl) from its
elements, an electrically charged atom of sodium, called a sodium ion,
Na4", has been produced from a sodium atom by removal of its outer
electron. A charged atom of chlorine, called a chloride ion, Cl~, has been
produced from a chlorine atom by gain of an extra electron. Each now
has a quota of eight electrons in its outermost shell.
These two kinds of ions have opposite charges and attract each other
with a force sufficient to hold them together as a solid crystal. The ions
are arranged alternately in the cubic crystal of salt so that no two ions
of the same kind are adjacent. (See Fig. 11-9.) In any visible salt crystal
many millions of cubical units are joined together. Each ion is surrounded
in space by six of the opposite kind. (See Fig. 11-9.) No sodium ion is
attached to any particular chloride ion, although the total number of
each is the same. Rather, the whole crystal forms a latticelike pattern.
Because of this regular arrangement of particles within the crystal, they
can be examined by X rays and the location of the ions determined. The
unit sometimes called a "sodium chloride molecule " is merely a con-
venient name for a pair of ions. Strictly speaking, sodium chloride does
not exist as molecules. We should represent it as Na+Cl~~. Table salt,
like potassium nitrate or sodium hydroxide, is an example of an ionic
compound.
Within the Atom. An assortment of other atom-dust particles has
been announced, and others have been predicted. Now we stand at a new
CHARACTERISTICS OF PARTICLES
Symbol
Charge
Mass (weight)
(in terms of H atom)
Positron
e+
+ 1
0.00054
Electron
e~
-1
0.00054
Proton (H+)
p+
+ 1
1
Neutron
n
0
1
Deuteron (D+)
d
+1
2
Alpha particle (He++)*
a.
+2
4
* This particle will be discussed in Chap. 37.
196 CHEMISTRY FOR OUR TIMES
frontier. As our tools, skill, and knowledge improve, we shall penetrate
more and more into the secrets of nature. The number of investigators
who are interested in this problem is increasing steadily. Teachers and
writers are equally busy consolidating the results of research and inter-
preting them.
SUMMARY
The electron was discovered by Sir J. J. Thomson by passing an electric cur-
rent through glass tubes containing gas at very low pressure. An electron is a unit
particle of negative electricity. It is very light and movable; easily shifting from
one atom to another. Electrons are not always attached to atoms but can exist as
independent particles. Electrons are attracted to positively (+) charged places,
where electrons are lacking; they repel each other. An ordinary atom is electrically
neutral because it has a balance of + and — electrical charges. When one or more
electrons become attached to or detached from a gas molecule, the molecule be-
comes an electrically charged ion; + if electrons have left and — if electrons have
become attached.
The hydrogen atom has the simplest structure. Its nucleus, or center, con-
sists of a single positively (+) charged proton. Spinning about the nucleus is a
single electron (e-). If the outer electron becomes detached, the remainder is a
hydrogen ion (H+) or a proton (p+).
Protons are very dense and have one unit of positive (+) electric charge, and
they readily attach themselves to other particles.
A neutron (n) is a close combination of a proton and an electron, and it is
electrically neutral. Positrons (e+) are short-lived, lightweight, positively charged
units.
The helium atom has a nucleus consisting of two neutrons and two protons.
The outer orbit has two electrons. Since this atom exhibits no chemical activity,
we believe that the outer orbit is filled. If the helium atom loses its two outer, or
planetary, electrons, it becomes a helium ion (He4"1"). The nucleus of an atom
is exceedingly dense, and it always bears a positive charge. The number of units
of positive charge in the nucleus, that is, the number of protons, is equal to the
atomic number.
Isotopes are atoms of the same element that have identical chemical actions
but differ in atomic weight. They have the same electron pattern but differ in the
nucleus.
The electrons of an element are located in outer orbits or shells. When com-
pletely filled, these shells may hold 2, 8, 18, . . . electrons in successive layers.
Salts are compounds that have high melting points, conduct electricity when
melted, and have ionic structures. An example is common salt (Na+Cl~). This is
a typical ionic compound. The number of charges on an ion is equal to its com-
bining number and it is called its ionic valence or electrovalence.
Compounds that contain molecules usually have low melting points. They are
nonconductors of electricity when liquid, and the atoms in the molecules are
joined by covalent bonds consisting of shared pairs of electrons. The number of
covalent bonds of an atom in such a molecule corresponds to the combining num-
ber. An example is methane (CH4).
THE STOCKROOM-PARTICLES OF THE ATOM 197
Coordinate covalence is involved in compounds formed from two molecules
that combine, using otherwise unused electrons. It is met less frequently than
ionic or covalence bonds.
QUESTIONS
21. List five salts other than those given on page 194, and write after each
the ions from which they are formed.
22. Write an equation for the burning of calcium. Under it show the electron
structure and electron transfer by simplified diagrams, following the pattern of
page 194.
23. Write an equation for the replacement reaction that takes place when a
steel knife blade (iron) is dipped into copper sulfate solution. Below the equation
show the electron transfer as in question 22.
24. Of what units is a crystal of table salt (sodium chloride) composed?
25. Which sort of valence is exhibited in: (a) ammonia (NH3); (6) phosphorus
pentoxide (P2Os); (c) sulfur dioxide (802)?
MORE CHALLENGING QUESTIONS
26. What percentage of the weight of a regular hydrogen atom is due to the
electron?
27. Make atom-structure diagrams for the atoms of three metals.
28. Show in terms of atom-structure diagrams the union of lithium with
fluorine.
29. How many (a) electrons, (b) neutrons, and (c) protons are present in a
molecule of (1) ordinary water (dihydrogen oxide) and (2) heavy water
(dideutenum oxide)?
REVIEW— DENSITY
All gases are measured at standara conditions. One liter of oxygen weighs 1.43
grams; of hydrogen, 0.09 gram; of air, 1.29 grams; of liquid water, 1000 grams.
Find the weight of: (1) 1 milliliter (or 1 cubic centimeter) of water; (2) 1
milliliter of oxygen; (3) 25 milliliters of hydrogen; (4) 100 liters of air. Find the
volume occupied by: (5) 50 grams of water; (6) 50 grams of oxygen; (7) 51.6 grams
of air; (8) 72 grams of hydrogen. (9) Find the density in grams per liter and grams
per milliliter of a gas 500 milliliters of which weighs 1.55 grams. (10) The weight
of 120 milliliters of a certain liquid is 1.632 kilograms. Find its density.
UNIT
THREE
Courtesy of General Electric Company
DISPERSIONS OF MATTER
WE have studied water and have learned something about
its commonplace yet remarkable property of being a solvent.
We are now to investigate this property in detail. Water easily
dissolves many substances, forming solutions.
Common salt (sodium chloride) dissolves in water, as does
sugar. However, a solution of salt conducts electricity, but a solu-
tion of sugar does not. We believe that a salt solution contains
electrically charged particles called ions, meaning "wanderers,"
while a sugar solution contains only uncharged molecules. The ions
carry the electric current.
If we alter the electrical condition of the ions, new substances
will be formed. This process, called electrolysis, consists in
passing an electric current through a solution. Chemical changes
invariably occur. Interesting and useful products are made in this
way, and cheaply, too. Such needed chemicals as chlorine and lye
are made by electrolysis of a solution of common salt.
Also, we have those near solutions, called colloidal disper-
sions, formed particularly by gluelike materials. Jelly, foam, smoke,
fog, rubber, textiles, and most foods are colloidal dispersions.
Courtesy of Dow Magnesium Corporation and the Austin Company.
These huge tanks show the large scale in which solutions and precipitates are used
in industrial processes.
Courtesy of Charles B. Knox Gelatine Company, /nc.
Selected bones (1), 75 per cent mineral and 25 per cent collagen (the organic part
of the bone), are separated into dicalcium phosphate (2) and collagen (3). From
collagen is made gelatin (4), the colloidal substance that is the basis for prepared
gelatin desserts.
UNIT THREE CHAPTER XII
SOLUTIONS
A bottle of ordinary soda water is an example of a solution. A uniform
and attractive color is often imparted to it by adding a bit of harmless
dye to the water; a pleasant taste is given by the addition of fruit flavor-
ing, real or artificial; the sweetening is done by adding sugar. The sirup
containing these substances is mixed with carbonated water and capped
immediately. The result is an agreeable thirst-quenching beverage.
Carbonated water consists of clear water with carbon dioxide gas
added to it under a pressure greater than that of the atmosphere. The
carbon dioxide dissolves in the water, part of it joining chemically with
the water, forming a weak acid (carbonic acid).
H20 + C02 -> H2C03
A number of interesting experiments may be made with these bever-
ages. The presence of the dye may be shown by boiling in the liquid a
piece of white woolen cloth, which absorbs the dye; the cloth becomes
colored and the soda water almost colorless. Or the bottle may be shaken
or warmed (with care) before it is opened. Then, if the cap is removed,
the gas will escape with so much force that some of the contents will
forcibly spout up like a miniature geyser. To prevent this the soda
is ordinarily served cold. The fluid loses the gas in the warm mouth,
giving a tingling sensation on the tongue.
Common Solutions. The bottle of soda water, physically considered,
is a solution of several solids and one gas in the same solvent, water.
Liquids that absorb substances into themselves, as water does sugar, are
called solvents. The substance that is dissolved, the sugar in this case,
is called the solute. Together the water and sugar make a clear solution,
composed of solute and solvent.
We are familiar with many solutions. Brine consists of a solution of
table salt in water. Sea water is composed of many solutes in the nearly
New Terms
solvent effervescence molar solution
solute endothermic fractional distillation
tincture exothermic supersaturated
solubility anhydrous
901
202 CHEMISTRY FOR OUR TIMES
universal solvent, water. The druggist provides us with many fluids.
Some of them, for example iodine solution used as an antiseptic, are
called tinctures or spirits. Tincture of iodine is a solution of the element
iodine (I*) in common, or grain, alcohol (C2H5OH). " Spirits of camphor7'
is made from the compound camphor dissolved in alcohol. Other liquids
besides alcohol are good solvents for substances that do not dissolve
readily in water. A mechanic uses gasoline to clean his hands because
this material dissolves grease.
Importance of Solutions. Solutions are important in photography,
dry cleaning, medicine, painting, and many other processes. Our digestive
system is a complicated arrangement for getting our food into a solution,
for undissolved food does not nourish the body. Plants get their food
from solutions, too.
In chemical work solutions are used extensively. They are useful
because (1) they provide a convenient way of handling substances; (2)
a very small amount of material may be uniformly spread out when it
is used in solution ; and (3) many chemical actions, especially ionic actions,
proceed readily when substances are brought together in solutions.
How to Make a Solution. If we wish to dissolve sugar in water
rapidly, we select fine sugar crystals or for quicker action grind up the
crystals and stir them in water vigorously, using warm water rather than
cold. The same directions hold true for most solids. Since it is evident
that dissolving must proceed at the surface of a substance, the more
surface of solute in contact with the solvent, the more rapidly the solu-
tion will be formed. To dissolve much gas in water, on the other hand,
we cool the water, and exert pressure greater than that of the atmosphere
on the gas.
A substance that dissolves easily in water, Epsom salts (MgS04'7H20)
for example, is said to be soluble in water. Road rock and concrete do
not dissolve noticeably in water and are said to be insoluble in water.
Nothing is absolutely insoluble, however.
The amount of solute that can be dissolved in a specified amount of
solvent at a given temperature is called the solubility of a substance. The
units must be stated, as for example, the number of grams in 100 grams
of solvent. Most solid substances dissolve more readily when the tem-
perature of the solvent is raised (that is, the number of grams of solute
which can be dissolved in 100 g of solvent becomes greater) . For example,
about twice as much saltpeter (KNOs) can be dissolved in 100 g of water
at 40°C as can be dissolved in the same amount of water at room tem-
perature (20°C). Some exceptions should be mentioned, however. Ordi-
nary salt (NaCl), which is moderately soluble in cold water, does not
change much in solubility with changes in temperature; also, a few
SOLUTIONS
203
substances, especially calcium hydroxide [Ca(OH)2] and calcium sul-
fate (CaS04), are less soluble in very hot water than in water at room
temperature.
Contrary to the general rule for solids, gases decrease rapidly in
solubility as the temperature is raised. In fact, a suitable way to free
water of dissolved gas is to heat the water to the boiling point. For this
reason, distilled water, lacking dissolved air, tastes flat, and unstoppered
bottles of household ammonia (essentially a solution of ammonia gas in
water) lose their strength if heated.
Opening a bottle of soda water causes an escape of the dissqjved gas
as the pressure is reduced. Stirred in a glass, it fizzes. This fizzing is called
effervescence. Reducing the pressure or heating a solution containing
any gas causes effervescence.
Heat and Solutions. Let us pour 100 g of water from some melting ice into
a thin glass beaker and place the beaker on a moistened piece of wood. Now we
add 50 g of ammonium nitrate to the water and stir rapidly. In a very short time
we find that the beaker is frozen to the wood. The temperature of the solution in
the beaker falls to 10 or 12° below 0°C. The dissolving of the ammonium nitrate
in water thus absorbs heat. This, like all changes that take in heat, is called an
endothermic process.
In general, substances like ammonium nitrate (NH4NO3) and sodium
thiosulfate (Na2S203), also called "hypo," that are more soluble in water
when the temperature is raised take in heat when they dissolve. On the
other hand, substances like calcium sulfate (CaS04) that are less soluble
in water when the temperature is raised give off heat when they dis-
solve. A salt that shows decreasing solubility with temperature rise more
markedly than most is cerium sulfate
[062(804)3], and it is recommended for
a demonstration of this behavior.
Let us prepare a supersaturated so-
lution of sodium thiosulfate, or "hy-
po," and allow it to crystallize,
observing its temperature during the
process (see page 207). This, like all
changes that give out heat, is called an
exothermic process. The act of crystal-
lizing will raise the temperature
several degrees.
H20
A heat change due to another cause
may be noticed when solutions form. Let
us pour 20 ml of water into a large test
tube, then add 10 ml of concentrated sul-
furic acid, 1 ml at a time, stirring briefly
FIG. 12-1. — Pour sulfuric acid into
water, not water into sulfuric acid.
Only a few drops of sulfuric acid
should be added to water at one time,
and the mixture should be stirred
after each addition.
804 CHEMISTRY FOR OUR TIMES
with a thermometer after each addition. (See Fig. 12-1.) A temperature well over
100°C may soon be reached. The great increase in heat from this mixing is
thought to be caused by adding water (hydration) to the hydrogen ions of the sul-
furic acid, forming hydronium ions.
H+ + H2O -+ H,O+ (+ heat)
In addition to illustrating one source of heat, this experiment also
shows how an accident may sometimes be caused in shops, battery service
stations, dyehouses, and laboratories. When sulfuric acid and water are
mixed, the denser acid should always be poured into the water while
stirring it vigorously. Then the acid goes down through the water, mixing
in as it falls. The entire mixture becomes hot. If this procedure is reversed
and the water is poured onto the acid, the less dense water tends to float
on the acid, forming a zone of intense heat where the two liquids meet.
Often the temperature is high enough to cause so much steam that the
liquids are thrown out violently. In laboratory work it is often necessary
to mix sulfuric acid and water. Obviously, this should be done with care.
Another case of heat transfer is interesting. If we gently heat some copper sul-
fate, or blue vitriol, crystals (CuS04*5H2O) (see page 113) until all the blue color
is gone, an almost colorless powder remains (CuSO^. If the powder is to be kept
in this dry, or anhydrous, condition, it must be placed in a desiccator. (See
Fig. 6-2.)
Continuing the experiment, let us place the vessel containing the anhydrous
(without water) powder on the hand of someone who is willing to investigate the
temperature change. As we add water to the powder from a medicine dropper,
not only will the blue color begin to return, but the investigator will soon need to
take the vessel from his hand to avoid being burned by the heat from the vessel.
When more water is added to the blue crystals, a blue solution is formed. The
copper ion is thought to be hydrated in this solution, actually [Cu(H20)4]++,
although we customarily write Cu++ to represent the ion.
Our picture of the action that takes place when a crystal is dissolved
in water is something like this. The water molecules add themselves to
the positive, or metal, ions, weakening the force of their attraction for the
negative ions in the crystal. This causes a breakdown of the crystal
lattice, and the highly nonconducting water molecules separate the two
sorts of ions, which are now swimming around in the water. Ordinary
salt (sodium chloride) in solution has sodium ions surrounded by at least
six molecules of water and chloride ions surrounded by another cluster
of water molecules. Heat is taken in when the ions are separated from
one another and is liberated when the molecules of water attach them-
selves to the ions. Whether heat is absorbed or evolved when a salt is
dtsSolved in water thus depends upon which of these processes predomi-
nates— that in which heat is absorbed or that in which heat is evolved.
SOLUTIONS 205
Concentration of Solutions. When we boil potatoes, we add a
pinch of salt to the water in which the potatoes are to be cooked. The
salt crystals dissolve in the water. The sodium and chloride ions have
separated from each other, and between them has come a large number
of water molecules. In cases where there is little solute we say that the
solution is dilute. Solutions that have much solute with relatively little
Courtesy of Koppera Company, Inc.
FIG. 12-2. — These mine timbers are treated with a solution of zinc chloride in order to
preserve them.
solvent, such as honey or molasses, are called concentrated solutions.
The terms dilute and concentrated are relative terms and have no exact
meaning.
QUESTIONS
1. Name three solvents for grease.
2. Name three substances for which water is a good solvent. Can ail three
dissolve in water together?
3. How could you show that tincture of iodine is a solution?
4. 'A certain solution has 100 grams of solute in 1 liter of water. When 999
liters of pure water is added, what is the amount of solute in each liter?
5. Give directions for making quickly a solution of potassium nitrate
(KN08).
6. Name a substance which increases in solubility with increase in tern-
206
CHEMISTRY FOR OUR TIMES
perature; one which decreases in solubility with increase in temperature; one for
which a temperature change has little effect on solubility.
7. Define solubility.
8. Explain the cooling effect noticed when ammonium nitrate (NH4N03)
solution is formed.
9. Explain the temperature rise that is observed when concentrated sul-
furic acid is diluted.
10. Explain the temperature rise that takes place when a little water is added
to anhydrous barium chloride (BaCl2).
Solutions of Definite Concentration. Molar solutions, on the
other hand, have a known concentration. They hold a gram-formula
weight (1 mole) of solute in 1 liter of solution. A molar solution of common
salt contains 1 mole, 58.5 g of salt with enough water to make 1 liter
IMa + Cl -> NaCI
23 + 35.5 = 58.5
of solution; a molar sugar solution contains 1 mole, 342 g of sugar
(Ci2H22Oii) in enough water to make 1 liter of solution.
Saturated Solution
Crystallization
Undissolved Crystals
-Dissolving
FIG. 12-3. — In a saturated solution in contact with undissolved solute, the processes of
dissolving and crystallizing are both going on at the same time.
Some solutions hold all the solute that they can absorb at that tem-
perature. Such solutions are called saturated solutions. If a solution has
been shaken but some of the solute still remains undissolved in the bottom
of the vessel indefinitely, then we may be sure that the solution is saturated.
Substances Leaving Solutions. During a storm, sea water dashed
up oh a high rock. Some of the water remained in a shallow natural basin.
Afterward the sun came out, and the water dried up. A white deposit
SOLUTIONS 207
was observed around the rim and in the bottom of the rock basin. Some
of the deposit was readily recognized by its cubical form as crystals of
common salt. The conditions necessary for the obtaining of crystals from
a solution are illustrated in this example.
A solution becomes saturated if enough of the solvent is evaporated
from it. If still more of the solvent is removed by evaporation, some of
the solute separates out in the form of crystals. If the solvent is removed
slowly by gradual evaporation, the molecules or ions have time to arrange
themselves on crystals already present, forming larger crystals. The mak-
ing of sizable crystals (as large as several pounds for a single crystal) is a
fascinating hobby. Projecting crystal formation on a screen is a valuable
demonstration, for it shows the unsuspected beauty in natural formations.
Separating Liquids. Gases usually leave solutions when the solu-
tions are heated, but the separation of two liquids that are mutually
dissolved is not always a simple matter. Petroleum contains several
mutually soluble liquids, each of which has considerable vapor pressure
at the boiling points of the others. It is extremely difficult to separate
these compounds by distillation. For this reason the individual com-
pounds in petroleum are not separated for ordinary fuel use. Instead of
selecting the distillate at one boiling point, it is customary to collect all
the substances (gasoline, kerosene, fuel oil) that leave the mixture between
a given range of boiling points. The process of heating a mixture and
collecting the distillate that boils over between two given temperatures
is called fractional distillation. The gasoline fraction separates out from
petroleum in the boiling-point range of 40 to 225°C, and it is a mixture
of several compounds.
Supersaturation. When a saturated solution evaporates, crystals
usually form about the edge of the vessel. But we should remember
that the formation of crystals depends on the arranging of ions or mole-
cules into definite patterns, for crystals of each kind of substance are
always definite in their shape, in the angles between surfaces, and in
appearance. Sometimes, when a saturated solution cools, the conditions
necessary for crystallization are not reached immediately, especially if
the solution is left undisturbed and kept free of dust. The solution may
cool to room temperature without change. Under these conditions, crys-
tallization can be brought on at a rapid rate throughout the vessel if the
solution is now stirred, if the vessel is scratched on the inside surface in
contact with the feolution, or, best of all, if a seed crystal is dropped into
the solution. Sometimes the material forms a solid mass of crystals almost
immediately, and much heat is liberated. Such an unstable solution formed
by cooling a saturated solution in which no crystallization has taken
place is called a supersaturated solution because it holds more solute than
208
CHEMISTRY FOR OUR TIMES
the liquid is normally able to absorb at the low temperature it has reached.
Solutions of sodium acetate
(NaC2H3O2), borax (Na2B4O7),
and photographer's "hypo"
(Na2S2O3) show this effect. It
must be emphasized that the con-
dition of supersaturation is easily
upset. Normally, when solutions
are cooled and become saturated,
crystals begin to form at once.
Glass is an example of a super-
saturated solution, or an under-
cooled liquid. (See Fig. 12-4.)
Useful glass has not crystallized
but has formed an apparently solid
mass at a temperature that is far
below the normal freezing point
of the compounds in it.
Owing to the fact that some
Courtesy of Corning Glass Works
FIG. 12-4. — Shown here is a glass build-
ing block. Glass keeps its useful properties
only as long as it remains an under-pooled
liquid. If crystals form in glass, it is
worthless.
liquids form supersaturated solu-
tions, we must be careful in our
definition of freezing point. The
freezing point is the temperature at which the solid and liquid conditions
of the same substance may be mixed without a change in the temperature
of either.
Effects of Dissolved Materials. Let us examine the following labora-
tory information about a solution of sodium chloride.
SOME PROPERTIES OF SODIUM CHLORIDE SOLUTION
Grams of
NaCl/liter
Moles /liter
(58.5 g is one
formula weight
or one mole)
Vapor pressure
observed at
100°C, mm.
Vapor pressure
of water at
100°O, mm
Drop in vapor
pressure due
to salt, mm
58.5
117
1
2
734.8
707.9
760
760
25.2
52.1
We notice that doubling the amount of salt in solution in this case
practically doubles the drop in vapor pressure.
Considering substances that do not ionize, we shall find that one
mole in 1000 g of solvent (molal solution)1 on the average raises the boil-
ing point 0.52°C. The boiling point of a solution containing 342 g of sugar
1 Not to be confused with molar solutions. See Glossary.
SOLUTIONS
209
(one mole) in 1 kg of water is actually 100.55°C (760 mm); for 171 g
(one-half mole), 100.27°C. Sugar has the formula CitHuOn.
Let us consider a solution of sugar and water in which is contained
one molecule of sugar for every nine molecules of water. At the surface
of the solution the tendency for the vapor of the water molecules (sugar
does not vaporize) to escape from the solution is nine-tenths that of a
similar amount of pure watel\ We may say, therefore, that in general the
addition of a dissolved solid material to a liquid decreases the vapor
pressure of the liquid. Consequently, the temperature at which boiling
occurs must be higher than that of the pure solvent alone, since boiling
takes place when the vapor pressure of the liquid just exceeds the pressure
of the gases above the liquid. If molecules or ions of a nonvolatile dis-
solved material hinder the escape of solvent molecules, it is evident that
the temperature must be raised above the usual boiling temperature
before sufficient vapor pressure is obtained to overcome the air pressure
above. In this manner we explain the fact that the boiling point of salt
water is higher than that of pure water.
In similar manner, formation of crystals is hindered by molecules of
the solute. Fresh-water ice freezes out from sea water, but an extremely
cold day is needed to freeze over an arm of the sea. Experiments show
that a gram-molecular weight (one mole) of a nonionizing substance [32
g of wood alcohol (CH3OH), for example] lowers the freezing point of
1000 g of water by — 1.81°C. On the average, the lowering caused by a
mole of all nonionized substances is 1.86°C. >
Antifreeze Mixture. The formulas of four commonly used antifreeze
liquids and some information about them is given in the following table.
This information applies to the^ure compounds only.
PROPERTIES OF ANTIFREEZE COMPOUNDS
Name
Formula
Molecular
weight
Boiling
point, deg C
Methanol or wood, alcohol (poison)
CH8OH
32
64 7
Ethanol, or ethyl alcohol (sold denatured)
(poison)
C2H6OH
46
78 5
Ethylene glycol
Glycerol or glycerin . . .
CH2OH
CH2OH
CH2OH
62
09
197.2
900
CHOH
CH2OH
Let us compare alcohol with glycerin as an antifreeze. One gram of
210 CHEMISTRY FOR OUR TIMES
f
ethyl alcohol is twice as effective as 1 g of glycerin in lowering the freezing
point, for alcohol has one-half the molecular weight of glycerin. On the
other hand, alcohol has a boiling point below that of water and hence
evaporates readily. There is no loss of glycerin by evaporation in the
ordinary car, but glycerin solution is much more viscous (thick) at low
temperatures and does not flow well through radiator tubes.
For the same amount of protection, loss' of ethyl alcohol by evapora-
tion is greater than loss of methyl alcohol, since much less methyl alcohol
is needed. Also, the boiling point of methyl alcohol-water is lower than
that of an ethyl alcohol-water mixture of the same freezing point.
A mixture of water 70 per cent, glycerin 15 per cent, and ethyl alcohol
15 per cent by volume has a freezing point of — 20°C ( — 4°F) and a
higher boiling point than an equivalent alcohol-water mixture.
Ethylene glycol is considered by many people to be the most reliable
and effective antifreeze, but it is quite expensive. If it is saved from one
winter to the next, however, the expense becomes a factor of less impor-
tance. Some antifreeze solutions also contain materials that prevent
corrosion of the engine block. Such considerations as well as price should
be weighed in selecting an antifreeze liquid.
Freezing mixtures containing ionized substances give very large
freezing-point lowerings. This is to be expected, for ionized solutions
have a larger number of particles than nonionized solutions. Icemaker's
brine contains a large amount of dissolved calcium chloride (CaCl2), and
<*its freezing point is so low it can be kept very cold. Cans of pure water
are frozen to ice rapidly when immersed in the cold brine. Solutions of
salts have not been found satisfactory for automobile radiators and are
not generally used.
Equilibrium. A pupil in the chemistry laboratory has made a solu-
tion of sugar and water. Sugar has been added to a given weight of water
at room temperature and the mixture shaken until apparently no more
sugar will dissolve, for some remains in the bottom of the vessel undis-
solved. Has the process by which sugar dissolves stopped functioning?
The answer is "no."
That this answer is correct can be demonstrated by the "repair"
of crystals. If small or fractured crystals are allowed to remain in con-
tact with a saturated solution, the small crystals disappear and large
ones are formed; the imperfections are filled in; and the crystals develop
more perfect edges. This is a result of the continuous dissolving and
recrystallizing of the solution.
Experiments show that dissolving proceeds continuously at the sur-
face of the sugar crystals. This is to be expected, for in the haphazard
molecular turmoil within a solution a condition of unsaturation must
exist at some places here and there. Also, the condition for crystallization
SOLUTIONS
211
Ammonia
Molecules
Water Vapor
Molecules
to take place must exist at other places within the liquid. In fact, when
the solution is saturated and in contact with undissolved solute, the two
processes of dissolving and crystallizing are each proceeding at equal
rates, each producing the opposite effect. A balance, or equilibrium, of
actions is the result.
crystallizing
Water + undissolved sugar ( ~7 sugar solution
dissolving
Another example of equilibrium is found in a closed bottle of house-
hold ammonia. This solution consists
essentially of water and ammonia gas.
The free space above the liquid con-
tains air, water vapor, and ammonia
molecules. Ammonia and water mole-
cules are continually leaving and re-
turning to the solution. When a bottle
has stood a while at a given tempera-
ture, the rates of leaving and return-
ing of the molecules are just equal.
Since the effects of the two are oppo-
site, an equilibrium is established. (See
Fig. 12-5.)
Summarizing, we can readily tell
whether a solution of a solid in a
liquid is unsaturated, saturated, or
supersaturated by adding a crystal
of the solute. If the crystal dissolves,
the solution is unsaturated. If the
crystal remains unchanged, the solu-
tion is saturated at that temperature.
If the addition of the crystal causes immediate crystallization, then the
solution is supersaturated.
SUMMARY
Solutions consist of solvent and solute. Although water is the most common
solvent, many others are used. Solutions are used extensively because (1) they
are convenient, (2) they have uniform distribution of solute, and (3) chemical
actions take place readily in them.
The solubility of a substance is the amount of substance that can be dissolved
in a given amount of solvent at a given temperature. We commonly express it as
the number of grams of solute in 100 g of solvent. For most solid solutes, solubility
of a substance increases with an increase of temperature. Gases are less soluble at
increased temperature but more soluble with increased pressure.
Temperature changes affect solubility. Substances that increase in solubility
as the temperature rises absorb heat when they dissolve (endo thermic change).
FIG. 12-5. — An equilibrium be-
tween moving molecules is illustrated
in a closed bottle of household
ammonia. The rate of evaporation is
balanced by the rate of condensation.
212 CHEMISTRY FOR OUR TIMES
Substances that decrease in solubility as the temperature rises liberate heat when
they dissolve (exothermic change). Temperature changes may be due in part to
addition of H+ ions to solvent water molecules. Mixing sulfuric acid and water is
dangerous because of the heat evolved. The hydration of an anhydrous substance
also liberates heat.
CuSO4 + 5H2O -4 CuSO4 5H2O (+ heat)
The concentration of solutions used in chemical work is often given in terms
of molecular units. A molar solution holds one gram-molecular weight (one mole)
of solute in 1 liter of solution.
Saturated solutions hold a maximum amount of dissolved solute in the pres-
ence of excess solute at a given temperature.
Crystallization is the process of separating a solute from a solution in the
form of crystals. Supersaturation results when crystals do not form from a satu-
rated solution under special conditions.
The freezing point of a solution is the temperature at which the liquid and
solid forms of a substance can be mixed without change in temperature.
The addition of solid solute lowers the vapor pressure and freezing point of a
solution. The boiling point of a solution is the temperature at which its vapor
pressure just exceeds the pressure above the liquid. The addition of a solid non-
volatile solute raises the boiling point of a solution.
The ideal automobile antifreeze liquid has low freezing point, high boiling
point, low vapor pressure, low cost, and does not cause deterioration of rubber
connections or corrode metal.
Excess solute in contact with a saturated solution is continually dissolving
and recrystallizing at the same rate at a given temperature. This is an example
of a dynamic equilibrium.
QUESTIONS
11. Distinguish a dilute from a concentrated solution.
12. How many grams of solute per liter are contained in molar solutions of
each of the following compounds: NH4N03; KN03; dextrose (CeHi206); MgS04;
CuS04?
13. Of what can we be sure when undissolved solute remains in a solution
after shaking?
14. The solubility of potassium nitrate is 31.6 grams in 100 grams of water at
20°C and 247 grams at 100°C. What happens when a saturated solution of
potassium nitrate at 100°C is cooled to 20°C?
15. What conditions usually produce a saturated solution? A supersaturated
solution?
16. What conditions disturb a supersaturated solution?
17. Define freezing point; boiling point.
18. What is the effect on freezing point, boiling point, and vapor pressure of
a solution of a nonvolatile solute in water of: (a) adding more solute; (6) adding
more solvent; (c) lowering the temperature?
SOLUTIONS 213
19. What is the expected boiling point of a solution containing 1000 grams of
water and 360 grams of dextrose (C«Hi206)?
20. How much glycerin in 1000 grams of water will produce the same freezing
point lowering as 32 grams of methyl alcohol (CHaOH)?
MORE CHALLENGING QUESTIONS
21. One of the lowest temperatures that can be reached by mixing substances
(— 55°C) is obtained by mixing 1 pint of CaCl2*6H20 with 0.7 pint of snow in a
vacuum bottle. Account for this very low temperature.
22. Calcium chloride solution has a low freezing point. Is this solution a satis-
factory antifreeze liquid for automobile radiators? Is kerosene a satisfactory
antifreeze liquid for radiators?
23. Examine or make some large crystals of sugar (rock candy), and tell how
they were made.
24. Crystals sometimes form in jelly. As the jelly continues to stand, will the
crystals change in size?
25. What happens to a liquid left standing in the open if: (a) it has a high
vapor pressure; (6) it has a very low vapor pressure; (c) the circulation of air
over the top increases?
26. Describe an experiment by which you can find*the freezing point of giacia
acetic acid. Demonstrate the experiment.
REVIEW
1. What is the percentage composition of dextrose (CeHnOs)?
2. What is the density of phosphine gas (PH3) at STP?
3. Find the molecular weight of a compound if 500 milliliters of its vapor
weighs 1.03 grams.
4. Balance the following equations (do not write in this book):
(a) Zn + H3P04 -» Zn3(PO4)2 + H,
(6) AI(OH), + HCI -» AlCIs 4- H20
(c) NH4NO, (heated) -+ H2O + N2O
(d) NaOH + CO* -+ Na,CO, + H2O
(e) AgNO3 + Cu -> Cu(NO,), + Ag
_ A (sheep , . . (1 . , . // 950 \ . A , . , . ,
5. A { drinks j^ Quarts of water I 1 IQAQ grams ) from a tub in which
ice is floating. How many calories does she supply to raise the temperature of
(40
this water to her body temperature -L- °C?
6. A solution is made by using 250 grams of CuS04-5H20 in enough water
to make 1 liter. What is the concentration of the solution in moles per liter?
UNIT THREE CHAPTER XIII
ACID AND ALKALINE SOLUTIONS:
NEUTRALIZATION
The sour taste of vinegar, pickled pigs' feet, sauerkraut, or pickles is
due to an acid, acetic acid (H*C2H3O2). Unripe fruits, such as green apples,
contain free acid. Some weeds, for example sour grass, taste sour because
they contain free acid. Sour milk contains lactic acid (H'CaHsOs), and
rancid butter develops the unpleasant taste of butyric acid (H'C^yC^).
The odorous reputation of male goats is said to be due to acids that are
present in their perspiration.
The acids commonly used in chemical laboratories, however, are fre-
quently much more active substances than those found in natural sources.
They include hydrochloric acid (HC1), nitric acid (HNO3), and sulfuric
acid (H2SO4). Sulfuric acid is commonly used in industries; for example,
it is used in one step of the process of making nails.
Opposed to the group of acid compounds is another group of com-
pounds called bases or alkalies. Their water solutions have a bitter taste
and a soapy feeling. Many such bases contain the hydroxyl group (OH)
combined with a metal and are therefore represented by metallic hydrox-
ides. The mild metallic hydroxides, limewater [Ca(OH)2] and milk of
magnesia [Mg(OH)2], are sometimes used for internal medicine; but, like
the strong acids, the strong hydroxides are too caustic to be taken into
the mouth. The substance known as lye (NaOH) and household ammonia
(NH3 solution) are alkaline substances that are commonly used in the
chemical laboratory and in the home. Sodium hydroxide (NaOH) and
potassium hydroxide (KOH) are most often used in solution. These are
soluble bases, called alkalies. Some parts of the body, the fluid of the
small intestine for example, are alkaline.
We have discovered some members of a third group of useful com-
pounds, salts. Common salt (NaCl) is the most familiar member of this
New Terms
dissociate alkali precipitation
monobasic acid titration exothermic
hydronium burette tubes completion
indicator concentration
215
416 CHEMISTRY FOR OUR TIMES
class. We shall notice that the formulas for metallic salts do not start
with the element hydrogen as do the formulas for acids. These compounds
are ionized solids containing a positive metallic ion or its equivalent and
another part, such as a negative chloride, nitrate, or sulfate ion.
Salts play many roles in our lives. The salts sometimes used for
medicine (a "dose of salts ") are indeed salts. Epsom salts (MgSO^TEUO)
is used extensively both inside and outside the body. Rochelle salt was
formerly used internally for the same purpose as Epsom salts, as a purga-
tive. Both Epsom and Rochelle salts obtained their names before chemical
compounds were named systematically.
Acids. Experiments with strong acids in dilute solution show that
they have a sour taste, change a dye called litmus from blue to red,
liberate hydrogen gas when placed with zinc or magnesium, act on car-
bonates to free carbon dioxide gas, and in general counteract the prop-
erties of bases. In water solution we notice that they all produce hydrogen
ions.
HCI -» H+ + Cl- H,P94 -> 2H+ + HPO;-
hydrochlorio acid phosphoric acid
H2SOf -4 2H+ + SO;- H-C2H3O2 -> H+ + C2H,O7
sulfuric acid acetic acid (slightly)
These properties, or characteristics, of water solutions of acids are due
to the one common factor in these solutions, namely, the hydrogen ion.
We have pointed out that one property of an acid is its ability to
counteract the properties of, or neutralize, a base. So important is this
reaction that it can be given as a definition of an acid; that is, an acid is a
compound that neutralizes a base.
How Acids Are Made. Many acids are found in nature, and some-
times one method of obtaining them is extraction from the original source,
Tartaric acid is obtained from grapes indirectly. The alchemists obtained
formic acid by grinding up red ants in a mortar with a pestle. The name
formic means "pertaining to ants." Formic acid is injected under our
skin by such insects as bees, mosquitoes, or hornets when they sting us.
A second method of obtaining acids is by using water and an acidic
oxide. The oxides of all nonmetals produce acid solutions of varying
strengths. The following equations show how some of these act :
CO2 -f H2O -» HzCOs carbonic acid
SO, -f- H2O -4 H2SO3 sulfurous acid
- P2O6 + 3H2O -4 2H3PO4 phosphoric acid
SO, -f H2O -4 H2SO4 sulfuric acid
These oxides, since they merely lack the water to make them an acid,
are often called acid anhydrides. Nitric pentoxide (N206) is an anhydride
of nitric acid. Sand (SiOi) is the anhydride of silicic acid (H2Si08),
ACID AND ALKALINE SOLUTIONS 217
although everyone knows that little chemical action takes place between
the sea and the sand of the beach.
A third method of obtaining acids is to mix sulfurio acid with a salt
of another acid. Sulfuric acid, a stable, cheap compound, has a boiling
point higher than that of any other common acid. Consequently, the
other acid may be changed to a vapor by heating and distilled out of
Courtesy of The Travelers Insurance Company
Kui. 13-1. — When compressed air is forced into this carboy of sulfuric acid, the liquid
is forced out. Is this method of transfer safer than pouring?
the reaction mixture. Nitric and hydrochloric acids are manufactured in
this way.
NaNO3 -f H,SO4 -4 HNO3 + NaHSO4 (1)
NaCI -f H2SO4 -4 HCI + NaHSO4 (2)
At a higher temperature the sodium hydrogen sulfate acts with more
salt,
NaCI -f NaHSO4 -* HCI + Na2SO4 (3)
and therefore the net result of reactions (2) and (3) is
2NaCI -f H2SO4 -+ 2HCI + Na2SO4 (4)
Reactions, such as the last two, that proceed in different steps are
common in chemistry. Reaction (3) is interesting, for by this means
children can make hydrogen chloride in toy chemistry sets without using
the hazardous sulfuric acid. Note that this salt, NaHS04, has the action
of a strong acid.
218 CHEMISTRY FOR OUR TIMES
How Acids Dissociate. Some acids, hydrochloric acid for example,
form one hydrogen ion or proton, H+, per formula. HC1 — » H+ + Cl~.
When an acid of this kind acts with sodium hydroxide, a base containing
one hydroxyl group or radical per formula, it takes but one formula
weight of this metallic hydroxide to act completely with a formula weight
of acid. Such an acid is called a monobasic acid.
Other acids form two hydrogen ions per formula; sulfuric acid is an
example. H2S04 — > 2H+ + SO^ ~~. When the acid acts on sodium hydrox-
ide, it takes two formula weights of this base to act with one formula
weight of the acid.
2H+ + SO" + 2Na+ + 2OH~ -4 2Na+ + SO" + 2HOH
Such an acid is called a dibasic acid. Dibasic acids dissociate in two steps.
(1) H2S04 -> H+ + HSOr. Then the hydrogen sulfate ion, which as we
have already seen can act as an acid itself, dissociates into more simple
parts. (2) HS07 -> H+ + 807".
Strength of Acids. Not all acids dissociate into ions by action with
water with equal ease. Those which split off ions well and appear to have
split off a large percentage of hydrogen ions or protons when dissolved
in a lot of water are called strong acids; those which split off ions poorly,
producing a small percentage of hydrogen ions when dissolved in water,
are called weak acids. In a dilute solution, hydrochloric acid is com-
pletely ionized; it is therefore a strong acid. Acetic acid in vinegar and
carbonic acid in "soda water " are very weakly ionized and are weak
acids.
Further, it is known that the hydrogen ion or proton is a very addi-
tive particle; that is, it attaches itself to some substances easily. It is
thought to attach itself quite readily to solvent water molecules, making
H+ + H20 -* H30+ or H2OH+, called the hydronium ion. Hence it
would be more accurate to use the term hydronium ion instead of hydro-
gen ion, and in chemical writings both terms are encountered. We shall
in general use H+.
More evidence of the additive nature of the hydrogen ion may be
secured from other common substances. If a hydrogen ion attaches itself
to an ammonia molecule, an ammonium ion is formed. Two cases will
illustrate this point.
NH3 + H+ -4 NHf
NH8 + HCI (dry) -> NH+Ch (solid)
Possibly this added ammonia molecule does not completely neutralize
the acid properties of the hydrogen ion. We add concentrated ammonium
chloride solution to magnesium and find that hydrogen is liberated just
as it would be from any acid, but at a much slower rate.
ACID AND ALKALINE SOLUTIONS 819
*— >
Mg + 2H3O+ + 2CI- -4 Mg++ + 2CI~ + H8 1 + 2H2O \ (ionic
Mg + 2NH* + 2CI- -» Mg++ + 2Ch + H2t + 2NH3t J equations)
The ammonium ion, like the hydronium ion, is capable of giving up a
proton and is thus an acid.
QUESTIONS
1. Define add.
2. List four properties of acids.
3. To what common factor are the properties of the acids due?
4. Define and give an example of an acid anhydride.
5. What relationship does the compound NaHSO4 bear to the compounds
H2S04 and Na2S04?
6. Complete, write in formulas, and balance the following equations (do not
write in this book):
Carbon dioxide + water —>
Nitrogen pentoxide + water —»
Sulfur trioxide + water — >
7. (Answer in tabular form.) Write the formulas for three important acids.
How many removable hydrogen atoms does each contain? Write the formulas of
the ions formed when the acids dissociate. Are the afeids strong or weak?
8. Distinguish a strong acid from a weak acid, and give an example of each.
9. Write the formula equation for the action of hydrochloric acid on sodium,
calcium, and aluminum, respectively. Beneath each write the ionic equation.
10. Repeat question 9, substituting sulfuric acid for hydrochloric acid.
Soluble Metallic Hydroxides. In testing soluble metallic hydroxides
(alkalies), satisfactory personal contact can be made by dipping the
finger tips into an alkaline solution of a soluble metallic hydroxide
(NaOH, KOH); when rubbed together the fingers feel slippery. Such
solutions change red litmus to blue and form a cerise-red color with
phenolphthalein, an indicator of the same general use as litmus dye.
They also act with carbon dioxide to form carbonates. If we examine
the formulas of several metallic hydroxides, we find that they all contain
hydroxyl (hydroxide) ions. When these compounds are soluble in water,
the solutions are also found to contain hydroxyl ions
Solid Solution Solid Solution
Hydroxide in Water Hydroxide in Water
Na+OH- -4 Na+ + OH- Ba++(OH)a -» Ba++ + 2OH~
K+OH- -» K+ + OH- Ca++(OH);f -4 Ca++ + 2OH~
The* properties that are common to alkaline solutions of hydroxides
must be due to the hydroxyl ions (OH~) present. The properties char-
220
CHEMISTRY FOR OUR TIMES
Courtesy of The Mathieson Alkali Works, Inc.
(a) (b)
FIG. 13-2. — (a) A drum of solid sodium hydroxide (caustic) must be opened by using
an axe. (6) Here a solid mass of sodium hydroxide is being lowered into a tank to
prepare sodium hydroxide solution.
Courtcay of The Matkieaon Alkali Works, Inc.
FIG. 13-3. — Unloading a tank carload of sodium hydroxide solution is a relatively
simple matter.
ACID AND ALJKALINE SOLUTIONS 221
acteristic of the hydroxyl ion are said to be those of a base. A partial
definition of a base is a compound that produces hydroxyl ions when
dissolved in water. Compounds^ such as copper hydroxide [Cu(OH)2]
and aluminum hydroxide [A1(OH)3], that dissolve very little in water
contain hydroxyl ions; they are not considered to be active as bases
because they do not dissolve sufficiently in water. The most active bases,
caustic soda (NaOH) and caustic potash (KOH), are often called alkalies.
A solution of ammonia in water was called volatile alkali by the alchemists
because the basic properties would entirely disappear when the solution
was warmed.
NHt + OH- -> NH3 r + H2O t .
This solution is only weakly basic because the reaction
NH3 4- H2O -4 NHJ + OH~
does not proceed very far.
99%
NH+ 4- OH- 7~* NHS 4- H2O.
1%
The compound NH4OH does not exist as a solid. Ammonia water is a
better name than ammonium hydroxide.
How Metallic Hydroxides Are Made. Many bases of importance
are found in nature. These include carbonates and boratcs, sodium
carbonate and borax being common examples. Certain regions are called
" alkali country" because of these bases present in the soil.
If soluble metallic hydroxides are exposed to air, they absorb both
moisture and carbon dioxide an$ change to carbonates.
2NaOH 4- H2CO8 -+ Na2CO, +2H2O.
Unlike the carbonates, these hydroxides are not found in nature.
A method of making hydroxides is to add one of the highly active
metals to water. Hydrogen is replaced and a solution of the hydrox-
ide formed. Evaporating to dryness leaves the hydroxide in the pure
condition.
2Na 4- 2HOH -> 2NaOH 4- H, | •
This method is interesting from a theoretical standpoint, but it is not
used practically except when very pure bases are needed.
Another method of making hydroxides is to add water to a metallic
oxide. This has a more practical application. It may be best illustrated by
the slaking of lime.
CaO 4- HiO -» Ca(OH),.
222 CHEMISTRY FOR OUR TIMES
Preparation of Insoluble Hydroxides. The two methods just
described are somewhat limited. Hydroxides that do not dissolve in water
may be made by the same methods by which any insoluble compound is
produced; namely, a soluble salt containing the ion of the desired metal
and an alkaline hydroxide are put together in solution. The hydroxide
ions combine with the metal ion and form an insoluble compound called
a precipitate, which can be removed from the liquid by filtering. For
example, zinc chloride solution mixed with a limited amount of sodium
hydroxide solution forms a thick gelatinous precipitate of zinc hydroxide.
ZnCI2 + 2NaOH -+ Zn(OH)2 1 + 2NaCl or Zn++ + 2OH~ -4 Zn(OH)2 1 .
insoluble
Actions of Acids and Bases Together; Neutralization. .A famous
rhyme (Eugene Field, 1850-1895) tells the story of how
"The gingham dog and the calico cat
Side by side on the table sat. . . . "
During the night the two toys began to quarrel and then to fight.
In the morning, much to the owner's dismay, both had disappeared. The
poem concludes with the explanation,
. . . "They ate each other up."
The action of a strong acid on a strong base is like that. When
brought together in the right amounts (formula- weight proportions),
such bases and acids destroy each other's characteristic properties.
All the properties of the acid disappear, as do all the properties of the
base. But in chemistry we cannot, with poetic license, have nothing left;
experience stated in the law of conservation of matter tells us that some-
thing is left. The products formed are usually a salt and water. For
example,
NaOH 4- HCI . -> NaCI + HOH
base acid salt water
Sodium hydroxide + hydrochloric acid — > sodium chloride -f water
In terms of ions the same reaction is represented in this way:
Na+ + OH- + H+ + Cl- -4 Na+ + Cl~ + HOH
We may consider that the sodium and the chloride ions were present both
before and after the action; therefore, they have not changed. The action
is essentially
H+ + OH- -4 HOH or H,O+ + OH- -f 2HOH
The action between a base and an acid is called neutralization. In
solution, water is formed, and the ions of a salt remain. If solid salt is
desired, the water is evaporated.
ACID AND ALKALINE SOLUTIONS
223
11. Define base.
QUESTIONS
12. To what common ion are the properties of the soluble metallic hydroxides
due?
13. Need hasps be hydroxides? Need hydroxides be bases?
14. Define alkali; alkaline solution.
15. Write equations for the reaction of carbon dioxide on solutions of (a)
potassium hydroxide, (6) calcium hydroxide, (c) barium hydroxide, (d) lithium
hydroxide. (Li has combining number 1.)
16. Show by equation how to prepare by precipitation aluminum hydroxide,
copper hydroxide, and zinc hydroxide.
17. Write formula equations for the neutral-
ization of hydrochloric acid by (a) sodium hy-
droxide, (6) calcium hydroxide, (c) aluminum
hydroxide, and (d) sodium carbonate. Beneath
each write the ionic equation.
18. Repeat question 17, using sulfuric acid in
place of hydrochloric acid.
19. What is the only important change that
takes place in the process of neutralization of an
alkaline solution by an acidic solution?
Base
•Acid
20. What
[Ca(OH)2]on(
is the effect of slaked
'sour" soil? Of limestone?
lime
Titration. When an experiment illustrating
neutralization is carried out in the laboratory,
the pupil selects the proper acid and base. For
example, to make potassium sulfate by neutrali- solution
zation, molar solutions of potassium hydroxide
and sulfuric acid are selected. About twice as
much potassium hydroxide solution as sulfuric
acid is required; they are mixed in a suitable
vessel. The volume of the two solutions is usu-
Neutral
FIG. 13-4. — These burette tubes
are used in titrating.
ally measured in long graduated tubes called burettes. (See Fig. 13-4.)
2K+ + 2OH- + 2H+ 4- SO" -» 2K+ + SO" + 2HOH
A sample is removed on a stirring rod and a drop placed on pieces of litmus paper
of both colors. If the red paper turns blue, the base is in excess and more acid is
added. If the blue paper still turns red, then more base is added cautiously, until
one drop of the reagent is required to make the litmus indicator change color.
The end point is then said to have been reached, and the salt may now be ob-
tained by evaporation of the water.
224
CHEMISTRY FOR OUR TIMES
B A S
An experimenter wishes to use this knowledge about acids and bases to find
out the percentage of acetic acid in vinegar; this should be 4 per cent by law. He
makes up a solution of a base, sodium hydroxide, of known concentration. He
then measures out a definite amount of vinegar.
While stirring he adds the base solution slowly to the
vinegar until, as evidenced by use of the indicator,
the end point, or complete neutralization, is reached.
Much base will be needed if the acid in the vinegar is
abundant, and little will be needed if the acid con-
centration is low. After measuring the volumes of
vinegar and base solution used, the strength of the
vinegar may be calculated.
R
ACID
FIG. 13-5. — The litmus
color changes are easily
remembered by this mem-
ory aid.
The Acid-base Measuring Stick. A cer-
tain descriptive poem tells of the visit of some
blind men to an elephant. Each gained an im-
pression from the portion of the beast that he
happened to touch, and each impression was different.
Water (HOH or H+OII-), like the elephant, apparent ly differs accord-
ing to the angle of approach.
Viewed from one end it shows the
hydrogen ion, the mark of an acid;
'viewed from the other end it shows
the hydroxyl ion, the sign of a
base. Viewed face on, it is both
acid and base at the same time —
hence, neither.
Thus our study of neutraliza-
tion actions has shown that water
is a compound which contains
both the hydrogen ion of the
acid and the hydroxyl ion of the
base, but so nicely balanced that
it is neutral. The position of water
between acids and bases has given
chemists the suggestion that a
scale of acid strength and base
strength can be made with water
included at the middle point.
Convenience shows that 14 divis-
ions are needed on this scale,
water being placed at the seventh
division. A molar solution of hydrochloric acid lies at the 0 (zero)
position, and a molar solution of sodium hydroxide lies at the position
14. Thus,
L'ourtesy of The Travelers Insurance Company
FIG. 13-6. — Chemist Joseph Ficklen
carries out a titration. Experimental work
such as this gives facts that can be used to
promote better health conditions in
factories.
ACID AND ALKALINE SOLUTIONS 225
. pH SCALE
acid strength increasing water base strength increasing
0123456 7 8 9 10 11 12 13 14
neutral
The position of a substance in reference to the scale is called its pH,
a term widely used today by persons in agriculture and in many indus-
tries. The pH of pure water is 7. This is an exact balance between hydroxyl
and hydrogen (hydronium) ions. Acid solutions have pH lower than 7,
and basic solutions have pH higher than 7. An acid of pH 2 has ten times
higher concentration of hydrogen (hydronium) ions than a solution of
pH3.
A set of indicators of standard colors can be made in test tubes, each
hue corresponding to a certain pH value. The experimenter follows a
definite procedure and finds that the solution in his test tube has a color
depending on its pH value. To find the position of the substance being
tested on the scale, the experimenter makes a color comparison. The
method is rapid, and in the hands of an experienced worker accurate
enough results can be obtained for most industrial purposes. Litmus
indicator is red in solutions with pH less than 7 and blue in solutions of
pH more than 7, the depth of shade of color giving some clue as to how
far from neutral the solution is. Many other indicators are known for
the different pH ranges. Phenolphthalein is cerise red in solutions more
alkaline than approximately pH 9. Test papers that show the approxi-
mate pH value of a solution by color changes are available. Hydrion B
paper is one example. The paper is dipped into the solution to be tested.
The pH value is then estimated by comparing the resulting color of the
paper with a chart. The range is pH 1 to 11, and the colors vary from
red through green in the same order as in the rainbow.
pH control is used in sugar manufacturing, water purification, paper
manufacturing, baking, jelly making, canning, and other food industries,
soil testing, bacteriology, and medicine.
pH Values pH Values
Apples 2.9-3.3 Milk (cow's) 6.4-6.8
Beans 7.3-7.5 Oranges 3.0-4.0
Blood (human) 7.3-7.5 Peaches 3.4-3.6
Bread, white. .' 5.0-6.0 Pumpkin 4.&-S.2
Blackberries 3.2-3.6 Rhubarb 3.1-3.2
Corn 6.0-6.5 Saliva (human) 6.0-7.6
Flour, wheat 6.0-6.5 Soil, "sweet" 7.0-9.0
Grapes 3.5-4.5 Soil, " sour" 4.0-6.9
Ginger ale 2.0-4.0 Tomatoes 4.1-4.4
Fruit jelly 3.0-3.5 Vinegar 2.4-3.4
Lemons 2.2-2.4 Mineral water 6.2-9.4
Limes 1.8-2.0 Distilled water* 5.2-6.0
Molasses 5.0-5.4 Wines 2.8-3.8
* Due to COt from air.
226 CHEMISTRY FOR OUR TIMES
QUESTIONS
21. In a certain titration experiment twice as much acid as sodium hydroxide
solution was required for neutralization. What is known about the relative con-
centration of the acid and the base?
22. At what point on the pH scale should an indicator change color if it is to
show exact neutralization?
23. A certain soil changes blue litmus paper to pink. Suggest a possible pH
value for this soil.
24. Is distilled water always exactly neutral (pH 7) ?
25. Why is the method of testing with litmus paper by putting a drop of the
liquid on the paper better for most purposes than dipping the paper into the
solution?
Methods of Preparing Soluble Salts. 1. Reaction of Acids and
Bases. The other substances concerned in the examples of neutralization
given were salts. Examination shows that these salts are related to both
the acid and the base. They have the metallic ion from the hydroxide and
all the acid except the hydrogen ion. Calcium nitrate, a salt, can be made
by the action of calcium hydroxide on nitric acid and the resulting water
removed by evaporation.
Ca(OH)2 + 2HNO3 -* Ca(NO8)2 + 2H2O (formula
equation)
Ca++ + 2OH- + 2H+ + 2NO^ -* Ca++ + 2NO^ + 2H2O (ionic
equation)
Here again it may be seen that such neutralizations consist in allow-
ing the hydrogen ion and the hydroxyl ion to form water. Many soluble
salts may be formed in this way.
2. Reaction of Metal and Acid.
Ca + 2HNO3 -» H2 + Ca(NO3)2 (formula equation)
Ca + 2H+ 4- 2NO7 -4 H2| -f- Ca+++ 2NO^ (ionic equation)
3. Reaction of Metal Oxide and Acid.
CaO -f 2HNO3 -» H2O -f Ca(NO3)2 (formula equation)
CaO + 2H+ + 2NO7 -4 H2O -f Ca++ + 2NO^ (ionic equation)
4. Reaction of Metal Carbonate and Acid
CaCO3 + 2HNO3 -4 Ca(NO3)2 + H2O -f CO2 1 (formula
equation)
CaCO, + 2H+ -j- 2NOr -> Ca++ + 2NO7 + H2O + CO2 T (ionic
equation)
ACID AND ALKALINE SOLUTIONS 227
5. Special Methods.
Ca(NO2)2 + O2 -4 Ca(NO8)2 (oxidation)
( Zn(IMO8)2 + Ca -4 Zn + Ca(NO3)2 (formula equation)
lZn++ -f 2NO7 + Ca -4 Zn + Ca++ + 2NO™ (ionic equation)
f CaCI2.+ 2AgNO8 -4 2AgCI | + Ca(NO3)2 (formula equation)
lCa++ + 2CI- -f 2Ag+ -f 2NOr -4 2Ag+CI- J + Ca++ -f 2NOr (ionic equation)
(precipitation of another compound at the same time)
Which Metallic Compounds Are Soluble? Experiments may be
performed to show which compounds dissolve in water. The substances
are shaken in water and the results recorded. Summarized, they are as
follows:
Except
Nitrates, chlorates, acetates, bi-
carbonates .................. Soluble
Sodium, potassium, ammonium
compounds .................. Soluble
Chlorides ...................... Soluble Ag, Hg+, Pb (PbCl2 soluble in hot H2O)
Sulfates ....................... Soluble Ba, Pb, Ca slightly
Carbonates, phosphates ......... Insoluble Na, K, NH4
Sulfides, hydroxides ............ Insoluble Na, K, NH4, Ca, Ba
Kinds of Chemical Changes. Chemical changes are classified ac-
cording to type or sort. Some common types are combination, decompo-
sition, displacement or replacement, and double replacement or double
decomposition.
1. Combination. Two or more substances join to form one sub-
stance. This may be the result of a combination of two elements, an
element and a compound, or two compounds. One compound is formed.
2H2 -f O2 -4 2H2O
Zn + S ->• ZnS
2SO2 + O2 -» 2SO3
CaO -f H20 -4 Ca(OH),
The general type of equation for an addition or combination reaction is
A + B -4 AB
2. Decomposition. A single compound breaks down into two or more
simpler substances. This sort of change is just the opposite of combi-
nation. The products formed may be elements, an element and a com-
pound, or simpler compounds. Examples are
2H2O -f 2H2 + O2
2KCIO3 -4 2KCI +3O2
CaCO8 -4 CaO -f CO2
NH4NO2 -4 2H2O + N2
The general type of equation for a decomposition reaction is
AB -4 A -f- B
228 CHEMISTRY FOR OUR TIMES
3. Displacement or Replacement. Several examples of exchange
Replacement ructions have been given in the description of the chemical
Series actions of water with metals. One element, being more
£a active than another in a compound, takes the place of that
Na element. One element and the solution of a compound form
A16 a new compound while a different element is liberated.
Zn Examples are
Fe 2Na + 2H2O -> 2NaOH + H2
Sn (sodium replaces part of the hydrogen in water)
I? Fe + CuCO4 -» FeSO4 + Cu
p (copper is exchanged for iron)
Hg Zn + 2HCI -+ ZnCI2 + H,
Ag (hydrogen in the acid is exchanged for zinc)
Pt 2NaBr + CI2 -> 2NaCI + Br2
Au (chlorine replaces bromine)
The general type of equation for an exchange is
AC + B -> AB + C
or
AC + B -» BC + A
4. Double Replacement, or Double Exchange. This sort of chem-
ical change is like an exchange of partners in an old-fashioned square
dance. It is also often called double decomposition. The second part of
one compound exchanges with the second part of another compound.
The same parts are written first in each compound. For example,
CaO + 2HCI -> CaCI2 + H2O
AgN03 + NaCI -> AgCI J + NaNO3
BaCI2 + H2SO4 -* BaSO4 1 -f 2HCI
NaOH -f HCI -> NaCI + H2O
Double-replacement reactions may often be considered as a special case
of combination. The last three equations are combination actions when
simplified in terms of ions.
Ag+ + Cl- -» AgCI |
Ba++ + SO" -^ BaSO4 I
H^ -f OH- -> H2O
The general type of equation for double replacement is
AC -h BD -f AD + BC
Reversible Chemical Actions. Nearly all chemical actions are
reversible; that is, once the product (s) are formed, they act on each other
to a greater or less extent to form the original substances. For example,
let us consider the chemical action that takes place in a bottle of soda
water as it stands on the grocer's shelf. The dissolved carbon dioxide gas
molecules in the water solution are continually colliding with water mole-
cules. The conditions are often just right for these collisions to result
in chemical action, forming carbonic acid. H30 + C(>2 — > H2CO8. The
ACID AND ALKALINE SOLUTIONS 829
unstable carbonic acid is in turn continuously breaking down, again
forming water and carbon dioxide. HjCOs — » H20 + C02. Both reac-
tions are proceeding at the same rate, but they have the opposite effect.
Under a given set of conditions, an equilibrium is maintained between
a liquid and its vapor in the closed space above the liquid. We use the
double arrow to represent this situation.
H2O + CO2 ;{=* H2CO8
The equilibrium condition means that a mixture of reacting sub-
stances and products is formed. In the example just given, a capped
bottle of soda water contains .water, carbon dioxide, and carbonic acid
in solution.
Extent of Chemical Actions. Several factors influence the amount
of each reacting substance present in an equilibrium. Important is the
effect of temperature. In the reversible reaction
H2O + CO2 & H2C03
the carbon dioxide gas is less soluble at higher temperatures. Increasing
the temperature, therefore, would favor the decomposition of carbonic
acid, or the reaction indicated by the left-pointing arrow. An equilibrium
would be established in which a small percentage of carbonic acid was
present. *
The higher the temperature, the faster the molecules move. Faster
motion means more chance for collision and hence more opportunities
for chemical reaction. A rise in temperature of 10°C frequently doubles
the rate of a chemical reaction. A reaction that requires 20 minutes or
1200 seconds to complete itself at 20°C may be ended in 1 second if the
temperature is 120°C.
The effect of pressure changes may also be noted. Gases are soluble
in water in proportion to the pressure applied on them (Henry's law). A
bottle of soda is capped under pressure in order to increase the amount
of dissolved carbon dioxide in the liquid. The greater the pressure (within
limits) with which the bottle is capped, the more carbonic acid is formed.
What is the reaction favored when a bottle of soda is uncapped?
Another example of the effect of pressure is seen in the synthesis of
ammonia, a reversible action, N2 + 3H2 «=* 2NH3. One volume of
nitrogen and three volumes of hydrogen, four in all, make two volumes
of ammonia gas. We should expect that an increase of pressure would
favor the change from four volumes to two volumes, as indeed it does.
We can say, then, that in reversible reactions temperature or pressure
changes may favor one of the reactions more than the other and may thus
alter the point at which an equilibrium is established.
A third substance introduced into an equilibrium may catalyze both
actions. The result is that the equilibrium is established more quickly
230 CHEMISTRY FOR OUR TIMES
than without it. Even if the pressure is low, the formation of ammonia
from its elements is greatly helped by a catalyst and its formation
hindered if the catalyst becomes poisoned by impurities. Catalysts can-
not start a reaction that does not proceed slowly by itself, and they do
not affect the final concentration of products and reactants at the point
of equilibrium.
Now let us consider a closed bottle of hydrogen and nitrogen. Nitrogen
and hydrogen together act very slowly to form some ammonia. As soon
as ammonia is formed, some of it begins to decompose. But meanwhile
more nitrogen and hydrogen combine. Eventually the rate of formation
is equaled by the rate of decomposition; and an equilibrium is estab-
lished. It has been found that at 500°C and a pressure of 300 times that
of normal air about 25 per cent of a proper mixture of nitrogen and
hydrogen is changed into ammonia. In the presence of a catalyst this
same ratio of nitrogen and hydrogen to ammonia is reached more quickly.
The sign +± represents a chemical " push-of-war " game. Two actions
are struggling against each other. If one team (chemical reaction) is
to gain the advantage, there are just two possibilities: (1) it must be
strengthened or (2) its opponent must be weakened.
A way to strengthen one chemical reaction so that it will gain ground
over the other is to have an increased amount of one of the reacting
substances crowded into the same space. If the equilibrium reaction
N2 + 3H2 +=*• 2NH3 is considered again, it will be seen that, when the
percentage of hydrogen is increased, the chances of hydrogen colliding
and reacting with nitrogen are improved. It is as if someone in a milling
crowd were counting how often he met people wearing eyeglasses. If he
secured someone to help him observe, the chances are that the two would
observe twice as many bespectacled people. If suddenly twice as many
people in the same crowd should put on glasses, the chances of the two
observers meeting people wearing eyeglasses would again be doubled.
In chemical terms, the general rule is that the speed of a simple chemical
action increases as the concentration of the reacting substances is in-
creased. The concentration is defined as the amount of material in a given
volume of space, for example, the number of moles per liter.
In the blast furnace in which pig iron is produced, the iron oxide ore
comes in contact with hot carbon monoxide gas. Carbon dioxide and iron
are formed. At the high temperature within the furnace, the iron is able to
remove oxygen from carbon dioxide; therefore, the reaction is reversible.
Fe2O3 + 3CO & 2Fe + 3CO2
ore
But do the smelters of iron allow the hard-won iron to be turned back
into ore? No more than they can avoid. They provide such an excess of
ACID AND ALKALINE SOLUTIONS 231
carbon monoxide that the carbon dioxide molecules are crowded away
from the hot iron; they increase the concentration of carbon monoxide
and reduce the concentration of carbon dioxide.
The principle involved is called the principle of mass action, and may
be stated thus: An equilibrium reaction may be made to resemble a
nearly completed reaction by increasing the concentration of one of the
reacting substances or by decreasing the concentration of the product.
The chemical way to weaken the opposition is to provide some means
of removing one of the products as fast as it is formed. Four cases are
worth investigating.
Completed Reversible Chemical Actions. Chemical actions that
continue until one or more of the reacting substances is nearly used up
are called " completed" actions. In what proportions were the reacting
substances present if they are nearly used up at the same time?
1. One Product Is Removed. A completed or nearly completed
action can be obtained from a reversible reaction by applying the principle
of mass action, namely, removing one of the products as fast as it is
formed and thus reducing its concentration. If we heat ammonia gas, it
decomposes and establishes an equilibrium.
2NH3 *± N2 + 3H2
If the vessel is constructed in part of palladium, the hydrogen may
pass through the palladium wall but the larger molecules of both nitrogen
and ammonia do not. Removing the hydrogen reduces the extent of the
reverse action and favors the decomposition reaction.
2. A Gas Escapes. Often a gas may be removed from the mixture
of reacting substances. In the action CaCOa <=* CaO + C02|, the carbon
dioxide is a gas at the temperature of the reaction. If it is allowed to
escape, limestone changes into lime. There is no chance for the reverse
action to occur.
Likewise, in the case NH4C1 + NaOH «=* NaCl + NH3 1 + H2O,the
ammonia is allowed to escape as a gas. Substances that leave the reaction
as a gas (sometimes when the temperature is raised) are fittingly marked
by the upward-pointing arrow ( | ).
3. A Solid Crystallises. In the action AgN08 (solution) + HC1
(solution) — > AgCl | (solid) + HN03 (solution), the silver chloride is a
solid that is insoluble in water; it therefore leaves the region of the reac-
tion, taking no more part in it than the container holding the reacting
solutions. NH3 (gas) + HC1 (gas) -> NH4C1 j (solid) is a chemical
example of a reaction that resembles the physical process of rain con-
densing from water vapor. Both cases are called precipitation, a word
connected in meaning with the act of falling down. The insoluble
J32 CHEMISTRY FOR OUR TIMES
substance formed, called a precipitate, may be marked by the downward-
pointing arrow. Barium sulf ate precipitates in the following reaction :
BaCU (solution) -f H2SO4 (solution) -> BaSO4J, (solid) -f 2HCI (solution)
This is another example of a reaction that goes on nearly to completion.
It is obvious here that the reacting substances must be somewhat soluble
in water and one product, possibly more, insoluble. The barium sulfate
formed in the example is a very insoluble substance. The rules for the
insolubility of common compounds have already been given (page 227).
When insoluble substances separate, the reversible reaction proceeds
nearly to completion.
4. An Un-ionized Product Is Formed. Whenever an un-ionized
or slightly ionized product is formed, a reaction goes to completion. Water
is a familiar example of a slightly ionized compound. When water is
formed from the hydrogen ion of an acid and the hydroxyl ion of a base,
the reaction is carried to completion.
Na+ + OH- + H+ + Cl- -> Na+ + Cl~ + H2O
is an illustration. The details of this reaction have already been described
(page 222).
Hydrolysis. The experiment of neutralization (page 223) shows that
when sodium hydroxide neutralizes hydrochloric acid the resulting solu-
tion is neutral and has pH 7. A solution of sodium chloride was prepared
by mixing the acid and the alkaline solutions in the exact proportions to
form sodium chloride and water. Sodium hydroxide is a highly dissociated
basic substance, and in solution hydrochloric acid is a highly dissociated
acid.
Suppose we substitute acetic acid, a weakly dissociated compound,
for the hydrochloric acid and attempt to neutralize it with sodium
hydroxide. We find that, when we have added the acid and the base in
equivalent reacting quantities, the solution is still quite strongly alkaline.
We can accomplish the same result by dissolving crystals of pure sodium
acetate in distilled water and testing the solution with litmus. The red
litmus turns blue since the solution is alkaline and not neutral. Since
acetic acid is weakly dissociated, it does not release as many hydro-
gen ions to the solution as does hydrochloric acid, and hydroxyl
ions from sodium hydroxide are in excess. The acetate ion in sodium
acetate actually takes up hydrogen ions from the water, thus:
Na+ + C2H8Oi- + H2O *± Na+ + HC2H3O2 + OH-
Sodium carbonate solution is also basic. This is due to the weak
dissociation of carbonic acid or even of the hydrogen carbonate ion.
2Na+ + CO" + H2O *± 2Na+ + HCOr + OH~
HCOr + H20 *± Na+ + H2CO, + OH-
ACID AND ALKALINE SOLUTIONS 233
Hydrolysis is defined as the action of an ion with water. It is a very
common type of reversible reaction and is the reason why solutions of
many salts are alkaline. For example, trisodium phosphate (NaaPOO,
borax (Na2B407'10H2O), sodium sulfite (Na2SO3), sodium sulfide (Na2S),
and potassium cyanide (KCN) are all salts containing an ion derived
from a weak acid.
A solution of ammonium chloride in distilled water is acidic, as can
readily be determined by testing. This is due to the fact that the ammo-
nium ion is an acid in itself (page 218).
NHJ + Cl- + H2O 7± WH3 + H3O+ + Cl~
A solution of ammonium chloride is sufficiently acid to release hydrogen
when placed on carefully cleaned magnesium.
Salts like copper sulfate (CuSO4), aluminum chloride (A1CU), and
zinc chloride (ZnCU) also form acid solutions. Their positive ions react
with water, and hydrogen ions are produced in the solution. The follow-
ing equation in part explains the complicated type of reaction that
occurs:
Cu++ + H2O -> [Cu(OH)]+ + H+
Copper hydroxide [Cu(OH)2] is insoluble; but since no precipitate forms
when copper sulfate is dissolved in distilled water, it would not be correct
to say that copper hydroxide is a product of ttie reversible reaction of
copper sulfate with water. Because the acidity can be traced to the action
of the positive ion (Cu"1"4" in this case) with water, it is an example of
hydrolysis.
In some instances an insoluble product of hydrolysis does form. This
product can be separated and analyzed.
BiCI3 -f H2O -4 BiOCI 1 -f 2HCI (formula equation)
Bi++4 + 3CI- + 3H2O -4 (BiO+CI~) -f 2H3O1 + 2Cl~ (ionic equation)
Complete hydrolysis may occur.
TiCU 4- 4H2O -» Ti(OH)4 -f 4HCI
The titanium hydroxide immediately decomposes.
Ti(OH)4 -+ TiO2 -f 2H2O
The hydrolysis of titanium tetrachloride is a reaction used in making
smoke screens; for titanium dioxide is a dense white material, and hydro-
gen chloride forms a fog in moist air.
Energy Changes in Chemical Changes. If a firecracker is set off,
a boisterous explosion results. The compounds formed by the chemical
change have less energy than those which went into the change. The
energy liberated heated the products and their surroundings so quickly
that they expanded forcibly, chiefly in the gaseous state.
234 CHEMISTRY FOR OUR TIMES
If we strike a match so that it catches fire, heat and light are pro-
duced in the rapid combustion. The compounds formed by the burning
have less energy than those on the original match. The extra energy is
converted into heat and light energy. The production of electrical energy
may be the result of chemical changes, such as those which occur inside
the battery of a hand flashlight. Let us recall that reactions which liberate
energy are called exothermic.
In the electrolysis of water, energy is absorbed ; therefore, it must be
provided by the battery or generator. Frequently chemical changes must
have energy supplied by outside means in order to maintain the reac-
tion. Heating is necessary to maintain the reaction of steam on coke.
H20 + C — » H2 + CO. These substances do not react when they are
cold; and since heat is absorbed during the reaction, the mixture will
cool unless heating is continued. Again we should remember that reac-
tions which absorb heat are called endothermic.
Starting Chemical Reactions. Sometimes a high temperature is
required for a chemical change to start. Thereafter the reaction furnishes
its own heat, maintaining the temperature necessary to keep it going.
When gasoline vapor and air are raised to a high temperature by a very
hot spark jumping across a spark-plug gap on the cylinder of an auto-
mobile motor, the mixture explodes. The expanding gas furnishes the
power to drive, the car. Hydrogen and oxygen can be mixed safely when
they are cold; but when a lighted match is applied to the mixture, the
spread of the flame throughout the gas is so rapid that it cannot be
readily measured. Hydrogen passed over copper oxide gives no reaction
unless the oxide is warmed. When, however, the chemical action occurs
readily, enough heat comes from it to cause a glow to spread throughout
the mass. When finely divided iron and sulfur are heated together in the
right proportions, the heat liberated by their reaction maintains the high
temperature. Fe + S -» FeS (+ heat).
A balance between chemical changes giving out heat and physical
changes taking in heat (evaporation in this case) may be illustrated by
an experiment.
Equal volumes of carbon tetrachloride (CCU) and carbon disulfide (CSz) are
mixed in a dish. The mixture is set on fire by applying a lighted match. The flame
is not uncomfortably warm, as may be demonstrated by dipping the hand into
the burning liquid and bringing it out covered with flames. This experiment must
be performed in a well-ventilated hood, for ill-smelling and poisonous gases are
formed by the chemical change.
The general principle relating energy changes to chemical changes
may be expressed as follows: Compounds that liberate much energy when
they are formed are stable. This energy is called the heat of formation.
ACID AND ALKALINE SOLUTIONS
235
Unstable compounds give out little energy or even take in energy when
they are formed.
HEAT OF FORMATION
(For a gram formula weight at 18°C)
Name
Symbol
Real
Aluminum chloride
A1C13
166.8
Ammonium nitrate
NH4NOi
87.9
Ammonium nitrite ... ... ....
NH4NO2
62.2
Calcium carbide . ....
CaC2
14 6
Calcium oxide
CaO
151 7
Carbon dioxide
CO2
94.4
Carbon disulfide (liquid)
as.
f
-22.0*
Copper oxide
CuO
34.9
Dihydrogen oxide (water)
H2O
68.4
Hydrogen peroxide
H2O2
44.5
Lead azide (detonator)
Pb(N«)»
-100.6*
Mercury fulminate (detonator)
Mercury oxide . . .
HgC2N202
HgO
-64.5*
21.7
Phosphorus oxide
P2O6
365 8
Sodium chloride
NaCl
98.4
Sodium bromide
NaBr
86.3
Sodium iodide
Nal
69.5
* Endothermic.
So important are the energy changes of chemical reactions that
chemists learn many of the facts of chemistry by their study. Other
practical people are also much interested in the energy that comes from
chemical changes. Every fuel is valued because of the energy it produces
when burned, not for the products of combustion alone.
Theories Change. As we shall see, Mendeleyev's first great general-
ization of the periodic law was later improved by Moseley. Moseley's
addition in no way lessens the value of Mendeleyev's contribution to the
progress of science.
The kinetic molecular theory in its original form does not describe
exactly the behavior of gases, for it assumes that the gas molecules them-
selves occupy no space and that they have no forces of attraction for each
other. Refinements of measurement, especially at higher pressures than
are used in elementary laboratories, show that additions must be made
to Boyle's law. Then the behavior of gas volumes is described more pre-
cisely. The more exact statement of the law is used, for example, by the
designers of Diesel engines.
The fact that Boyle's law is limited in its description of the behavior
of gases does not detract from its great usefulness.
In a similar fashion, the theory of ion formation and of the actions
236 CHEMISTRY FOR OUR TIMES
of solutions has been developed further. We live in a world in which the
chemistry is chiefly a chemistry of water solutions. Certainly all life
processes are tied up with the chemistry of water solutions. In describing
his theory of ionization in 1887, Svante August Arrhenius (1859-1927) of
Sweden did not have the benefit of the knowledge of atomic structure
that we possess today. Also, he limited his consideration to the chemistry
of water solutions, naturally enough.
Since the time his theory of ionization was stated, other developments
have taken into account the knowledge of atomic structure and have
broadened the theory to include all types of solutions. These theories
have been stated by P. Debye, E. Hiickel, J. N. Br0nsted, T. M. Lowry,
M. Usanovich, G. N. Lewis, and many others. The details of their experi-
ments and theories are beyond the scope of an elementary book on
chemistry.
SUMMARY
Acids have the following general properties: They taste sour; change blue
litmus paper to red; act with active metals, liberating hydrogen; act with car-
bonates, liberating carbon dioxide; and neutralize alkalies. These properties are
all thought to be due to the presence of hydrogen ions (H+), or protons, in water
solutions of acids.
Some acids are found in nature in plant or animal bodies. Acids can be made
by the action of an oxide of a nonmetal with water and by the action of sulfuric
acid on a salt. Soluble acids dissociate hydrogen ions in water solution; strong
acids dissociate well and weak acids poorly. Hydrogen ions, or protons, attach
themselves readily to water and to ammonia to form hydronium (H3O+) ions
or ammonium (NHJ") ions.
Soluble metallic hydroxides are alkalies, or bases, but the term base includes
other compounds, also. Soluble metallic hydroxides have the following general
properties: They have an unpleasant bitter taste; feel slippery to the fingers;
form alkaline solutions; change red litmus dye to blue; absorb carbon dioxide
to form carbonates; and neutralize acids. These properties are thought to be due
very largely to the presence of hydroxyl ions (OH~) in their solutions in water.
A base has the properties of the hydroxyl ion in solution, and it can neutralize
an acid. A substance with marked basic properties is an alkali.
Few metallic hydroxides are found in nature. They are prepared by the action
of an active metal on water, liberating hydrogen, and by the interaction of oxides
of active metals with water. Insoluble hydroxides are prepared by precipitation.
Neutralization is the interaction of a base and an acid. In water solutions,
essentially it is
H+ + OH- -> H20
or
H<O+ + OH- -4 2H20
Titration is a method of carrying on neutralization or similar reactions and
measuring the amounts of solutions used. Titration may be used to find the total
concentration of an unknown base or acid.
ACID AND ALKALINE SOLUTIONS 837
The pH scale numbers show the relative strength of an acidic or alkaline
solution. Water has pH 7, acids less than 7, and bases more than 7. Indicators
are sensitive within certain pH ranges. Litmus changes color at almost pH 7.
Salts may be prepared by neutralization; by metal plus acid; by metal oxide
plus acid; by metal carbonate and acid; and by special methods. The solubility of
salts is summarized in solubility rules.
Chemical changes may be classified according to types:
1. Combination. One product is formed from at least two starting materials.
2. Decomposition. Starting with one substance, at least two products form.
3. Displacement. An element reacts with a compound, liberating a second
element and forming a new compound.
4. Double replacement. Two compounds interchange parts.
The replacement, or electromotive, series is a list of elements in order of
decreasing chemical activity.
Some reactions are reversible. In reversible reactions, an equilibrium of two
opposite chemical reactions is set up, under a given set of conditions of concen-
trations, temperature, and pressure.
The rate of a chemical reaction is influenced by temperature ; by pressure if a
gas is among the reacting substances or products; by the presence of a catalyst;
and by the concentration.
The principle of mass action may be expressed as follows: A reversible equi-
librium reaction can be made to approach a nearly complete reaction by increas-
ing the concentration of one of the reacting substances or by decreasing the
concentration of the product. *
Without changing the temperature or pressure, a nearly completed chemical
reaction results when (1) a gas escapes, (2) a solid crystallizes from solution, or
(3) an un-ionized product forms from ions.
Chemical actions that liberate energy are called exothermic. Chemical actions
that absorb energy are called endothermic. Compounds that liberate much heat
when they form are -stable; others are unstable.
Hydrolysis is the action of an ion on water. Owing to hydrolysis, solutions of
some salts act alkaline to litmus, and others acidic. If the salt removes hydrogen
ions, then its solution is alkaline; if hydroxyl ions are removed, then the solution
is acid.
QUESTIONS
26. Write equations showing how the following salts may be prepared by
neutralization: KNO3; CaCl2; MgSO4; Zn(C2H3O2)2; A1C13.
27. Show by formula equations how to prepare (a) copper chloride (cupric)
in three ways; (6) zinc nitrate in five ways; (c) magnesium sulfate in five ways.
28. List four important types of chemical changes, and give an example of
each.
29. To what type of chemical changes do neutralization reactions belong?
(Form of answer: "Neutralization reactions belong to the double-replacement
type." — good. "Double replacement." — not so good. The answer should be in
the form of a complete sentence.)
238 CHEMISTRY FOR OUR TIMES
30. List three factors that influence the rate of chemical reactions. State
clearly the effect of each.
31. State the principle of mass action.
32. Under what three conditions may the double-replacement type of chem-
ical actions be made to go to completion?
33. Illustrate each type mentioned in question 32 by a balanced formula
equation.
34. Which compound is easier to decompose, carbon disulfide or water? (HINT:
Use table, and calculate heat of formation in kilocalories per gram.)
MORE CHALLENGING QUESTIONS
36. Concentrated sulfuric acid dissociates one hydrogen ion more readily than
two. Write the equation for both dissociations.
36. Look up in the dictionary the definition of the word alkali, especially
the original meaning. From what language does the word come? List some other
terms used in chemistry or elsewhere that come from the same language.
37. Write equations for the reactions of acetic acid, nitric acid, sulfurous acid,
and phosphoric acid each on potassium hydroxide, ammonium hydroxide, and
calcium hydroxide (12 equations in all). Under each formula equation, write the
ionic equation.
38. In a certain titration three times as much acid as base was required for
complete neutralization. What is the relative concentration of the acid and the
base? In general in a titration, what relationship exists between the volume of
liquid used and its concentration?
39. Write equations for the reaction of sulfuric acid on both sodium carbonate
and trisodium phosphate, showing in each case the various stages in the process
of neutralization.
40. Explain in terms of ions the hydrolysis of solutions of: (a) zinc chloride;
(b) sodium acetate; (c) sodium phosphate; (d) aluminum sulfate; (e) cupric
chloride.
UNIT THREE CHAPTER XIV
ELECTRICITY AND CHEMISTRY
We are all familiar with the many useful services performed by elec-
tricity. By harnessing this valuable servant, which Benjamin Franklin
first drew down from the skies on a kite string, we can now conveniently
sew, sweep, cure the sick, start automobiles, send messages, and shave.
Also, we find that interesting results are obtained when the relationships
between electricity and chemistry are investigated.
When electricity is passing through any metallic conductor, solid or
liquid, such as a copper wire or a pool of mercury, it may be noticed (1)
that the metal gets warmer than it would be otherwise and (2) that the
region around the metal influences a compass needle. We say that a
magnetic field is set up. Likewise, when electricity is passing through
a water solution of a salt these same two effects may be noted and also a
third. The solution becomes changed chemically; new substances are
formed. This chemical process of making changes in composition in a
liquid by means of electricity we call electrolysis. These statements refer,
in general, to the electric current from a dry cell, a storage battery, a
rectifier, or a direct-current generator (one-directional current) (d.c.).
The type of electric current supplied to many homes today is called
alternating current (a.c.) because it changes its direction rapidly — in most
localities sixty times each second.
Chemists are able to produce substances that carry or conduct elec-
tricity well. Copper is the most important commercial carrier of elec-
tricity. Such metallic carriers of electricity, common metals and carbon
in the form of graphite, are good conductors. Melted salts and solutions
of acids, bases, and salts in water are fair electrolytic conductors. All
other products of the chemist's art are poor conductors of electricity.
These substances, such as hard rubber, glass, porcelain, sulfur, and
synthetic resins like Bakelite and Lucite, are called insulators. Obviously
New Terms
anode inhibitor anodized
cathode graphite cell
conductor silicon electroplating
electrolyte abrasive
239
240
CHEMISTRY FOR OUR TIMES
if we are to control electricity we must have both suitable insulators and
suitable conductors.
A Simple Electrolysis Experiment. We can learn the principles of elec-
trolysis by a simple apparatus. (See Fig. 14-1.) It consists of a drinking glass
partly filled with copper sulfate solution (CuSO-i), the electrolytic solution.
'Copper sulfate is the electrolyte in this case. Two rods, one of carbon and the
other of copper, hang into the solution without touching each other. The copper
strip is connected to the positive (+) post of a dry cell and is called the anode.
Copper .
Electrode
Anode
1 f
Solution
of
Blue Vitriol
(CuS04)
-*-Cathode
^ Carbon
Electrode
Storage
Battery
FIG. 14-1. — This apparatus is called a cell. Two general types of cells are used : one,
dry cell or storage battery, for examplo, generates electricity by chemical actions; in the
other, as in this case, a chemical change is carried out when electricity is sent through
the cell.
The carbon strip is connected to the negative ( — ) post of the dry cell and is
called the cathode. The copper ions (Cu++) in the copper sulfate solution are
attracted to the negative carbon strip and move in the solution to this cathode.
There they receive two electrons per ion from the cathode, which is crowded with
extra electrons, and become copper atoms.
Cu++ -f 2«- -4 Cu° (e~ » electron)
reduction of copper atom
The copper atoms plate out, or deposit themselves, on the carbon rod as metallic
copper. A thin layer of pink copper is noticed on the carbon cathode soon after
the wires are connected to the apparatus. This apparatus does simple copper-
plating! It can be shown that the amount of deposit on the carbon rod depends
upon the amount of current flowing and also upon the length of time that the
current flows.
Meanwhile, at the anode the copper rod is losing weight. The copper atoms
are oxidized to copper ions, and these are supplying ions to the solution.
Cu° -4 Cu++ -f 2<r
If we desire to clean the carbon strip after the experiment, we can immerse it
nitric acid, which attacks the copper but not the carbon. A more appropriate
ELECTRICITY AND CHEMISTRY
241
method, however, is to reverse the flow of electrons by changing the connections
to the dry cell. The copper ions now deposit on the copper strip, which becomes
the cathode, and copper atoms are taken off the inactive carbon anode, leaving it
black and uncoated as it was at the start.
Commercial electroplating processes use the principles brought out in
the previous experiment. If, for example, an electroplater wishes to coat
silver over a spoon of less expensive metal, the spoon is first scrupulously
cleaned. Then, without touching it by hand, the spoon is made the cathode
in a solution that contains silver ions (commercially, silver and cyanide
ions). The anode is a bar of pure silver. When the current is turned on,
a deposit of silver forms on the spoon. This may be polished to give a
fine luster. The evenness of the plating, the strength with which the coat
is bonded to the spoon, and its cost depend on the skill of the worker.
Inter-celL
connector
Cover
Positive
strap
Positive
plate
Container
Vent plug
Post
Negative
strap
Partition
Separator
Negative
plate
Rib
FIG. 14-2. — A complete storage battery cell (without acid) is cut away in order to
show details.
Depositing copper and zinc together on a cathode produces a plate of
brass. Even rubber latex particles can be deposited by the electrolytic
process to produce rubber-coated articles. The metal work on automobiles
and hundreds of articles of household hardware and office machinery are
electroplated with metals, chromium, nickel, brass, or cadmium, often with
copper plating beneath. Some jewelry is gold-plated; even inexpensive
containers for lipstick and other cosmetics are sometimes covered with
a thin layer of pure gold, applied by electroplating.
We have examined a chemical change brought about by passing an
electric current through a solution. Now let us investigate the reverse
process, namely, the chemical actions occurring in a cell by which elec-
tricity is generated.
242
CHEMISTRY FOR OUR TIMES
r-?
Producing Electricity. Many chemical actions, burning for example,
produce heat. Most oxidation-reduction reactions can be made to liberate
electrical energy as well. The chemical action in a storage battery is a
good example of an oxidation-reduction reaction that produces elec-
tricity. The charged battery has two sorts of plates immersed in dilute
sulfuric acid. The gray lead plates are
the negative ( — ) plates, and the choc-
olate-colored lead dioxide (PbO2) plates
are the positive (+) ones. (See Fig.
14-2.)
At the cathode of a discharging
storage battery the lead becomes lead
sulfate. The lead loses two electrons per
atom, or is oxidized to form lead ions.
These join sulfate ions, precipitating as
insoluble lead sulfate.
^1.280
V"
1.150
Pb°
Pb++ + SO"
Pb++ + 2e~
Pb++SOr-|
The two electrons (accompanied by
millions more) run around the circuit
outside the battery, possibly lighting a
headlight on the way, and arrive at the
lead dioxide anode. Here they reduce
lead dioxide to lead ions, which also
precipitate as lead sulfate.
Courtesy of Exide Battery Company
FIG. 14-3. — The float rides higher
in the hydrometer when the sample
of liquid is taken from a fully
charged battery than it does when
the acid is taken from a discharged
battery. The hydrometer reading to
the left is 1.280 for a charged battery
and to the right 1.150 for a dis-
charged battery.
2e~
PbO2 -f 4H+
b++ + SO"
The total reaction is
Pb + PbO2 + 2H2SO4 -
Pb++ + 2H2O
2PbSO4 1 + 2H20
when the battery furnishes current.
As this chemical action goes on,
both plates gradually become changed
to lead sulfate, sulfuric acid is used up, and the liquid becomes diluted
with water. The density of the liquid falls to 1.150 g per ml, almost that
of water, 1.00. (See Fig. 14-3.) The supply of electrons rushes through
the starting motor of a car over wires when we push the starting button.
We say that an electric current is "flowing." More chemical action takes
place to maintain the supply of electrons. There is a limit to this action,
however, for after a while the battery will "go dead."
After the car is operating, the engine of the car runs a generator that
ELECTRICITY AND CHEMISTRY 243
supplies electricity to the battery, charging it again for future startings.
In the battery, the chemical action is reversed, and the plates restored
to their original composition — one to lead and the other to lead dioxide.
Meanwhile, the liquid becomes more concentrated with sulfuric acid and
more dense because the acid is exchanged for water. A fully charged
FIG. 14-4. — A chemical change in the storage battery here sends an electric current
through some dynamite. The violent chemical change that follows sets up vibrations
in the earth. The seismograph records these earth vibrations, and by them the explorer
locates oil — maybe.
battery should have a sulfuric acid-water mixture of density about 1.280 g
per ml, or " twelve-eighty."
In charging the battery the following equation applies:
2PbSO4 + 2H2O -> Pb + PbO2 + 2H2SO4
Electrons are restored to some lead ions of the lead sulfate at one elec-
trode and removed from an equal number at the other electrode.
2Rb++ -» Pb° + Pb++++
The storage battery, then, is a specialized chemical device designed
to carry out a chemical change that produces electricity. The battery
stores " chemicals," not electricity.
The Dry Cell. The "dry" cell with which we light our flashlight
and operate bells and buzzers is wet inside. Contained in the zinc cup
244
CHEMISTRY FOR OUR TIMES
that forms the outer metal case is a paste consisting of the following:
graphite; an oxidizing agent, usually manganese dioxide (MnO2); and
the acid, ammonium chloride (sal ammoniac, NH4C1). In the center is a
carbon rod, which is sometimes labeled positive (+). (See Fig. 14-5.)
Chemical action proceeds rapidly in the cell when the + and — terminals
are connected by wires to form a circuit as is the case when a person
Steel
Cover
Sealing
Material
Cardboard
Cardboard
Soaked with
Zinc Chloride
Paste
Carbon
FIG. 14-5. — This cross section of a dry cell shows that it is actually wet inside.
lights a flashlight. The zinc is oxidized, releasing electrons and placing
them on the zinc cup itself, which becomes the negative ( — ) terminal.
Zn° -* Zn++ + 2e~
Zinc ions (Zn++) are formed in the solution. At the anode manganese
dioxide is reduced in a rather complicated action.
2e~ + 2Mn02 + 2NH+ -> Mn2O, + H2O + 2NH8 f
When either the zinc cup or the paste becomes used up, the cell is
worthless. No way has yet been discovered to reverse this action satis-
factorily, but dry cells may be partly recharged if not allowed to run down
too far.
ELECTRICITY AND CHEMISTRY 245
QUESTIONS
1. Distinguish a conductor from an insulator of electricity.
2. Make a labeled diagram of a ceil for the electrolysis of silver nitrate
solution, using a silver anode and a platinum cathode.
3. Trace the path of silver from anode to cathode in silver plating.
4. Name three electroplated articles on an automobile or at home; name
both the foundation metal and the coating metal in each case.
5. Rhodium is a precious metal about twice as expensive as gold. Account
for the fact that rhodium-plated articles can be purchased at a five-and-ten-cent
store.
6. Distinguish a storage cell from a dry cell.
7. List three "dos" and three "don'ts" in taking care of a storage battery.
8. Why should pure water be added to a storage battery from time to time?
9. What is the most satisfactory method of testing the condition of charge
of a storage cell?
10. Does any useful metal remain in a worn-out storage battery? In a worn-
out dry cell?
Producing Metals by Electricity. Cherrrists are faced with a chal-
lenge today. There is a steady demand for light metals, but such metals
are also active chemically and hard to extract from the natural materials
in which they are discovered in the earth. Heating them with powerful
reducing agents, such as coke, hydrogen, or carbon monoxide, is not a
vigorous enough treatment to free them. In 1807 Sir Humphry Davy
(1778-1829) first used electricity to liberate these very active metals.
Sodium is one of these metals. There is plenty of this element on the
earth, but it is locked tightly in a chemical compound with chlorine, in
the form of sodium chloride, or common salt. To unlock the element
sodium from the salt, we first melt the salt by heating it carefully. An
anode and a cathode are placed in the molten or fused liquid in a Downs
cell, but no water is present. The sodium ions respond when the current
is turned on and move to the cathode.
Na+ (ion) + e~ -4 Na° (atom)
In a similar manner the chloride ions carry electrons to the anode, lose
their burden at the anode, become free chlorine atoms, seek a partner,
and escape as chlorine molecules.
2CI~lose 1e~ per atom -> 2CI° (atoms)
2CI (atoms) -* CI2 (molecute, a package of two atoms)
This experiment must be done with care if the sodium is to be ob-
246 » CHEMISTRY FOR OUR TIMES
tained. When this was first accomplished, Sir Humphrey Davy, who used
melted sodium hydroxide instead of melted salt, soon discovered that
the shiny metal, sodium, had to be protected from contact with substances
that attack it. These include air, water, and the substances formed at the
anode.
Davy describes his product from the electrolysis of potassium hydrox-
ide (KOH), a previous experiment in 1807, thus:
. . . small globules, having a high metallic lustre, and being precisely similar
in visible characteristics to quicksilver, appeared; some of which burned with
explosion, and bright flame, as soon as they were formed, others remained, and
were merely tarnished, and finally covered with a film, which formed on their
surfaces. These globules, numerous experiments soon showed to be the sub-
stance I was in search of, and a peculiar inflammable principle the basis of
potash.
Sodium metal is soft and silverlike when fresh. Care must be taken to
avoid contact between this metal and water, and for this reason it is
shipped in vacuum-sealed tin cans and kept immersed in kerosene in
the laboratory. In contact with water, sodium liberates hydrogen by
replacing it from the water so vigorously that the gas may catch fire.
The gas escapes so quickly that an explosion may be caused and hot lye
spattered around the neighborhood.
2Na + 2HOH -4 2NaOH + H2
The element sodium is too active for the purposes to which ordinary
metals are put. It is too soft for hardware. Most of the sodium produced
is used in the making of sodium cyanide (NaCN) and tetraethyl lead for
gasolines. Sodium finds many special uses in chemical laboratories; and
we may find it inside sodium-vapor lights — the road lights that give out
a yellow glow. In these lights the sodium and the inert gas neon are
enclosed together in a sealed glass tube. No chemical action takes place
in the sodium-vapor light; the sodium vapor glows. The same yellow glow
can be duplicated easily by throwing salt in a fire. A sensitive test for
sodium is to clap one's hands near a colorless flame of a Bunsen burner.
The dust will give a yellow flash in the flame.
Compounds made from the element sodium include sodium cyanide
(NaCN) used in electroplating, hardening steel, and in obtaining gold;
and sodium peroxide (Na202) used in bleaching.
The method for making potassium is similar to that for making
sodium. Magnesium, calcium, beryllium, and the important metal
aluminum are also made by electrolysis of fused salts. In each instance
theJfused compounds of the metals are used for the electrolyte, water,
which would prevent the formation of the metal, being avoided.
ELECTRICITY AND CHEMISTRY
247
Purifying Metals by Electricity.
Ordinary copper in wires for carrying
electricity is remarkably pure, 99.8 per
cent. Impure copper not only carries
electricity poorly but in addition wastes
it by converting it to heat. An electro-
lytic method is employed in making this
exceptionally pure commercial product
cheaply. Slabs of cast impure (blister)
copper to serve as anodes are hung in a
tank of copper sulfate solution. Sand-
wiched between these, but not touching
them, are cathodes of thin pure copper
sheets. (See Fig. 14-6.) An enormous
surge of electrons at a low voltage is used.
When the current is turned on, the cath-
odes grow at the expense of the anodes.
(See Fig. 14-7.) Impurities drop out and
Pure Sheet Copper
Anode Slime
KK;. 14-6. — This type of cell is
used for refining copper. The cop-
per forms ions at the anode, and
these ions deposit on the cathode.
Elect rical energy provides the mov-
ing force. The impurities in the
anode sink to the bottom of the
liquid.
settle to the bottom of the tank. Among them are metallic silver and
Courtesy of Anaconda Copper Mining Company
FIG. 14-7. — Cathodes of pink pure copper are lifted from the commercial cell after
refining. Most of this metal is destined to be used for such electrical purposes as
wiring houses for electric lights.
gold. These precious metals when recovered from the sludge in the tank
may be of sufficient value to pay most of the cost of refining the copper.
248 CHEMISTRY FOR OUR TIMES
Some lead and zinc are refined by electrolysis, and highly pure iron
may also be prepared by this method.
At the Anode. We should not overlook the fact that valuable prod-
ucts come from chemical changes occurring at the anode as well as at
the cathode. When a silver spoon is to be replated, all former platings
are first removed by making the spoon an anode in an electrolytic bath.
Afterward it is ready for an even, fresh coating. Such an " anodizing''
process saves silver. Some metals, aluminum for example, are anodized
(oxidized at the anode) to give them special finishes and to make them
Courtesy of E. I. duPont de Nemours A Company, Incm/
FIG. 14-8. — Highly concentrated hydrogen peroxide is now available in carload lots.
corrosion resistant. The important gas chlorine is collected at the anode.
Potassium permanganate is produced commercially by anodic oxidation
of manganese ions.
Making Hydrogen Peroxide. Hydrogen peroxide, often used at
home as a mild antiseptic or bleaching agent, is made at the anode in a
cooled electrolytic cell containing ammonium sulfate [(NH^SO*] and
sulfuric acid. The product is obtained by adding concentrated sulfuric
acid to the material obtained at the anode, peroxysulfuric acid, and dis-
tilling the hydrogen peroxide under reduced pressure. The 3 per cent
solution sold at retail stores is often labeled "10 volume" peroxide. One
pint of this liquid will produce 10 pints of oxygen at standard tempera-
ture and pressure. Manganese dioxide (Mn02) serves as a catalyst,
or promoter, of the decomposition of hydrogen peroxide; acetanilide
(C«H6NHCOCH,), as a retarder.
ELECTRICITY AND CHEMISTRY 249
The compound is unstable, especially if impure. It breaks down
easily, even explosively, into water and oxygen.
2H2O2 -4 2H2O + O2
As prepared for the market, an inhibitor like acetanilide is usually in-
cluded to retard decomposition. Hydrogen peroxide is used commercially
for bleaching animal products — silk, hair, wool, and feathers — and to
make other peroxides. When it is poured slowly on a wound, oxygen
bubbles are released from the blood and this helps cleanse the wound.
Peroxides have an oxygen-to-oxygen valence bond. In hydrogen peroxide
we may represent it as H : 0 : : 0 : H or H — 0 — 0 — H.
QUESTIONS
11. In what part of the replacement series are the metals that are produced
by electrolysis of fused salts located?
12. Write formula equations for (a) decomposition of sodium hydroxide into
elements by electrolysis; (6) burning of sodium to form sodium peroxide; (c)
action of sodium on water; (d) action of sodium on melted aluminum chloride.
13. What test is used to identify the presence of sodium in a compound?
14. Why must water be avoided in the preparation of metallic calcium?
15. Point out an advantage gained by the electrolytic refining of copper.
16. Make a labeled diagram of a cell for the refining of copper, (a) at the
start of the process and (6) at the close of the process.
17. For what purpose are aluminum airplane parts anodized?
18. Why should we not represent hydrogen peroxide (H202) by the formula
HO?
19. Give three uses for hydrogen peroxide.
20. Write formula equations for (a) the decomposition of hydrogen peroxide
when heated; (6) the action of hydrogen peroxide on sulfurous acid; (c) the action
of sodium peroxide on potassium nitrite solution; (d) the action of hydrogen
peroxide on sodium sulfite solution; (e) the action when hydrogen sulfide is
bubbled into hydrogen peroxide (free sulfur is one product).
Chemical Changes Brought About by Electric Heat. The
modern electric light bulb is a light source of reasonably high efficiency.
But it is also an electric furnace of a sort, for part of the electricity
produces heat. The changing of electricity into heat has some advantages,
namely: (1) A very high temperature can be obtained. (2) The heat can
be directed where it will do the most good. (3) Very little energy is wasted
in the change from electricity to heat.
Two chief types of furnaces are in use today for changing electricity
250
CHEMISTRY FOR OUR TIMES
into heat: (1) the arc furnace; (2) the resistance furnace. The arc furnace
(see Fig. 14-9), first developed by Henri Moissan (1852-1907), a French
scientist of great ingenuity, consists essentially of two carbon rods that
are allowed to touch and then are drawn slightly apart. When connected
to a source of electricity, an arc, or spark, of carbon vapor at an exceed-
ingly high temperature will enable the electricity to jump the gap. This
electric arc is one of the hottest spots on earth. Its temperature is esti-
Courtexy of American Iron and Sted Institute
FIG. 14-9. — In this large electric arc furnace for refining steel, the entire furnace
serves as a crucible. Three white-hot electrodes are seen at the top. The liquid metal
pours out over the cup-shaped lip in the foreground when the furnace is tipped.
mated at 4100°C. That of the sun's surface is thought to be 6200°C.
A crucible placed directly beneath the arc becomes heated intensely.
The other type of furnace depends upon the resistance, or opposition,
that certain substances offer to the passage of electricity through them.
A flatiron contains a high-resistance unit that becomes warm when elec-
tricity is turned on. A toaster or hair curler contains nichrome (an alloy
of nickel and chromium) wires or other wires that do not oxidize easily
but glow red-hot when they carry the current. Heating elements of this
sort embedded in the walls of a furnace make a convenient and con-
centrated source of heat used for steel analysis, hardening metals, and
annealing.
ELECTRICITY AND CHEMISTRY
Graphite. Graphite occurs naturally as a mineral, but it is
also manufactured in electric-resistance furnaces. To make graphite,
a bed of hard coal is placed between two huge conductors of electricity.
The coal offers great resistance to the passage of the current, and little
arcs, or sparks, jump between the lumps of coal. The heat converts the
coal into crystalline carbon, or graphite. Most of the impurities are
vaporized.
Graphite (plumbago) is a suitable material for making crucibles be-
cause it melts at a very high temperature. It is a good lubricant, for
the crystals are thin plates that slide over one another easily. Graphite
with more or less clay is the writing substance in so-called "lead" pencils.
Powdered graphite dusted over objects makes them conducting so that
they may be electroplated.
Silicon. If we wish to produce silicon to use in preparing special
steels, a furnace similar to the graphite furnace is loaded with mixed
sand and coke. A sand covering over the top of the charge shuts out air
as in the graphite furnace. A core of carbon through the charge in the
furnace ensures a conducting path of high resistance. A great surge of
current rushes through the furnace when the power is turned on. Great
heat is produced, and the sand and coke act on each other.
SiO2 + 2C -> 2CO t -f Si
sand coke carbon silicon
monoxide
The carbon monoxide gas escapes through the loose walls of the furnace
and burns as soon as it reaches the air.
Silicon Carbide. Useful silicon carbide can be made by a process
similar to that of making silicon except that a larger proportion of pow-
dered coke is used in the mixture. In practical work some sawdust and
salt are mixed with the sand and coke in order that the mass may be
somewhat porous.
The extra coke this time reacts with the silicon to form silicon carbide
(SiC).
Si + C -*> SiC
Silicon carbide is crystalline, shiny, and so extremely hard that it will
scratch glass; it is used extensively at home and in factories for grinding
steel. Such hard substances are called abrasives. Many carbides are very
hard. Masses of iridescent crystals are found near the cdre of the silicon
carbide furnace, glistening and handsome. Prepared for market, the
crystals are crushed, graded according to size, and bonded with clay,
rubber, Bakelite or other plastics to form a whetstone, or grinding wheel.
Trade names for silicon carbide include Carborundum and Crystolon.
252 CHEMISTRY FOR OUR TIMES
Phosphorus. In another application of the electric-resistance fur-
nace elementary phosphorus is produced. The furnace is loaded with
quarried rock phosphate [Ca»(P04) J, sand, and coke. Let us call calcium
phosphate [Ca8(PO4)2] equivalent to 3CaO and P2O5. The action that
occurs may be described by the following equations:
6CaO + 6SiO2 -> 6CaSiO8
2P2O6 -f 10C -f 10CO| + Pit
The phosphorus vapor leaves the furnace with the carbon monoxide gas,
and both are run through cold water. The phosphorus condenses to a
white, waxlike solid, but the carbon monoxide continues through as a
gas. The calcium silicate is a liquid at the temperature of the furnace and
is allowed to run off from time to time.
Carbon Bisulfide. Another useful substance prepared by electric
heat is carbon disulfide. The furnace is charged (loaded) with mixed coke
and sulfur. The sulfur is a nonconductor, but the carbon carries the
electricity and produces heat in so doing. At a high temperature the
sulfur vaporizes. The sulfur vapor passes through the arc between
the carbon electrodes and joins with the carbon.
C + 2S -> CS2
The carbon disulfide formed in the furnace is a gas. It is led off through
an opening near the top and cooled; a clear, sparkling liquid is formed.
Pure carbon disulfide is reported to have no objectionable odor. The mate-
rial used in most laboratories, however, has a disagreeable odor. The
odor may be endured to some degree, but no more than is necessary, for
it is poisonous. The liquid is very useful as a solvent; it dissolves rubber,
sulfur, phosphorus, and many other materials insoluble in water. Also,
it is used to make another solvent, carbon tetrachloride.
CS2 + 3CI2 -+ CCI4 -f S2CI2
carbon chlorine carbon sulfur
disulfide tetrachloride chloride
Chloroform, used as an anesthetic and a solvent, can be obtained by
reduction of carbon tetrachloride.
CCU + H2 -» CHCU + HCI
carbon tetra- hydrogen chloroform hydrogen chloride
chloride
"Carbide" and Aluminum Oxide. The electric furnace led to the
discovery of calcium carbide. Lime and coke were heated together in an
arc-type furnace at an exceedingly high temperature. The new sub-
stance formed, calcium carbide (CaC2), was gray-brown, and it liber-
ated much gas when thrown into a pail of water. The gas, which was
found to burn readily with a sooty flame, was recognized as acetylene
(H — C=C — H). In the furnace the reaction is
ELECTRICITY AND CHEMISTRY
253
CaO + 3C
lime coke
In water the action is
CaC2 + 2H2O
calcium water
carbide
CaC2 + COT
calcium carbon
carbide monoxide
Ca(OH)2 -f C2H,
slaked acetylene
lime
Aluminum oxide melted in an electric furnace (see Fig. 14-10) and
then cooled and crushed makes an ex-
cellent abrasive. It is hard and has
sharp edges. Many tons of this ma-
terial, called corundum, are used to
make emery wheels for grinding steel.
Making Mirrors by Evapora-
tion of Metals. Electric light bulbs
that have been used for a long while
become darkened by a deposit of
tungsten on the inside of the glass.
This metal comes from the glowing
hot-filament wire, which is made of
tungsten. The filament has evaporated
some of its metal; the metal has then
condensed on the glass. A miniature
distillation has occurred inside the
bulb.
The evaporation of tungsten can be
retarded by filling the bulb with some
inactive gas, argon or nitrogen. Con-
versely, the evaporation is hastened
if as much gas as possible is drawn out
of the bulb. By hanging other metals
on the tungsten filament, a mirror can
be made. The metal and the sub-
K$a^8^^
FIG. 14-10.— The cure for tooth-
ache starts in an electric furnace. A
hard fused aluminum oxide abrasive is
manufactured by electric heat. Fine
grains of abrasive are made into
grinding tools for dentists. The rest
of the story is left to the reader's
imagination.
stance to be coated are placed parallel in a high vacuum. Then electricity
heats the tungsten filament, which in turn melts the metal. Evapora-
tion of the metal and the depositing of a mirrorlike metallic film follow.
In this fashion many large astronomical reflectors are coated, the
famous 200-in. mirror for the telescope in the observatory on Palomar
Mountain, for example. (See Fig. 14-11.)
Flash Bulbs. A bulb like an electric light bulb is filled with oxygen
and with metal foil or wire of aluminum or magnesium. Also included
is a filament that becomes hot when an electric current runs through it.
This arrangement produces the photographer's flash bulb. At present,
such bulbs can be used only once.
254 CHEMISTRY FOR OUR TIMES
A radio tube, on the other hand, does not have oxygen in it; it is,
in fact, as nearly a perfect vacuum as can be obtained. Magnesium metal,
a silvery dense metal, has remarkable ability to absorb gases. This
" getter" metal is included in some radio tubes to remove traces of gas
not taken out by the vacuum pump when the bulbs are made. Barium is
also used for a simila
Courtesy of Corning Glass Works
FIG. 14-11. — The curious ribbed back structure of the 200-in. telescope mirror
was designed to decrease weight and to stiffen the mirror. The mirroi surface will be
on the opposite side.
Opportunities in Electrochemistry. The application of electricity
to chemistry has merely started. New and purer chemical compounds
may be made in the future by electrical means. New types of cells, changes
at both the anode and the cathode, and electrolysis in various solvents
all offer possibilities.
In the induction type of electric furnace, the furnace itself does not
become very hot. Only certain heavy metals placed within its powerful
and rapidly changing magnetic field become heated. If the hand is held
in the furnace, it will not be affected unless a metal ring is being worn.
The ring, however, would become so hot that a painful burn would result.
It is possible to reach 2500°C or even higher with such equipfnent.
Economical ways of producing electricity should be further investi-
gated. In a dry cell, zinc is used up, and the quantity of electrical power
produced is small. Larger amounts of electrical power are produced by
burning coal: The heat of the fire boils water; the steam formed passes
through a turbine, causing the turbine to turn an electric generator. Each
step in the process suffers a loss of energy, and as a result we waste more
of the coal than we utilize. Fame, fortune, and the gratitude of the world
ELECTRICITY AND CHEMISTRY 255
await the person who can show how to transform coal directly into elec-
tricity in an economical manner.
SUMMARY
Electrolysis is the process of causing chemical changes in a liquid by passing
a direct electric current through it. The liquid may be a solution or a melted salt.
The positive (+) plate is called the anode, the negative ( — ) plate the cathode,
and the liquid the electrolyte.
Metallic ions are positive and are discharged at the cathode. Electroplating
is an application of simple electrolysis, depositing metal on a cathode.
Two common cells for producing electricity are the storage cell and the dry
cell. The storage cell has lead, lead dioxide, and dilute sulfuric acid as the elec-
trolyte. Charging the battery increases the density of electrolyte; discharging
the battery decreases its density. The dry cell has zinc ( — ), carbon (+), and
sal ammoniac (NH4C1) solution in paste form. Manganese dioxide is also present
to oxidize liberated hydrogen to water.
Active metals are prepared by electrolysis of fused salts. Sodium collects at
the cathode from melted sodium chloride. The metal must be protected from air
and water. Sodium is a soft, silvery metal that tarnishes easily. It reacts explo-
sively with water. Sodium is used for the preparation of tetraethyl lead and to
make sodium compounds, such as sodium cyanide (NaCN) and sodium peroxide
(Na2O2). Potassium, magnesium, calcium, and aluminum are made similarly.
Refining metals by electrolysis is an important industry. The impure metal
is placed at the anode, pure sheet at the cathode; metal ions in electrolyte are
discharged at the cathode and deposited.
Electric heating is convenient. In an arc furnace a very high temperature is
reached. The resistance furnace is extensively used.
Products of electric furnaces include graphite (crystallized carbon), used for
a lubricant and a refractory; silicon, used in steelmaking; carbides, such as silicon
carbide (SiC), used as an abrasive because it is a very hard substance; white
phosphorus, used for making phosphorus sesquisulfide (P4S3) for matches; carbon
disulfide (€82), a solvent, also used to prepare carbon tetrachloride (CC14);
calcium carbide (CaC2), used to make acetylene (C2H2) ; and cyanamide (CaCN2) ;
and aluminum oxide (fused A^Os), an important commercial abrasive.
Sputtering is a process of depositing a metallic mirror by the evaporation
of a metal heated electrically in high vacuum.
Flash bulbs contain magnesium or aluminum foil or wire and oxygen.
QUESTIONS
21. Give at least two advantages and two disadvantages of electric; heating
compared with heating by burning a fuel.
22. Which type of electric furnace does an ordinary electric light bulb
resemble?
23. Cite one advantage and one disadvantage of graphite when compared
with oil as a lubricant.
256 CHEMISTRY FOR OUR TIMES
24. What property of graphite accounts for its use as an ingredient of the
paste within a dry cell?
26. In an electric furnace for producing silicon, the reaction mixture contains
salt and sawdust in addition to sand and coke. Suggest a reason for using the
extra materials.
26. Write an equation for the burning of the carbon monoxide outside a
silicon-producing furnace in action.
27. List five useful products of electric-resistance furnaces.
28. Why is air generally excluded from an electric-resistance furnace?
29. Write formula equations for (a) burning carbon disulfide; (6) chiorination
of carbon disulfide; (c) reduction of carbon tetrachloride by hydrogen.
30. A few drops of carbon disulfide are poured into a large, tall glass jar.
A warmed glass rod is brought to the mouth of the jar. Then a sheet of blue
flame starts near the mouth and burns downward. The walls of the jar become
coated with a light yellow deposit. Explain these observations.
31. When nitrogen is passed over calcium carbide in an electric furnace, cal-
cium cyanamide (CaCN2) is formed. Carbon is the other product. Write the
equation to represent this change.
32. What properties has carbon tetrachloride that make it (a) a good ex-
tinguisher for small fires; (6) a good clothes cleaner?
33. What is the percentage of chlorine in carbon tetrachloride?
34. What type of valence bonding is exhibited in chloroform (CHCU)?
MORE CHALLENGING QUESTIONS
36. What is the difference between an 80-ampere-hour storage battery and a
100-ampere-hour battery?
36. Make a labeled diagram of a Downs cell. Consult a book on industrial
chemistry, for example, the one by Reigel.1
37. A certain compound contains 10.05 per cent carbon, 0.84 per cent hydro-
gen, and 89.1 per cent chlorine. Find its simplest formula. Also, 100 ml of its
vapor at STP weighs 0.538 g. Find its molecular formula.
38. The following equations are taken from a publication of the American
Chemical Society.2 In summarizing three electrolytic processes for making hydro-
gen peroxide, J. 8. Reichert gives these equations. Balance each (do not write in
this book).
1. Cell reaction H2SO4 -* H2S2O8 + H2
Steam distillation H2S2O8 + H2O -4 H2SO4 + H2O2
Over-all balance RjO HTHa + H2O2
1 Reinhold Publishing Corporation, New York.
1 Chemical and Engineering News, vol. 21, No. 7.
ELECTRICITY AND CHEMISTRY 257
2.
3.
Cell reaction
Steam distillation
Over-all balance
Cell reaction
Conversion
Steam distillation
Over-all balance
NH4HS04
(NH4)2S208 H
-¥
hH20 ->
(NH4)2S208 H
NH4HSO4 H
- H2
- H202
NH4HS04
(NH4)2S2O8 H
K2S208
H2O -»
h KHSO4 -»
hH20 ->
(NH4)2S208 H
NH4HSO4 H
2KHSO4 H
h H2O2
h H2
h K2S208
hH202
H2O -»
H2 H
h H202
39. The tank car pictured in Fig. 14-8 holds 8000 Ib of hydrogen peroxide
solution, of which 27.6 per cent by weight is hydrogen peroxide. What is the
weight of the actual hydrogen peroxide in the car? What weight of oxygen is
available from the peroxide when it is all decomposed?
40. Balance the following equation (do not write in this book).
KMnO4 + H2SO4 + H2O2 -* K2SO4 +.MnSO4 + H2O + O2
41. What is meant by 10-volume and by 100-volume hydrogen peroxide?
42. Trace the flow of electrons through a circuit consisting of a charged lead
storage battery connected by means of copper wires to a cell consisting of two
copper electrodes dipping into a solution of copper bromide (CuBr2).
UNIT THREE CHAPTER XV
COLLOIDS
Many of us may have wondered why scum forms on hot milk or cocoa
while it cools or why a cake of soap is sometimes surrounded by a jelly-
like slush. We may have noticed that sometimes jelly does not "jell,"
that the petal of a white lily has no white substance in it, or that hot
water at first is not always best for washing clothes. We may have found
ice crystals in ice cream and wondered why frozen desserts and puddings
are usually so "smooth" to the taste. Questions like these and many
more were investigated by Thomas Graham (1805-1869), a Scottish
scientist. He studied various liquids and the way in which they soaked
through parchment paper and animal membranes. He found that solu-
tions of salt and sugar, true solutions, diffuse through these thin, skin-
like sheets readily but that liquids such as gelatin and glue in water do
not go through so quickly. He called the second group of materials "glue-
like" or colloids. Although Graham is called the "father of colloid chem-
istry" for his work, several other workers of the generation before him
prepared and studied colloids also. Since Graham's time, numerous inves-
tigators have worked with colloids.
Up to this point in this book we have been investigating pure sub-
stances and have thus developed several principles of chemistry. Some
of these principles have been described by laws. Now we depart for a
while from the study of pure substances and investigate natural mate-
rials, substances just as they are found in nature to a great extent. This
is practical chemistry indeed, applied chemistry. But it is not a new
chemistry. The story of colloid chemistry is told by applying known
principles to a special condition of matter.
What is Colloidal Dispersion? Following Prof. Graham's investi-
gations, it was found that "colloids" differ from true solutions in respect
to the size of the dispersed particles. We can see large chips of material
with the unaided eye. We can also see smaller bits of substances when
we use a microscope. Atoms and molecules are very much smaller still,
New Terms
absorb coagulation diffuse
adsorb protective colloid Tyndall effect
259
260
CHEMISTRY FOR OUR TIMES
most of them too small to be seen even under an electron microscope,
The particles in a colloidal dispersion are intermediate in size; that is.
they are too small to be seen by the ordinary microscope but too large
to be true atoms or simple molecules. Some of the larger molecules
are of colloidal size; the size range is thus general rather than precise.
Colloids are like true solutions in many respects. It is possible, there-
fore, to think of each of the three states of matter mixed into each of
the three states acting as solvents. Here are some examples:
Substance suspended
Suspended
Example
Gaseous bubbles
Liquid droplets
Iln a gas
In a liquid
In a solid
In a gas
In a liquid
Impossible
A foam — whipped cream
Air in certain porous minerals — meer-
schaum, pumice- or in floating soap
A mist or a fog — clouds
An emulsion — salad dressing
Solid particles
In a solid
In a gas
In a liquid
Water in butterfat
A smoke
Colloidal metals in water; house paint
In a solid
Wings of butterflies; some alloys
However, colloids differ from true solutions in many respects. They do
not pass readily through parchment membranes, as Graham found, and
they show the path of a beam of light. Just as an automobile headlight
sends many streamers of light beams out into the fog, so a light beam
shows its path in a colloidal suspension. This effect, called the Faraday-
Tyndall effect, sometimes serves to distinguish colloids from true
solutions.
How Colloids Are Made. Some colloids occur naturally. Nature
makes starch particles colloidal in size. In fact, it is well known that
starch does not make a true clear solution with warm water. Glue, gums,
flesh, and many plant parts are already in colloidal-size particles. Soap
put into water makes, not a true solution, but a colloidal suspension of
soap in water. Milk is a colloid of casein and butterfat suspended in
water. Rubber latex resembles milk in appearance and contains tiny
particles of rubber hydrocarbon.
Since colloidal particles are a matter of size, there are only two gen-
eral ways of making them: (1) making extremely small particles larger;
(2) making large particles smaller.
1. Let us start with a solution in the molecular or in the ionic condition.
Then let us cause a precipitation to take place in this solution in such a
fashion that the particles formed are of colloidal size. Here we can be guided by
a principle well known to the druggist. Concentrated or extremely dilute solu-
COLLOIDS
261
Microscope
tions and rapid precipitation cause small-sized crystals. Moderately concentrated
solutions and slow separation of the material produce large-sized particles. A de-
layed precipitation is startling to watch and illustrates the point under discussion.
If we put hydrochloric acid into a solution of photographer's "hypo,"
colloidal sulfur forms in the solution after a short while. It is white and
opalescent but does not settle out completely.
Na2S2Oa + 2HCI -> 2NaCI + H2SO, + Si
hypo hydrochloric salt sulfurous sulfur
acid acid
Let us shake a small amount of solid ferric-chloride with cold water. A yellow-
brown solution forms that contains Fe+ ++ ions and Cl~ ions.
Using the same amount of the chloride, let us add it to a sim-
ilar amount of water that is boiling vigorously. This time a
garnet-red colloid is produced, ferric hydroxide suspension.
FeCI, + 3HOH -» Fe(OH)8| + 3HCI
Colloidal arsenic sulfide is formed when hydrogen
sulfide acts on arsenious acid (HgAsOs), and sometimes
silver ions and chloride ions together form silver chlo-
ride, which becomes suspended in the solution in col-
loidal-sized particles. Gold chloride solution treated
with a reducing agent, fresh tannic acid solution for ex-
ample, forms metallic gold colloids, red when heated,
violet or blue when cooled and diluted. The color de-
pends on the size of the particle, not its composition.
2. Let some potato starch and water be stirred together.
Then let the solution be poured into a folded filter paper and
the filtrate tested for starch. A drop of iodine solution pro-
duces a blue color if starch is present. No color is produced at
first. Now let the starch be ground vigorously in a chemist's
mortar with a pestle and the experiment repeated. This time
some of the starch has been made small enough to pass
through a piece of filter paper. This is finely divided, or col-
loidal, starch.
Mechanical grinding by means of mills produces
powders that are colloidal in size. These mills are used
to prepare paints, medicines, insecticides, and mayon-
naise dressing. In one type of mill, the grinding is
done between two parallel, horizontal, hard steel plates
that are so close together that a page of this book could
not be placed between them without touching.
Umrtof -*-
Ultra
Microscope
bmil of -*-
Ordinary
Microscope
Cottotdal
Particles
Microscopic
Particles
Visible
bits of
matter
FIG. 15-1.—
The size scale of
particles.
A trace of washing soda is added to some water and two silver wires or coins
are connected to a 11 5- volt direct-current source that can deliver 6 to 12 amperes
262
CHEMISTRY FOR OUR TIMES
in series with an adjustable resistor. (See Fig. 15-2.) Dark-brown colloidal silver
suspension forms in the water when the silver wires are touched and then sepa-
, 110-115 V. A.C.
Glass Handle
-Metal Rod
Rub Metals
• Together
FIG. 15-2. — This apparatus produces a colloidal dispersion by the Bredig arc method.
A spark is caused to jump between two metals that are immersed in a liquid.
rated a bit. Again, when mercury is poured in the funnel of the apparatus shown
in Fig. 15-3 the metal drops form an electric spark across the gap in the level bulb
that contains ordinary water. It is thought that the metal vaporizes and then is
condensed in the cold water to gray-
green colloidal particles of elementary
mercury.
Properties of Colloids. Many
colloids have attractive colors.
Colloidal gold suspended in glass
is purple or red. Oil films of col-
loidal thickness give opalescent,
peacock colors when spread out
on water. In fact, the color of
some flower blossoms and birds'
feathers is thought to be caused
by air bubbles of colloidal size or
thin plates, for we can discover no
colored material (pigment) in
them. Nor is any blue substance
found in blue eyes. The colloidal
FIG. 15-3. — The Bredig arc method
may be applied to a liquid metal by using
the apparatus above.
substances in the eye break up light and reflect only blue.
Colloidal suspensions in liquids show the path of a beam of light.
They pass through an ordinary filter paper. Just as a dog runs through
a forest, so a colloidal particle finds its way through the mat of fibers
that compose paper.
Let us find out a few things about the effect of surface. To use a
homely example, any housekeeper knows that dust gathers on furniture
surfaces. The greater the amount of surface, the greater the amount of
dust.
Now suppose that we have a cube of cheese one centimeter on an edge.
It has six square centimeters of surface. If we slice it parallel to any face,
the surface is increased by the area of both sides of the cut, or two square
COLLOIDS
263
centimeters more. (See Fig. 15-4.) Many thin slices or, better still, grind-
ing will give much more surface, as the table below shows.
EFFECT OF CUTTING A 1-cM3 LUMP OF SUGAR INTO SMALLER CUBES
Length of
edge, cm
Number of cubes
Total surface
Comparable area
1
1
6 cm2
A large postage stamp .
0.001
1,000,000,000
6000 cm2
A small rug
(1 X tO9)
0.000,001
1 X 1018
600 meters2
A home-size building lot
0.000,000,01
1 X 1024
15 acres
A city block
That is, the surface from a lump of sugar, fine pulverized, is more
than all the floor space in a large high school. Any surface effect, then,
is brought out in colloids to a re-
markable extent.
Colloids adsorb many substances
readily; that is, substances cling to
the surface of a colloid. Notable in
this respect is activated charcoal,
made by charring selected vegetable
material. Brown sugar solution is
boiled with activated charcoal, and
the coloring materials are adsorbed.
The sugar becomes colorless. Bone
black also shows the same property,
but not so much as activated char-
coal. Activated charcoal is used as an
FIG. 15-4. — Cutting or grinding
material exposes new surface.
adsorbing agent in general military defensive gas masks and for purifying
water. Ordinary charcoal spread over vile-smelling, putrid organic matter
will make it tolerable for a while. From a bottle full of freshly heated
and air-cooled activated charcoal, several bottles full of air may be col-
lected by pouring in water. This is because the charcoal has adsorbed
so much air. (See Fig. 15-5.)
Experiments also show that particles in a colloid are usually charged
electrically. In ferric hydroxide, for example, all the particles are charged
with the same kind of electricity, positive. Hence, the colloidal particles
repel each other and tend to stay suspended and apart. Colloidal arsenic
sulfide has a negative charge. The electric charge on colloidal mist is
thought to be connected with thunderstorms.
The fact that colloids are usually electrically charged accounts for
some of their most interesting properties. Indeed, colloidal particles
264
CHEMISTRY FOR OUR TIMES
behave quite like ions at times. Rubber colloids may be electrically
plated onto metal articles, producing adhering coatings.
To summarize, colloidal particles (1) give color effects, (2) show the
path of a strong beam of light, (3) adsorb gases or impurities from liquids
because of their large surface, and (4) carry an electric charge.
Air
Freshly Activated A Bottle
Charcoal of Air
FIG. 15-5. — Interesting and true: More than one bottle of air can be displaced from a
bottle of freshly activated charcoal.
QUESTIONS
1. What is the meaning of the word colloid?
2. How did Graham distinguish colloidal dispersions from true solutions?
3. Mention the state of matter of both the dispersed material and the dis-
persing medium in each of the following: beaten egg white; cigar smoke; bentonite
clay used as drilling mud in an oil well; atmospheric dust; slippery soil; mayon-
naise salad dressing; cold cream.
4. Account for the fact that darkened crankcase oil cannot be restored to its
former clear, amber condition by filtering through newspaper.
6. Ordinary gold is yellow, but gold precipitated from gold chloride solution
by tannin solution is purple. Account for the difference in color.
6. Name three types of industries that a salesman for colloid mills should
visit.
7. Some samples of coal have iridescent surfaces. Explain this appearance.
8. A druggist finds that a certain caramel solution is too dark for his needs.
How can he lighten the color?
9. Some of the colloidal gold dispersions prepared by Faraday in 1857 are
still preserved in the Royal Institute. They show no tendency to settle out. What
property of colloidal dispersions is illustrated by their behavior?
10. Point out a similarity between a colloidal particle and an ion.
COLLOIDS 265
Causing Colloidal Particles to Come Together. Frying or boiling
an egg causes a change, familiar to all of us, in the appearance of the egg
yellow and egg white. After heating, we obtain a lumping of all the little
colloidal particles, a coagulation. Heating or souring milk likewise causes
a coagulation of the casein. Cooling and even exposing to sunlight may
help jellies to "set"; hence, a change in temperature may cause coagula-
tion of colloids. Blood stains, for example, must first be washed from
clothing with cold water to remove the protein material. Very hot water
on soiled clothes causes the colloidal proteins in the dirt to coagulate,
or "set," and then wash out clean with difficulty.
Courtesy of Western Precipitation Corporation
FIG. 15-6. — A dust precipitator installation looks like this.
The opposite electric charge will neutralize the charge already on a
colloid and cause it to coagulate. F. G. Cottrell applied this fact to stop
the smoke nuisance from smelters and factories. (See Figs. 15-6, 15-7.)
He found that by passing the smoke between highly charged plates the
charged colloidal particles become discharged and collected. By using
the Cottrell method of coagulation of smoke, smelters and factories have
become better neighbors; purer and cleaner chemical products, such as
sulfuric acid and fertilizers, can be made; potash is recovered from the
stack of cement kilns; zinc oxide is recovered from brass foundries; and
precious metals are no longer lost from refineries. Household dust is
reduced by use of small model electric precipitators. In general, wastes
and nuisances have been turned into a source of profit, and our natural
resources have been saved.
Soap when first made sometimes forms a colloidal jelly like mass that
266
CHEMISTRY FOR OUR TIMES
^High Tension Line Carrying
Rectified Current
. Upper
Header
Lower
Header
Oust Laden
Gases Enter
Low Tension
Line from
Switchboard
Discharge Electrode
— -Collecting Electrode.
Suspended Material
Collects on Inside of
Collecting Electrode
and Drops into Hopper
Weight
Hopper
RECTIFIER
TRANSFORMER
PRECIPITATOR
Courtesy of Western Precipitation Corporation
FIG. 15-7. — Cottrell precipitator.
6 Volts, D C
FIG. 15-8. — How a demonstration dust precipitator may be built for the laboratory.
COLLOIDS
267
cannot be sold in cake form. (See Fig. 15-9.) The soapmaker avoids this
condition by "salting out" his soap with a saturated solution of salt. In
so doing he copies a process seen in nature. Clay and mud in a river settle
near its mouth, not only because the river slows up there, but also be-
cause the colloidal-size particles are coagulated by the action of the salt
in the sea water. Witness the enormous deltas the Mississippi and Nile
rivers have built by this process.
Courtesy of Manhattan Soap Company
FIG. 15-9.— The soapmaker's art uses the principles of colloid chemistry. These huge
tanks hold several carloads of soap.
We can tan hides to leather by using common salt, but a more cus-
tomary way is to precipitate the colloidal skin by means of alum or by
tannins S rom the bark of trees. Both are acid substances. Eskimo women
produce the same effect by chewing hides. Latex from a rubber tree is
changed into rubber as we know it by means of dilute acetic acid or by
smoke, which is slightly acid (smoked Par& rubber). When milk sours,
bacteria form lactic acid from milk sugar. The acid changes the colloidal
casein into a curd. What happens to milk in the human stomach, which
contains 0.2 per cent hydrochloric acid? From these examples it can be
seen that adding an acid often coagulates a colloid. Adding a base may
also produce the same result.
Mixing two oppositely charged colloids may produce coagulation of
268
CHEMISTRY FOR OUR TIMES
both. Ferric hydroxide and arsenic sulfide colloids (previously mentioned)
are oppositely charged; put together, both precipitate.
Causing Colloid Particles to Stay Suspended. In a colloid, tiny
particles may absorb electrically charged particles, ions, or another
colloid and thus form an electri-
cally charged shell. The charged
particles serve as a covering, a
protective colloid. For this reason
we add gum to India (drawing)
ink to prevent carbon from set-
tling out, gelatin to ice cream to
prevent the formation of large
crystals, and soap or other deter-
gents to insecticides to make them
spread better. Without the tannins
present in straw the ancient He-
brews had trouble making bricks
for Pharaoh, according to the fifth
chapter of Exodus in the Bible.
Colloidal graphite suspended in
water (Aquadag) is held there by
a protective colloid. Oil may also
be used for the suspending medi-
um. In both cases an excellent lub-
ricant is formed.
Ordinary washing depends up-
on a similar action. Grease holds
dirt to hands and clothes. If nothing held the dirt, we could blow it off and
become clean. Grease and water do not mix, but grease does form a sus-
pension in soapy water. The soap is thought to surround each grease
droplet, acting as a protective colloid. The dirt comes off with the grease.
In general, a colloid will remain as a colloid indefinitely if no condi-
tion exists to cause it to coagulate. Olive oil and water beaten together
do not make a permanent emulsion; but if egg yolk is added to the mix-
ture and it is beaten again, mayonnaise forms and keeps well.
Other Cases of Colloids. Colloids may be droplets or particles.
But in some cases the colloidal size may extend in one or two directions
but not in the other. That is, threads may be colloidal except in length;
sheets may be of colloidal thickness. A web of films or sheets into which
much fruit has been adsorbed is a jelly.
We may notice that a jelly sometimes has drops of liquid on it. The
colloidal membranes of which it is made are under some tension or pull,
Photographed by La Tour
FIG. 15-10. — Colloidal rotary-drilling
mud is flowing into the mud pit at an oil
well. This special type mud, developed by
petroleum engineers and chemists, is
pumped into a drilling well to clear the
cuttings from the drill bit and then is
forced up the outside of the drill pipe to
seal the walls of the hole, to prevent caving,
and to maintain gas pressure.
COLLOIDS 269
apparently, and tend to squeeze out drops of liquid. It is interesting to
observe that unripe fruit contains more of the jelly-forming material,
pectin, than does ripe fruit. For this reason jellies are sometimes made
by using ripe fruit juices and a preparation that " jells7' readily, a pectin
preparation.
High explosives and photographic films also have a spongelike struc-
ture of colloidal webs.
' 'Canned heat," jelly that has adsorbed alcohol, is easily prepared in the
laboratory by adding saturated calcium acetate [Ca (€211302)2] solution to
ordinary (95 per cent) alcohol in the volume proportion of 1 to 9. Silica gel is
readily made by adding dilute hydrochloric acid to diluted commercial water-
glass solution.
Dried silica gel is extensively used as a catalyst and as an adsorbing
agent. Agate, flint, and opal are minerals that are essentially dried silica
gels.
To prevent rusting during shipment or storage, machine parts, guns,
and other equipment are packed in moisture-proof containers, together
with a small porous bag containing silica gel. The silica gel adsorbs
residual moisture from the air in the enclosed space and checks rusting.
SUMMARY
Colloidal dispersions differ from a true solution in the size of the dispersed
particles. Colloids may be classified according to the state of matter of the sus-
pended material, which may be solid, liquid, or gas. Some natural colloids are
available.
Colloidal dispersions may be prepared by precipitation under unusual condi-
tions and by grinding or arcing under water.
The properties of colloids are often due to the size of the particles. Some sus-
pensions are colored. They show the path of a beam of light. They pass through
ordinary filter paper. Colloids have extensive surface and adsorb some substances.
Particles carry an electric charge.
Coagulation of colloids is caused by heat, salt solutions, acid or alkali, electric
precipitation, and mixing with an oppositely charged colloid.
The colloidal condition is maintained by a protective colloid surrounding the
dispersed particles and by the electric charge possessed by each.
Colloidal dimensions are found in films and filaments. Examples are soap
bubbles and spider's silk, respectively.
QUESTIONS
11. If kerosene and water are shaken together, the two liquids separate soon
after the mixture comes to rest. If soap is now added and the experiment repeated,
the separation is delayed. What part does the soap play in the experiment?
12. What is the effect of (a) alum on hides; (6) smoke on rubber latex; (c) lac-
tic acid on fresh milk; (d) tannins from coffee beans or tea leaves on milk?
270 _ CHEMISTRY FOR OUR TIMES _
13. Point out two ways in which the Cottrell process of dust precipitation has
proved its value.
14. Explain how a gas mask protects the wearer. Is the wearer protected from
all poisonous gases or smokes?
15. Hemoglobin in the blood is in the form of a positively charged colloidal
dispersion. How may hemoglobin be precipitated?
16. What purpose is served by the charcoal in some brands of dog-food mix-
tures?
17. Butter churns more readily from sour cream than from sweet cream.
Explain in terms of colloidal chemistry.
18. A cake disturbed while baking in the oven refuses thereafter to "rise."
Explain.
19. Why do jellies form better when made from slightly unripe fruit than
from completely ripened fruit?
20. Tell how to separate a mixture of starch and salt so that both substances
are recovered dry and separated from the other.
21. Investigate and report about the Precipitron.
REVIEW
1. Find the density of methyl chloride vapor (CHsCl) in grams per liter.
2. What is the percentage of sulfur in "hypo" crystals (Na2S203-5H2O)?
3. Write formula equations for (a) action of zinc on lead acetate solution;
(b) burning copper in sulfur vapor; (c) effect of heating mercuric oxide; (d) action
of barium chloride solution on sodium sulfate solution, (e) Name the type of
reaction represented in each case.
4. What is the percentage composition of calcium carbide
6. Explain the hydrolysis of zinc sulfate in solution. Use an equation.
UNIT
FOUR
CHEMISTRY OF THE EARTH'S CRUST
9
MAN'S first important use of sea water as a source' of raw
materials was the extraction of bromine. Although sea
water contains less than 70 parts per million of the element, this
has proved a sufficient supply. Now two plants for extracting
bromine from sea water are in operation.
The sea water, bearing bromine in solution, pounds through an
intake (1) on its way to the settling basin, where powerful pumps
(2) lift 137,000 gal per minute over the dam. The water then flows
4000 ft to a rotary screen (3), where debris is turned aside.
The diagram flow sheet of the process (4) shows the relation-
ship of the operations. Acid and chlorine are added to sea water on
its way to the blowing-out tower, where bromine vapor is liberated
by a countercurrent of air into the absorption tower.
The effluent from the plant (5) presents a challenge. Almost
all the bromine has been removed, but tons of other precious ele-
ments remain in every cubic mile of it.
In the absorption towers the liberated bromine is captured by
passing it into sodium carbonate solution (6). Here a mixture of
sodium bromate and sodium bromide forms in solution.
Once more the bromine is set free. This time sulfuric acid is
added to the bromate-bromide solution to accomplish the liber'
ation. In this building (7), free concentrated bromine is produced.
Later the bromine is collected and made into useful compounds.
Courtesy of Dow Chemical Company
UNIT FOUR CHAPTER XVI
THE EARTH AND ITS ORES
The planet earth, on which we live, is almost a perfect sphere with an
8000-mile diameter. The weight of the earth is known, and its volume can
be estimated quite easily. From these facts we find that the average
density of the earth is 5.5 times that of water. We do not know definitely
of what the earth is made, however, for the pressure and other conditions
deep within the earth are not accurately known.
Explorations show that, the deeper we go into the earth, (1) the higher
the temperature and (2) the greater the pressure exerted by the weight
of material above. The practical use of earth heat and earth pressure is
an unsolved problem.
If we represented the earth as the size of an apple, the skin of the apple
would be too thick to represent to scale the extent that man has explored
the earth, measuring from the deepest boring (about 3 miles) to the
highest stratosphere flight into the air. Yet this thin shell is a remarkable
region. Here exists life. Here are found 92 elements. Here is a region of
ceaseless activity, of chemical and physical changes. Here the great forces
of the air, the sea, the earth, and life act on each other. This is our region.
The changes in it include our chemistry. Here we must use intelligence
to overcome natural obstacles that stand in the way of our gaining food,
clothing, and shelter.
In this unit our purpose is to consider the solid and liquid part of
earth as it affects our welfare. We shall see how minerals are obtained
and put to use. We shall learn how the sea is yielding chemical treasure.
Rocks, Minerals, and Ores. We call almost any hard, dense ma-
terial a rock. Rocks are found abundantly, even in open fields. They
make huge mountains. A very short distance below the soil continuous
bedrock is reached.
Rocks that have definite chemical composition are called minerals.
Granite, composed of a mixture of the minerals feldspar and mica ce-
New Terms
mineral gravity separation flux
rock froth flotation metallurgy
gangue leaching slag
2t3
274 CHEMISTRY FOR OUR TIMES
mented together by mineral silica, is considered a rock, but limestone,
chiefly calcium carbonate (CaC03), and sandstone, chiefly silica (Si02),
are nearly pure minerals.
Minerals from which a useful substance, metal or compound, can be
extracted with profit are called ores. It follows that an improved or
cheapened process for extracting a metal will, in many cases, increase
the supply of available ores.
Photo bit , ,•...,
FIG. 16-1. — Outcroppings of rocks on the surface tell their story to the prospector for
minerals. Petroleum, coal, and metallic minerals are eagerly sought.
If in ages past an arm of the sea became enclosed by land and water
evaporated from it faster than water came in, a salt deposit was formed.
'The Great Salt Lake in Utah is slowly drying up and forming a solid
mass of salt. Such deposits formed in ancient time may be far below the
surface, as are the famous Stassfurt mines in Alsace.
Again, in this country, several dried-up lakes, such as Searles Lake
in Trona, California, yield not/ only salt but borax (Na2B4O7), soda
(Na2CO3), and potassium compounds as well.
When sea water is warmed and evaporated slightly, a deposit of calcium sul-
fate falls out of solution. From this experiment it is a simple matter to see how
deposits of gypsum (CaSO4'2H20) might be formed.
Rocks with Special Uses. Stones for buildings or monuments should
resist the weather well. An observation of the stones in an old cemetery
will show which are durable. Here we find that sandstone (SiO2) slabs
tend to peel off layers as the natural cementing material weathers away.
Limestone, or marble (CaCO3), crumbles and powders away in time,
THE EARTH AND ITS ORES
275
especially if it is near a manufacturing city. Granite (feldspar, mica, and
silica) weathers much more slowly than the other two sorts of rocks.
Large sheets of mica (isinglass) are used as electrical insulators that
withstand heat. Limestone and marble are popular building stones. The
less attractive pieces are used to make lime and to serve as a flux
in furnaces. Powdered limestone is used to "sweeten" acid soils. Gyp-
sum is used to make wallboard,
building blocks, and plaster of
Paris [2(CaSO4)-lH20]. Road
stone is secured from any local
supply of hard rock. Magnesite
(Mff( X)3) and dolomite (MgCO8-
CaCO3) are both used for furnace
linings.
Minerals with Special Uses.
One of the most curious rocks is
asbestos. Although it is a hard
mineral, it can be shredded into
fibers readily. These fibers can be
spun into a thread, and from the
threads cloth can be woven. Such
cloth is fireproof and a good insu-
lator. It finds many uses with
which we are all familiar.
Some minerals have a definite
color and are used for pigments —
coloring matter in paints. Titani-
um dioxide (TiO2) is white, and
iron oxide (Fe20s) is found in a
variety of brown and red shades.
A few minerals are used for cleansing. These have a range from coarse
to fine and from hard to soft. Sand, powdered pumice, powdered mica,
and ground seismotite are all popular scouring minerals in household
and industrial cleansers. (See Fig. 16-3.)
Ores. From a chemical standpoint, the chief useful ores are native
elements, oxides, sulfides, and carbonates. Other ores are silicates, phos-
phates, chlorides, and sulfates.
Native elements, found free or uncombined but mixed with other sub-
stances, include gold, copper, sulfur., and many others in smaller amounts.
Useful oxides include those of iron (hematite, Fe^O3, and magnetite,
Fe304), copper (cuprite, Cu20), tin (cassiterite, SnOt), and aluminum
(bauxite, A1203-2H20).
Courtesy of Corning Class Worlcs
FIG. 16-2. — Borosilieate glass is made
from sand, borax, and other materials. The
first two important ingredients are found
as natural minerals, silica and kernite. The
glassware shown here is passing into an
electric annealing oven.
276
CHEMISTRY FOR OUR TIMES
Many sulfides are useful ores. Copper sulfide (chalcocite, Cii2S, and
chalcopyrite, CuFeS2), lead sulfide (galena, PbS), zinc sulfide (sphalerite,
ZnS), and mercury sulfide (cinnabar, HgS) are important ores of their
respective metals.
Courtesy of Buffalo Museum u/ Science
FIG. 16-3. — Exhibit of useful minerals, from top to bottom shelf:
graphite mica garnet
silver turquoise copper
sphalerite asbestos hematite sulfur galena
halite calcite pyrite
The important ores of iron in addition to hematite and magnetite
are limonite (Fe203'H20) and siderite (FeCO3). Thus we see that some
metals are derived from several ores.
We shall now consider how the ores are " dressed/' or concentrated
for the removal of the valuable metal. We shall also investigate the
chemical and physical principles that are employed in separating the
metals from their ores.
Concentration of Ores. Ores are usually blasted from their location
in rock layers by the use of an explosive. Some of the rock fragments
THE EARTH AND ITS ORES 277
loosened by the blast are useful, and some are worthless. The worthless
rock is called gangue. The problem of the ore dresser now is to separate
ore from gangue, or to concentrate the ore. Concentration may be done
in many ways, depending upon conditions.
Courtesy of Anaconda Copper Mining
FIG. 16-4. — Minerals may be ground in a ball mill. These Hardinge ball mills are used
in the preparation of copper ore for the smelter.
1. Hand Sorting. Hand sorting is expensive, but sometimes it is the
only effective way to pick out good ore. Only the promising-looking
chunks of radium ores are transported by air from the Far North to the
refinery (see page 639). In some mines pieces of slate are removed from
coal by hand. Many other ores pass under the eyes of experienced workers,
who cull out unprofitable chunks of gangue from conveyer belts loaded
with ore.
2. Gravity Separation. Air to be used in an automobile engine may
be cleaned by whirling it. The denser particles of dirt go to the outside,
and the engine draws cleaned air from the center of the air cleaner. If a
mixture of sandlike material is placed on a slightly sloping board that
jigs back and forth, the denser particles tend to go to one side and the
lighter to the other. Other ore-concentration processes use the same
principles of gravity separation illustrated in the examples given.
In addition to such dry methods, the ores may be suspended in moving
water, the densest particles being least buoyed up by the stream. The
278
CHEMISTRY FOR OUR TIMES
classifying machine effectively combines the use of moving water, a slop-
ing trough, and mechanical raking to concentrate large amounts of ore
cheaply. Coal is separated from slate by floating the coal on a dense
calcium chloride solution. The slate sinks.
A sluice in placer gold mining is a simple example of gravity separa-
tion by the wet method. Cleats are firmly nailed across the bottom of
the sloping trough, which is called the sluice. A stream of water is directed
through the sluice and gold-bearing sand shoveled in hopefully. The gold
Crushed Ore
* Slush of Gangue
and Water
Concentrated
Ore
FIG. 16-5. — The slanting table shakes north-south and east-west at the same time,
a double motion, while a stream of crushed ore and water flows onto the upper part
and then over its surface. A separation of light from dense particles is accomplished.
if any, settles against the cleats while the lighter rock particles wash over
them. (See Fig. 16-5.)
3. Surface- tension Separation. Cheap oil and acid are churned
into a froth. When ground sulfide ores are stirred into this suds, the par-
ticles of ore stick to the foam. The gangue sinks. Skimming off the foam
brings about a neat separation of a sulfide ore from useless rock. This
unique method of froth flotation has been developed to apply satisfactorily
to many sorts of ores. New flotation reagents have extended the appli-
cations of this method.
4. Leaching. In order that the useful part of an ore can be made
soluble, crushed rock is sometimes soaked in a solvent to leach out the
valuable mineral. Gold is soluble in sodium cyanide (NaCN) solution in
the presence of air. Leaching rocks that were once tailings from previous
extraction processes has proved profitable when new extraction methods
are applied.
THE EARTH AND ITS ORES 279
Roasting. Many ores must be heated as another distinct step in their
preparation. They are spread out on open trays and put into a furnace,
where they are either burned or heated strongly. Carbonates change to
oxides in this process, and many sulfide ores are roasted (burned) to
remove part or all of their sulfur. This treatment produces an oxide,
which is then readily reduced with carbon. Zinc ores illustrate well the
effect of roasting. If the ore is zinc blende, or sphalerite (ZnS), both ele-
ments in the. compound burn in the supply of hot oxygen (air) available
in a roasting furnace.
22nS + 3O2 -* 2ZnO + 2SO2
The sulfur dioxide may be captured and made into sulfuric acid as
a by-product. The calcined or roasted zinc ore is a brown powder, for
it contains substances other than zinc oxide, which is white when pure.
The impure zinc oxide is now ready to be reduced to the metal.
If the ore is smithsonite (ZnCO3), roasting drives out carbon dioxide.
This sort of action is general for carbonate ores when they are heated.
ZnCO3 -4 ZnO + CO2 T
Fluxing. In roasting an ore, a flux is sometimes used. A flux is almost
always used in the final stop of reducing the ore to the metal.
The word flux means "flows" and refers«to fluid treatment. From
one viewpoint the process is similar to laundering, or washing, the impuri-
ties out of an ore in a furnace at a high temperature. The liquid most
suitable for this purpose is a glass (see page 409). Such a mixture of
silicates flows around the hot rock as a pasty, sticky fluid, acts chemi-
cally on some materials, and gathers in the rest of the gangue. The glass
is not added to the furnace as such ; rather, it is formed in the furnace by
the addition of a flux. Usually the gangue is a mixture of silicate rocks
or silica. Limestone is a suitable flux to remove impurities of this sort.
CaCO3 + SiO2 -> CaSi03 4-CO2|
flux silica or glassy slag
silicates in gangue
The resulting slag is a very dirty glass indeed, not transparent. When
it is cool it is hard, brittle, full of holes due to gas bubbles, and seldom
of much use.
Reduction. After all the preliminary steps of purification are per-
formed, we are ready for the "big show." This step is the actual smelting,
or obtaining the metal from its ore.
If the metal is a very active one, the reduction must be carried on
by electrolysis of molten salts, in the absence of water, or in a few cases
by heating with a more active metal. These processes are expensive, but
are necessary for aluminum, magnesuim, sodium, and a few other metals.
280
CHEMISTRY FOR OUR TIMES
Examples are
2NaOH -> 2Na + O2| 4- H
fused at cathode
2AI + Cr2O3 ->• 2Cr -f AI2O3
(electrolysis)
(replacement)
Usually coke, coal, or carbon monoxide are used as the reducing
agents. The oxide is heated strongly, with carbon present in excess. A
transfer of oxygen takes place, freeing the metal in its elementary state.
For example,
ZnO + C
Zn -f
CO
In general,
Metal oxide -j" carbon — » free metal + carbon monoxide
Zn°
Refining. If the metal as prepared is not pure enough for some of its
commercial uses, it must be refined. Zinc (b.p. 907°C) and mercury (b.p.
356. 9°C) are refined by simply heating them and condensing the vapors.
Copper, zinc, and several other metals are refined by electrolysis (see
page 247). The impure metal is
made the anode in an electrolytic
cell, and the pure metal plates out
on the cathode.
Example of Ore Treatment.
Let us assume that a large deposit
of a sulfide ore has been discovered
by a prospector. It is located close
enough to a road and a railroad to
make its mining an attractive
venture.
A sample of the ore is sent to
the assayer's laboratory, and the
report received shows that it con-
tains 15 per cent of the valuable
mineral compound of which 10 per
cent, or two-thirds, is the metallic
part. By concentration of the ore
at the mine, enough material is re-
jected to bring the concentration up to 48 per cent ore, or 32 per cent
metal. The ore is shipped and treated at the smelter. Roasting changes
sulfides to oxides and consequently reduces the formula weight 16 units
(S = 32; 0 = 16; 32 - 16 = 16). The ore now weighs less and has in-
creased slightly in percentage purity, but no gangue (unless volatile) is
removed by roasting alone.
It is advisable to remove gangue at this stage if the temperature of
Courtesy of American Iron and Steel Institute
FIG. 16-6. — A highly polished small
section of steel is being examined at high
magnification. The metallurgist gains
much information concerning the quality
of steel by this method.
THE EARTH AND ITS ORES 2811
roasting is hot enough to melt a flux. Let us assume in this case that a
flux was added and that a slag was formed.
Flux + gangue — > slag
Many of the impurities are taken into the slag. Therefore, the mate-
rial ready for the final reduction is 75 per cent metallic oxide or 50 per
cent available metal.
The oxide is now reduced by mixing it with the cheapest form of
carbon available for the purpose and heating. Again a slag is used to
gather in the impurities. The reducing furnace produces two streams of
fluids, one the molten metal, the other the slag floating on top of the
metal.
The metal is now 95 per cent pure. The remaining 5 per cent consists
of other metals that were chiefly present in the original ore, carbon, or
slag inclusions. In most cases the metal is refined by heat or electricity.
A metal of purity 99.5 per cent or better results. All figures given in this
example are not actual but are included to help visualize the effect of
each treatment of an ore.
Metallurgy. The study of extracting a metal from its ore is a part
of metallurgy. Metallurgy includes another equally important part,
namely, the relationship of metals, their treatment and composition, to
their properties.
IMPORTANT SOURCES OF METAL ORES
Aluminum United States, Germany, Russia
Antimony China, Mexico
Beryllium Germany, France, United States
Bismuth Peru, Bolivia, Mexico, Canada
Cadmium United States, Mexico, Canada
Calcium Germany, United States, Sweden
Chromium Russia, Rhodesia, Turkey
Cobalt Belgian Congo, Canada
Copper United States, Chile, Africa
Gold Transvaal, Russia, United States, Canada
Iron United States, Germany, Russia
Lead United States, Mexico, Australia, Canada
Magnesium Germany, United States, France
Manganese Russia, Africa, India
Mercury Spain, Italy, United States
Molybdenum United States
Nickel Canada, New Caledonia
Platinum mclala Russia, Canada, Colombia
Silver Mexico, United States, Peru
Tin Malaya, Bolivia
Tungsten Burma, China, Malaya
Vanadium Peru, Africa, United States
Zinc United States, Belgium, Canada, Germany
282
CHEMISTRY FOR OUR TIMES
Cast Iron
4.0 % Carbon
Cast Iron
3.0 % Carbon
Cast Iron
25 % Carbon
Steel
1.5 % Carbon
Steel
1.20 % Carbon
Steel
0.90 % Carbon
Steel
0.50 % Carbon
Steel
0.20 % Carbon
Courtesy of General .V ' ' a/ton
FIG. 16-7.— A series of photomicrographs shows the effect of the percentage of carbon
on the grain structure of steel and iron.
THE EARTH AND ITS ORES 283
Metallurgists carry out tests for tensile strength, hardness, elasticity,
and other properties of metals. They also examine the microstructure of
metals. A carefully polished sample of metal or alloy is etched with acid
and viewed under the microscope. From a study of the size and arrange-
ment of the crystals a real insight is gained into the cause of its strength
or weakness. A photomicrograph such as is used by a metallurgist is
shown here. (See Fig. 16-7.)
SUMMARY
Rocks are solid, stony matter of the earth; they are usually mixtures of min-
erals. Minerals are substances of definite chemical composition found in the earth.
A mineral from which a metal may be extracted with profit is called an ore.
Most ores consist of native elements, oxides, sulfides, or carbonates. Ore
dressing, or concentration of ore from gangue, is accomplished by hand sorting;
gravity methods of separation, wet or dry; froth flotation; and leaching.
In the preparation of a metal from an ore, active metals are prepared by
electrolysis of fused salts or by replacement by a more active metal. Sulfide or
carbonate ores are roasted, forming oxides. Fluxing may be used with this process
as well as with the reduction process. In general, a flux plus gangue forms a slag.
Reduction with hot carbon is the most common method of smelting metals
of moderate activity. Some metals are refined by electrolysis or by distillation.
Metallurgy studies the obtaining of the metals from their ores, the properties
of the metals, and their alloys. In this branch of applied science photomicrographs
of etched metals are used extensively.
QUESTIONS
1. Define stone; rock; mineral; ore.
2. Which of the above four terms may be used in describing anthracite coal?
3. Some memorials consist of a bronze tablet bolted to a quartz boulder.
How lasting is such a memorial, provided that it is not disturbed?
4. What minerals are used for (a) insulating steam pipes; (b) insulating
electrical wires; (c) coloring cosmetics; (d) coloring house paint; (e) making
plaster of Paris; (/) making lime; (g) lining furnaces; (h) sweetening sour soil; (i)
making scouring powder; (j) adsorbing colors from liquids?
6. In what forms are most of our useful ores found in nature?
6. Define concentration; gangue; flux; slag.
7. What is accomplished by roasting (a) a sulfide ore; (6) a carbonate ore?
Illustrate each process with an equation.
8. What flux should be used for an ore that contains limestone as a gangue?
9. What useful substance does slag resemble in its chemical composition?
10. Each of the following equations represents the preparation of a metal by
the reduction of its oxide with powdered aluminum. Balance each of the follow-
ing (do not write in this book):
584 CHEMISTRY FOR OUR TIMES
Fe8O4 + Al -f AI2O8 + Fe
Fe2O8 + Al -> AI2O8 + Fe
Mn8O4 -h Al -4 AI2O8 -f Mn
Cr2O8 + Al -» AI2O8 4- Cr
WO8 -f Al -4 AI2O8 + W
11. Complete and balance the following equations (do not write in this book):
B2O3 + Al ->
Co8O4 4- Al -f
12. Which ore contains the higher percentage of iron, Fe2O3 or FeaO4?
13. As between zinc carbonate, 85 per cent gangue, and zinc oxide, 90 per
cent gangue. which ore is richer in zinc?
14. Find the percentage of titanium in TiG2.
15. Trace the flow of electrons from the electric generator through a cell in
which molten magnesium chloride is being electrolyzed; a cast-steel pot serves
as the cathode, and graphite bars serve as anodes.
UNIT FOUR CHAPTER XVII
THE EARTH AND ITS SOIL
The earth under our feet consists of sand, clay, decayed organic
matter (called humus), more or less moisture, and living organisms. The
first two items are formed by the weathering of rocks. Chemically, sand
is silica (Si02), and clay is a complex aluminum silicate with more or less
water. Clay is formed by the weathering of feldspar.
2KAISi8O8 + 2H2O + CO2 -+ H4AI2Si2O9 + 4SiO2 + K2CO8
feldspar clay
Clay adsorbs many other substances, notably water and iron oxide.
Mixed throughout are the oxidized fragments of former plant and animal
life, or humus.
Living plants, seeds, roots, bacteria, spores, insects, worms, and other
creatures are found in the soil.
Soil Horizons. Layers, or horizons, of the soil, designated A, J5, and
C from the top downward, make up the soil profile. The A horizon is the
upper, or surface, soil, where life is most abundant and organic matter
is plentiful. This is the region commonly plowed. The B horizon has a
deeper color than the A, and a heavier texture in humid regions. It might
be called " reserve " soil, but ordinarily it is too low in organic matter to
be used successfully for crops without treatment. The C horizon consists
of weathered, unconsolidated material below the B horizon. It is called
the parent material.
The structure of the horizons determines the ease with which the
roots of plants can penetrate the soil. A granular or crumblike structure is
the most favorable for the growth of crops.
Movement of soil water is influenced by gravity, evaporation, and
capillary action (rise of water in small tubes or pores). In regions of high
rainfall, minerals are carried downward from the A horizon. In dry
regions where subsurface water rises in the soil, dissolved minerals are
carried upward by capillary action and deposited in the A horizon when
the water evaporates.
New Terms
caliche hydroponics fertility
sour soil soil horizons nodules
285
286
CHEMISTRY FOR OUR TIMES
Our Use of the Soil. Almost all our food comes from the soil, directly
or indirectly. No more striking evidence of the importance of the soil
could be given.
The productivity of the soil is so important that in former years
people estimated the limit of population of a country on the basis of the
ability of the soil to produce crops. In arriving at their figure they failed
to foresee two important develop-
ments. These are (1) modern agri-
cultural machinery and (2)
chemical fertilizers.
In former years it was neces-
sary to allow land to lie fallow or
idle every second or third year
in order to restore its fertility. It
is no longer necessary to do this,
for chemical fertilizers can be
added to the soil. In fact, it is
possible in very sunny regions to
produce more than one crop per
year of quick-growing produce.
Today a man with a tractor can
plow or cultivate many times the
acres that a man with a horse
could till a generation ago.
Plant Food. Plants take car-
bon dioxide from the air through
their leaves and stems. Moisture
with some mineral matter is
brought up from the ground
through the roots. The carbon di-
oxide and the water combine to
make starch in the presence of
Courtesy of U.S. Forest Service
FIG. 17-1. — Every tree is a chemical
factory with a complicated plumbing
system. Not only do trees manufacture
wood fibers and lignin, but some trees also
produce valuable gums and resins. This
mixed stand of short leaf and loblolly pine
in Arkansas is about 50 years old. The
wood will be used for making paper.
sunshine. This change is brought
about by chlorophyll, the green coloring matter in leaves, and the process
is called photosynthesis.
6CO2 + 5H2O -» (CeHioOs)* + 6O2
starch
This is the most important of all chemical reactions.
Plants in sunlight remove carbon dioxide from the air, supplying
oxygen to the air and building organic matter. We should notice that
this process is essentially the opposite of burning, decay, or oxidation.
It is a reduction process, taking in light energy, and by this means
energy is stored.
THE EARTH AND ITS SOIL
287
The process of photosynthesis, however, is not as simple as the equa-
tion above would indicate. Obviously, plants are not all starch; they
must build other tissues in order to carry out the whole of their life cycle.
Plants need an abundant supply of compounds of nitrogen, for they
build proteins into their tissues. Proteins are complex compounds con-
taining carbon, hydrogen, oxygen, and nitrogen and sometimes sulfur,
phosphorus, and other elements.
Plants must take the nitrogen compounds for building proteins in
through their roots. These compounds of nitrogen, soluble nitrates and
Nitrogen
in Plant
Proteins
Free
Nitrogen
in Air
iz
1
Q
•z.
Nitrogenous
Compounds
in Soil
FIG. 17-2. — The nitrogen cycle in nature. Notice the missing link.
ammonium compounds, must*be present in the soil. Nitrites apparently
are poisonous to more complex plants, but fortunately bacteria change
soil nitrites into nitrates quite promptly. (See Fig. 17-2.)
Important minerals that are easily exhausted from the soil are potas-
sium compounds, phosphates, and sulfates, especially the phosphate and
sulfate of calcium.
The three primary plant needs are compounds of nitrogen, potassium,
and phosphorus. The chief secondary needs are compounds of calcium,
sulfur, and magnesium. Other elements that may -be needed include
boron, copper, manganese, zinc, and iron in trace amounts. In some regions,
plants sometimes cannot obtain enough of one or more of the common
elements from the soil. It is known, for example, that chlorophyll con-
tains magnesium and that without magnesium *a plant cannot grow
normally, Iron is usually abundant in soils, and certain plants, spinach,
288
CHEMISTRY FOR OUR TIMES
for example, require iron. When any of these elements is completely
lacking, plants develop abnormalities or even wither and die.
When a crop grows, these essential elements are removed to some
extent from the soil. Unless they are resupplied or an adequate amount
remains in the earth, the soil becomes worthless for crops the following
year. Some idea of the amount of material taken from the soil can be
gained from the fact that the average variety of sugar cane removes
824 Ib of potash, 235 Ib of lime, and 124 Ib of phosphoric acid per acre
for the parts of the plant above the earth.
Nature's Fertilization Program. Certain plants of the legume
family — including peas, beans, alfalfa, clover, vetch, and peanuts — are
Courtesy of Bureau of Plant Indu.ff i >/, Soil*, ami Agricultural Enuinr.enng, U.S. Department of Agriculture
FIG. 17-3. — The nodules on clover roots resemble little potatoes. They contain
bacteria that can take free nitrogen gas from the air and form compounds of nitrogen
useful for fertilizer. Mankind has not yet found a way to carry on this change at a low
temperature.
host to species of bacteria that live attached to their roots. These bacteria
have the remarkable ability to take free, elementary nitrogen from the
air and make it into nitrates. This chemical change is notable because no
chemical laboratory can duplicate it at the low temperature used by the
bacteria. The nitrates produced by the bacteria are left with the plant
in small pockets on the roots, resembling miniature potatoes. These
THE EARTH AND ITS SOIL 889
nodules (see Fig. 17-3) are scattered throughout the soil when the plant
is plowed under or decays, enriching the soil. Nitrogen-producing crops
that are grown to be plowed under are called green manure. The nitrates
in the nodules can furnish fertilizer to the host plants as well as to follow-
ing crops. In return for the nitrates, the bacteria take some starch and
mineral matter from the host plants. The good effect of planting legumes
was noticed by early Roman farmers, but the real cause of the benefit
was not discovered until 1886- Anyone who takes the trouble to dig up
a clover plant carefully can see the nodules on the roots.
QUESTIONS
1. What is the general composition of soil?
2. From what source does the soil obtain (a) sand; (6) clay; (c) humus?
3. What horizon of the soil "profile" is commonly reached in plowing?
4. Do all soils have all three horizons well developed and in distinct layers?
6. Name five useful substances, other than chlorophyll, that plants (includ-
ing trees) produce.
6. Define photosynthesis.
7. Certain plants, for example mushrooms, have no green coloring matter
in them. Do they produce starch? Do they carry on photosynthesis?
8. Give three examples of important bacterial actions within the soil.
9. List the three primary mineral requirements of most plants.
10. Of what value is a cover crop of clover, sown in the fall and plowed under
in the spring?
Lightning. Nitrogen is also carried into the soil in the form of ni-
trates as a result of thundershowers. The U.S. Weather Bureau estimates
a yearly average of 12 Ib of fixed nitrogen per acre from lightning, or
770 million tons for the entire earth. In the lightning flash some of the
energy of the electric discharge causes oxygen and nitrogen to unite.
N2 + O* -4 2NO
2ND + 02 -4 2NO,
3NO2 + H2O -4 2HNO3 + NO
The nitric oxide formed is oxidized easily to nitrogen dioxide, dis-
solved in the rain, and carried to the earth in the form of a bath of dilute
nitric acid. Limestone or other basic substances in the soil act quickly,
on the nitric acid to convert it into calcium nitrate, a readily soluble
plant food.
CaCO, + 2HNO. -4 Ca(NO,)s + H,O + CO,T
limestone nitric aoid calcium
nitrate
290 CHEMISTRY FOR OUR TIMES
Physical Condition of the Soil. Several facts about a good soil are
evident on close observation. (1) The soil particles should be of the right
size. If they are too large, they permit moisture to leave too rapidly. If
they are too fine, they may pack and form a rocklike layer into which
roots can hardly penetrate. (2) The soil should contain the right amount
of moisture. Dry regions must be irrigated and swampy soils drained.
(3) The moisture in the soil should be well distributed over the growing
season. Most crops require about 20 in. of rainfall per year or an equiva-
lent amount of water from irrigation. (4) A soil too sandy will not keep
moisture or grow most crops well. A soil too rich in clay is hard to culti-
vate, slimy in wet weather, and hard-baked in dry. A soil rich in loam is
inclined to become acid, a condition unfavorable to some crops. Obvi-
ously, a proper mixture of sand, clay, and humus is desirable. The most
desirable set of conditions depends, of course, upon the crop to be raised.
Good soil should contain enough clay to make it jellylike when moist.
In such a condition the soluble plant food will not wash away readily
in the rainfall. Moreover, the soil should contain enough organic matter to
retain moisture in the soil where the plants can obtain it. The moisture-
retaining property is one of the most valuable qualities of barnyard
fertilizers and peat moss.
Sources of Nitrogen Compounds. In addition to those nitrogen
compounds which nature supplies, our principal sources of nitrogen in-
clude the following :
1. Chile Saltpeter (NaNO3). This compound is imported from
Chile, where it is found as a rocky deposit called caliche. The crude mate-
rial is refined to 95 to 98 per cent purity by crystallization. It is equivalent
to 15.6 to 16 per cent of nitrogen, readily soluble in water, and is used
to force the growing of crops.
Synthetic sodium nitrate, or saltpeter, is now available. It is formed
by running nitric acid onto soda ash.
2HNO3 + Na2CO3 -4 2NaNO3 + H2O + CO2|
2. Ammonium Salts. Ammonia, a by-product of the destructive
distillation of soft coal (see page 386), is run into acid. The resulting
compound, depending upon the acid used, may be ammonium sulfate
[(NH4)2S04], ammonium chloride (NH4C1), ammonium nitrate (NH4NO3),
ammonium dihydrogen phosphate (NH4H2PO4), or diammonium hydro-
gen phosphate [(NH4)2HPO4]. The equation for the reaction in the last
case is
2NH8 + H8PO4 -> (NH4)2HPO4
Today, great supplies of ammonium compounds are manufactured by
synthetic processes.
THE EARTH AND ITS SOIL 2911
3. Calcium Cyanamide (CaCN2). This compound is made by pass-
ing nitrogen over calcium carbide heated in an electric furnace (see page
252). It may be used directly as a fertilizer in limited amounts.
CaC2 + N2 -» CaCN2 + C
4. Urea [CO(NH2)2]« This compound is found in the urine of mammals
and undoubtedly accounts for some of the fertilizing value of barnyard
manures. Today, urea is produced synthetically in large quantities. It is
soluble in water, and the commercial product contains about 46 per cent
nitrogen. A small amount of synthetic urea is added to stock food.
5. Organic Nitrogen- containing Materials. (The figures in paren-
theses are the percentages of available nitrogen.) These include the meal
from cottonseed, linseed, and castor beans after the oil has been extracted ;
scraps and tankage of many sorts including dried blood (12), fish scrap
(8), garbage tankage (3), sewage sludge (2.5), and slaughterhouse tankage
(10).
Fertilizer containing ammonium compounds should not be added to
freshly limed soil since a reaction may take place that will result in a loss
of nitrogen.
(NH4)>SO4 + Ca(OH), -> CaSO4 + 2H2O + 2NH3t
Sources of Phosphates for Fertilizers. The chief source of phos-
phates is from natural rock phosphate, crude calcium phosphate
[Ca3(P()4)2]. This is treated to make phosphoric acid (H3PO4) (see page
368), or " superphosphate, " although sometimes it is finely ground and
applied to the soil without treatment.
7. Superphosphate. Ground rock phosphate is treated with about
an equal weight of dilute sulfuric acid. The resulting mixture is composed
of a calcium dihydrogen phosphate and calcium sulfate dihydrate. Both
compounds are more soluble than calcium phosphate, but only moder-
ately soluble, a desirable condition.
Ca3(PO4)2 4- 2H2SO4 + 5H2O -4 Ca(H,PO4)2-H2O + 2CaSO4-2H2O
tncalcium phosphate calcium dihydrogen phosphate -f- gypsum
"superphosphate" of lime
Triple superphosphate, which contains 40 to 48 per cent available
P206 against 16 to 20 per cent for the ordinary superphosphate, is made
by using phosphoric acid instead of sulfuric acid. Calcium dihydrogen
phosphate soon becomes converted to insoluble tricalcium phosphate in
alkaline soil, making it unavailable to plants. This difficulty is overcome
by applying it in rows parallel to the crops, where it does not become
so thoroughly mixed with the alkaline soil.
2. Bones. Bones may be ground and used directly as a fertilizer. Their
action is slow but lasting. They contain 20 to 25 per cent available
292
CHEMISTRY FOR OUR TIMES
P2O5 and also about 3.5 per cent nitrogen. Their action may be hastened
by treatment with sulfuric acid. In this case they become similar to
superphosphate.
3. Slag. This waste product from the making of steel contains phos-
phorus, an undesired impurity in the steel. Experiments show that ground
Courtesy of Oliver United FilLrs, Inc.
FIG. 17-4. — This continuous vacuum filter is handling potash at Trona, California.
Potash is used extensively in fertilizers. The operating principle of such a filter is rela-
tively simple. Can you explain it?
slag has beneficial effects on certain types of soil. This slag is a mixture
of tricalcium phosphate and calcium silicate.
Sources of Potassium Compounds for Fertilizers. 1. Mineral
Deposits. The famous Stassfurt deposits of kainite (MgS04-MgCl2-
K2S04-6H2O) and carnallite (KCl'MgCl2'6H2O) furnish enormous quan-
tities of potash salts. Other European deposits also provide large amounts
of potash. Deposits of potash minerals in the United States are found
at Searles Lake in California (see Fig. 17-4) and in the Permian bed,
which lies beneath portions of Texas and New Mexico.
2. Miscellaneous Sources. Flue dust, from cement kilns or blast
furnaces, and wood ashes are rich in potash. These are saved and used
for fertilizer. Wastes from sugar beet and molasses contain usable potash,
as do seaweeds and tobacco by-products. By using all the miscellaneous
_ THE EARTH AND ITS SOIL _ 293
sources and exploiting the natural resources within the country, the
supply within the United States has been found adequate to meet the
demand without depending upon European potash.
For the Land's Sake. Analyzed mixed fertilizers with certain per-
centages of plant food are available. Three figures, such as 4-16-4, are
plainly shown to the purchaser. In most states the first figure means the
percentage of available nitrogen calculated as N, the second the per-
centage of phosphorus calculated as P205, and the third the percentage
of potash calculated as K2O. Many states require that commercial
fertilizer mixtures contain a certain minimum figure for total plant food,
such as 16, 14, or 12.
The correct fertilizer for a farm depends upon (1) the crop to be
grown, (2) the plant food already available in the soil, (3) the degree
, Sample ^ ,
f Surf ace
FIG. 17-5. — A proper method of sampling soil. A soil sample should not be taken from
the surface only.
of acidity (pH) of the soil, (4) the moisture content of the soil, and (5)
the state of maturity of the crop.
While the higher analysis mixed fertilizers cost more per ton, the
increased percentage of available plant food often makes them really
less expensive in the long run. In fact, usually fertilizers that contain less
than 16 per cent total plant food, such as 3-8-3, are not economical,
although they are very easily spread.
Soils should be analyzed to determine their fertility. Farmers are
finding that a yearly analysis of the soil, not only for nitrogen, phos-
phorus, and potash, but also for trace elements, leads to better yields and
better quality crops. Experiment stations in many state universities and
elsewhere will analyze samples of soil submitted to them. The instructor
may obtain a pamphlet1 that summarizes the methods used, so that the
student can analyze soils himself. Soil-testing kits are available from
farm-supply companies.
Sour Soil. When plants and rocks decay, the remains in the soil are
acid. Unless the soil contains an abundance of carbonates, such as lime-
stone (CaCOs) or dolomite (CaCOs-MgCOs), in finely divided condition,
1 MORGAN, M. F., Chemical Soil Analysis by the Universal Soil Testing System,
Bulletin 460 (October, 1941), Connecticut Agricultural Experiment Station, New
Haven, Conn.
294 CHEMISTRY FOR OUR TIMES
the acid will remain. Most plants do not grow well unless the soil is
neutral or slightly alkaline.
The cheapest and most effective way to sweeten sour soil is to "lime"
it. Slaked lime [Ca(OH)2] or quarry dust from marble or limestone
(CaC03) deposits is an effective neutralizer of soil acids. In addition,
lime improves the physical condition of the soil and makes plant foods
generally more available. When the soil is too alkaline, ammonium sulfate
;<x.v "/ ('-iirrpillar Tractor Company
FIG. 17-6. — Contour farming on a slope saves soil. Tins is a wide-gauge diesel-engine-
powered tractor pulling a combine near Walla Walla, Washington.
[(NH4)2SO4] is spread over it to neutralize the excess lime and to add
nitrogen.
Hydroponics. Many experiments have recently been carried out on
the growing of plants without soil. The seeds are planted in a tank con-
taining a solution of mineral salts, adjusted to the ideal condition for
the growth of a plant. The plant stalk and roots are supported by wires
and excelsior. The results show that extra-large vegetables and fruit can
be produced whjen a plant is grown under these ideal conditions. For
many, hydroponics has become an interesting hobby as well as a business.
Growing plants without soil, however, only emphasizes the importance
of good soil.
Keeping the Soil. With modern farm machinery many more acres
can be plowed and harrowed than was possible by the use of horse-drawn
THE EARTH AND ITS SOIL 295
implements. Using chemical fertilizers and rotating crops instead of
waiting for soils to revive after use have decreased the amount of idle
land on a farm. The net result is that more acres per farmer are cultivated
than formerly. Many acres lie open, prepared for a crop or awaiting a
growing crop. Such land has very few binding roots to hold the soil in
place. When strong winds or rain comes, this soil is easily moved, resulting
in a loss to the farmer.
Soil has always been movable and is constantly on the move. New
soil is constantly being formed. Under some conditions at present, how-
ever, the rate of loss far exceeds the rate of recovery of the soil. Intel-
ligence must be used to conserve the valuable part of a farm, the soil.
(See Fig. 17-6.)
SUMMARY
Soil consists of sand, clay, humus, and moisture. Humus comes from decayed
organic matter. Clay and sand come from weathered rocks.
Soil may be classified in layers or horizons. The A horizon represents topsoil,
rich in humus. The B horizon represents reserve soil, lacking humus. The C ho-
rizon represents parent material.
Plant food consists of minerals and moisture from soil and carbon dioxide
from the air. Compound building by plants is a reduction process, the opposite of
the oxidation processes carried on by most of man's, activities; it is accomplished
by chlorophyll in the presence of sunlight. Nitrogen, potassium, and phosphorus
compounds are most readily exhausted from the soil by plant growth. Many other
elements are essential to plant growth.
Natural fertilization is supplied in three ways:
1. Legumes supply nitrates through bacterial action.
2. Lightning storms add nitrates.
3. Soil water may bring minerals up from lower depths or from adjacent lands.
For continued farming, minerals must be supplied by fertilizer.
Important aspects of the physical condition of the soil are
1. Size of soil particles
2. Amount of moisture and its distribution throughout the growing season
3. Acid or alkaline conditions of the soil
4. Amount and distribution of humus •
Sources of nitrogen for fertilizing soils include nitrogen compounds obtained
from Chile saltpeter, nitrates from fixation of atmospheric nitrogen, ammonium
compounds, calcium cyanamide, urea, manures, and refuse material.
Sources of phosphates for fertilizing include rock phosphate, or superphos-
phate; bones; and some slags.
Sources of potash for fertilizing include mineral potash deposits in ancient
lake beds, ashes, and wastes.
Fertilizers are rated by a three-number system: The first number is the per-
centage of available nitrogen. The second number is the percentage of phosphorus,
calculated as p20s. The third number is the percentage of potassium, calculated
as K20.
296 CHEMISTRY FOR OUR TIMES
Alkaline soils can be treated with decayed vegetation or ammonium sulfate
if more acidity is required. Sour soils may be treated with limestone,*dolomite, or
hydrated lime.
Erosion is an important soil problem. Successful farming uses methods of
binding the soil to the farm to prevent loss of topsoil by wind and rain erosion.
QUESTIONS
11. Tropical vegetation grows in lush abundance in regions of many thunder-
storms. Give three conditions that favor plant growth in these regions.
12. Would adding carbon dioxide to the air in a greenhouse be of value?
13. What treatment is recommended for changing the following into good
farming land: a desert; a swamp; sour soil; hard-packed clay; a boulder-strewn
field; land covered with stumps of trees?
14. During World War II a certain brand of fertilizer changed from 6-8-6
rating to 2-8-6. Account for the change.
16. For what purpose would (a) sodium nitrate be more desirable to use on
crops than organic nitrogen compounds; (6) organic nitrogen compounds rather
than sodium nitrate?
16. List the sources of synthetic nitrogen compounds.
17. Compare the availability to plants of the mineral matter in (1) dog-
buried bones, (2) bone meal, (3) bone meal treated with sulfuric acid.
18. Is mineral fertilizer alone, used year after year, sufficient to grow success-
ful crops, or is the addition of barnyard manure desirable?
19. Point out an advantage of ground dolomite over ground limestone for
sweetening the soil.
20. Hillsides are sometimes cultivated in strips, by leaving grasslands between
cultivated areas and plowing along contour lines. Point out the advantages of
this practice.
21. What is the percentage of nitrogen in (a) sodium nitrate; (6) urea; (c)
calcium nitrate?
22. Wnat is the percentage of phosphorus in tricaicium phosphate? In "super-
phosphate"?
23. What is the percentage of PzO* available from calcium phosphate?
24. What is the percentage of K20 in potash (K2C08)?
25. Account for the odor of ammonia near a manure pile. Tell why such a
condition should be avoided.
26. What is " compost " ? State one advantage and one disadvantage in adding
compost to soil.
27. Has kitchen garbage any value as fertilizer?
UNITFOUR CHAPTER XVIII
CHEMISTRY OF THE SEA—
THE HALOGEN SALTS
The general conditions of life in the sea are not vastly different from those
on land; plants must live and grow by the process of photosynthesis, absorbing
at the same time nutrient substances, such as phosphate and nitrate, from their
surroundings; the smaller animals "graze" upon the plants and are in turn
consumed by the larger animals. And when they finally die, large and small,
all decay and are decomposed by the ever-present bacteria, and their substance
is thrown back into solution again in the form of carbon dioxide, nitrate, phos-
phate, and the like. One of the chemist's principal contributions has been the
study of this cycle, particularly the role played by nitrate and phosphate in
the fertility of the sea. For different parts of the sea are as vastly different as
are different parts of the land. The sea has its barren deserts, where little life goes
on, as well as its areas of abundant growth.
A nitrogen cycle exists in the sea as on land. The ammonia resulting from
protein decay is oxidized successively to nitrite and nitrate, and it is likely
that under certain conditions this process may also be reversed. These changes
are brought about by means of bacteria similar to, if not identical with, those
which bring about the same changes on land. These organisms inhabit the
water, but apparently occur in very much larger numbers in the bottom mud
of shallow seas, where most of this oxidation probably takes place. The condi-
tions of the deep-sea bottom are largely known. Although nitrogen-fixing bac-
teria, capable of utilizing atmospheric nitrogen, have been isolated from the
sea, it is rather unlikely that they play an important part in the marine nitrogen
cycle.1
Composition of the Sea. The most impressive fact about the sea is
its tremendous extent. We all know that the sea covers 70.73 per cent of
the earth's surface and that most of the uninhabited portion of this globe
lies under water. Only recently have chemists made the sea a source of
raw materials.
New Terms
halogens chlorine iodine
fluorine bromine sublime
1 RAKESTRAW, NORBIS W., "The Chemistry of Sea Water," Report, New England
Association of Chemistry Teachers, vol. 35, No, 1, 1933.
897
298 CHEMISTRY FOR OUR TIMES
One liter of sea water weighs about 1030 g. A liter of pure water
weighs 1000 g. We say that the specific gravity of sea water is 1.03.
Water makes up about 993.7 g of the 1030 g, or 96.4 per cent of the
weight of sea water. Ordinary salt (NaCl) accounts for 27.87 g, or 2.79
per cent. Other constituents are magnesium chloride (MgCl2) 3.78 g;
Epsom salts (MgSOO 2.37 g; calcium sulfate (CaS04) 1. 45 g; potassium
chloride (KC1) 0.79 g; calcium carbonate (CaC03) 0.03 g; and magnesium
bromide (MgBr2) 0.03 g.
Let us take 1 cubic mile of sea water out of the 331 million cubic miles of
whole ocean. This 1 cubic mile will contain 128 million tons of sodium chloride
(NaCl), 18 million tons of magnesium chloride (MgCl2), 358,000 tons of magne-
sium bromide (MgBr2), 1400 tons of fluorine, and so on, in solution. The
deposits of the bottom contain the insoluble excesses as precipitates, probably
in quantity even greater than that which is dissolved and in solution.1
In the sea water these salts are dissolved and are of course present
only in the form of ions rather than being associated into definite com-
pounds. They are given as compounds to show the relative amounts. As
such, the principal metal ions in the sea are sodium (Na+), magnesium
(Mg4^), calcium (Ca++), and potassium (K+). The chief nonmetal ions
are chloride (Cl~), sulfate (SO"), and bromide (Br~).
Gold from the Sea. The total amount of gold in the sea is more than
has ever been mined on land. This fact comes as a result of simple arith-
metic. A tiny trace multiplied enough times will give an amazingly large
figure.
Many attempts have been organized to extract gold from sea water,
and many clever chemical methods have been proposed to accomplish
this. Some of these proposals are the result of overenthusiasm or possibly
fraud, as we shall see presently.
After Fritz Haber of Germany had worked so hard and with so great
a measure of success during World War I to solve his country's nitrogen-
fixation problem (see page 387), with the coming of peace he turned his
attention to a possible solution of her economic troubles — the securing
of gold from sea or river water. With remarkable diligence he perfected
a method of analysis for gold in sea water that was reliable to an extent
never before approached. The results of his analysis were most disappoint-
ing to his hopes, however. He found, a result recently confirmed by
William E. Caldwell of Oregon State College, that the value of the gold
in a metric ton of sea water was about one one-hundredth of a cent
($0.0001).
It now becomes evident that, if gold is to be obtained from sea water,
1 TAYLOR, HARDEN F., " Chemical Resources of the Ocean," The Chemist, vol. 19,
No. 4, 1942.
CHEMISTRY OF THE SEA
299
most of it will be obtained by the sale of other substances obtained from
the sea. Small samples of gold, however, have been prepared from sea
water. Their cost at present far exceeds their value as metal.
Sea Salt. The salt we use today is either from the sea directly or from
arms of the sea that have long since dried up, leaving the dissolved salt
as crystals. Enormous deposits of such salt beds are known, one of them
under the city of Detroit, Michigan. Vast quantities of salt are found in
the United States in New York, California, Kansas, Utah, and Louisiana.
Courtesy of Oliver United Filters, Inc.
FIG. 18-1. — Salt from an ancient sea is mined and filtered in Ohio. The picture shows
rotary niters in operation.
Mines that have been worked for hundreds of years are famous in con-
tinental Europe. While salt deposits only 8 ft thick are worked in some
places, a Texas salt dome is known to be 3000 ft thick. The Stassfurt salt
deposit that underlies the potash deposit is several thousand feet deep.
Some of the salt is harvested as solid mineral from ancient deposits
as high as 99.4 per cent pure, as at Avery Island, Louisiana. Sometimes
it is brought out of the earth as brine and used without purification after
evaporation of the water. In the Great Salt Lake area and around San
Francisco Bay the salt water is evaporated by the heat of the sun. Salt
is concentrated by freezing out the water in northern Russia.
Common salt cakes, or sticks together, in moist weather. This effect
is caused by the presence of small amounts of magnesium chloride (MgCl2)
and calcium chloride (CaCl2) in the salt. These impurities absorb moisture
300 CHEMISTRY FOR OUR TIMES
from the air. Their effect can be counteracted by adding about 1 pea-
cent of calcium carbonate (CaCOa) or tricalcium phosphate [Caa(P04)2]
to the salt. Starch will also produce a similar result.
Salt is a necessity for life. Human beings and animals crave salt if
it is not supplied in sufficient quantities in the diet. Salt licks in dairy
barns are a familiar sight. Because of the common human need for salt,
this compound has sometimes served for money among primitive peoples.
Salt is a well-known symbol of friendship. Many stories and traditions
have arisen dealing with this substance.
The Ancient Use of Salt. In the Bible we read, "Ye are the salt of
the earth: but if the salt have lost his savour, wherewith shall it be
salted? It is thenceforth good for nothing, but to be cast out, and to
be trodden under foot of men."1
The Palestinian housewife used sea salt for cooking, but it was often
dirty from mud gathered with the salt. She therefore tied the salt and
dirt together in a little cloth bag and used the salt bag to season her
cooking in a manner similar to the use of tea bags today. When the flavor
of the salt was gone, the contents were worthless.
Uses of Salt. In addition to its obvious use for flavoring, great
amounts of salt are employed for preserving meats and fish, glazing pot-
tery, printing textiles, making soap, and making brines for refrigerating.
Salt is the starting substance from which are made all chlorides and
compounds of sodium as well as the elements sodium and chlorine them-
selves. This includes the manufacture of such needed substances as lye
(NaOH), baking soda (NaHC03), washing soda (Na2CO3), hydrochloric
acid (HC1), sodium sulfate (Na2SO4), and trisodium phosphate (Na3PO4).
Sodium fluoride, sodium bromide, and sodium iodide as well as
bromine and iodine can be made from sea water, directly or indirectly.
These elements are found together in group Vllb of the periodic table
(page 329).
The Halogens. The family name, halogen, of the four elements
fluorine, chlorine, bromine, and iodine, means "salt producer." They
all have similar properties, for each element has an ionic charge and a
combining number of 1. Each has seven electrons in its outermost orbit
and a pronounced tendency to fill the one remaining space. As the atomic
weight of the elements increases from F 19 to I 127, the chemical re-
activity decreases from fluorine, most active, to iodine, least active. The
compounds are graded similarly in stability from hydrogen fluoride
(H2F2), most stable, to hydrogen iodide (HI), least stable.
Fluorine. This element is so active that for 75 years it challenged the
ingenuity of chemists to isolate it. Although it was thought that it could
1 Matthew 5: 13.
CHEMISTRY OF THE SEA 3<M
be produced by the strong reducing action of an electric current, it
always reacted with the apparatus as soon as it was liberated. Finally,
Henri Moissan made a platinum apparatus in which, in 1886, he elec-
trolyzed potassium fluoride (KF) in liquid hydrogen fluoride (H2F2). He
was successful in obtaining a pale yellow gas, which he kept in a bottle
carved from transparent mineral fluorite (CaF2). Copper vessels are now
used.
Fluorine is the most active of all chemical elements. It acts violently
with water, and because of its fierce untamable activity it is not used
frequently in the free state. Recently, however, it has found some use
in chemical syntheses.
Fluorides. Traces of fluorides are found in the enamel of the teeth.
Fluorite (CaF2) and cryolite, a complex fluoride of sodium and aluminum
(NasAlF6), are useful compounds of fluorine found in nature.
In some regions traces of fluorides are found in the drinking water.
People living in these regions are much less subject to dental caries (tooth
decay) than those in other regions. Since excess fluorides cause mottled
teeth and even serious poisoning, it is not safe for a person to add this
element to his drinking water.
Some insect poisons contain sodium fluoride (NaF). The dust from
fluorides is poisonous, and should not be breathed. Some of the new
harmless, nonflammable refrigerants contain fluorine, difluoro-dichloro-
methane (CF2C12), for example.
Hydrogen Fluoride. Hydrogen fluoride can be made by the action
of sulfuric acid on powdered fluorite. The materials are mixed in a lead
dish
CaF2 + H2SO4 -4 CaSO4 + H2F2 T
At room temperature hydrogen fluoride is a gas that dissolves in water,
forming hydrofluoric acid, a weak acid. The most remarkable property
of this acid is its attack on glass, or sand.
SiO2 + 2H2F2 -4 SiF4T + 2H2O
Sand, or silica (Si02), can be considered the most inactive portion of
common glass, so the equation above describes the action of the acid
on glass, simplified. The silicon tetrafluoride (SiF4) escapes as a gas, and
the reaction tends to go to completion.
Hydrofluoric acid is used for marking or etching glassware and light
bulbs. The portions of the glass that are to be shielded from its corrosive
action are covered with paraffin. Of course, we cannot keep this acid in
glass bottles. Bottles made of Bakelite or ceresin, a mineral waxlike
paraffin, are suitable for this purpose. A paste containing ammonium
fluoride (NH4F) is also used for etching glass.
302
CHEMISTRY FOR OUR TIMES
Chlorine. Like fluorine and the other members of the halogen family,
chlorine is too active to be found free in nature. It is found in chlorides,
chiefly common salt (sodium chloride).
Chlorine can be freed from sodium chloride by electrolysis of its solu-
tion in water. We shall again consider this change in connection with
the making of sodium hydroxide. (See page '374.) Chlorine can also be
cone. HCI
SH20 BCD *NaOH
FIG. 18-2. — Chlorine may be prepared and its properties demonstrated by use of
this apparatus. Chlorine has little effect on the pieces of dry cloth in B, but it bleaches
the moist cloth in C. Bottle D may be replaced when it is filled with chlorine.
freed from salt by first changing it into hydrogen chloride and then
oxidizing the hydrogen chloride. (See Fig. 18-2.) The two actions are
NaCI
4HCI
H2SO4
MnO2
HCI t + NaHSO4
2H2O + MnCI2 + CUT
QUESTIONS
1. Point out three similarities and one difference between life in the ocean
and life on land.
(80
QQ per cent of the bromine is removed from some sea
water, how many tons of magnesium bromide remain in a cubic mile of the water?
3. List the seven most abundant ions in sea water.
4. Review the reasoning which leads to the conclusion that obtaining gold
from sea water is likely to be unprofitable.
5. What compounds other than sodium chloride are obtained by evapora-
tion of sea water?
CHEMISTRY OF THE SEA 303
6. List 10 uses for common salt.
7. List the halogens in order of increasing chemical activity.
8. Write formula equations for (a) the explosive reaction of fluorine on
water; (6) action of concentrated suifuric acid on calcium fluoride; (c) action of
hydrofluoric acid on sand; (d) action of ammonium fluoride on sand.
9. Point out two ways to obtain elementary chlorine from common salt.
10. Write formula equations for (a) electrolysis of common salt in water; (b)
reaction of salt with concentrated suifuric acid ; (c) reaction of salt solution with
silver nitrate solution; (d) electrolysis of melted salt.
What Is Chlorine Like? Chlorine is a pale-green gas at room tem-
perature. Its color can be observed easily when a piece of white paper is
held behind a bottle or test tube containing the gas. This gas was first
observed by Scheele, of Sweden, in 1774 and was later proved to be an
element by Sir Humphry Davy. The gas is about 2% times as dense as
air and dissolves moderately well in water.
When breathed, chlorine irritates the throat and lungs. Large amounts
may be fatal, but in very small concentrations the gas has been tried as
a cure for colds. The results were not favorable.
Chlorine burns quietly in hydrogen, but a mixture of the two gases
will explode if ignited or even brought into strong light.
H2 + Clj -» 2HCI
So ready is this element to combine with hydrogen that chlorine will take
hydrogen out of compounds. Warmed turpentine, a compound of hydro-
gen and carbon, or a wax candle, also of the same two elements, burn
in a jar of chlorine with a yellow, sooty flame, forming carbon.
CXHU 4- 1 CI2 -4 xC + j/HCI
In the equation, x stands for the number of carbon atoms and y for the
number of both hydrogen and chlorine atoms.
Metals will glow or burn in chlorine. A warmed sheet of thin copper
becomes red-hot in the gas while copper chloride is formed. Sodium's
action on the gas is so violent that it may be observed safely only from
behind a suitable protecting barrier. Pieces of arsenic or antimony rubbed
together over a bottle of chlorine drop off chips that burn spontaneously
in the gas, forming a white smoke. The equations are
Cu + CI2 -4 CuCI2
2Na + Cl» -4 2NaCI
2As + 3CU -4 2AsCU
2Sb + 3CU -4 2SbCU
We should expect phosphorus, a nonmetal, also to combine with
304 CHEMISTRY FOR OUR TIMES
chlorine. This occurs readily, forming the higher-valence compound of
phosphorus, phosphorus pentachloride.
2P + 5CI2 -» 2PCU
Chlorine acts slowly on water in which it has dissolved. The eventual
product of the action is oxygen.
2CI2 4- 2H2O -4 4HCI 4- O,
Evidence shows that this action is one that proceeds in interesting stages.
In the first step the action is
HOH 4- CICI -> HCI 4- HCIO
hydrochloric hypochlorous
acid acid
The hypochlorous acid is quite unstable, ready to part with its oxygen
for the second step.
HCIO -4 HCI 4- [O]
At the moment of its liberation the oxygen is very active because of
the energy of the chemical action. This freshly made element is said to
be in the nascent condition. It will oxidize germs in drinking water or
sewage or will bleach oxidizable dyes.
When chlorine is passed into dilute lye solution, sodium hypochlorite
is formed.
2NaOH 4- CICI -4 NaCI + NaCIO 4- H2O
This solution, with a stabilizer to prevent its too rapid decomposition,
is sold under various trade names as a household bleach. In hospitals a
0.5 per cent solution of sodium hypochlorite with sodium hydrogen
carbonate (NaHCO3) is used to irrigate infected wounds. It is called
Dakin's solution. The product of its decomposition is merely salt water
of such a concentration that it will not smart in an open wound.
NaCIO -4 NaCI 4- [O]
How Chlorine Is Sent to Market, Chlorine is sent to the local
grocer's in two forms. (1) Household bleach (NaOCl) has already been
mentioned. (2) Chlorinated lime (incorrectly " chloride of lime")> used
for bleaching purposes, is a convenient substance from which chlorine
can be liberated by the action of any acid, even carbonic acid from the
air. It is made by passing chlorine gas over moist slaked lime.
,CI
Ca(OH)2 4- CI2 -> Ca 4- H2O
*0-C\
Common bleaching powder is a mixed compound, part calcium chloride
and part calcium hypochlorite (CaOCl2).
Recently a method of making true calcium hypochlorite [Ca(OCl)2]
CHEMISTRY OF THE SEA
305
has been developed. This is marketed under the trade names H.T.H.
(high-test hypochlorite) and Perchloron, among others. Because of its
increased strength it is more effective for killing germs than the older
bleaching powder. Solutions of calcium hypochlorite are used in wading
pools to prevent the spread of foot-borne infection at public baths.
Chlorine also is sold in strong steel tanks. Compressed under moderate
pressure, the gas turns to a liquid. Many cities buy tanks of liquid
chlorine for purifying water supplies. (See Fig. 18-3.)
Uses for Chlorine. The uses of chlorine for bleaching, for purifying
water, and for making chlorides have been mentioned. Most of our paper
is bleached with chlorine, and some textiles, cotton for example, are
? Courtesy of Pennsylvania Salt Manufacturing Company
FIG. 18-3. — Chlorine is shipped in strong steel tanks. The tanks contain liquified gas
(no water). Commercial chlorine is made from salt by the electrolysis of brine.
similarly whitened. Many useful substances are made from chlorine —
chlorates, bromine, and chlorinated compounds of all sorts. The produc-
tion of this gas in the United States alone is about 2000 tons per day,
more in wartime.
QUESTIONS
11. Write the formula equation for the action of chlorine with (a) hydrogen;
(b) zinc; (c) aluminum; (d) water; (e) methane (CH4). Assume complete chlor-
ination.
12. Why should chlorine water for bleaching be freshly prepared?
13. Distinguish these three compounds in respect to composition: calcium
chloride; bleaching powder; calcium hypochlorite.
14. Soldiers are sometimes supplied with hypochlorite tablets. For what pur-
pose may they be used?
306 CHEMISTRY FOR OUR TIMES
15. A strong steel tank is being filled with compressed chlorine. How will the
operator know when the tank is full?
16. What percentage of common salt is chlorine?
17. From the formula Cla, find the density of chlorine gas at STP.
18. What two conditions are helpful for changing gaseous chlorine into a
liquid?
19. In what form is chlorine purchased to disinfect small swimming pools?
20. Suggest a reason why book paper in wartime has a grayish cast rather
than its customary white appearance.
Bromine. Sea water contains about 0.0064 per cent bromine. This is
less than 70 parts in a million. Nevertheless, patient research and experi-
menting have shown that this valuable element can be obtained profitably
from the sea. This achievement is a masterpiece of technical skill.
A bromine plant is located at the mouth of the Cape Fear River, North
Carolina, and another at Freeport, Texas. Sea water is pumped into the
plant, acidified, and treated with chlorine. The bromine, which is present
as bromide ions, is replaced by the more active chlorine.
CI2 + 2Br~ -4 2CI- -I- Br2 (ionic equation)
The freed bromine, 15,000 pounds a day, is blown by air into an
absorbing agent and then made into ethylene dibromide (C2H4Br2),
which is chiefly used as a part of the Ethyl fluid in gasoline.
It is interesting to note that most of both the bromine and the sodium
prepared in the United States goes into the manufacture of leaded
gasoline.
Bromine is also obtained from salt brine residues in Michigan, Ohio,
West Virginia, Stassfurt (Germany), and Tunis (North Africa).
In the laboratory we prepare bromine by mixing a bromide with an
oxidizing agent and moistening the mixture with concentrated sulfuric
acjid. Manganese dioxide is a convenient oxidizing agent, although sodium
chlorate is used commercially.
2NaBr + MnO2 + 2H2SO4 -* Na2SO4 + MnSO4 + 2H2O + Br2|
The bromine is separated as a gas when the mixture is heated. When
cooled to 63°C, it forms a brown-red liquid, which vaporizes easily.
Bromine can also be made by electrolysis. A solution of sodium bro-
mide is used. The element collects at the anode. The process is similar
to the electrolysis of sodium chloride solution (see page 374).
Bromine is unpleasant and very irritating to breathe. Its name comes
from a Greek word meaning "stench." Liquid bromine, if spilled on the
hands, destroys the tissue and causes sores that are very painful and slow
to heal.
CHEMISTRY OF THE SEA 307
Bromine joins with active metals, zinc or magnesium, and will also
add to phosphorus.
Mg 4- Br2 -> MgBr2
2P + 3Br2 -4 2PBr8
It is less active than chlorine, and it will not replace chlorine from chlo-
rides. It does, however, replace iodine from iodides.
2Nal -f Br2 -+ 2NaBr + I2
Uses of Bromine. Bromine is used in many chemical syntheses,
especially those in organic chemistry. It is also used in the preparation
of some dyes. Some of its compounds are used as "tear gas" by law-
enforcement officers. Silver bromide is the most important compound in
photographic films. By far the largest use of bromine is in the preparation
of compounds that go into "leaded gasoline/'
Iodine. " Iodine " when placed on a cut stings and smarts. This
"iodine" is a tincture or alcohol solution of iodine prepared by the
druggist. It contains potassium iodide as well. We may use "iodized salt"
at home, that is, ordinary salt to which $ small amount of potassium
iodide has been added. The use of iodized salt helps prevent simple goiter,
a disease of the thyroid gland in the neck, sometimes caused by lack of
sufficient iodine in the body. ,
Iodine comes from two sources: (1) An impurity in Chile saltpeter,
sodium iodate (NaIO3), is separated from the main deposit of sodium
nitrate (NaNOs) by crystallization. Iodine is prepared easily from the
iodate. (2) The water found under certain oil wells contains small quanti-
ties of iodides. These wells are in California, Texas, Russia, and Italy.
The iodine is prepared in a fashion similar to that of making bromine
(see page 306).
A laboratory method of preparing iodine is to mix sodium iodide
with an oxidizing agent and concentrated sulfuric acid. When warmed,
vapors of iodine arise from this mixture and condense as a solid on a
cooled surface above. When manganese dioxide is used for the oxidizing
agent, the equation is
MnO2 + 2Nal + 2H2SO4 -4 Na2SO4 + MnSO4 4- 2H2O + I2|
The disagreeable odor of hydrogen sulfide is noticeable when this mix-
ture is prepared. Some hydrogen iodide forms and reduces the sulfuric
acid.
H2SO4 4- SHI -4 4I2| + H2S 4- 4H2O
Both reactions produce iodine.
Iodine can also be made from the ashes of some seaweeds or kelps.
These ashes are also a source of potassium compounds.
308 CHEMISTRY FOR OUR TIMES
What Is Iodine Like? Iodine forms glistening, dark crystals, which
make a brown mark on paper. The crystals dissolve in benzene (Celle),
carbon tetrachloride (CC14), and several other solvents, forming a purple
solution. They dissolve in water containing potassium iodide (KI) or in
alcohol, forming a brown solution. When iodine is heated, a purple vapor
forms, which crystallizes as steel-gray needles on a cold surface. Appar-
ently iodine can change from a solid to a vapor, and vice versa, without
forming a liquid. Solids like iodine and solid carbon dioxide (Dry Ice)
that omit the liquid state when they evaporate at atmospheric pressure
are said to sublime. When the pressure is higher, both these substances
exist as liquids.
Tincture of iodine is an effective antiseptic; in fact, iodine is used
extensively in medicine. It is also used to make some dyes an$ as a
catalyst. Silver iodide is used in photography. Methylene iodide (CH2l2),
specific gravity 3.325, is one of the densest liquids at room temperature.
It is used in mineral separation experiments.
Tests for Halogens. As has been previously stated fluorides act
with concentrated sulfuric acid to produce a gas that when dissolved in
water produces an acid that will eat into glass. This experiment serves
as a convenient test to recognize a fluoride.
A soluble chloride forms a curdy white precipitate when silver nitrate
solution is added. The precipitate is soluble in ammonium hydroxide and
insoluble in nitric acid.
To the solution to be tested for bromide or iodide ion, we add fresh chlorine
water. We then obtain the free element bromine or iodine, shown by a darkening
of the solution. Next we add carbon tetrachloride (CC14) to the mixture arid shako
well. The carbon tetrachloride, which is not soluble in water, dissolves the halogen
and forms, if bromine, a red-brown layer; if iodine, a violet-purple layer.
Free elementary iodine colors starch blue. When this test is applied to foods,
it is better to boil the food before making the test. The steam formed ruptures
the woody wall that surrounds the starch grains. An iodide or, better, iodide ions
will not give this test with starch.
Replacement of Negative Ions. Chlorine will replace bromine from
a solution of a bromide or iodine from a solution of an iodide.
CI2 -f MgBr2 -4 MgCI2 + Br2
C|2 + 2KI -> 2KCI + I2
Bromine will replace iodine from an iodide solution, but bromine does
not act on the solution of a chloride.
Br2 + 2Nal -4 2NaBr + I2
Iodine will not act on a chloride or a bromide. Hence it has the least
replacing ability.
CHEMISTRY OF THE SEA
309
From such experiments as these we can make fin activity list
of the halogens. Obviously, the very active fluorine comes first,
followed by chlorine, bromine, and iodine in that order. We are
not surprised to find that this order is identical with that given in
the periodic table (see page 329).
F
Cl
Br
I
NaBr Bromine Nal
X'M4\'HA . . r t*'*£Aj>
Iodine
Glass Wool
Glass Wool
To I
Hood *
Courtesy of Journal of Chemical Education
FIG. 18-4. — This apparatus can be used to show successive replacement of the
halogens. Reading from left to right, chlorine 13 generated, replaces bromine, which
in turn displaces iodine.
This sort of replacement is similar to the replacement of hydrogen
by zinc, except that it is replacement of negative ions.
(formula equation)
2NaBr -f CI2 -4 2NaCI -f Br2 ^x^^o, C4u»nV
2Na+ 4- 2Br~ -f CI2 -4 2Na+ -f 2CI~ -f Br2 (complete ionic
equation)
(ionic equation)
2Br~ -f CI, -4 2CI- -f Br2
That is, each chlorine atom takes an electron from a less active bro-
mide ion. The chlorine atom becomes a chloride ion, and the bromide
ion changes into the free element.
Comparison of the Halogens. The following table shows a regular
gradation in the properties of the four halogens.
310
CHEMISTRY FOR OUR TIMES
Atomic
weight
(approx.)
Color
Boiling
point,
°C
Density
Heat of forma-
tion of hydro-
gen halide, cal
Fluorine
19
Pale yellow
-187
1.108
63,991
(liquid)
Chlorine
35.5
Yellow-green
- 33.7
1.567
22 , 030
(liquid)
Bromine
80
Red-brown
58.78
3.19
8,650
(liquid)
Iodine
127
Black ; vapor
183
4.93
-5,926
violet
(solid)
SUMMARY
The sea and the land both have a nitrogen cycle; both depend upon bacterial
action to maintain balanced life cycles. The sea is a source of enormous quanti-
ties of raw materials for chemical manufacturing. Common salt occurs abundantly
in sea water and in salt deposits in many places. Impurities of CaCl2 and MgCl2
in common salt cause it to absorb moisture from the air. Common salt is used
for seasoning, preserving, soapmaking, and chemical manufacturing.
The halogen family is in group Vllb of the periodic table. The family includes
fluorine, chlorine, bromine, and iodine. Fluorine is very active, it is prepared by
electrolysis of KF in liquid H2F2 in absence of water. Important fluorides include
cryolite (NasAlF6), used in the preparation of aluminum, and fluorite (CaF2),
the source of hydrofluoric acid. Fluorides are used in some insect powders.
Hydrogen fluoride is prepared by action of concentrated sulfuric acid on
calcium fluoride. A solution of the gas, called hydrofluoric acid, is used to etch
glass.
Chlorine is prepared: (1) By the electrolysis of brine
2NaCI + 2H2O -> 2NaOH + CI2| + H2|
(2) By the oxidation of hydrochloric acid by manganese dioxide or other
strong oxidizing agents.
The physical properties of chlorine are that it (1) is a pale-green gas at room
conditions, (2) has a density of 3.2 g per liter, (3) is easily liquefied, and (4) is
moderately soluble in water.
The chemical properties of chlorine are that it (1) is an active element; (2)
burns or explodes with elementary hydrogen; (3) combines with hydrogen in
compounds; (4) unites with metals to form metal chlorides; (5) unites with some
nonmetals, such as phosphorus, to form chlorides; (6) decomposes water slowly,
forming hydrochloric and hypochlorous acids; and (7) acts on a solution of lye,
forming common salt and sodium hypochlorite.
Elements at the time of liberation from a compound (nascent condition) have
extra energy and are extra active chemically. Uses of chlorine are as a bleach, for
purifying water, as a disinfectant, and for the preparation of chlorides and of
bromine.
CHEMISTRY OF THE SEA
Bromine is now obtained from bromides in sea water. Bromine is prepared
by (1) oxidation of sodium bromide in the presence of manganese dioxide and
concentrated sulfuric acid, (2) replacement from a bromide by chloririe, and (3)
electrolysis of sodium bromide solution.
The physical properties of bromine are that it (1) is a red-brown liquid, (2)
vaporizes readily at room temperature, (3) is very irritating to breathe, (4) forms
a red-brown solution in carbon tetrachloride.
The chemical properties of bromine are similar to those of chlorine, but
bromine is less active.
Bromine is used to make Ethyl fluid for gasoline and in the manufacture of
drugs and photographic compounds.
Iodine is found as an impurity in Chile saltpeter and in water in some oil
wells.
The preparation of iodine is by methods similar to those for preparing bromine.
The physical properties of iodine are that it (1) has metallic gray crystals;
(2) makes a brown mark on paper or on the hand; (3) is soluble in alcohol, carbon
tetrachloride (purple solution), and potassium iodide solution; and (4) sublimes
when heated, forming purple vapor.
Iodine is an important antiseptic. It is used to make medicines and photo-
graphic compounds. Also, iodine is important to the health of the body.
QUESTIONS
21. What percentage of sodium bromide is bromine?
*
22. In what respect is the modern source of bromine significant?
23. Write formula equations for (a) preparation of bromine from fused sodium
bromide; (b) preparation of bromine by electrolysis of sodium bromide solution;
(c) preparation of bromine from sodium bromide by oxidation; (d) replacement
of bromine from potassium bromide solution by chlorine; (e) action of bromine
on zinc.
24. Name two nonmetallic elements that bromine will not replace from their
compounds and one that can be replaced by bromine.
25. Describe in detail a chemical test by which sodium chloride can be dis-
tinguished from sodium bromide.
26. From what two sources is iodine obtained commercially?
27. A certain sample of Chile saltpeter weighing \ pounds contains 1 per cent
lo
sodium iodate. What weight of elementary iodine could be secured from it,
(50 . o
assuming |70 per cent recovery?
28. Write formula equations for the following reactions: (a) chlorine and
sodium iodide solution; (b) bromine &nd potassium iodide solution; (c) manganese
dioxide, sodium bromide, and concentrated sulfuric acid; (d) hydriodic and
hypochlorous acids; (e) hydriodic acid and hydrogen peroxide.
312 CHEMISTRY FOR OUR TIMES
29. Graphite and iodine are both dark metallic crystalline substances. Tell
how to distinguish them from each other.
30. A certain white crystalline compound colors a Bunsen flame yellow. When
it is mixed with potassium dichromate (K2Cr2O7), a strong oxidizing agent, and
a few drops of concentrated sulfuric acid and heated, a purple vapor arises. What
are the probable name and formula of this compound?
MORE CHALLENGING QUESTIONS
31. To make potassium iodide from elementary iodide, 'the clement is added
to caustic potash solution. Write the equation for the reaction that takes place.
Assume that the action is similar to that of chlorine on sodium hydroxide solution.
32. What is the purpose of using chlorine solution in the test for iodide ion?
33. Which has the higher percentage of iodine, sodium iodate or sodium
iodide?
34. What is the density of Freon gas (CF2C12)?
35. Dichloro-ethane contains 14.1 per cent carbon, 2.4 per cent hydrogen,
and 83.5 per cent chlorine. One liter of the gas weighs 3.83 grams. Find its mo-
lecular formula.
36. If a factory is designed to make < tons of chlorine per day, what weight
of common salt must be supplied daily?
37. Investigate the properties of iodine in detail, using as a reference an
advanced chemistry book. Find out why iodine dissolves better in potassium
iodide solution than in pure water.
UNIT FOUR CHAPTER XIX
CRYSTALS OF COMMERCE
Among the most interesting crystals used commercially are those we
commonly call gem stones or jewels. In this chapter we shall consider,
among other jewels, diamonds (see page 318), which are made of pure
crystalline 'carbon and are used as sparkling gems in jewelry and as c\it-
Courtesy of American Museum of Natural History
FIG. 19-1. — The ruby and sapphire are chiefly aluminum oxide. These gem stones were
removed from display when the military emergency arose.
ting stones in shops and in oil fields. Their commercial use depends upon
their extreme hardness.
Rubies, usually deep red in color, sapphires, often pale blue, and
emeralds, dark green, are also gem stones of high hardness and attractive
appearance. Rubies and sapphires are crystalline aluminum oxide (A^Os)
with a slight amount of impurity. Rubies are found in India, Ceylon, and
Siam. Emeralds are also definite green crystals; chemically they are
alum
New Terms
mordant
313
lake
314 CHEMISTRY FOR OUR TIMES
beryl [beryllium aluminum silicate (BeaAUSieOis)]. They are found in
Colombia, South America, and in the Ural Mountains, U.S.S.R. (See
Fig. 19-1.)
Watches may contain between 7 and 23 jewels. Watch jewels are
drilled and used as hard bearing sockets for the axles of the watch gear
wheels. (See Fig. 19-2.) Jewels for watches and
i-e-Geared wheel meters may be rubies, sapphires, garnets, synthetic
jewel sapphires, or even glass. Contrary to the common
belief, these small gems are not necessarily expen-
sive. They cost from a few cents to approximately
$1 each.
In addition to the natural supply, /synthetic
rubies and sapphires are made by fusing aluminum
FIG 19-2 _ oxide in a high- temperature flame. These synthetic
Drilled jewels are stones are practically identical with those found
used for bearings in naturally, and it is almost impossible for an expert
watches. to distinguish them-
Emery. Natural aluminum oxide, colored black by impurities, is called
emery. Crushed and sorted for size, this material is familiar to all as an
abrasive, a hard scratching substance. Emery cloth is more abrasive than
sandpaper or garnet paper. All are used similarly. In making them a high
electric voltage is applied to the grains as they rest on the cloth or paper
backing. Under the influence of the electric charge, the sharpest cutting
edges point outward, and the grains space themselves evenly.
Fused Aluminum Oxide Abrasives. Natural corundum (A12O3)
may be dark or light. In fact, sapphires, rubies, and emery are all ex-
amples of corundum. This mineral is extremely hard and is therefore
used for grinding wheels and whetstones.
Experience shows that white grinding wheels run cooler than black
ones — hence the demand for light-colored abrasives. When aluminum
oxide is made by fusing bauxite (hydrated aluminum oxide) in an elec-
tric furnace, the product is usually light brown to white. The product
has several trade names, and many tons are used each year for grinding
metals and for lining furnaces. Perfectly white, fused, and crystallized
aluminum oxide can also be made in an electric furnace, but in this case
purer aluminum oxide is used as a starting material.
Borax. We usually associate borax with Death Valley, California.
From this famous valley the mineral from which borax was obtained
was once hauled by 20-mule teams. Our sources of this material at
present are the brines of Searles Lake, California, and a mineral called
rasorite (Na2Ba407'4H2O) found in Kern County of the same state. This
mineral is merely dissolved, filtered, and recrystallized as the borax of
CRYSTALS OF COMMERCE
315
commerce (Na2B4O7*10H2O). It is used as a softener for water, as an
aid to cleaning, and as a flux in brazing. Large amounts of borax are
used in making Pyrex and other borosilicate glass (see page 412).
Underwood and Underwooa
FIG. 19-3. — Crystals used in industry are found sometimes in desert regions. This
picture shows the neart of a valuable gypsum deposit, 270 miles long, in New Mexico.
Boric Acid. When borax solution is treated with sulfuric acid, boric
acid precipitates.
Na2B4O7 + H2SO4 + 5H2O -* 4H3BO3| + Na2SO4
As a powder or as shiny, thin, slippery crystals, boric acid is well
known to us, for it is used in solution as an eyewash. A saturated solu-
tion is mildly antiseptic; also, it is impossible to dissolve enough boric
acid in slightly warm water to injure normal eyes, for at 20°C only 4.8 g
of boric acid dissolves in 100 g of water. Not all authorities agree on the
value of boric acid as an eyewash.
The test for borates used by both prospector and laboratory workers is to
burn alcohol (either grain or wood) to which the powdered borate has been added.
The addition of a little sulfuric acid aids the test. A flame fringed with deep green
results if a borate is present.
Alums. Among the most beautiful and perfectly formed crystals of
commerce is a class of compounds called alums. These are double sul-
fates that crystallize from solutions containing singly charged metal ions
such as Na+ , K+, Ag+, or NH|, triply charged ions such as A1+++, Cr+++,
Fe+++, and so on, and the sulfate ion (SO") or its equivalent. They
are represented by the following names and formulas: potassium alu-
minum sulfate {common alum [KA1(S04)2'12H2O]}, ferric ammonium
316
CHEMISTRY FOR OUR TIMES
sulfate [NH4Fe(S04)2*12H20], potassium chromium sulfate {chrome alum
[KCr(SO4)2%12H20]}. Formulas double the above were once given for
these alums, but the simpler formulas are now considered to be the cor-
rect ones.
Chrome alum forms deep purple crystals, perfect octahedra. These
are easy to grow, and they may be made the basis of fascinating experi-
ments. One single, well-formed crystal is re-
ported to have been grown from a saturated
solution to weigh over 80 Ib.1
In solutions the ions of alums are not com-
bined, but each gives its usual reactions with-
out interference. Common alum, for example,
acts like a mixture of K+ ions, A1+++ ions, and
SO" ions. The solution is acid owing to
hydrolysis (page 233) just as is aluminum
sulfate solution. For this reason, sodium
aluminum alum is used in baking powders and
common alum in foam fire extinguishers.
Common alum is a cheap and convenient
source of soluble aluminum ions. When it is
added to an alkali, a colloidal, gelatinous,
sticky precipitate of aluminum hydroxide
forms.
AI+++ 4- 3OH- -4 AI(OH)3 j
Courtesy of American Museum of
Natural History
FIG. 19-4.— This quartz
crystal was not cut. It was
found in nature just this way.
All crystals grow in definite
patterns. This one grew in
Hot Springs, Arkansas.
This sticky precipitate collects particles as it
settles through muddy water, leaving a clear
liquid above. It is used to clarify water on a
large scale. Also, dyes cling to aluminum hy-
droxide when it is precipitated on cotton fibers.
When used in dyeing it serves as a mordant,
a fastening agent between fiber and dyestuff. The resulting colored pre-
cipitate is called a lake. Cotton, rayon, and linen can be dyed fast to
washing by using a mordant.
Salt Cake. Salt cake is not a bakery delicacy but the commercial
name for sodium sulfate (Na2S04). Some salt cake is mined from natural
deposits, but larger amounts are made from sodium hydrogen sulfate
(NaHS04), the by-product from making either hydrochloric or nitric acid
with sulfuric acid (see pages 358 and 361). The sodium hydrogen sulfate
is mixed with the proper amount of salt and heated. Hydrogen chloride
1 FLIEDNER, L. J., " A Crystal Grows Up," Journal of Chemical Education, vol. 18,
No. 1, January, 1941.
CRYSTALS OF COMMERCE
317
is formed, and salt cake is a valuable by-product.
NaHSO4
NaCI
salt
Na2SO4 + HCI
salt cake
The salt cake in the anhydrous condition is used to make kraft paper,
glass, and sodium sulfide. When it
is dissolved in water and crystal-
lized, Glauber's salt forms (Na2-
S04-10H2O). The Glauber's salt
crystals are beautiful, long, color-
less needles. They lose water read-
ily in air (efflorescence) (see page
114) and form a white, anhydrous
powder. Glauber's salt is used
chiefly in the dye industry to cause
the dye to precipitate onto the
fabric.
Diamonds. The interest of
chemistry pupils in diamonds is not
altogether chemical. Every year
the freshman class in a certain col-
lege is called into the chemistry
laboratory. A diamond, which has
previously been on exhibition, is
burned by the chemistry instructor
World Wide Photo
FIG. 19-5. — Cutting the "ice" is a
slow process. The high-speed revolving
disk impregnated with diamond dust cuts
through a one-carat diamond in eight
hours. The cutting of the Jonker dia-
mond, shown here, was undertaken after
a year of study, for a cut on a wrong plane
would shatter the gem and destroy mil-
lions of dollars of value.
in pure oxygen in a suitable appa-
ratus as a lecture demonstration. The gas formed by burning the di-
amond is collected and run through limewater. A white precipitate
forms. The chemical actions are described by the equations:
C02 4- H20
HjCO, -f Ca(OH)2
C02
H2CO,
CaCOai +2H20
This is a convincing, but expensive, proof that
a diamond is carbon. The experiment was first
performed by Lavoisier.
Hardness. When two different substances are
rubbed together each is worn away, but the
harder substance makes a far deeper scratch on
the softer one. An arrangement of minerals in
order of hardness is given in the accompanying
table. Diamond, last in the list; is the hardest
substance; it will scratch everything else. The list,
HARDNESS SCALE
1. Talc
2. Rock salt
3. Calcite
4. Fluorite
5. Apatite
6. Feldspar
7. Quartz
8. Topaz
9. Corundum
10. Diamond
however, is not even-
318
CHEMISTRY FOR OUR TIMES
Courtesy of American Museum of Natural Jlixtory
FIG. 19-6.— Regent of Pitt (136*4); Kohinoor— recut (125); Piggot (82;; Eugenie
(51) ; Kassak (78%); Saney (53); OrlofT (194^); Great Mogul (297); Shah (95); Polar
Star (40); Florentine (139H); Hope (44^); Star of the South (125); Kohinoor— first
cut (186^); Pasha of Egypt (40). Weights are in carats.
CRYSTALS OF COMMERCE 319
spaced. The interval between 1 and 2 is much smaller than that between
9 and 10. Silicon carbide (see page 251) and boron carbide are synthetic
abrasives that fall between 9 and 10. More satisfactory hardness tests than
scratching are made by the Brinell or Rockwell methods.
The uses of diamonds for dressing grinding wheels and drilling into
the earth and for dies through which wire is drawn into a smaller size
all depend on the extreme hardness of this beautiful crystalline form of
carbon.
SUMMARY
Rubies and sapphires are natural crystalline aluminum oxide, colored with
slight impurities. They are used for ornamental gems and also for bearings in
precision instruments. They can be produced synthetically. Emery, an impure
aluminum oxide, is used as an abrasive. Borax (Na2B407*10H20) is mined from
salt deposits of ancient lakes. It is used to make glass, to soften water, and as a
flux. Boric acid, made from borax, is used as a mild antiseptic.
Alums are double sulfates, hydrated. Potassium aluminum alum is used to
clarify muddy water and in dyeing. Sodium aluminum alum is used in baking
powder.
Sodium sulfate (Na2S04) is called salt cake. Na2SO4-10H2O is Glauber's salt,
which is used in the dye industry.
Diamond (crystallized carbon), extremely hard, is used for gems and in cut-
ting tools. The relative hardness of metals is determined roughly by scratching
and more accurately by the Rockwell test and other methods.
QUESTIONS
1. List four gem stones, and with each give the chemical composition and the
usual color.
2. State a reason for using jewels for bearings in watches.
3. What important properties of aluminum oxide make different forms of it
useful for (a) gems; (6) abrasives; (c) furnace lining?
4. List three uses for borax.
6. Write formula equations for the following reactions: (a) calcium borate
and sodium carbonate solutions; (6) sulfuric acid, borax, and water; (c) boric acid
heated.
6. Flame tests for barium, copper, and borax all involve a green-colored
flame. What distinguishes the borax test from the others?
7. Write the formula for (a) common alum; (6) ammonium iron alum; (c)
ammonium aluminum alum; (d) burnt (dehydrated) alum.
8. List three uses for common alum.
ft. When Glauber's salt is dehydrated to form salt cake, what is the percentr
age loss of weight?
380 CHEMISTRY FOR OUR TIMES
10. Beryllium is obtained from crystalline beryl. What is the percentage of the
element in the crystal?
SPECIAL REPORTS
1. Make a report on the six main classes of crystals. Illustrate each by a card-
board model of an ideal crystal and a model of the axes. Place each with a sample
of a representative chemical compound.
2. Report on the history of borax mining in Death Valley, California.
3. Become a local expert on gems, both precious and semiprecious. A collec-
tion of gems can be obtained without too great expense if small samples are used
to start.
4. For what purposes do machinists use diamonds? Well drillers? Make a
report on the Kimberley (South Africa) diamond mines; the cutting of diamonds;
the grading and valuation of diamonds; famous diamonds.
5. Make a report on new synthetic abrasives and cutting-tool tips, including
boron carbide and tungsten carbido, and show their importance in the modern
machine-tool industries.
UNIT FOUR CHAPTER XX
THE GREAT CLASSIFICATION
"Spy work! We must get to the bottom of this and find out who is
the sender of this secret code message/7 agreed the Soviet officials.
A letter had been mailed by a New York college student to his sister
in the U.S.S.R. The letter, along with other information, contained a
chart quite similar to the table on page 324. This table, in 1931, was
refused admission to the very country where it originated over 60 years
before. The sender and receiver of the letter were both suspected of being
spies because tho chart was thought to bs the key to a secret code.
FIG. 20-1. — The U.S.S.R. honored Mendclcyev in 1934 by issuing commemorative
postage stamps. Both the 5 and 10 kopek values shown here have the periodic table
in the background.
The chart is the periodic table of the elements, one of the truly great
generalizations of chemistry. It is found in some form in almost every
book on elementary chemistry. It contains no secrets. While it might be
used as a code, we have no evidence that the suspicions of the U.S.S.R.
officials were correct.
Three years later, some compensation was made for this serious
blunder. Other officials of the U.S.S.R. saw fit to commemorate the one
hundredth anniversary of the birth of Dmitri Ivanovich Mendeleyev
(1834-1907) of Tobolsk, Siberia. A special set of postage stamps (see
New Terms
periodic law atomic weight phosphorus
atomic number periodic table
321
322
CHEMISTRY FOR OUR TIMES
Fig. 20-1) was issued in his honor. On one stamp a portrait of the dis-
tinguished scientist appears in the foreground, surrounded by a laurel
wreath. In the background we find the periodic chart of the elements,
which he was largely instrumental in developing.
In addition to learning about the work of this famous Russian, we
are also to follow the lengthening shadow of John Dalton and his thinking
(page 141), until we arrive at modern cyclotrons (atom smashers) and
induced radioactivity.
Similarities Among Elements. We have already noted how similar
oxygen is to sulfur in many respects. Oxides resemble sulfides in a chem-
ical way (see page 61). Again, if a chemist runs short of a sodium com-
pound he may often substitute a potassium compound with entirely
satisfactory results, provided that he adjusts the amount to be used and
disregards the difference in cost. In like manner, a bromide or an iodide
may often serve if a chloride is not available. There are many such cases
of similar elements, substances that are more or less like each other.
Early Classifications of the Elements. If we consider the three
elements, lithium (atomic weight 7), sodium (23), and potassium (39),
which are surprisingly alike, we find that the atomic weight of the middle
one, 23, is about the average of the weights of the other two :
7 + 39
= 23.
Chlorine (35.5), bromine (80), and iodine (127) show a similar relation-
ship, as does the group calcium (40), strontium (87.6), and barium (137).
These groups of three similar elements, along with some others that are
less impressive and some that are inaccurate, were pointed out by a
German professor of chemistry, Johann Wolfgang Dobereiner (1780-
1849), as early as 1839.
After several other workers had noticed more comparisons and the
accuracy of finding atomic weights had improved, John Newlands (1838-
1898), in England, set down the following list of the then known elements
in order of their increasing atomic weights, starting with lithium.
NEWLANDS' LIST OF ELEMENTS AND THEIR ATOMIC WEIGHTS (1866)
Li 7
Be 9
B 11
C 12
N 14
O 16
F 19
Na23
Mg24
A127
Si 28
P31
832
C135.5
K39
Ca40
If we start with lithium and count until we reach an element very
similar to lithium, sodium, it will be the eighth element in the list. If we
THE GREAT CLASSIFICATION 383
count further, the eighth element beyond sodium is potassium, which
is similar to both lithium and sodium in its properties. Likewise, from
oxygen to sulfur, or from fluorine to chlorine, or from one to the other
of any pair of similar elements the interval is eight. Prof. Newlands in
1866 reported this to the English Chemical Society and pointed out the
similarity to the octave of the musical scale, with its interval of eight
notes. "The similar properties come back every eighth element/7 he said,
in effect.
This was a long step forward in organizing chemistry into a systematic
science and was also a great help to all learners of the subject. Neverthe-
less, Newlands' thanks were at first jeers and laughter. One fellow
chemist even asked what he could learn by arranging the elements
alphabetically. We are glad to find that jeers eventually changed to
praise; 20 years later he was awarded a medal in honor of his discovery.
A Famous Russian Prophet. After Newlands, Julius Lothar Meyer
(1830-1895), in Germany, and the famous chemist Mendeleyev, in
Russia, continued this study on the similarity of elements. Mendeleyev
also organized the elements by their atomic weights into a table (see
page 324). While his arrangement was quite similar to that of Newlands,
he made the following important advances: (1) He left spaces for elements
that might some day be discovered. (2) After comparing the properties
of certain elements with those of other elements, he boldly placed them
where he thought they belonged in the table on the basis of their proper-
ties, disregarding atomic weights when necessary. He assumed that the
atomic weights as then known might be somewhat in error. (3) He saw
the necessity for subgroups within the groups or families (vertical
columns). For example, in Group I, lithium, sodium, potassium, rubi-
dium, and cesium are placed to the left-hand side in one family, for these
elements are alike. Copper, silver, and gold are quite similar to each
other; they are in the same group, but on the right-hand side.
Mendeleyev was a distinguished teacher, author, and chemist. He
had the vision to call this regularity of nature, which he observed from
the study of his table, the periodic law (page 326). For a better under-
standing, let us examine the table as Mendeleyev built it with the addi-
tion of some elements discovered since his time. (See page 324).
The natural elements are arranged according to increasing atomic
weights, the lowest, hydrogen, first and the highest, uranium (240, now
238), last. There are eight columns, or groups, and 10 rows, or periods.
Hydrogen is separately classified, the only element in the first period.
Like Newlands, Mendeleyev started with lithium and arranged the ele-
ments with seven in a row. When he reached iron (56), he had to make
an eighth column, with the three elements iron, cobalt, and nickel in it.
Much later, to accommodate the newly discovered inert elements of the
324
CHEMISTRY FOR OUR TIMES
o
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oo PQ gj
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2S:
o
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OS
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THE GREAT CLASSIFICATION
325
air it was found necessary to add another group, Group 0, containing
helium, neon, argon, krypton, and xenon (and later radon) to the left-
hand side of the table.
Elements of atomic number 93, 94, 95, and 96, not found in nature,
have been synthesized in connection with work on atomic bombs. Their
position in the periodic table has not yet been established.
What Mendeleyev's Table Did for Chemistry. To chemists,
Mendeleyev's periodic table became a card catalogue, filing system, refer-
ence chart, and comparison table all rolled into one. Roughly speaking,
instead of learning 92 different chemistries, 1 for each element, 8 chem-
istries suffice.
There are three important contributions of the periodic grouping:
1. It has classified and systematized our chemistry; therefore, this
discovery is called the great unifying force within the science.
2. It has suggested~new elements. In fact, not only were they sug-
gested, but hints were given as to where they could be found and what
they would be like. Mendeleyev ventured to predict three of these ele-
ments, all of which were discovered within his lifetime. He stated, " When
in 1871 I wrote a paper on the application of the periodic law to the
determination of the properties of as yet undiscovered elements, I did
not think that I should live to see the verification of this consequence
of the law, but such was to be the case."
How fine a piece of work he did in predicting can be judged from the
following chart.
MENDELEYEV'S PREDICTION FULFILLED
Prediction of proper-
ties for an element
like silicon —
1871
Properties found later
for this element,
named germanium —
1886
Atomic weight
72.0
72.3
Specific gravity
5.5
5 47
Specific gravity of oxide
4 7
4 7
Boiling point of chloride
100°C or less
86°C
Boiling point of ethyl compound . . .
Formula of oxide
160°C
XO2
160°C
GeO2
Formula of chloride
XC14
GeCU
3. Atomic weights were checked critically, and instances of possible
errors were located. Many errors in atomic weights were corrected. For
example the atomic weight of indium was shown to be 114, not 76 as
originally suggested. We may be sure that much work has been expended
on the atomic weights of iodine and tellurium, cobalt and nickel, and
326 CHEMISTRY FOR OUR TIMES
later the pair argon and potassium, for they were out of order in the table
and still are. From a chemical standpoint, however, tellurium is like
sulfur and selenium, and iodine obviously belongs in the family with
chlorine and bromine. Also, argon, an inert gas, goes with neon, not with
sodium.
Difficulties Presented by Mendeleyev's Periodic Table. A few
difficulties are easily observed when we examine the periodic table of
Mendeleyev: (1) The "rare earths/' a group of 15 similar elements, have
to be crowded into one place in the table. (2) Group VIII with its three
sets of three elements is out of place, for these metals are located where
the nonmetals belong. (3) The system of families within the groups is a
makeshift and is on the whole unsatisfactory. (4) As has already been
pointed out, certain elements are not in order of their atomic weights.
To explain this, two possibilities suggest themselves: (a) Perhaps the
arrangement of the table according to Mendeleyev's method is not the
most satisfactory method, (b) Perhaps the atomic weight is not the funda-
mental property of atoms on which to base a table.
The Periodic Law. In spite of these difficulties, the genius of
Mendeleyev glistens. In spite of the imperfections of the arrange-
ment, in spite of all complications, the outstanding truth he discovered
shone out clearly. He called this truth the periodic law, namely: The
chemical properties of the elements are a periodic function of their
atomic weights.
The different phases of the moon — new moon, first quarter, and so
on — are a periodic function of the moon's revolution. These moon phases
occur again after a definite time, or period — after 28 days. Just so, as we
proceed from element to element, the similar properties repeat them-
selves after a definite interval. Among the lighter elements in the periodic
table (omitting the inert gases) this interval is found to be the octave
as discovered by Newlands, and a repetition of properties occurs on
simply counting eight elements ahead.
Later Progress in Periodic Grouping. A young Englishman, H. J.
Moseley (1887-1915), who died fighting for his country .in World War I,
made another step forward in the study of atoms and periodic grouping.
He was, of course, using the work of many other experimenters as a
foundation and building on into the unknown in his own brilliant fashion.
In his experiments he used an X-ray tube (see Fig. 20-3), a glass bulb
from which the air had beon removed and provided with suitable elec-
trodes. When a high electric pressure or voltage is applied to such a tube,
the cathode ( — ) shoots out streams of electrons, tiny bits of electricity
(page 179). The cathode is curved so that these electrons strike upon a
target as if they were focused. Just as a stone striking the surface of a
THE GREAT CLASSIFICATION
327
Cathode,
33
34
35
37
38
1 Electrons-"',
-X rays-
FIG. 20-3. — A simple X-ray tube is a device in which cathode rays (a stream of
electrons) hit a target. The excited target sends out penetrating X rays.
pond sets up water waves caused by the disturbance, so the electrons
hitting the target set up X rays from the
target.
When the electron stream strikes the
target, the material of the target becomes
energized, or excited. It becomes a source
of energy radiating X rays. X rays are quite
like visible light, except that their wave
lengths are very short, too short for our eyes
to observe.
Moseley arranged his X-ray tubes so
that different elements could be brought
into position as targets and determined the
wave lengths of the X rays. He analyzed
them by means of a spectroscope (page
48), using a crystal to reflect and focus the
rays upon a photographic plate. (See Fig.
20-3.) Although our eyes are not sensitive
As
Se
Br
Rb
Sr
FIG. 20-4.— The principal
lines in the X-ray spectra of the
elements are shown here. The
atomic numbers assigned by
Moseley are at the left. Notice
that as the atomic number in-
creases, the lines shift to the left
in a fairly regular fashion.
to X rays, everyone is familiar with the fact that X rays affect a photo-
graphic plate.
Square Root
of Frequency
1 92
Atomic Numbers
FIG. 20-5. — Moseley 's results show that the atomic numbers of the elements are
directly related to the square root of the frequency of their X rays.
The result of these experiments was a series of pairs of lines on the
plate. (See Fig. 20-4.) With elements of successively increasing atomic
weight he found that the positions of the line pairs on the plate were
different. These line pairs were regularly spaced, one space apart for
328
CHEMISTRY FOR OUR TIMES
each element of the next higher atomic weight. Further, when he made
a chart on graph paper of the results of calculations based on his experi-
ments (see Fig. 20-5), he found a perfectly regular straight-line conclu-
sion. All the elements had lined up! lie numbered the positions of the
elements on the chart and called these consecutive numbers atomic
numbers. Spaces were left for missing elements.
Now comes the startling advance. Moseley's chart showed this
straight-line regularity only when he used atomic numbers, instead of
atomic weights. Apparently, then,
the atomic number is a more
fundamental fact about an atom
than its atomic weight. If so, then
we can restate the periodic law in
more modern form: The chemical
properties cf the elements are a
periodic function of their atomic
numbers.
A Modern Periodic Table. A
preferred classification of the ele-
ments is given on page 329. This
arrangement consists of 18 verti-
cal columns and seven rows. The
first row contains hydrogen and
helium only; the second and third
rows contain eight elements each.
In these two rows are included
most of the elements important
in elementary chemistry. The ele-
ments in Group 0 are the inert
gases; these resemble each other,
as do all elements in the same
column or group.
All the elements in Groups la and Vllb have a combining number
of 1. Salts are readily formed between the members of these two groups,
as, for example, lithium and fluorine, potassium and chlorine, and
sodium and iodine. Salts are formed when active metals combine with
active nonmetals.
Combining numbers may be listed as follows:
Courtesy of The Travelers Insurance Company
FIG. 20-6 — We should not forget that
generalizing in chemistry and all theories
are based on facts. The great source of
facts is the laboratory. This chemist is
carrying on the laboratory operation called
filtering.
Group
Combining
numbers
Group
Combining
numbers
la
Ha
Ilia
1
2
3
Vllb
VIb
Vb
1
2
3
THE GREAT CLASSIFICATION
329
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330 CHEMISTRY FOR OUR TIMES
In the modern table the light metals are located at the left in Groups
la, Ha, and Illb, in the upper periods (omitting hydrogen). Here we
look for metals suitable for airplane construction.
The nonmetals are generally in the upper right-hand corner (omitting
Group 0) and extend by a diagonal line roughly from carbon (diamond)
through phosphorus, sulfur, selenium, and iodine to radon.
The low-melting heavy metals extend from atomic numbers 80 to 83
and directly above; the high-melting heavy metals extend from 22 to 29
and below. The strongly active metals are in Groups la to Ilia, and the
strongly active nonmetals are in Groups Vllb to Vb.
Advantages of the Modern Table. The basis of the arrangement
of the modern table is atomic numbers and atomic structure (page 187).
Hence many of the difficulties found in older tables are avoided.
Four sorts of elements are evident in this classification. They are
1. Normal elements (Groups la, Ha, Ib to Vllb)
2. Transitional elements (Groups Ilia to VIII)
3. Inert gases (Group O)
4. Rare-earth elements (in Group Ilia, No. 58 to 71)
We find from this table that there are nine sorts of normal elements.
The metals are in general on the left of the table, the nonmetals on the
right. The inert gases are separated in a group by themselves.
The so-called " transitional " elements are alike in that all have more
than one combining number. Furthermore, the use of the modern table
has great advantages over the older one in the study of atomic structure.
We can predict the properties of an element from its position in this
table more clearly than with Mendeleyev's earlier table.
The location of elements Th(90), Pa (91), and II (92), which occur
naturally and elements Np(93), Pu(94), Am (95), and Cm (96), which
were synthesized in connection with the atomic-bomb project during
World War II, is not established. It is believed, however, that all these
seven elements will be assigned to Group Ilia, in which they will con-
stitute a group similar to the rare-earth elements.
From Periodic Table to Production. A striking example of apply-
ing the periodic table as a very useful tool in research work is pointed
out by the late Thomas Midgley, Jr., director of a research project for
finding a nonflammable, nontoxic refrigerant.
. . . the elements on the right-hand side are the only ones sufficiently
volatile ... for the purpose in hand. In fact, only a certain number need be
considered. Volatile compounds of boron, silicon, phosphorus, arsenic, anti-
mony, bismuth, selenium, tellurium, and iodine are all too unstable and toxic to
consider. The inert gases are too low in boiling point. Now look over the remain-
ing elements. (See Fig. 20-8.) Every refrigerant used has been made from com-
binations of these elements. Flammability decreases from left to right. Toxicity
THE GREAT CLASSIFICATION 3311
(in general) decreases from the heavy elements at the bottom to the lighter
elements on top. These two desiderata1 focus on fluorine. It was an exciting
deduction. Seemingly, no one previously had TABLE USED TO FIND
considered it possible that fluorine might be ^ REFRIGERANT
nontoxic in some of its compounds. This pos-
sibility had certainly been disregarded by the
refrigeration engineers. If the problem before
us was solvable by the use of a single com-
pound, then that compound would certainly
contain fluorine.
Br
The final result of this search was the
IVb Vb VIb Vllb
N O
S Cl
discovery of Freon (CF2C12) as a refrigerant. Fla- 20-8— This is the part
* . •! , . . ,1 u , ,, i of the periodic table that was
A similar story is told about the search used byp Thomag Midgleyj Jr<)
for Ethyl fluid, which is used with gasoline, to find a refrigerant.
We abandoned the Edisonian method2 in favor of a correlational procedure
based on the periodic tafile. What had seemed at times a hopeless quest, cover-
ing many years and costing a considerable amount of money, rapidly turned
into a "fox hunt." Predictions began fulfilling themselves instead of fizzling.
. . . We thereupon predicted that tetraethyl lead would solve the problem.
The record of the past decade has borne out that prediction.
*
In fact, Ethyl fluid containing tetraethyl lead is used in over 70 per
cent of the nation's cars, and it has flown with Admiral Byrd over
both poles.
QUESTIONS
1. List the names of three investigators who contributed to the periodic
classification of the elements. Tell briefly the contribution of each.
2. What was the amount of error in Mendeleyev's prediction of the atomic
weight of germanium? What was the percentage of error?
3. What reasons are given for placing argon in Group 0 instead of Group la
in place of potassium?
4. Explain the term periodic function, using the seasons of the year as an
example.
6. Point out the difference between the periodic law stated by Mendeleyev
and that stated by Moseley.
6. Does the fact that the original wording of the periodic law was improved
show that it was entirely wrong at first? Valueless at first? Is it possible that the
law may be further restated?
1 Latin — things desired.
2 Enlightened trial and error.
332
CHEMISTRY FOR OUR TIMES
7. In the modern periodic table, which are the longest groups? The shortest?
How many periods are there? Judging by the position of hydrogen and of oxygen,
which part of the table do we discuss most in elementary chemistry?
8. Name two elements similar to each of the following: sodium; sulfur;
bromine; aluminum; neon.
Applying the Table. Let us investigate the elements in Group Vb,
studying them together. They are nitrogen, phosphorus, arsenic, anti-
mony, and bismuth. They all have a combining number of 3 and some-
times of 5. With oxygen they have a combining number of 5 as in N2O&
(nitrogen pentoxide) and PgOs (phosphorus pentoxide). With hydrogen
the combining number is 3 as in NH3 (ammonia), PHs (phosphine),
AsH3 (arsine), SbH3 (stibine), and the unstable BiH8.
This group shows a gradual change of properties. If we start with
nitrogen, a typical nonmetal, and go down the list, the metallic prop-
erties become stronger at the expense of the nonmetallic properties.
Finally we arrive at bismuth, which is really a metal. Arsenic is inter-
mediate. It has a metallic luster and forms alloys, but its oxide (As2C>5)
forms an acid, arsenic acid (H3AsO4).
Nitrogen. The first member of the family, nitrogen, differs consider-
ably from the others in its chemical properties. This inactive gas has
already been discussed (see page 44). Later we shall consider its two
very important compounds, nitric acid (HNO3) and ammonia (NH3).
GROUP Vb
Element
M.P.,
°c
B.P.,
°C
Density,
g/ml
Formulas of .oxides
7 (at. no.)
N
14 (at. wt.)
-195.8
-209.9
0.00125
gas at 0°C
N,08
N20fi
15
P
30.9
44
280
Y 1.82
112.2
P208
P206
33
As
74.9
Sublimes
615
5.73
AsaOg
As206
51
Sb
121.7
630
1635
6.68
Sb2O,
Sb,Ofi
S3
• Bi
209
271
1450
9.78
BiaO,
BiaO»
(unstable)
THE GREAT CLASSIFICATION 333
A comparison of the elements in this group may be had from the
table on page 332. We should not be surprised to find a few exceptions to
a regular gradation of properties. The surprising thing is that the ele-
ments and compounds change so regularly when they are compared in
tabular form.
Phosphorus. When a popular brand of breakfast food is advertised
as a source of " phosphorus and iron/' this means that these two elements
are present in the grains from which the breakfast food was made, in
the form of compounds. Phosphorus compounds are indeed necessary
for our bodies. We need calcium phosphate [Ca3(PO4)2] in our bones and
lecithin, a complex protein compound containing phosphorus, in our
nerve tissues and brain. We get phosphorus from compounds in our food,
especially wheat, nuts, the white of eggs, fish, and milk.
Natural deposits of calcium phosphate, called mineral phosphate,
are extensive. Great quantities are quarried in northern Africa and in
the United States, especially in Florida, Tennessee, and South Carolina.
This compound is by far the most important phosphorus mineral. Most
of it is used in making fertilizers. Phosphorus is never found in nature
as a free element for it undergoes spontaneous ignition when left exposed
to air.
Let our imagination go back to 1669 in 'Bavaria, Germany, where
we shall see an alchemist named Brand (or Brandt) performing a curious
experiment over a charcoal fire. He is evaporating human urine and from
this is obtaining a solid material, microcosmic salt (NaNH4HPO4'4H2O),
a phosphorus-containing compound. To this witches7 brew he now adds
sand and charcoal, places the mixture within a retort having a long neck,
and heats it once more to redness. While he works, darkness falls, but
he labors on into the night. From the mouth of the retort a white smoke
is seen to arise. He places an earthen dinner plate above the white smoke
and catches some of the smoke as a deposit on the plate. He then carries
the plate into a dark part of the laboratory, where it glows by itself
for quite a while. Here surely is something wonderful! He scrapes
a quantity of the material off the plate, and it catches fire spontaneously.
In those days of powerful superstitions, Brand's achievement seemed
magical. He was invited to the royal courts all over Europe to demon-
strate his experiment. Anyone could see that he was but a step away
from the true elixir of eternal life!
The modern method of making phosphorus from ores is similar to
that of the alchemist except that heat is applied in an electric furnace
(see page 252). A mixture of rock phosphate, sand, and coke is supplied
to the furnace. The phosphorus issues from the furnace in the form of a
vapor. This may be run directly into a waiting tank car and condensed
under water, or it may be sealed in air-free cans.
334
CHEMISTRY FOR OUR TIMES
White or Yellow Phosphorus. Except for military purposes, white
phosphorus is of interest chiefly in the chemical laboratory. In this form
the element is waxy and white if pure and often slightly yellow if impure.
It dissolves \vdl in carbon disulfido, but not in water. Because it ignites
in air spontaneously, it is usually kept under water. (See Fig. 20-9.)
If exposed to air, it reaches its kindling temperature by its own oxida-
tion (see page 55). White phosphorus can be easily cut with a knife if
Courtesy of Chemical Warfare Service, U.S. Army Pkotoyraph
FIG. 20-9. — The burst of a projector shell filled with white phosphorus. The burning
element provides enough light to take its own picture at night.
it is held under warm water while the operation is performed. But care
must be used not to allow it to touch the fingers, for it causes burns that
are painful and slow to heal. It is a poison to the body both externally
and internally, although small amounts are sometimes used in certain
medicines.
Purple or Red Phosphorus. When heated in an airtight retort, yel-
low phosphorus changes into a purple form, composed of very fine,
mealy, garnet-red crystals. This form is not nearly so poisonous as the
white, does not dissolve in carbon disulfide, and does not spontaneously
ignite in air. Such forms of the same element, differing probably in the
number of atoms per molecule, are called allotropic forms.
With an ample air supply, both forms of phosphorus and other
allotropic forms of the element that are less well known burn to form
phosphorus pentoxide. The burning may be summarized by the equation
P4 + 5O2 -» 2P2O6
Phosphorus vapor -f- oxygen from air — * phosphorus pentoxide
THE GREAT CLASSIFICATION 335
This common oxide of phosphorus is a soft, white powder. It combines
readily with water, and can be used for drying gases, but not those with
which it reacts chemically. When the oxide joins with water, its out-
standing action, it finally becomes phosphoric acid solution:
P2O6 + 3H2O -> 2H3PO<
Matches. One of the most interesting uses of phosphorus is in making
matches, although its compounds are used also in making fertilizers,
baking powder, cleaners, and water softeners.
White phosphorus alone is no longer used in the manufacture of
matches; instead, a compound of unpleasant odor, phosphorus sesqui-
sulfide (P4S3), is substituted. This is because the workers in match
factories where white phosphorus was once used suffered from a horrible
Tip, P4 S3, KCI03v Striking
Stick Treated with
Ammonium Phosphate
Bulb-
Oxidizing Agent
and
Combustible Filler ^^ws*™^ KC|Q
Sb2S33,
FIG. 20-10. — Matches must be heated in order to start a fire. Striking a match
changes friction (motion) energy into heat energy. The heat energy starts a chemical
change on the head of the match.
disease that attacked the bones of the face. A prohibitive tax on matches
made with white phosphorus now protects workers.
A match consists of (1) a low-kindling material, such as P4Sa; (2)
some substance that burns readily, such as a mixture of rosin and potas-
sium nitrate (KN08); and (3) potassium chlorate, with other oxidizing
agents. These are held together by glue and mixed with grit, which
increases friction. Matches so made will " strike anywhere."
In safety matches, the low-kindling material is on the box, separate
from the match head, which contains potassium chlorate and antimony
trisulfide (Sb2S8). Let us strike a safety match in the dark. We notice
that the dark, rough material (the low-kindling material) on the booklet
or box burns first. It consists of a thin layer of red phosphorus, antimony
trisulfide, and powdered glass mixed with glue. The whole lighting sur-
face does not take fire because the kindling temperature of phosphorus
in contact with potassium chlorate is lower than that of phogphorus and
air alone. The diagrams illustrate the composition of typical matches.
(See Fig. 20-10.)
336 CHEMISTRY FOR OUR TIMES
QUESTIONS
9. In which group of the periodic table are the elements of the nitrogen family?
10. Tabulate the elements of the nitrogen family, their atomic weights,
atomic numbers, and combining numbers.
11. What is the chief use of the most important compound of phosphorus?
12. Why is phosphorus never found free hi nature?
13. Why should phosphorus be kept under water?
14. Water containing a lump of white phosphorus is boiled. What observation
may be made?
16. Tongs are used when phosphorus is handled. Phosphorus is cut while it
is in water. Give reasons for these ways of handling the element.
16. Some phosphorus is placed in a disli that is floating on water in a con-
tainer. Both dish and container are then covered with a large inverted jar. Soon
the air within the jar (a) decreases in volume, (6) becomes filled with a dense
white smoke that (c) later disappears. Explain each event.
17. Define attotropic forms; give an example.
18. Name one use of phosphorus pentoxide.
19. Write equations for (a) burning phosphorus; (6) dissolving the product
of burning phosphorus in water; (c) burning phosphorus sesquisulfide (PiSs) —
SOz is one product.
20. Compare the use on the head of matches of phosphorus sesquisulfide with
that of white phosphorus.
21. Give a military use for phosphorus.
Arsenic: "Poison, Beware." "These trees have been sprayed with
arsenate of lead/' is a familiar sign. Calcium arsenate is also a well-
known insect poison. Arsenic poisons sprayed on cotton plants kill the
boll weevil; this is often done from an airplane.
The outstanding uses of arsenic depend on its poisonous nature.
White arsenic, or arsenic trioxide (As2C>3), is the substance usually meant
when a person mentions arsenic. Some mountaineers, however, are said
to eat tiny doses of this powder to increase their endurance. By gradually
increasing the amount they build up a tolerance until they can take
many times the normal fatal dose. Surely it would be better to put
arsenic oxide to its regular uses of making certain kinds of glass, of pre-
serving skins of animals, and of making Paris green, copper aceto-
arsenite [3Qu(AsO2)2*lCu(C2H302)2], which is used as an insecticide.
One case is known in which a woman became seriously sick from
eating apples that had been sprayed with arsenic insecticides — from her
THE GREAT CLASSIFICATION
337
own trees, too. Careful washing, especially in dilute hydrochloric acid,
is good treatment for arsenic-sprayed fruit. Egg white is a ready antidote
for arsenic poisoning.
Arsenic has been known since ancient times. The element is silvery
bright when newly made but in time becomes dull gray, hard, and porous.
It burns easily when a fresh chip is dropped into a jar of chlorine. It
also will burn in air. One-half to 1 per cent of arsenic, alloyed with lead,
makes lead shot harder and helps in the manufacture of the shot.
Antimony. The symbol for antimony is Sb; it comes from the Latin
word stibnium. This element also was known to ancient people. Black
antimony sulfide (stibnite) was used as a cosmetic for coloring the eye-
brows in Egypt perhaps as early as 5000 years ago.
Elementary antimony is sometimes found free, but the sulfide is the
chief ore. Red-rubber hot-water bottles, laboratory tubing, and other
such goods are prepared with antimony sulfide (Sb2Sa) as a filler, the
same compound that is used in safety matches.
The element has extensive use in alloys, often with lead. This metal
makes possible the linotype machine, the mechanical type-casting device,
which in turn makes possible the modern newspaper. Antimony in the
type metal causes the latter to expand slightly as it solidifies and to
take a clear impression of the mold into which it was cast or poured.
Other uses for antimony alloys include storage-battery plate grids, bear-
ings, and the coverings of telephone cables (see the next table).
Bismuth. In the Gay Nineties practical joking is said to have reached
the heights of a fine art. For example, a guest at dinner might be supplied
with a spoon that looked like the rest of the tableware but that was
really made of low-melting alloy. A very hot cup of tea would then be
served. Imagine the surprise of the
guest to find his spoon melt away
as he stirred the tea, leaving just
the upper part of the spoon handle
in his hand. In the bottom of his
teacup would remain a silvery
liquid, resembling mercury.
Wood's metal alloy [Bi (4
parts), Pb (2), Sn (1), Cd (1)]
melts easily in hot water. This
substance is called & fusible alloy.
We see it or similar alloys in fire-
protection equipment, used as a
solder to hold together the parts
of a sprinkler head. (See Fig. 20-
Bronze
Screws into
Water Pipe
Deflecting Cap
Parts
Under Tension
Soldered with
Fusible Metal
Cap Flies Off
When Solder
Melts
FIG. 20-11. — Heat from a fire melts the
Wood's metal solder of the sprinkler head.
The parts then fly away from the head,
allowing water to rush forth and douse the
flame.
11.) When a fire starts, the fusible part melts and the parts which are
338
CHEMISTRY FOR OUR TIMES
under tensipn spring out, allowing water to flow from the pipe to which the
sprinkler head is attached, dousing whatever is below. We can notice
these sprinkler heads in stores, theaters, schools, warehouses, and shops,
awaiting a temperature rise to put them into action. Many fire-protec-
tion devices depend on a fusible alloy that melts and flows away when
the temperature rises, thus allowing doors to close, curtains to drop, or
the electric current to stop. A widely used fusible alloy melts at 155°F
(68.3°C).
ALLOYS CONTAINING ANTIMONY OR BISMUTH
Name
Percentage composition
Uses
Babbitt metal ....
Britannia metal . . .
Battery plate
Sn 90, Sb 7, Cu 3
Sn 90, Sb 10
Pb 94, Sb 6
Antifriction bearings
Tableware
In storage batteries
White metal . .
Sn 82, Sb 12, Cu 6
Bearing metal
Type metal
Pewter
Pb 82, Sb 15, Sn 3
Sn 85, Cu 6.8, Bi 6, Sb 1.7
Printing type
Dishes
Wood's metal
Bi 50, Pb 25, Sri 12.5, Cd 12.5
Low-melting alloy, 60°C
Rose metal
Lipowitz alloy ....
Bi 50, Pb 27.1, Sn 22.9
Bi 50, Pb 27, Sn 13, Cd 10
Low-melting alloy, 93.75°C
Low-melting alloy, 70-74°C
The bismuth for this alloy may come from Bolivia, where it is found
both free and combined in oxides and sulfides. The metal has a notice-
able pink tint, although it is in general silvery. It is brittle and by far
the densest of the members of this group of elements. Some bismuth is
obtained in the United States as a by-product of the electrolytic refining
of lead.
When we shake bismuth nitrate with water, we find that a clear solu-
tion is not produced. The compound acts on water to produce a white
substance.
O
Bi(NO3)3 + H2O
Bi
2HNO8
NO3
This bismuth compound, bismuth oxynitrate, along with others that
may form at the same time, is called bismuth subnitrate, a well-known
medicinal. The same material has been used in face powders for hundreds
of years. It has been discovered that the compound acts with perspira-
tion to make nitric acid. Nitric acid turns the flesh yellow and is irritat-
ing. The desirability of using this compound in cosmetics is at least
questionable.
SUMMARY
Earljj history of classification of elements: Dftbereiner arranged groups of
three similar elements and showed that the atomic weight of the middle element
THE GREAT CLASSIFICATION 339
of a group was approximately that of the average of the other two. Newlands
arranged elements according to atomic weights and discovered a repetition of
properties in octaves. Meyer and Mendeleyev, especially, constructed a periodic
table. Mendeieyev first stated the periodic law, pointing out the periodic relation-
ship of the properties of the elements, as follows: The chemical properties of the
elements are a periodic function of their atomic weights.
The usefulness of Mendeleyev's table lay in the fact that it
1. Classified the elements
2. Aided in the discovery of new elements
3. Provided a check on the accuracy of atomic weights
The work of Moseley, who used the X-ray spectrograph, led to a new state-
ment of the periodic law, as follows : The properties of the elements are a periodic
function of their atomic numbers.
A modern periodic classification of elements has advantages over the old
because the altered form is (1) superior in a study of atomic structure and (2) a more
useful tool in chemical investigations.
The nitrogen family, Group Vb : phosphorus is never free in nature. Its chief
compound is calcium phosphate, which is found in rock phosphate and in bones.
Some organic proteins contain phosphorus.
Elementary phosphorus is prepared by heating rock phosphate with coke and
sand in an electric furnace without air. Phosphorus vaporizes and is condensed
under water in the white form. White phosphorus is a waxy solid, soluble in
carbon disulfide and insoluble in water. White phosphorus ignites spontaneously
and is poisonous. The red form of phosphorus is not soluble in carbon disulfide,
it has a higher kindling temperature than the white, and it is not so poisonous.
Both allotropic forms burn, forming phosphorus pentoxide, a powerful dehydrat-
ing agent.
Matches are classified as " strike anywhere" and safety. Strike-anywhere
match heads contain phosphorus sesquisulfide, rosin, potassium chlorate, glue,
and grit. Safety match heads contain antimony sulfide, potassium chlorate, glue,
and grit; there is red phosphorus on the box. The sticks are treated to prevent
afterglow.
Arsenic compounds are poisonous and are used extensively as insecticides.
Elementary arsenic is used to harden lead shot.
Antimony is found free in nature or as a sulfide. Its chief use is in the prepara-
tion of alloys, especially type and bearing metals.
Bismuth is found free in nature. It is an ingredient of certain fusible (low-
melting) alloys. Compounds of bismuth are used to some exent in medicines.
QUESTIONS
22. Name an important use for each of the following : white arsenic ; antimony
sulfide; bismuth oxynitrate; lead arsenate.
23. Name one alloy containing each of the following elements: (a) arsenic;
(b) antimony; (c) bismuth. Tell the other elements in each alloy.
24. Explain the means of protecting a theater audience from a fire within
the projection booth. (See Fig. 20-12.)
340
CHEMISTRY FOR OUR TIMES
FIG. 20-12. — Flammable film is a fire hazard in theaters. Fusible alloys protect both
audience and operator.
MORE CHALLENGING QUESTIONS
25. What is the percentage of copper in Paris green?
26. Which contains the higher percentage of arsenic, calcium arsenate
[Ca3(AsO4)2] or lead arsenate [Pb8(AsO4)2]?
27. White phosphorus may be copperplated by placing a stick of it in copper
sulfate solution. A deposit of metallic copper coats the stick, making it easier to
handle. Balance the following equation:
P + CuSO4 + H2O -f Cu + H2SO4 + H8PO4
This reaction illustrates the use of copper sulfate solution as a remedy for phos-
phorus burns.
UNIT
FIVE
Courtesy of Texas Gulf Sulphur Company
CHEMICAL INDUSTRIES
IN 1865 a group of geologists drilled a hole in the earth in Louisiana
in the hope of finding oil beneath the surface. No oil was found,
but at a depth of about 500 ft sulfur was discovered. Attempts to
mine this sulfur resulted in disaster; for the shaft had sunk through
quicksand and poisonous hydrogen sulfide fumes overcame the
miners.
Then a young chemist, Herman Frasch (1852-1914), solved the
problem by studying the properties of sulfur. The melting point of
sulfur is 112.8°C, a little above the boiling point of water, 100°C.
Frasch had the idea of melting the sulfur in the earth by using water
heated under pressure. Then the molten sulfur could be raised to
the surface by pumping it through pipes. Here is the story of the
critical trial in his own words:
When everything was ready to make the first trial . . . , we raised steam
in the boilers and sent the superheated water into the ground without a hitch.
After permitting the melting fluid to go into the ground for 24 hours, I
decided that sufficient material must have been melted to produce some sulfur.
The pumping engine was started on the sulfur line, and the increasing strain
against the engine showed that work was being done. . . . More steam was
supplied, until the man at the throttle sang out at the top of his voice, " She's
pumping." A liquid appeared on the polished rod, and when I wiped it off I
found my finger covered with sulfur. Within five minutes the receptacles under
pressure were opened, and a beautiful stream of the golden fluid shot into the
barrels we had ready to receive the product. After pumping for about 1 5 min-
utes the 40 barrels we had supplied were seen to be inadequate. Quickly we
threw up embankments and lined them with boards to receive the sulfur that
was gushing forth; and since that day no further attempt has been made to pro-
vide a vessel or a mold into which to put the sulfur.
When the sun went down we stopped the pump to hold the liquid sulfur
below until we could prepare to receive more in the morning. The material
on the ground had to be removed, and willing hands helped to make a clear
slate for the next day. When everything had been finished, the sulfur all piled
up in one heap, and the men had departed, I enjoyed all by myself this
demonstration of success. I mounted the sulfur pile and seated myself on the
very top. It pleased me to hear the slight noise caused by the contraction of
the warm sulfur, which was like a greeting from below — proof that my object
had been accomplished. ...
This was especially gratifying as the criticisms I had received from tech-
nical papers and people who had heard what I was attempting to do had been
very adverse. ... A fair illustration is the remark ofrthe mail boy who drove
me to the railroad the morning after our first pumping. He said: "Well, you
pumped sulfur sure, but nobody believed it but the old carpenter, and they say
he's half crazy!"
This solid lump of sulfur covers about six
acres and is five stories high.
Courtesy of Texas Gulf Sulphur Company
The load of sulfur on this conveyer
belt is automatically weighed as it passes
the shed.
UNIT FIVE CHAPTER XXI
THE ACID HEAVY CHEMICALS
We are now ready to discuss the big business of chemistry. The acid
heavy chemicals — sulfuric, nitric, hydrochloric, and phosphoric acids —
are important in a big way. Demands for these Bubstances are for car-
load lots, not test tubes full. Chemists control the manufacture of these
acids; chemical engineers design the apparatus and containers for them;
and chemists with their specially designed apparatus take samples and
check on their purity. In a recent year about 8 million tons of (dilute)
sulfuric acid valued at about $8 per ton were used in the United States
alone. Although these^acids are not spectacular, they are the necessary
background for the more flashy products of the chemist's art. They are
the lifeblood of our industrial organism.
At a modern plant for producing sulfuric acid, a truck drives up with
some sulfur and dumps it into a bin. No other sign of activity is noted.
The attendant checks the meter readings and makes certain routine
tests. The operation is practically automatic. Yet many tons of sulfuric
acid are being produced by this plant daily. It is shipped out through
pipes or in tank cars or tank trucks that have acid-resisting linings.
These acids are needed for the making of fertilizers, rayon, explo-
sives, motion-picture films, and paper, for refining petroleum, and for
hundreds of other purposes.
The Source of Sulfuric Acid — Sulfur. Some of the sulfur used for
making sulfuric acid is found in compounds: hydrogen sulfide (H2S),
metal sulfides such as iron pyrites [fool's gold (FeS2)], and zinc blende
(ZnS). A large amount of the sulfuric acid of commerce today, however,
is made directly from sulfur. (See Fig. 21-1.)
Free sulfur is found around volcanic regions in Sicily, Japan, Greece,
and Mexico; there are deposits below the surface of the earth in Texas
and Louisiana. Sulfides of many metals are commonly found — lead,
iron, copper, zinc, and arsenic. Gypsum (CaSO4'2H2O), Epsom salts
New Terms'
rhombic oleum polymer
monclinic aqua fortis polymerization
desiccator
343
344
CHEMISTRY FOR OUR TIMES
(MgSO4'7H2O), and barite (BaSOO are among the sulfates found in
nature. Also, certain proteins contain sulfur; compounds found in eggs
and in any other food that turns a silver spoon black have sulfur combined
in them.
Sulfur is a yellow substance, hard and brittle if in the cylindrical,
or roll, sulfur form or a soft yellow powder if in the form called flowers
Courtesy of Texas Gulf Sulphur Company
FIG. 21-1. — This is the Frasch method of mining sulfur — notice the three concentric
pipes. The break in the diagram represents 700 ft of rock. In order to get the water
(outermost pipe) hot enough to melt sulfur, a high pressure is used.
of sulfur. It is about twice as dense as water, insoluble in water, soluble
in carbon disulfide (082), a nonconductor of electricity, and without
marked odor.
Let us put some sulfur into a test tube and heat it very slowly so that the heat
has time to enter the poorly conducting sulfur. When the sulfur reaches 112.8°C,
it forms a clear, straw-colored liquid, which rapidly darkens to amber color and
thickens when the temperature is raised. At about 160°C the test tube can be
THE ACID HEAVY CHEMICALS
345
inverted without loss of the sulfur, for it is now like thick, dark tar. (See Fig. 21-2,)
More heating makes it flow again while still dark, and finally it boils at 444.6°C.
The vapor of sulfur formed in such an experiment is cloudy, with some condensed
sulfur in it. When the sulfur is boiling, some of the vapor con-
denses in the form of a yellow powder (flowers of sulfur) on
the cooler walls of the test tube. The hot sulfur vapor burns
when it reaches the air. A blue flame shows this, and a color-
less gas that has a sharp and choking odor is formed (sulfur
dioxide).
If this molten sulfur is quickly chilled by pouring it into
cold water, a dark, sticky mass is formed that resembles
smoked rubber in appearance. This plastic form of sulfur can
be molded into any desired form while warm, but it cools
quickly and hardens into a shapeless, dark mass, which
gradually becomes yellow again.
The ordinary crystalline form of sulfur is called
rhombic sulfur, and it consists of a matted group of
crystals. Separate crystals are obtained by making a
solution of sulfur in carbon disulfide (CS2) and evapo-
rating the solvent slowly. (See Fig. 21-3 A.) A second
crystalline form can be made by pouring sulfur that
has been heated above 115°C into a paper cone held in a funnel.
The crystals this time are needlelike in shape, and they start to
form on the cooler top and at the sides first. (See Fig. 21-3JB.) As soon
FIG. 21-2.—
Plastic sulfur flows
like tar at 160°C.
When cooled, it
resembles well-
chewed chewing
gum for a while.
Finally it hardens
to the stable rhom-
bic form.
A Rhombic
B Monoclinic
C Cooled Monoclinic Crystals become
Matted Tiny Rhombic Crystals
FIG. 21-3. — A, stable crystals of sulfur are diamondlike rhombs. B, above 115°C,
sulfur crystallizes in the monoclinic form. C, after monoclinic crystals have cooled, the
rhombic form is present although the general outline remains the same.
as the top has formed a crust, it is pierced with a matchstick and the
excess molten sulfur poured off. Then the paper is broken open, and. a
bristling miniature forest of monoclinic sulfur crystals is discovered. (See
346 CHEMISTRY FOR OUR TIMES
Fig. 21-3C.) These crystals are stable as long as the temperature remains
above 95.5°C. When they are cooled below this temperature, they slowly
change into the ordinary rhombic form, although retaining the same
outward needlelike form.
Sulfur burns readily, S + 02 — » S02, and joins directly with many
other elements. Zinc dust mixed with powdered sulfur and heated burns
rapidly. Zn + S — > ZnS. Copper will join sulfur easily. 2Cu + S — » Cu2S.
Courtesy of Koppers Company, Inc.
FIG. 21-4. — The sulfur candle as a means of fumigation has a limited use. Thor-
oughly scrubbing a room with soap and water while admitting sunlight and fresh air
is considered a satisfactory disinfection after a contagious disease.
Lead, mercury, silver, arsenic, chlorine, and carbon all form sulfides when
joined to sulfur; and when hydrogen is bubbled through melted sulfur,
some hydrogen sulfide is formed. Sulfur is quite like oxygen chemically,
and the sulfides correspond to oxides.
Most of today's sulfur is used to make acids and chemical products,
but over one-fourth of it, about 2.5 million tons yearly, is used to make
sulfuric acid for fertilizers. The making of paper requires much sulfur
dioxide, made by burning sulfur. Free sulfur goes into making gun-
powder, and a little goes into medicines. The use of finely divided sulfur
on plants and pets to kill pests depends in part on the fact that sulfur
very slowly oxidizes and forms some sulfur dioxide.
QUESTIONS
1. In what three forms is sulfur found in nature?
2. Describe in detail the changes that can be noticed when sulfur vapor cools
slowly.
3. Tell how to prepare (a) rhombic sulfur crystals; (6) monoclinic sulfur
crystals; (c) plastic sulfur.
THE ACID HEAVY CHEMICALS
347
4. Where are the world's most important supplies of sulfur located?
5. What commercial form of sulfur would be selected for making (a) lime-
sulfur spray; (6) dusting sulfur for agricultural use?
6. Write formula equations for (a) the burning of sulfur; (6) union of sulfur
with magnesium; (c) with zinc; (d) with iron; (e) with hydrogen; (/) with copper.
7. What is the most important use of sulfur?
8. For what purpose is sulfur used (a) in paper making; (6) in straw-hat
making; (c) in a drugstore; (d) in agriculture; (e) by
stonemasons? l*~Deflagrating
Spoon
9. What property of sulfur makes it a useful part of
certain types of electrical apparatus? What other prop-
erty of sulfur limits this use? X."lc*S Cardboard
10. The early Spanish explorers in Mexico obtained
sulfur from the mouths of volcanoes in that country. For
what purpose did the Spaniards use the sulfur they
obtained?
FIG. 21-5.— One of
Sulfur Dioxide. The simplest way to make sul- the simplest ways to
fur dioxide is to burn sulfur or a sulfide. (See Fig. make sulfur dioxide is
21-5.) Both these fuels form oxides when heated to burn sulfur'
in air. Sulfur dioxide issues from volcanoes as a secondary product, but
fortunately there is not much of it, for it kills vegetation.
FIG. 21-6. — Any sulfite or bisulfite plus an acid yields sulfur dioxide gas. This appara-
tus is a suitable one in which to carry out the reaction.
Sulfurous acid in water solution can be made in several ways, one
of the simplest being the action of an acid on a sodium hydrogen sulfite
NaHSOa + HCI -» NaCI + H2SO3
348
CHEMISTRY FOR OUR TIMES
We make sulfur dioxide gas in the laboratory by decomposing sulfurous
acid (H2SOi). (See Fig, 21-6.)
H2S04— £ 7i H2SO, -+ H20 + SO* T
The acid is quite unstable and, like car-
bonic acid, cannot be made and isolated
in the pure state.
Hot concentrated sulfuric acid will ox-
idize copper and is reduced to sulfur di-
oxide. (See Fig. 21-7.)
Cu + 2H2SO4 -» CuSO4 -f 2H3O + SO2 T
When sulfur dioxide is made by burn-
ing sulfur, a slight amount of the hot
sulfur dioxide acts on more oxygen of the
air to form a higher oxide of sulfur, sul-
fur trioxide (S03).
2SO2.4-O2 -4 2SO8
This change is a desired one; it has been
studied by chemists to discover how it
may be encouraged. The metal platinum,
as a catalyst, has the desired effect, but
because of its high cost iron oxide
(Fe203), molybdenum oxide, and vanadium
oxide are also used.
A Bleach for a Season. Sulfur dioxide in
solution is essentially sulfurous acid. It acts as
a mild acid, tastes sour, and acts on bases to
form sulfites.
Sulfurous acid absorbs oxygen readily; it is
therefore a good reducing agent.
FIG. 21-7. — When hot concen-
trated sulfuric acid is used to at-
tack copper, the experiment
should be performed in a venti-
lated hood. The acid has a similar
action on sulfur or carbon.
H2S08 + [O] -4 H2S04
Some bright-colored flowers lose their color
and wilt in moist sulfur dioxide. This acid,
then, is a bleaching agent. (See Fig. 21-8.)
Many straw hats are bleached with sulfur di-
oxide or dilute sulfurous acid. The bleaching
is accomplished by combination of the organic
matter in the straw with sulfur dioxide, form-
ing an unstable compound.
Now suppose a hat that has been bleached
with sulfur dioxide is worn for a season. Sun-
Potassium
Permanganate
Solution
KMn04
Sulfurous
Acid
H2S03
FIG. 21-8. — When purple
potassium permanganate so-
lution is mixed with sulfur-
ous acid, a startling loss of
color develops. The perman-
ganate ion (Mn(>7) is re-
duced, and the sulfite ion is
oxidized. Colorless products
are formed.
THE ACID HEAVY CHEMICALS 349
shine helps decompose the unstable compound, liberating sulfur dioxide
slowly. The yellow-brown color of the original straw returns, even if the
hat is kept carefully clean.
Sulfur dioxide changes orange shellac to white and bleaches dried
fruits, flour, silk, and feathers. It is sometimes added to molasses, dried
fruits, and canned corn, but the effect on health of the use of sulfur
dioxide in foods is questioned by some observers.
The chief use of this colorless gas is for making sulfuric acid, but much
of it is used as a refrigerant in household refrigerators because it readily
changes to a liquid. The choking, sharp-odored gas is quite soluble in
water; the refrigerator serviceman can therefore temporarily protect him-
self against escaping gas by using a damp cloth over the nose. Sulfur
dioxide is dense and tends to settle. One liter weighs over twice as
much as a liter of air at the same temperature and pressure.
QUESTIONS
11. Write equations for three ways of making sulfur dioxide.
12. Write formula equations for the actions of sulfur dioxide on (a) water; (6)
sodium hydroxide solution; (c) active oxygen.
13. List four physical properties of sulfur dioxide.
14. State four uses of sulfur dioxide.
16. Contrast the chemistry of bleaching by the use of sulfurous acid with that
by hypochiorous acid.
Modern Methods of Making Sulfuric Acid. The acid of the great-
est importance is sulfuric acid. Very little of it is stored. The tonnage of
sulfuric acid produced each month, therefore, is a reliable index of gen-
eral business conditions in an industrial nation.
Two general methods are used for making sulfuric acid. These will
be considered in turn. They are: (1) the contact process; (2) the chamber
process.
1. The contact process for making sulfuric acid, or oil of vitriol, gets
its name from the fact that a mixture of sulfur dioxide and oxygen changes
to sulfur trioxide rapidly when it comes in contact with the catalyst.
The steps in the process essentially are: (a) producing sulfur dioxide by
burning sulfur or a sulfide in air; (6) cleaning the gas from dust and
impurities that would tend to "poison" the catalyst; (c) passing sulfur
dioxide with more air at the right temperature over a catalyst and
obtaining sulfur trioxide; (d) absorbing the sulfur trioxide formed.
Equations for the reactions are
(a) S + Os -+ SO,
(c) 2SO2 + O* -» 2SO,
(d) SO, + H»O -4 H«SO4
350
CHEMISTRY FOR OUR TIMES
In actual practice the construction and operation of a sulfuric acid
plant require much more attention to details than the diagram suggests.
(See Fig. 21-11.) The equation (d), for example, shows that the sulfur
FIG. 21-9. — With this apparatus, the action of sulfur dioxide on iron is carried out.
trioxide is absorbed in water. It is found to be better economy, however
to use concentrated sulfuric acid instead of water, obtaining fuming
sulfuric acid, or oleum (H2S04'SO3), as a product, for the sulfur trioxide
SO;
Catalyst,
Platinized Asbestos
• Iron Oxide
To Fume
Hood
FIG. 21-10. — Sulfur trioxide, important industrially, may be prepared in the laboratory
by using this apparatus.
escapes through a spray of water as a mist. The addition of dilute sul-
furic acid to oleum makes the resulting acid of any desired concentration.
2. The lead-chamber process takes its name from the lead room, or
chamber, in which the action occurs. (See Fig. 21-12.) Sheets of lead
THE ACID HEAVY CHEMICALS
351
about as thick as this book and as large as a table top are melted together
at the edges and supported from steel girders by wires to form a room
about twice the size of a large schoolroom. Sulfur dioxide and air are
Purifier
Hopper
Sulfur
Burner
' Cold
Water
Catalyst
on Trays
Loose
Quartz
Oleum
(H2S04'S03)
FIG. 21-11. — A simplified diagram of a contact sulfuric acid plant shows the steps
in the process. Many such plants are manufacturing this important acid in huge
quantities daily.
introduced into this room along with steam and oxides of nitrogen. The
oxides of nitrogen serve as the catalyst, or carrier, of oxygen. They are
recovered, for the most part, and used time and time again with only a
Steam,
Oxides
of
Nitrogen
Lead Walls
Dilute Sulfuric
Acid
FIG. 21-12. — The broth from the sulfurous witches' brew shown above gathers on
the leaden floors of the chamber. Chemists call this method of making sulfuric acid the
chamber process.
little loss. The action in the lead chambers is complicated, but essentially
the following equations represent it:
(a) S + O2 -» SO2
(6) SO2 + H2O -» H2SO3
(from steam)
(c) H2SO3 + . [O] 4 -> H2SO4
(from oxides of nitrogen)
Inside the chamber a sour drizzle of acid falls slowly and collects on the
floor, ready to be drawn off for use.
Many industrial processes, such as smelting metals, produce sulfur
352 CHEMISTRY FOR OUR TIMES
dioxide. This gas would be wasted if it could not be sent into a lead
chamber and converted into sulfuric acid, and this is done in many
industrial establishments. The contact method is not used, for the
impure gas would " poison" the catalyst. Often the acid is used directly
by the company producing it.
Comparison of Contact and Lead-chamber Sulfuric Acid. Most
of the modern installations for making sulfuric acid are of the contact
type because the process is simple, cheap, and compact. A contact plant
can be erected on the space occupied by a large dwelling house and can
be clean and attractive enough for an afternoon fancy-dress bridge party.
Also, the contact process makes concentrated acid that is useful for many
purposes, such as the manufacture of dyes and explosives.
The liquid product of the lead chambers is called " chamber acid."
Chamber acid is dilute and is extensively used for fertilizer making. If
concentrated acid is needed from the lead-chamber product, the dilute
acid is heated in suitable vessels until the right amount of water has
evaporated. A purer acid can be made by the contact process, the chamber
acid often containing small amounts of lead sulfate, arsenic oxide, and
oxides of nitrogen. Contact acid can be made having a density of 1.84 g
per ml, (93 per cent H2S04 by weight), while the chamber product has
a density of 1.5 to 1.6 g per ml (60 to 70 per cent H2S04 by weight).
Sulfuric Acid, the Dr. Jeykl and Mr. Hyde of Chemistry. Dilute
sulfuric acid is a typical acid. It shows the actions of all good sources
of protons:
H2SO4 ?=i 2H+ + SOj -
It acts on blue litmus to turn it pink; it attacks active metals like zinc
and liberates hydrogen gas; it changes metal oxides, hydroxides, and
carbonates to sulfates.
The presence of sulfate ions can be proved by uniting them with
barium ions. A white precipitate of barium sulfate forms immediately.
Barium sulfate is insoluble in common acids. These facts serve as a test
for identification of the sulfate ion (SOj* "") in solution and to distinguish
it from sulfite ion (SOj "") since barium sulfite (BaSOs) dissolves in acids.
The following are used for testing for sulfate ion:
BaCI2 -f H2SO4 -f BaSO4 1 + 2HCI (formula equation)
(insoluble in acid)
Ba++ -f- SO" -» BaSO4| (ionic equation)
Concentrated sulfuric acid has vastly different properties from the
dilute. This oily liquid is almost twice as dense as water (1.84 g per ml)
and is a vicious liquid to use. First and foremost, it has a terrific thirst.
It seeks water from almost any source with such vigor that the heat
produced may change the water into steam and cause an explosion. In
THE ACID HEAVY CHEMICALS
353
fact, acid flying from this cause is an altogether too common accident-
For this reason we repeat the warning that it is necessary to pour the
denser acid into water with much stirring when
the acid is diluted, never in the reverse order.
(See Fig. 21-13.) The mixture is allowed to
cool before being used. Because of its strong
tendency to combine with moisture, concen-
trated sulfuric acid is often used in desic-
cators, containers in which materials are dried
and kept dry.
The elements of water are extracted by
concentrated sulfuric acid from wood, sugar,
or paper, leaving black carbon. (See Fig. 21-
14.) In like manner, water is extracted when
concentrated acid is left for even a short time
on the hands, causing a painful burn.
Second, concentrated sulfuric acid differs
from dilute in that the concentrated sulfuric
acid is an oxidizing agent. Thus, the action
may be considered to be
Acid
Into
Water
FIG. 21-13.— The correct
method of mixing sulfuric
acid and water can be re-
called by the letters:
acid
n
water
o
H2S04 = H20 + S02 + [O]
For this reason we were able to use concentrated sulfuric acid to attack
copper in making sulfur dioxide.
2H2SO4 + Cu -> CuSO4 H-
2H2O + SO2 1
Sugar
Black Charred
Material
Concentrated
Sulfuric Acid
FIG. 21-14. — The thirst of sulfuric
acid for water is emphasized by its mak-
ing a charred black biscuit from a tea-
spoonful of sugar.
Third, in spite of these vigorous
actions, concentrated sulfuric is not
dissociated into ions. The pure
liquid does not conduct electricity
and when cold does not affect met-
als like iron. It is shipped in steel
tank cars.
Fourth, concentrated sulfuric acid has a high boiling point, 338°C for
98 per cent pure acid. This temperature of boiling is higher than that
of almost all other acids, and for this reason sulfuric acid may be used
in their preparation. We shall examine the making of other acids in
detail after a brief description of the uses of sulfuric acid.
Uses of the King of Acids. A paper clip and a barbed-wire fence
both need sulfuric acid in the processes of their manufacture. When a
batch of steel wire is annealed (softened) in an oven and withdrawn,
the oxygen of the air forms a film of iron oxide on the surface of the wire.
354
CHEMISTRY FOR OUR TIMES
Before the wire can be drawn into smaller sizes, this oxide coating must
be removed or the wire will not be strong and uniform. "Pickling" in
sulfuric acid removes the coating. (See Fig. 21-15.) Afterward lime is
used to neutralize any acid remaining on the steel.
The refining of metals, electroplating, the making of many chemicals,
the refining of petroleum, and the making of rayon, smokeless powder
(guncotton) , TNT, and many other explosives all need sulfuric acid.
uourtesy oj The a. F. (jooancn Company and Pennsylvania salt Manufacturing company
FIG. 21-15. — The oxide scale on this copper wire is to be removed by dunking the
metal in a bath of dilute sulfuric acid. In order to prevent the tank from being attacked
also, it has been lined with rubber and acid-resisting bricks.
Gases are dried by bubbling them through concentrated sulfuric acid.
Chlorine, oxygen, hydrogen, or nitrogen may be so treated; but if am-
monia is bubbled into the acid, crystals of ammonium sulfate [(NH^SOJ,
an important fertilizer, form. Chief among the uses of sulfuric acid is its
action on certain salts to produce other acids (see page 357).
QUESTIONS
16. Write the formula that represents (a) oleum; (b) oil of vitriol; (c) dilute
suifuric acid; (d) concentrated sulfuric acid.
17. By what processes is sulfuric acid produced commercially?
18. Review the chief steps in the newer method of making sulfuric acid.
19. Review the chief steps in the older method of making sulfuric acid.
20. Compare sulfuric acid made by the two chief methods in respect to (a)
purity; (b) concentration; (c) uses.
21. Describe a test by which (a) sodium sulfide can be distinguished from
sodium sulfate; (b) sodium suifite from sodium sulfate.
22. In two parallel columns list four properties of dilute sulfuric acid and four
of concentrated sulfuric acid.
THE ACID HEAVY CHEMICALS
355
23. Tell the correct method of diluting concentrated sul-
furic acid, and point out the reason for doing the job in the
manner described.
24. Write formula equations for the action of dilute sul-
furic acid on (a) potassium hydroxide; (6) potassium car-
bonate; (c) zinc oxide; (d) calcium hydroxide; (e) ammonia.
»
25. What is the percentage of hydrogen in sulfuric acid?
Of sulfur?
Hydrogen Sulfide. When dilute sulfuric acid, or
hydrochloric acid, is placed on solid iron sulfide, an
odorous gas is evolved. It is this gas, hydrogen sulfide
(H2S) , more than any other that has given the odorous
reputation to chemical laboratories.
FeS -f H2SO4 -> FeSO4 + H2S \
TURK
07 m '
Courtesy of Matkeson
Company
FIG. 21-16.— A
steel bottle that
contains hydrogen
sulfide gas for use
in the laboratory.
The fact that this gas is noticed when eggs age
and decay and that it is present in the evil-smelling
waters of sulfur springs gives an ample idea of its
fragrance. It is used extensively in chemical analysis
and therefore merits our study. It can also be made
conveniently by adding water to aluminum sulfide or
by heating together powdered rosin or paraffin and
sulfur.
Hydrogen sulfide is a colorless gas that dissolves
moderately well in water and is slightly denser than
"air. When inhaled it is not only disagreeable but
extremely poisonous, almost equal to the
treacherous carbon monoxide in its death-
dealing effects. This gas is more gentlemanly
than carbon monoxide, however, for it gives
warning by its odor.
In laboratories it may be used from a
cylinder equipped with proper valves or may
be made by automatic gas generators. Sev-
eral designs of automatic gas generators are
used, but all depend on the pressure of the
gas acting on the surface of the liquid acid
to push it away from the solid, thus stop-
tor^l^'flS'T P™S f«rther c"al art^ «ntil more gas
gas coming from the source as is withdrawn from the generator. (See Fig.
soon as the supply is not in use. 21-17 )
E^bSdffi* ttPPtt"ltUS AS We haVe lea™ed' this *aS b«rnS J» ' ™
356 _ CHEMISTRY FOR OUR TIMES _
steps (see page 62). The first step may be seen when the flame is cooled
against a glass surface. Yellow sulfur deposits, and beads of moisture
collect.
2H2S + O2 -4 2H2O + 2S
When hydrogen sulfide is burning freely, the products are those expected
of complete burning, sulfur dioxide and water.
2H2S + 3O2 -» 2H2O + 2SO2
In solution with water, hydrogen sulfide dissociates in two steps,
splitting off two protons, one at a time.
H2S ;=* H+ + HS- *± H+ + S~-
The solution is weakly acidic, containing hydronium ions (H3O+) due to
the presence of these protons, and is called hydrosulfuric acid.
Many metal sulfides are insoluble in water. We find in nature a
number of metal sulfides that are important ores. These include lead
sulfide, galena (PbS); zinc sulfide, sphalerite (ZnS); and copper sulfide,
qjialcocite (Cu2S). Pyrite (FeS2), or fool's gold, is an ore of sulfur.
When hydrogen sulfide gas is bubbled into a solution containing ions
of a metal, if the acidity is not high, the metal and the sulfide ions may
unite, forming an insoluble sulfide. In some cases these sulfides are the
same as the natural sulfide ores. For example,
2AsCI3 + 3H2S -> As2S3 1 -f 6HCI (formula equation)
2As+ ++ -f 3S~ - -4 As2S3 1 yellow precipitate (ionic equation)
2Sb+++ -f- 3S~ ~ -» Sb2S3 1 orange precipitate (ionic equation)
2Ag+ + S~ ~ — » Ag2S j black precipitate (ionic equation)
Qu-f + _^_ s~ ~ Ht CuS | black precipitate (ionic equation)
+ S~ ~ -> PbS I black precipitate (ionic equation)
All these precipitates form in solutions that are feebly acid and some
even in strong hydrochloric acid. The last one listed is often used as a
test for the presence of the sulfide ion, for lead compounds in solution
easily turn black when they meet hydrogen sulfide. Some states require
that manufactured household fuel gas shall contain enough hydrogen
sulfide to cause a blackening of paper moistened with lead acetate solu-
tion. The hydrogen sulfide in fuel gas causes a stench that warns people
when there is a leak.
Pb(C2H3O2)2 + H2S -4 PbSl + 2HC2H3O2
lead acetate (black) acetic acid
Sulfides of iron and zinc do not precipitate if the solution is more
than slightly acidic. With an alkaline solution of ammonium sulfide a
white precipitate of zinc sulfide and a black precipitate of iron sulfide
can be formed readily.
(NH4)2S -f ZnCI2 -» 2NH4CI + ZnS|
(white)
THE ACID HEAVY CHEMICALS 357
Sodium, potassium, and calcium sulfides are very soluble and do not
precipitate from water solution.
When hydrogen sulfide is bubbled through hydrogen peroxide or a
similar oxidizing agent, a milky precipitate of sulfur, which may become
slighlly yellow, forms.
H2O2 + H2S -> 2H2O 4- S i
If ferric chloride solution is used and hydrogen sulfide gas bubbled
through it, a precipitate of sulfur forms likewise.
2FeCI3 4- H2S -4 2FeCI2 + S j + 2HCI
ferric ferrous
chloride chloride
This is clearly a case of electron transfer, or oxidation and reduction.
The S — ion loses two electrons, one to each of two ferric ions (Fe"1"4^),
converting them into two ferrous ions (Fe"*"1"). The ferric chloride is as
much the oxidizing agent in this case as was the hydrogen peroxide that
furnished oxygen in the previous equation. Hydrogen sulfide in both
illustrations furnishes sulfide ions, which act as the electron-lending,
or reducing, agent (see page 503).
QUESTIONS
26. Can hydrogen sulfide be prepared readily (a) by the action of hydrochloric
acid on copper sulfide; (6) by the action of nitric acid on iron sulfide?
27. When hydrogen sulfide is bubbled through hydrogen peroxide, a fine white
powder forms as a precipitate. Name the precipitate.
28. Write formula equations for (a) the action of water on aluminum sulfide;
(6) the action of ferrous sulfide and hydrochloric acid; (c) the action of ferrous
Bulfide and dilute sulfuric acid; (d) incomplete burning of hydrogen sulfide; (e)
complete burning of hydrogen sulfide.
29. Tell how to collect sulfur dioxide in the laboratory; hydrogen sulfide.
30. List five sulfide precipitates with their colors.
31. Classify as strong or weak all the acids so far mentioned in this chapter.
32. Tell how to form iron sulfide by precipitation.
33. Show by equations how hydrogen sulfide can be changed into sulfuric acid.
34. Show by equations how hydrogen sulfide can be produced, starting with
iron, sulfur, common salt, and sulfuric acid as raw materials.
36. From the formulas, find the density of each of the following gases: sulfur
dioxide; hydrogen sulfide; methyl mercaptan (CHjSH) vapor. How many times
as dense as air is each?
The Action of Sulfuric Acid on Common Salt — Hydrogen
Chloride. When sulfuric acid (HaSCh) is added to common salt, a foam
358 CHEMISTRY FOR OUR TIMES
forms made of bubbles of a sharp, choking gas that fumes f oglike in moist
air. This disagreeable gas is called hydrogen chloride, and its solution in
water is named hydrochloric acid in chemical laboratories and sometimes
muriatic acid in industries. The gas leaves the reaction mixture at room
temperatures, since its boiling point is low, — 83.7°C. Examination of
the solid remaining in the flask shows that just one hydrogen atom of
the sulfuric acid has been replaced and that sodium hydrogen sulfate
(sodium acid sulfate or bisulfate) is the other product.
NaCI 4- HHSO4 -> NaHSO4 -f HCI t
salt sulfuric acid sodium hydrogen hydrogen chloride
(concentrated) sulfate gas
This compound contains some of the hydrogen originally present in the
acid; therefore, it is sometimes called an acid salt. The HSOj" ion is an
acid.
At a higher temperature, sodium hydrogen sulfate will also act on
common salt.
NaCI + NaHSO4 -4 Na2SO4 -f HCI |
salt sodium hydrogen sodium sulfate hydrogen chloride
sulfate (normal salt) gas
Another method of making hydrogen chloride is by joining the ele-
ments hydrogen and chlorine directly.
H2 -f CI2 -4 2HCI
Both elementary gases can be obtained by the electrolysis of salt water
(see page 374). They join vigorously, liberating much heat as they burn
with a pale green flame.
Nature makes this acid in the stomachs of some animals, using a
temperature no higher than that of the body, and omits the sulfuric acid.
Chloride ions are gathered from salt in the food that we eat, and some
small amount (0.5 per cent) of hydrochloric acid is present normally in
the digestive fluid of the stomach, gastric juice, where it aids digestion of
fSbd.
If a person swallows a piece of bone, oyster shell, eggshell, or any
similar hard object that is part carbonate, the acid in the stomach
attacks it, rendering it harmless.
CaCO3 + 2HCI -4 CaCI2 -f H2O + CO2 1
(in shell) (in gastric juice) a soluble
compound
Hydrogen chloride as a dry gas or liquid fails to change the color of
blue litmus paper and is indifferent to zinc or magnesium, hydroxides,
and carbonates. This inactive gas quickly changes its reactions to those
of hydrochloric acid when moisture is present. The gas readily dissolves
in water, 442 volumes to 1 volume of water at room temperature. A
solution of hydrogen chloride, containing 20.24 per cent of hydrogen
THE ACID HEAVY CHEMICALS 359
chloride, has a boiling point of 110°C and is more dense than water. It
is called " constant-boiling " hydrochloric acid and can be distilled at
normal pressure with no change in composition.
Chemical Activity of Hydrochloric Acid. Hydrochloric acid is
widely used in laboratories and in commercial work because it is very
active chemically. It is a strong acid, dissociating 100 per cent in dilute
solutions. Indicators, such as litmus paper, respond to it. This acid, like
others, turns blue litmus paper red.
Hydrochloric acid readily attacks fairly active metals, such as zinc,
magnesium, or aluminum, but not copper.
Zn + 2HCI -> ZnCI2 + H2T
2AI +6HCI -> 2AICI8 + 3H2|
Sheet-metal workers use this acid to remove oxides from metals in
order to prepare a clean surface for soldering. Copper oxide film is neatly
removed from copper, and the fresh metal surface sticks well to the
solder. The same is true for zinc. Aluminum, however, does not solder
well. The chlorides formed are vaporized in the heat of the soldering
"iron" (made of copper).
CuO + 2HCI -> CuCI2 + H2O
ZnO + 2HCI -> ZnCI2 + H2O
Carbonates are easily attacked by this of other acids. If a stain on
marble (CaC03) is to be removed, this acid will take it out by removing
the part of the stone that is stained.
CaCO3 + 2HCI -+ CaCI2 + H2O -f CO2 1
Hydrochloric acid neutralizes alkalies. When milk of magnesia is
swallowed as a medicine, the amount of hydrochloric acid in the stomach
is diminished.
Mg(OH)2 + 2HCI -> MgCI2 4- 2H2O
Testing for Chlorides. How can the chemist prove that the sub-
stance he is using is a chloride, that is, contains chloride ions (Cl~)? By
experiment he finds that all the common metal chlorides except three
dissolve well in water. These exceptions are lead chloride (PbCl2), mer-
curous chloride (Hg2Cl2), and silver chloride (AgCl). Silver chloride is
selected as the best material to use for identification of a chloride ion.
Silver ions, present in silver nitrate solution, are brought together with
chloride ions, present in hydrochloric acid or any soluble chloride. The
insoluble solid, silver chloride (AgCl), precipitates as a curdy, cottage-
cheesy, white substance. A solid forms in the mixed solutions and settles
out, or precipitates.
AgNOs + HCI -» AgCl | + HNO8 (formula equation)
Ag+ H- Cl~ -4 AgCl J (ionic equation)
360 CHEMISTRY FOR OUR TIMES
*
Any soluble chloride acts in this way with silver nitrate solution, but
some other substances also form white precipitates when silver nitrate
solution is added to them. With sodium carbonate, for example, silver
carbonate precipitates. If the precipitate remains after nitric acid (HN08)
is added, we can be sure that a halide is really present, for carbonates
dissolve in acid. To distinguish silver chloride from silver bromide, we
place each in some ammonium hydroxide (NH4OH); the former dis-
solves in a little ammonium hydroxide, the latter requires much. This
second part of the test for a chloride is called the confirming test and is
necessary to avoid confusion. Other tests may be used to distinguish
chlorides from bromides (see page 308).
Uses of Hydrogen Chloride and Hydrochloric Acid. As already
mentioned, hydrochloric acid is used for cleaning metals that are to be
soldered, for cleaning limestone, marble, or other carbonates, and also
as a medicine in cases where the human stomach fails to produce the
acid in sufficient quantity. In addition to these uses, this acid finds an
interesting use in the wool industry. Sheep's wool, mixed with vegetable
burrs that have clung to the sheep as they graze, or " shoddy " (cotton
and wool mixed in a fabric) are treated with the gas (IIC1). The vegetable
matter becomes " carbonized, " or brittle, and in a condition in which it
can be crushed easily and blown away. The wool fibers remain unchanged
and are worked by regular woolworking machinery.
Carboys, or large bottles, of hydrochloric acid are shipped daily about
the streets of any large city. In addition, chemical manufacturing com-
panies use great tanks full of the solution. Many widely different uses
are made of the acid. It is involved in the making of aluminum, zinc,
and other chlorides, in making glue, dyes, and drugs, in cleaning iron,
and in changing starch to glucose. The total value of this acid used in
1 year in the United States is about 1 million dollars.
QUESTIONS
36. Write the formula for muriatic acid; muriate of soda; muriate of potash;
muriate of lime.
37. Write formula equations for (a) action of concentrated sulfuric acid on
calcium chloride; (b) sodium hydrogen sulfate and common salt; (c) burning of
hydrogen in chlorine; (d) common salt and cold concentrated sulfuric acid.
38. Write equations for the action of hydrochloric acid on (a) sodium hydrox-
ide; (6) sodium carbonate; (c) sodium hydrogen carbonate; (d) magnesium; (e)
copper oxide.
39. Assume that a piece of lead to be soldered has a thin coating of lead oxide
(PbO). What is the effect of the acid on the oxide? What is the effect of the heat of
the soldering iron on the products resulting from the action of the acid?
THE ACID HEAVY CHEMICALS
361
40. Common salt and Glauber's salt are both white solids. Tell how to identify
each by chemical tests.
41. List five uses of hydrochloric acid.
42. Account for the fact that dilute hydrochloric acid is active, while hydrogen
chloride gas is relatively inactive.
43. Write formula equations for the action of dilute hydrochloric acid on (a)
aluminum hydroxide; (b) calcium hydroxide; (c) metallic zinc; (d) ferrous oxide;
(e) calcium hydrogen carbonate.
44. Show by an equation how (a) hydrogen chloride in water dissociates into
ions; (b) hydrogen sulfate in water dissociates into ions.
46. Why may sulfuric acid be considered a more important acid than hydro-
chloric?
The Action of Sulfuric Acid on Saltpeter. Among the experiments
performed by the alchemists, we find one which was widely used, that of
making aqua fortis, or strong water, a liquid so called because of its
powerful dissolving action on metals. <n cone H2S04
"Heat oil of vitriol (H2S04) with salt-
peter (KNO3) in a retort, and distill
the vapors arising into a cooled ves-
sel," said the alchemists. This same
ancient discovery is still used today,
except that Chile saltpeter (NaN03)
is used instead of saltpeter (KNOs)
because it is cheaper and more easily
obtained.
Nitric Acid, or Hydrogen Ni-
trate. A modern apparatus for mak-
ing nitric acid is made of stainless
steel, Pyrex glass, or stoneware. Sul-
furic acid is heated gently with sodium
nitrate. (See Fig. 21-18.) The nitric
FIG. 21-18. — In the laboratory
preparation of nitric acid, good venti-
lation is needed. Note that no rubber
or cork stoppers are used — they react
with nitric acid.
acid vapors, which have a normal boiling point of 86°C, are helped to
leave the mixture by reducing the pressure on it and are condensed in a
cool vessel.
NaNO3 -f HHSO4
Chile saltpeter sulfurio
acid
NaHSO4
sodium hydrogen
sulfate
HNO,t
nitric acid
We should notice how similar this action is to that of sulfuric acid
on common salt (page 358). At a higher temperature sodium hydrogen
sulfate will act on more sodium nitrate, but the nitric acid decomposes.
The first action in this case is the practical limit.
362 CHEMISTRY FOR OUR TIMES
As a result of much work by skillful experimenters, synthetic ammonia
is now made cheaply and in large quantities. This gas is a suitable sub-
stance for making most of today's nitric acid. A platinum screen, at a
proper temperature, has been found to act as a catalyst in changing a
continuous stream of mixed ammonia and air into nitric acid.
NH, + 2O2 -» HNOs + H2O
ammonia from air nitric acid water
Nature makes some nitric acid in every thunderstorm. Hundreds of
'these disturbances daily give the earth a bath of very dilute nitric acid,
restoring fertility to the soil. The energy of the lightning spark forms
oxides of nitrogen from the elementary nitrogen and oxygen of the air,
for example.
N2 + O2 -4 2NO
This nitric oxide readily joins more oxygen, and with the water of the
storm nitric acid develops.
2NO + O2 -» 2NO2
3NO2 + H2O -> NO -f 2HNO3
Man's attempts to imitate nature's method of making nitric acid are
successful, but the cost of the electricity to make the spark is so great
that only in Norway has the process been profitable. Here the cheap
electricity generated by the abundant water power is used to make a
huge electric spark, spread out by magnets. Air passed through the spark
and suddenly cooled is found to contain oxides of nitrogen.
QUESTIONS
46. Distinguish pure nitric acid from the concentrated nitric acid of commerce.
47. Write a formula equation for the action of concentrated sulfuric acid on
saltpeter, or potassium nitrate.
48. A pupil prepared a sample of nitric acid in the laboratory. The sample was
light brown and showed by test that sulfate ions were present. Account for the
color and for the presence of sulfate ions in the prepared sample.
49. State a use for sulfuric acid for which neither nitric nor hydrochloric acid
can be used as an equivalent substitute.
50. Write formula equations for (a) preparation of nitric acid from Chile salt-
peter; (6) preparation of nitric acid from ammonia; (c) action of nitric acid on
calcium hydroxide; (d) on copper oxide; (e) on magnesium carbonate.
How to Recognize Nitric Acid. Nitric acid is a liquid at room tem-
perature and is colorless when pure. In sunlight it easily decomposes
into oxides of nitrogen. These dissolve in the nitric acid and color it
amber or brown. Nitric acid is about half again as dense as water, and
_ THE ACID HEAVY CHEMICALS _ 363
the concentrated nitric acid that is purchased for most chemical use
contains 68.6 per cent of HN08.
The formula weight of nitric acid is
H + N + 3O - 1 + 14 + (3 X 16) - 63.
Of these 63 parts by weight, 48 are oxygen, or about three-quarters.
The large percentage of oxygen is not remarkable, for water, for example,
has 88.81 per cent oxygen. The activity of the oxygen in pure nitric
acid, however, is notable. Here we have a card-house compound, one
ready to tumble down.
Let us put concentrated nitric acid on smoldering pencil sharpenings or saw-
dust. Oxygen from the nitric acid causes a vigorous flame to burst out. Then let
us add one part of concentrated nitric acid to three parts of concentrated hydro-
chloric acid. This mixture, called aqua regia, will dissolve even gold.
HNO3 + 3HCI -> [3CI] + 2H2O + NO |
Au+ [3CI] _ -+ AuCia __
or Au + HNO3 + 3HCI -4 AuCI3 + 2H2O -f NO |
The equation below the line represents the sum of the two. actions above it.
If nitric acid is placed on copper, a metal less active than hydrogen
and not attacked by hydrochloric acid, the copper is oxidized to copper
oxide and the copper oxide is attacked by more nitric acid. This action
is similar to that of concentrated sulfuric acid on copper (see page 348).
3Cu + 2HNO3 -f (3CuO) + H2O + 2NO | .
(3CuO) -f 6HNO3 -f 3Cu(NO3)2 + 3H2O _
_
or 3Cu -f 8HNO3 -4 3Cu(NO3)2 + 4H2O + 2NO |
Dilute nitric acid will produce such an attack on copper; but if concen-
trated nitric acid is used, brown nitrogen dioxide is produced.
Cu + 4HNO3 -+ Cu(NO8)2 + 2H2O + 2NO2|
In fact, the products of an action with nitric acid depend on the condi-
tions, especially the concentration of the acid. In general, no hydrogen
is formed, for it is oxidized to water. With zinc, a strong reducing agent,
some nitric acid may even be reduced to ammonia (the opposite action
of its production by the catalytic method), and one of the products will
be ammonium nitrate.
Nitric acid, then, readily dissolves metals (not aluminum), their
oxides, and, of course, metal carbonates and hydroxides to form nitrates.
It is a strong acid, dissociating ions well, and a vigorous acid in its wild,
unrestrained supplying of energetic oxygen.
Notable among the chemical actions of this acid is its ready attack
on living, or organic, matter. The skin, which contains protein or com-
plex nitrogen compounds, becomes colored yellow by it. So does silk,
364 CHEMISTRY FOR OUR TIMES
wool, and egg white. The yellow color is deepened to orange by the addi-
tion of ammonium hydroxide (NH4OH). This is one test for a protein.
Testing for a Nitrate. Nitric acid contains the group of elements
— NO3, called the nitrate radical. This group, present in all nitrates and
in nitric acid, may be identified in the laboratory by a test that requires
skill and care. The solution to be tested for the presence of the nitrate
radical is mixed in a test tube with some freshly prepared ferrous sulfate
solution (FeSCX). A long-stemmed funnel is placed in the test tube and
concentrated sulfuric acid poured slowly into the funnel, so that it goes
to the bottom of the tube. The acids form two layers, the denser sulfuric
acid on the bottom. If a brown ring forms just above the acid, a nitrate
must be present; for all nitrates act in this way, and no substances not
nitrates give the brown ring test.
We Use Nitric Acid. When we drive to the "movies" in an automo-
bile, we come in contact with many articles prepared through the use
of nitric acid. The lacquer paint on the car may be made from cotton
treated with nitric acid. The cushions on which we sit, if they are imita-
tion leather, are made from cloth coated with nitrated cotton. Also, the
film on which the motion pictures are printed is made of nitrated cotton;
and if we see a newsreel of battle-fleet target practice, we may hear that
highly nitrated cotton is used to propel shells and that nitrated toluene
(CeHsCHs), as the explosive inside the shells, causes them to burst as
they strike, their objectives. This explosive probably is TNT, trinitro-
toluene [C«HVCH8-(NO«)i].
Nitrating of cotton is accomplished by treating cotton with concen-
trated nitric acid, with some concentrated sulfuric acid present to re-
move water. Most of the nitric acid made is used for nitrating, which
is a very dangerous process in unskilled hands. Adding nitric acid to
phenol (CeH6OH), commonly called carbolic acid, produces trinitro-
phenol, or picric acid [CeH^'OHXNOo^L a high explosive and a yellow
dye. Nitrating glycerin [C3H6(OH)3', glycerol] forms glycerin nitrate, popu-
larly called nitroglycerin [CaH^NOs^] or "soup" in detective stories.
Glycerin nitrate is a sensitive explosive and is also used as a medicine
for heart trouble. Alfred Bernhard Nobel of Sweden found that glycerin
nitrate could be soaked up in sawdust and molded into a stick which
was a much more satisfactory explosive for farm and road work
than others employed, being less sensitive to shock. This invention of
dynamite was the cornerstone of his great fortune and led to the founding
of the famous Nobel prizes in literature, medicine, peace, physics, and
chemistry — five human enterprises Nobel thought worth encouraging.
Nitric acid is used to etch (eat into) metals. By using this acid, copper-
plates are prepared from which pictures can be printed. The original
THE ACID HEAVY CHEMICALS
365
plate from which the picture of Madame Curie on page 2 was printed
was prepared in this way. Nitric acid is also used to make nitrate
fertilizers; of course, the acid is not used directly on plants. Useful in
peace, essential in war, nitric acid has attracted the attention of every
military and civic leader, for no picture of national resources is com-
plete without considering this acid.
QUESTIONS
61. Describe in detail the test used to identify the nitrate radical.
52. Write the formula equations of the action of dilute nitric acid on (a) cop-
per, (6) silver; of concentrated nitric acid on (c) copper, (d) ammonium hydroxide.
53. What chemical treatment will change glycerin into glycerin nitrate?
54. Point out that nitric acid is necessary in peace and indispensable in war.
55. What percentage of nitric acid is nitrogen? Hydrogen?
Oxides of Nitrogen. When dilute nitric acid acts on copper chips in a test
tube, a gas bubbles up through the blue solution of copper nitrate that forms.
Close examination shows that the gas is colorless within the solution but that
upon striking the air it becomes brown. Care should be taken to avoid breathing
either gas, for they are both poisonous. The colorless gas is nitric oxide (NO), and
the brown gas is called nitrogen dioxide (N02).
3Cu + 8HNO3 -4 3Cu(NOa)2 + 4H2O -f
2NO -f O2
from air
2NO2
nitric oxide
colorless
Generator
nitrogen dioxide
brown
Nitric Oxide
Colorless
Cover
Colorless
Nitric Oxide
FIG. 21-19. — Nitric oxide is prepared by reducing dilute nitric acid with copper chips.
The resulting colorless gas darkens when exposed to air or pure oxygen.
If the experiment is repeated in a generator bottle and the gas collected over
water (see Fig. 21-19), we notice (1) that the generator bottle fills with brown gas
because of the air present at the start and (2) that the brown gas does not collect
in the receiver but a colorless gas does. Apparently the brown nitrogen dioxide is
readily soluble in water, and the colorless nitric oxide is much less soluble. After
366
CHEMISTRY FOR OUR TIMES
all the air has been swept out of the generator, we are ready to collect a measured
bottleful of pure, colorless nitric oxide. If the bottle of nitric oxide gas is now with-
drawn from the water and the cover plate lifted, the brown fumes form again
almost mysteriously where the gas meets the air.
If we wish an even more startling experiment, we can add slowly to the color-
less nitric oxide a half bottle of pure oxygen. With each addition of oxygen, the
brown nitrogen dioxide appears, but it soon dissolves in the water.
Nitrogen Tetroxide. If we chill a closed tube containing brown nitro-
gen dioxide, we notice that its color becomes lighter and that its density
increases. Cooled in Dry Ice, nitrogen tetroxide forms a pure white solid
(m.p. — 9.3°C). These effects are explained by assuming that in any given
amount of nitrogen dioxide, some colorless nitrogen tetroxide (NgC^) is
present with which it is in equilibrium.
favored by cooling
2N02 — » N204
brown / \ colorless
favored by warming
The tendency of molecules, such as nitrogen dioxide, to cluster into
larger groups is called polymerization, and the cluster is called a polymer.
Nitrogen tetroxide is a polymer of nitrogen dioxide.
Sulfamic Acid
(HOS02NH2)
H NH2S03
sWarm Water
FIG. 21-20.— A convenient way to generate nitrous oxide. A large flask containing
a little ammonium nitrate, clamped horizontally and equipped with a single delivery
tube, may be substituted for the generator shown.
Laughing Gas. If dilute nitric acid is saturated with ammonia, a
slush of ammonium nitrate crystals can be separated from the mixture.
HNO, + NH, -4 NH4NO, (formula equation)
ammonium nitrate
THE ACID HEAVY CHEMICALS
367
From the chemical point of view, ammonium nitrate with its two nitrogen
atoms per formula has two points of weakness in its structural design.
(1) It breaks apart so easily and nicely that it is used in some explosives.
(2) We must use reasonable caution when we heat this compound. When
this is done carefully, nitrous oxide (N2O), or dinitrogen oxide, escapes
as a gas. (See Fig. 21-20.)
NH4N03 -4 2H20
N20t
nitrous oxide
Nitrous oxide is a rather dense but colorless gas that may be col-
lected over warm water; it dis-
solves very little in hot water. It
is used by doctors and dentists as
an anesthetic in putting patients
to sleep. It may be given to a pa-
tient before using ether for an
anesthetic. In some cases of dental
work that require grinding a tooth
cavity, the patient may have a
supply of this gas, which he can
give to himself as needed, produc-
ing only partial anesthesia. Often
nitrous oxide is used with one-
quarter oxygen mixed with it.
The gas was first prepared by
Joseph Priestley and its physio-
logical properties discovered by
Sir Humphry Davy. It was first
used in a dental operation in 1844
by Dr. Horace Wells (1815-1848)
(see Fig. 21-21), who wrote his
last will and testament before try-
ing it on himself. Previous to this
time it had been used for purposes
of entertainment. People acted
strangely while recovering from
its effects. Some fought wildly,
some cried, others became nervous
and laughed hysterically (for this
reason it has been called laughing gas), and a fe\v died. This last result
was unexpected and stopped its use for entertainment.
Whipped-cream ejectors at soda fountains contain cream under pres-
sure with nitrous oxide. When the eject or valve is opened, the cream
spurts forth, fully whipped and filled with bubbles of the gas.
Courtesy of Triniiu College
Via. 21-21. — This pew end in Trinity
Chapel. Hartford, Connecticut, was dedi-
cated to Dr. Horace Wells (1815-1848), the
first person to use nitrous oxide in a dental
operation. The carved figure on top is that
of Aeseulapius, pod of healing.
368 CHEMISTRY FOR OUR TIMES
Burning substances continue to burn in nitrous oxide just as well as
or perhaps a little better than in air but not so well as in pure oxygen.
QUESTIONS
66. In a column, list the three most important oxides of nitrogen. Make a
table of (a) their names; (6) their formulas; (c) their colors; (d) their solubility in
water; (e) their densities as calculated from the formulas.
67. Bromine vapor and nitrogen dioxide are both dark-brown gases. Contrast
their behavior when (a) cooled; (6) placed in cold water; (c) passed into potassium
iodide solution.
68. Compare the effect of putting a lighted candle into a bottle containing
(a) ah*; (6) pure oxygen; (c) nitrous oxide.
59. What is the effect of cooling without pressure change on (a) iodine vapor;
(b) nitrogen dioxide; (c) nitrogen?
60. What volume of oxygen is required to convert \ , - cubic feet of nitric
oxide into nitrogen dioxide at the same temperature and pressure?
Phosphoric Acid. Common phosphoric acid is a siruplike liquid con-
taining some water. Without water, phosphoric acid (H3PO4) is a white
solid that melts at 42.3°C and has a density of 1.83 g per ml. Most
of it is made by treating the natural rock phosphate with sulfuric acid
and allowing the gypsumlike sludge of calcium sulfate to settle to the
bottom of the container. Later the phosphoric acid is drawn off the top.
Ca8(PO<)2 + 3H2SO4 4- 6H2O -» 3(CaSOr2H2O) 4- 2H3PO4
natural sulfuric gypsum phosphoric
phosphate acid acid
A purer grade is obtained by burning the elementary phosphorus as
it comes from the electric furnace where it is made. The phosphorus
pentoxide formed by the burning is dissolved directly in water.
P2O6 -f 3H2O -4 2H3PO4
Phosphoric acid may be used as a substitute for sulfuric acid in some
cases, since it has a high boiling point, but it is a weaker acid. It breaks
off three protons, one at a time. In orthophosphoric acid (H3P04) solu-
tions, tKree sorts of negative ions are in equilibrium with each other.
Under certain conditions we can represent the situation as
H+ H+ H+
H|PO4 3=t . and £t and £± and
H2PO1 HPO" PO"-
27 per cent 0.2 per cent 0.0002 per cent
di hydrogen monohvdrogen phosphate ion
phosphate ion phosphate ion
Consequently, phosphoric acid forms three sorts of salts. All three of
the sodium salts and the calcium salts are used commercially.
THE ACID HEAVY CHEMICALS 369
Sodium dihydrogen phosphate (NaHjPOO is an acid in baking pow-
ders; disodium hydrogen phosphate (Na2HPC>4) is the compound sold in
drugstores for medicinal sodium phosphate; and normal, or trisodium,
phosphate (Na3P04), or T S P, is used extensively to soften water,
to treat water for boilers, and in household cleaning powders. Its solu-
tion is very alkaline, nearly as strong as that of lye (NaOH).
A large amount of phosphoric acid is joined directly to ammonia to
form ammo'nium phosphate fertilizers.
SUMMARY
Sulfur (brimstone) is found free in volcanic regions of Sicily, Japan, Greece,
and Mexico and underground in Texas and Louisiana. This element is also found
combined with many metals as metallic sulfides and sulfates.
Physical properties: Sulfur is a yellow nonmetal; it is insoluble in water and
soluble in carbon disulfide; when heated it undergoes a series of changes. Sulfur
has several allotropic forms, rhombic, rnonociinic, and plastic.
Chemical properties: Sulfur burns with a pale-blue flame; it joins metals to
form metal sulfides; it is similar to oxygen in many chemical actions.
Sulfur is used to make sulfur dioxide and sulfuric acid, for an insecticide, and
for an agricultural spraying agent.
Sulfur dioxide occurs in some volcanic gases. It is prepared by
1. Burning sulfur or a sulfide
2. Decomposition of sulfurous acid, made from a sulfite (or hydrogen sulfite)
and hydrochloric acid
3. Reduction of hot concentrated sulfuric acid by copper
Sulfur dioxide is a colorless, irritating gas at room temperature. It is quite
dense, very soluble in water, and easily changed to a liquid by an increase in pres-
sure. These are physical properties.
The chemical properties of sulfur dioxide are that it
1. Joins water to form sulfurous acid
2. Oxidizes to form sulfur trioxide
3. Reacts with bases to form sulfites
The chemical properties of sulfurous acid (solution) are as follows:
1. It is a mild acid.
2. It joins oxygen to form sulfuric acid.
3. It is a good reducing agent.
Sulfur dioxide is used as a refrigerant, to make sulfuric acid, and as a food
preservative. Sulfurous acid is used as a bleaching agent.
Sulfuric acid (oil of vitriol) is prepared commercially by the contact and cham-
ber methods. In the contact method sulfur burns, forming sulfur dioxide. Sulfur
dioxide is in turn oxidized in the presence of a solid catalyst, forming sulfur tri-
oxide. The resulting sulfur trioxide is absorbed to make concentrated sulfluric acid.
In the chamber method a lead-lined room is used into which steam, sulfuric di-
oxide, and oxides of nitrogen are introduced. A mist of sulfuric acid forms, pro-
ducing dilute sulfuric acid.
The properties of dilute sulfuric acid are different from those of the concen-
370 CHEMISTRY FOR OUR TIMES
trated aqid. The dilute acid is strong, similar in strength to hydrochloric acid.
Concentrated sulfuric acid is an un-ionized acid. When mixed with a small amount
of water, the concentrated acid dissociates one proton more readily than two.
H2S04 — > H+ + HSOr. Concentrated suifuric acid is a strong dehydrating agent
and an oxidizing agent when hot. The concentrated acid should be diluted by
stirring into water with great care. Much heat is evolved in the process. Concen-
trated sulfuric acid acts on salts, forming other acids.
Sulfuric acid has many uses. Among them are pickling scale from steel prod-
ucts, making fertilizer, preparing other acids, electroplating, refining petroleum,
dehydrating, and manufacturing explosives. Its use is very general, and it is a
most important chemical substance in an industrial civilization.
Hydrogen sulfide is a very poisonous gas. It occurs in decaying sulfur-con-
taining organic matter and in some volcanic gases. Its laboratory preparation is
by action of hydrochloric or dilute sulfuric acid on ferrous sulfide.
The physical properties of hydrogen sulfide are that it is a colorless gas with
a disagreeable odor, it has a greater density than air, and has moderate solubility
in water.
Its chemical properties are as follows: It burns, either completely or par-
tially. It is a weak acid in solution. It acts with solutions of many metal salts,
forming sulfide precipitates. It is a good reducing agent. Hydrogen sulfide is used
extensively in chemical analytical work.
Hydrochloric acid (muriatic acid) occurs in dilute solution in the stomach of
some animals. The gas is prepared
1. By action of sulfuric acid on common salt
2. By action of sodium hydrogen sulfate on common salt
3. By direct synthesis, burning hydrogen in chlorine
The physical properties of hydrogen chloride are that it is a colorless gas with
a sharp odor, is very soluble in water, is denser than air, and produces a fog in
moist air.
Hydrogen chloride is inactive chemically when in the form of dry gas. In solu-
tion (hydrochloric acid) it shows marked chemical activity. Its actions are typical
of acids on hydroxides, oxides, carbonates, and active metals.
Hydrogen chloride or its solution is used in cleaning metals for soldering, car-
bonizing cotton in mixed textiles, changing starch to glucose, manufacturing
drugs and dyes, and testing for Ag+ ion. It is one of the most widely used labora-
tory reagents.
Nitric acid (aqua fortis) is prepared by the action of sulfuric acid on a nitrate
and by oxidation of ammonia in the presence of a catalyst (Ostwald method).
Some is formed in lightning storms.
The properties of nitric acid are that it is unstable, that is an oxidizing agent,
and that it dissolves metals, such as silver and copper, evolving oxides of nitro-
gen?—but not hydrogen. Nitric acid has the typical actions of a strong acid on
hydroxides, carbonates, and oxides; also, it changes protein to a yellow color.
Nitrates are identified by the following test : A brown ring is formed when ferrous
sulfate solution and concentrated sulfuric acid are added to a solution of the sam-
ple. Nitric acid is used in making explosives, lacquers, dyes, and fertilizers.
Nitric oxide is prepared by the action of copper on nitric acid. Its physical
THE ACID HEAVY CHEMICALS 371
properties are that it is colorless, slightly soluble in water, and a little denser than
air. Its most notable chemical property is the immediate change to brown nitro-
gen dioxide when in contact with oxygen.
Nitrogen dioxide is a brown, irritating gas; it is denser than air, is in equilib-
rium with NjCU, and is soluble in water.
Nitrous oxide (laughing gas) is prepared by decomposition of ammonium
nitrate by gentle heating. Its physical properties are that it is a colorless gas
with a faint odor and is insoluble in hot water. It resembles oxygen in chemical
actions but is not so vigorous an oxidizing agent. It is used as an anesthetic and
in making whipped cream at soda fountains.
Phosphoric acid is prepared
1. By action of sulfuric acid on rock phosphate
2. By action of phosphorus pentoxide with water
Phosphoric acid forms three series of salts. It is a moderately strong acid. It is
extensively employed to make fertilizers and in general chemical manufacturing.
QUESTIONS
61. What is the percentage of P208 in phosphoric acid? In rock phosphate?
62. Write formula equations for the neutralization of phosphoric acid by (a)
sodium hydroxide; (6) calcium hydroxide; (c) potassium carbonate; (d) zinc
oxide; (e) aluminum hydroxide.
63. Show by equations how to prepare phosphoric acid (a) using elementary
phosphorus prepared in an electric furnace; (6) using rock phosphate and sulfuric
acid.
64. Write the formulas and names of three different potassium salts of phos-
phoric acid.
65. Name the product formed when (a) a little | , , . is added to phos-
phoric acid; (b) when more lye is added; (c) when excess lye is added.
UNIT FIVE CHAPTER XXII
THE BASIC HEAVY CHEMICALS
After a lesson on soapmaking in his chemistry class, a pupil with an
eye to economy was eager to make soap at home. For a few cents he
purchased a 13-oz can of lye at a grocery store. He enlisted the aid of
his mother, and in a few weeks she had saved from cooking and stored
in jars 6 Ib of fat. Then he dissolved some lye in 1 qt of water. While
he waited for the lye solution to cool off, he cleaned the fat by melting
it and skimming off the dirt and absorbed the coloring matter from the
fat by cooking a few slices of potato in it. Then he mixed the warm liquid
fat and the lye solution while stirring. A change into soap and glycerin took
place. When the mixture was ready to harden, he poured it into card-
board boxes for molds. When hardened, he cut the molds into small
cakes, putting them aside to dry out a bit before use. He had made 12
cakes of soap suitable for laundry use that would certainly retail at 10
cents each.
When soap is made at home, it is necessary to use an iron kettle —
never aluminum or enamel ware, for a solution of lye acts chemically
on these vessels.
Imagine a train made up of 20 heavy steam locomotives. Such a
train would have an enormous weight, practically equal to the weight of
the lye (sodium hydroxide or caustic soda) made each day in the United
States. Yet, among alkalies, sodium hydroxide ranks third in order of
importance as a commercial base; sodium carbonate and lime are both
ahead of it.
When we think of bases, we consider sodium hydroxide first for it is
the compound that is used most extensively as a base in the chemical
laboratory.
Manufacture of Sodium Hydroxide (NaOH). Commercially,
sodium hydroxide (lye) is made by two processes, both of almost equal
importance: (1) the electrolytic method; (2) the chemical method.
New Terms
stalactite kiln slake
stalagmite limewater synthetic ammonia
373
374 CHEMISTRY FOR OUR TIMES
1. The electrolytic method is carried out by passing an electric cur-
rent through a salt-water solution in a cell specially designed to keep the
chlorine that is liberated at the anode separated from the lye that is
formed at the cathode. The reaction in the cell may be summed up as
follows :
2NaCI + 2H,O -4 2NaOH + H2| + CUT
This action has already been considered (see page 302) for the prepara-
tion of chlorine. If sodium hydroxide is the chief product, chlorine is a
Photograph />// /Vn7i'/» Arquavita
FIG. 22-1. — An assortment oi sodium compounds in different forms can he ohtained at
grocery stores. They include salt, baking soda, washing soda, lye, borax, and soap.
by-product. The value of the chlorine lowers the cost of the sodium
hydroxide.
2. The chemical method is carried out in iron kettles. A suspension
of calcium hydroxide is mixed with a solution of sodium carbonate
Ca(OH)2 + NaCO, -> CaCO3 1 4- 2NaOH
milk of sodium precipitated lye
lime carbonate chalk
The mixture is stirred by blowing steam through it for some time.
Then it is allowed to settle, and the solution of sodium hydroxide is
drawn off or filtered away from the solid calcium carbonate or precipi-
tated chalk. The lye solution is concentrated or crystallized by evaporat-
ing the water.
Both the electrolytic and the chemical methods make a somewhat
impure lye, but the products are suitable for many purposes.
How Sodium Hydroxide Acts. Sodium hydroxide is a white, inno-
cent-looking material. If a little of it is placed on the fingers, it feels
slippery; the compound changes the oils on the skin to a soap, which, of
course, is slippery. However, if lye remains in contact with the skin, it
causes a painful burn. Lye is also given the name caustic soda because
of its corrosive action. It destroys animal matter, and a hot solution
_ THE BASIC HEAVY CHEMICALS _ 375
dissolves wool or silk. These actions are all caused by the hydroxyl ion
(OH-).
Sodium hydroxide can be purchased in the form of brittle sticks,
flakes, pellets that resemble well-worn tips of billiard cues, a solid mass
in a steel drum, or a saturated solution in a tank car. All forms must
be kept tightly sealed, for the compound absorbs both moisture and
carbon dioxide from the air. Exposed to air, a part of the lye changes
into sodium carbonate
2NaOH + H8CO3 -* 2H2O + Na2CO»
Being a typical base, sodium hydroxide acts readily with strong acids.
2NaOH + H2SO4 -f 2H2O + Na2SO4
Sodium hydroxide is used in making rayon and photographic films.
Petroleum is freed from odorous sulfur compounds by the use of lye. Lye
is employed extensively in producing soap and chemicals. Cooking wood
chips in caustic solution is part of the process of making them into paper.
John Mercer (1791-1866), an English cotton spinner, found that cotton
cloth treated under tension with a lye solution became lustrous and
stronger. His discovery made the first mercerized cotton in 1850.
How Potassium Hydroxide Acts. Potassium hydroxide (KOH),
also called potash lye or caustic potash, is similar to sodium hydroxide
in its chemical actions. Both are very soluble in water, and both are
excellent sources of hydroxyl ions, although potassium hydroxide is some-
what more costly. The soap made with the potassium compound is softer
than that made with sodium hydroxide. Potassium hydroxide serves as
a material for absorbing carbon dioxide.
If it is desired to make a biological model of the blood vessels in a
freshly killed cat, quick-drying liquid plastic is injected into the tissue
selected. The cat is then placed in concentrated potassium hydroxide;
all animal matter dissolves, and the hardened plastic keeps the mold of
the tissues into which it was injected.
Sodium Carbonate (Soda Ash). Most of the world's supply of
sodium carbonate (Na2C03) and sodium hydrogen carbonate (NaHCOa)
is made by a process that Ernest Solvay (1838-1922), a Belgium chemist,
patented in 1864. Soda ash, as sodium carbonate is called commercially,
is the most important heavy basic chemical. Essentially, it is produced
from sodium hydroxide and carbon dioxide.
2NaOH -f CO, -+ Na^COs + H,O
It is easier to handle than sodium hydroxide since it is not so corrosive.
Also, as soon as it meets a strong acid, it loses carbon dioxide gas.
376 CHEMISTRY FOR OUR TIMES
The Solvay Process. Solvay's raw materials were four simple com-
mon substances, water, salt, carbon dioxide, and ammonia. The steps in
the process are essentially as follows: (1) Ammonia and carbon dioxide
Court f.'H of The Muthiwn Alkali \Vnrkn, Inc.
FIG. 22-2. — This workman is loading a box car with .soda ash. Industrial chemicals are
manufactured in large tonnages.
are bubbled into a saturated solution of brine. Both gases first join with
water and then join together.
H2O +CO2 & H2CO3
NH3 + H2O <=± NH4OH
NH4OH + HHCO., <=± NH4HCO3 + H2O
ammonium hydrogen
carbonate
(2) When the solution containing the ammonium hydrogen carbonate
acts with an excess of common salt under the proper conditions, the
moderately soluble sodium hydrogen carbonate (NaHCOa) precipitates.
NaCI + NH4HCO, -» NaHCOa j + NH4CI
(3) Most of the dried sodium hydrogen carbonate is heated, driving off
carbon dioxide and making anhydrous sodium carbonate.
2NaHCOa -> Na2CO3 + H2O + CO2T
The ammonia in this process is far more expensive than the sodium
compounds; therefore, the ammonium chloride is recovered by evapora-
THE BASIC HEAVY CHEMICALS
377
tion. Then limestone is heated to lime and carbon dioxide, and the lime
is slaked to form calcium hydroxide (see page 382). The ammonium
compound is then treated with this cheap basic material, freeing ammonia
gas for use once more.
Ca(OH)2 + 2NH4CI -4 CaCI2 + 2NH4 + 2H,O
As has been said, the raw materials for the Solvay process are water,
salt, carbon dioxide, limestone, and a little ammonia to make up for some
The products are either sodium hydrogen carbonate or sodium
Light Dense Fused Alkali
Soda Ash- 58 £ Sod a Ash -58?; Products
Powdered
Bicarb.- U.S.P.
Technical
Bicarb.
Dry Ice
(carbon dioxide
ice)
50% Liquid
Caustic Soda
73% Liquid
Caustic Soda
Solid Rake Carbonic
Caustic Soda Caustic Soda Gas
Courltxy of The Mathieson Alkali Works, Inc.
FIG. 22-3. — Flow chart of ammonia soda operations.
378 CHEMISTRY FOR OUR TIMES
carbonate, chiefly the second, and a by-product, calcium chloride. Little
use has been found for the calcium chloride aside from moistening gravel
roads and thus laying the dust. (See Fig. 22-3.)
•
The Mild Soda. The " baking soda" on the pantry shelf at home is
sodium hydrogen carbonate (NaHC03), or commonly bicarbonate of
soda. This white powder dissolves moderately well in water. Among its
household uses are as a relief for indigestion; with cream of tartar, as a
leavening agent for making cakes; with sour milk, as a leavening agent
for biscuits or gingerbread; and, with aluminum, as a mild alkali for
cleaning silverware. This is the sodium compound which is used in the
soda-acid type of fire extinguisher (see page 74), in effervescent tablets,
and in baking powders (see Appendix). All these uses are similar in chem-
ical action. The sodium hydrogen carbonate neutralizes acids and releases
carbon dioxide. A simple example is
NaHCOs + HCI -» NaCI + H2O + CO2t
«
The Strong Soda. The powdered white material, sodium carbonate
(Na2CO3, soda ash), is the usual form of this compound in commerce.
It is easily dissolved in water. For household use, however, the compound
is allowed to form washing soda crystals (Na2C03'10H20), or sal soda
(the soda from salt). These crystals lose water easily and become a
crumbly powder if the package is left open to the air.
Sodium carbonate is used for washing greasy pots and pans, for
cleaning automobile cooling systems, and for softening water, a laundry
aid. It is also used in many scouring powders. Among its most important
uses in the industrial world are in the making of glass, soap, and other
chemicals; in the neutralizing of acids; and in the treatment of textiles.
A relatively small amount of sodium carbonate is made from natu-
ral deposits of the dry material in Owens Lake and Searles Lake in
California.
The sodium hydrogen carbonate forms the normal carbonate on heat-
ing, driving off water and carbon dioxide. This chemical change was
mentioned as a part of the Solvay process.
The carbonate can be changed into the hydrogen carbonate by
reversing the process. A solution of sodium carbonate is treated with
an excess of carbon dioxide. Sodium hydrogen carbonate forms
Na2CO, + H2O + CO2 -> 2NaHCO3
QUESTIONS
1. Rank the four most important basic heavy chemicals in order of their
importance.
2. Give two commercial names for sodium hydroxide.
THE BASIC HEAVY CHEMICALS 379
3. Name two by-products of the preparation of sodium hydroxide by the
electrolysis of common salt solution.
4. Tell how sodium hydroxide is obtained in solid form in its preparation by
the chemical method.
6. Lye is sometimes shipped as a concentrated solution and sometimes as a
solid. State one advantage and one disadvantage of each method of shipping.
6. Write formula equations for the reactions of (a) sodium hydroxide and
(b) potassium hydroxide on (1) carbonic acid; (2) nitric acid; (3) acetic acid; (4)
suifuric acid (eight different equations).
7. Compare sodium hydroxide with potassium hydroxide, giving two points
of likeness and two of difference.
8. Write a set of six equations to represent the Soivay process, including
recovery of ammonia.
9. On a weight basis, which is the more effective alkali, sodium hydroxide
or potassium hydroxide? HINT: Which has the larger percentage of hydroxide?
10. Compare Na2C03 with NaHCOs in respect to scientific name, common
name, and two uses.
Lime from Limestone. The cheapest of the basic heavy chemicals
is calcium oxide, or lime. Its story starts with a limestone quarry. Lime-
stone is an abundant material among the surface rocks of the earth.
Chemically, it is impure calcium carbonate (CaCO3) mixed with sand,
clay, iron oxide, or other impurities. Probably at some earlier era it was
formed by the deposits of shells or skeletons of sea creatures. The famous
white cliffs of Dover, England, were certainly formed in this way, for
when examined under a microscope the chalk fragments are seen to be
composed of microscopic shells. We believe that inland mountains,
thousands of feet thick, which are composed chiefly of limestone, were
at one time likewise under the sea. Support for this view comes from the
fact that they frequently contain fossils and that almost all sea shells
and skeletons of marine creatures are comprised of calcium carbonate.
Coral and pearls are also made of this material.
Fine crystals of calcium carbonate in minerals are called calcite. A
transparent form, or Iceland spar, is almost pure. Marble is a form of
limestone that has had a more rugged geological history and has been
partly recrystallized. It will take a high polish and is useful for orna-
mental building stone and statutes.
When a limestone quarry yields building stones, as many do in
Indiana and elsewhere, many unimportant chunks of rock are taken out
along with the well-cut stones. These chunks may be sent to the lime-
kiln to be "burned." Actually, in the strict sense, they are heated rather
than burned, but the term "lime burning" has been used for centuries.
380
CHEMISTRY FOR OUR TIMES
Some sort of kiln (pronounced "kil") is provided. A simple one is
made like a tall vertical chimney. When
the fire from the fuel heats the contents
to about 1000°C, the limestone decom-
poses.
Cable Car
for Filling
Limestone
Grate
^.Xj^Une
FIG. 22-4. — Lime to make wall
plaster for the earliest houses in
America was made in kilns that re-
semble this one. Limestone was fed
into the top of the chimney. Huge
fires roared up the stack, heating
the limestone. The finished, or
"burned," lime was taken from the
bottom.
CaCO, ;?± CaO -f-CCM
At this temperature the chemical ac-
tion is reversible, but the carbon diox-
ide has no chance to reunite with the
lime, for it is forced away by a strong
draft. The white, crumbly lime is re-
moved from time to time at the bottom
of the kiln. The poorer grades may con-
tain the ashes from the fuel, but not if
the kiln is properly designed. (See Fig.
22-4.)
Another type of kiln is a horizontal
revolving tube, sloping slightly toward
the exit end. Crushed limestone is fed
into a hopper at one end, and fire enters
at the center of the other. The limestone
descending into the kiln meets the fire
ascending. The lime is removed at the
lowest spot. (See Fig. 22-5.)
Chunks of limestone are also used
for building roads. Ground limestone is
spread on the soil to counteract soil
acids. Chunks of limestone are used for
flux in furnaces where metals are re-
fined. The limestone acts together with
sand at the high temperature in the
furnace to form a liquid that absorbs
many worthless impurities.
CaCO8 4- SiO2
limestone sand
CaSips
calcium silicate
Tor the same reason furnaces are some-
times lined with dolomite (CaC(V-
MgC03).
Limestone Caves. Just as sodium
carbonate can be converted into sodium
hydrogen carbonate by an excess of carbon dioxide solution, so calcium
THE BASIC HEAVY CHEMICALS
381
carbonate can be changed into calcium hydrogen carbonate by water and
carbon dioxide.
CaCO3 -f H2CO3
insoluble
Ca(HCO3)2
slightly soluble
Since calcium hydrogen carbonate is moderately soluble in water, soil
water that contains carbon dioxide will dissolve limestone slowly. The
L\>,*, itoj, of Vermont Marble Company
FIG. 22-5. — A horizontal rotating kiln illustrates the counter-current principle.
The flames go up while the limestone tumbles down slowly. Notice the hopper for feed-
ing limestone, t he pipe to supply oil for the fire, the duct for air, the workman examin-
ing the interior of the kiln through a peep hole, and the bricks (foreground) used for
relining.
effect on the water is to make it "hard" (see page 606). The effect on
the rock is to leave an empty space. Many large caves have been formed
in this way. Mammoth Cave in Kentucky, Luray Caverns in Virginia,
and the Carlsbad Caverns in New Mexico are all examples of limestone
caves that have been formed by dissolving limestone.
As in the case of the corresponding sodium compounds, the carbonate-
hydrogen carbonate change is reversible. If moisture and carbon dioxide
are lost, the insoluble carbonate of calcium forms once more.
Ca(HCO3)2 -» CaCO3| + H2O + COat
A drop of water hanging from a projection in the roof of a cave evapo-
rates and loses some carbon dioxide. A tiny bit of limestone deposits.
The next drop falls to the floor. Very gradually from the roof of the cave
an icicle-like stalactite is built, and from the floor of the cave a similar
but pinnacle-like growth called a stalagmite is formed. Several centuries
382 CHEMISTRY FOR OUR TIMES
later, these may unite to form a column to support the cave roof. (See
Fig. 22-6.)
We Make Chalk. In spite of the fact that so many different forms of
calcium carbonate are available in nature (see Fig. 22-7), artificially made
calcium carbonate (whiting, or precipitated chalk), finds many uses,
competing with finely ground marble. It is made by the action of sodium
Courtesy of Luray Carerns Corporation and Virginia Conservation Commission
FIG. 22-6. — Grotesque limestone formations within Luray Caverns, Virginia, dwarf
a man observer.
carbonate solution on calcium chloride solution. The precipitated chalk
formed is filtered from the salt water (also formed), washed, and dried.
CaCI2 4- Na2CO3 -+ 2NaCI + CaCO3 1
Mixed with linseed oil, it is called putty. It is used in some paints
and is the scouring agent in most tooth-powder mixtures. Chemically,
it is simply rather pure limestone.
Calcium Oxide (CaO, Quicklime). The ancient term "quick"
means "live." Live lime, or quicklime, is thirsty. When its thirst is
quenched, or slaked (not slacked), the substance acts very much alive —
moving, swelling, and crumbling. In fact, it becomes so hot that it may
cause fires.
CaO + H2O -4 Ca(OH)2 (4- heat)
The water-slaked lime, calcium hydroxide [Ca(OH)2], is a white paste
if prepared without much regard to the amount of water being added;
THE BASIC HEAVY CHEMICALS
383
Courtesy of Vermont Marble Company
FIG. 22-7. — Power-driven saws cut huge blocks of marble in this Vermont quarry.
From such sources, we obtain stones for the architect's design or for the sculptor's
chisel.
FIG. 22-8.- Here a hug
column is being made from a
marble. Notice the power-driven abrasive
wheel used to cut the flutings.
;
fluted maible Courtesy of Vermont Marblr Company
block of Fw. 22-9. •--One of the most stately
buildings in the world is made from white
marble. Tan you identify this building?
384
CHEMISTRY FOR OUR TIMES
with the right amount of water it is a white powder. In the latter form
slaked lime is supplied to builders for making plaster walls and mortar.
Mortar is made with one part of slaked lime and three or four parts of
sand, with sufficient water to make a workable paste. Cement is used
more than lime mortar today, but most brick walls of older structures
were laid up with lime mortar. Lime mortar becomes hard owing to
drying and absorption of carbon dioxide.
Courtesy of Buffalo Museum of Science
FIG. 22-10. — Indiana limestone, chiefly calcium carbonate, is used extensively as a
building stone. Visitors to Buffalo are always welcomed at tbc Buffalo Museum of
Science in Humboldt Park. This structure has a limestone exterior.
Slaked lime is used for taking hair off hides in tanneries; extensively
for sweetening acid soils for crops; and making paper, sodium hydroxide,
some sorts of bricks, and bleaching powder.
Limewater. If a suspension of calcium hydroxide in water, milk of
lime, is filtered, a clear solution comes through the filter paper. This is
called limewater, and it is used in medicine. Although the calcium
hydroxide present in this solution is ionized and is a source of hydroxyl
(OH~) ions, very little calcium hydroxide dissolves and the solution is only
a rather mild source of hydroxyl ions.
When the stopper is left off a limewater bottle, a crust forma on top
of the solution. The carbon dioxide of the air is absorbed and forms
calcium carbonate, a milky precipitate. This chemical action is the well-
known laboratory test for the presence of carbon dioxide.
CafOH)2 -f CO2 -» CaCOa i -f H2O
THE BASIC HEAVY CHEMICALS
385
Tom Sawyer's Fence. In the famous story, Tom Sawyer, by Mark
Twain, Tom had to whitewash a fence; or, rather, he had to get a fence
whitewashed. Let us assume that we, like Tom, have induced our friends
to do the work of whitewashing for us so that we can sit back and con-
sider the composition of whitewash. Whitewash is primarily a suspension
of calcium hydroxide with some gluing material. When air acts on the
calcium hydroxide, forming insoluble calcium carbonate, the action is
described by the preceding equation. This action is deliberate; that is, it
takes place slowly. In a thin coat, such as that on Tom's fence, the action
is practically completed within a few days. In an ordinary brick wall,
however, 25 years may be needed, and in the walls of some plastered
houses almost 300 years may elapse before all the action in the plaster
is complete. Of course, the setting action proceeds rapidly at first, then
more and more slowly. Much wall plaster is slaked lime mixed with sand
and cheap fibers and water. The finish wall plaster, the outer layer, is
made from gypsum (CaS(V2H20) and is usually applied as plaster of
Paris (2CaS04-lH20).
QUESTIONS
11. Name four natural materials that are chiefly calcium carbonate.
12. State two chemical actions that are common to all forms of calcium
carbonate.
13. Write formula equations for (a) slaking lime; (b) setting of lime plaster;
(c) formation of limestone caves; (d) formation of stalactites in a cave; (e) forma-
tion of slag from silica in a dolomite-lined furnace.
14. When lime is kept open to the air, it "air slakes." Of what two compounds
is it then composed?
16. What use is made of precipitated chalk in (a) tooth-paste manufacturing;
(b) papermaking; (c) paint manufacturing; (d) setting glass in window sash?
16. Copy and complete the. following table for forms of calcium carbonate (do
not duplicate any common name, and do not write in this book):
Common name
Formula
Use
Limestone
—
—
—
Building stone
—
CaCOs-MgC03
—
Lime
—
—
—
Ca(OH)2
—
—
—
Testing for CO2
17. What is the value of putting slaked lime into a compost heap?
18. Why should ammonium suifate fertilizer not be added to a field that has
been treated recently with slaked lime?
386 CHEMISTRY FOR OUR TIMES
19. Explain in what sense this statement is true: Most houses are torn
down before the plaster is dry.
20. Calcium chloride is approximately 36 per cent calcium. What weight of
anhydrous calcium chloride must be decomposed by electrolysis in order to
{r> a
7'2 pounds of metallic calcium?
Ammonia. Strictly speaking, ammonia is not considered a heavy
basic chemical. In fact, it is a gas as we usually meet it, although some-
times it comes to the market as a liquefied gas, or in a water solution.
Ammonia is included here, however, because, like hydroxides, carbonates,
and other bases, it neutralizes acids. Ammonia may have received its
name from the oasis of Jupiter Ammon, at Siwa in the Sahara Desert,
where it arose from decomposing camel dung.
Sources of Ammonia. The odor of ammonia may be noticed near u
manure pile or from a bottle of household ammonia. Ammonia gas (NH3)
forms from the decay of nitrogen-containing organic matter. Nitrogen-
containing compounds found in living organisms are called proteins, and
their decay produces ammonia.
Proteins formed in plants ages ago are a modern commercial source
of ammonia. When these plants were changed to coal, some of the protein
remained in the coal. A ton of soft coal, heated in a modern by-product
coke oven, may produce as much as 6.5 Ib of ammonia. After purifica-
tion, the ammonia is run into sulfuric acid. Here it unites with protons
from the acid until a mush of ammonium sulfate crystals is formed.
2IMH3 + H2SO4 -» (NH4)2SO4
These are whirled dry in a centrifuge basket, making them ready to be
sold as fertilizer to the grower of cotton and other crops.
Synthetic Ammonia. Ammonia is such a useful and necessary sub-
stance that many attempts have been made to synthesize it from its
two elements. The chemical equation for the synthesis looks simple on
paper.
N2 + 3H2 -4 2NHa
The practical difficulty to be overcome in order to produce more than
a slight trace of ammonia is to make the lazy nitrogen join with hydrogen.
In general, we have learned that substances become more active chemi-
cally when they are heated. The idea then presents itself that a warmed
mixture of nitrogen and hydrogen in volume proportions of 1 to 3 might
give a satisfactory yield of ammonia. Such, however, is not the case.
Study shows two reasons for this. (1) When ammonia is formed, heat is
liberated. Raising the temperature, therefore, would hinder the forma-
THE BASIC HEAVY CHEMICALS 387
tion of ammonia. (2) At a raised temperature, ammonia decomposes
easily. This may be predicted from the first point.
2NH3 -+ N2 + 3H2
We are dealing with an equilibrium, or reversible, chemical action —
one that does not tend to go to completion by itself in the desired
direction.
An increase of pressure is the next obvious aid, for four volumes of
mixed elementary gases change to two volumes of ammonia. Experi-
ments show that high pressure is indeed a help in producing ammonia.
From laboratory experiments we learn that, from a 3 to 1 mixture of
hydrogen and nitrogen at a certain temperature and at the pressure of
the air, 15.3 per cent ammonia is formed; at 10 times air pressure, 50.66
per cent; at 100 times air pressure, 81.54 per cent; and, at 1000 times air
pressure, 98.29 per cent.
These high values are obtained only after waiting for the equilibrium
to establish itself. A successful commercial process must be both rapid
and continuous. To take care of this lag we now call in our third reserve,
the catalyst. A catalyst is selected that hastens most the establishment
of the equilibrium at the conditions of temperature and pressure chosen.
The Haber Process. The Haber process, developed in Germany in
1912, is the fundamental process for making ammonia from the ele-
ments. Many variations are used, but all are based on Haber's synthesis.
The development and improvement of this process were problems that
were attacked from two angles, (1) the manufacture of the gases hydrogen
and nitrogen and (2) the uniting of the gases to form ammonia. For this
process, a method of converting a mixture of nitrogen and hydrogen into
ammonia was developed by Fritz Ilaber (1868-1934); and the successful
production of the raw materials, nitrogen and hydrogen, was developed
by Karl Bosch (1874-1940).
1. To produce the nitrogen and hydrogen, steam is passed over hot
coke to form a mixture of hydrogen and carbon monoxide, called water
gas (see page 527).
C + H2O -> CO + H2
This gas mixture in turn is mixed with producer gas which is chiefly
nitrogen and carbon monoxide. These three gases are further mixed with
steam and passed over a catalyst to change the carbon monoxide and
steam into hydrogen and carbon dioxide.
CO + H2O -+ CO2 + H2
The carbon dioxide is removed from the mixture by forcing it into
water under pressure, and the last traces are scrubbed out by washing
with sodium hydroxide solution. A mixture containing hydrogen and
388 _ CHEMISTRY FOR OUR TIMES _
nitrogen remains. The nitrogen comes originally from the air and the
hydrogen from water.
2. The mixture of nitrogen and hydrogen is run over a suitable second
catalyst at proper temperature and pressure, forming a small amount of
ammonia. A minute later the ammonia is removed by liquefying it. The
unchanged elementary gases are recirculated to pass once more over the
catalyst.
The American Process. The Fixed Nitrogen Laboratory of the U.S.
Department of Agriculture at Washington, D.C., recommends iron oxide
promoted by 1 per cent potassium oxide and 3 per cent aluminum oxide,
prepared in a special way, as a catalyst for the making of ammonia.
Other catalysts are used, but iron oxide is the principal material.
In the American process air is mixed with an excess of hydrogen and
the mixture burned. The water formed is condensed out, leaving a mix-
ture of nitrogen and hydrogen. This process uses a much higher pressure
(900 to 2000 times air pressure) than that of the original Haber process.
The hydrogen may come from the electrolysis of water and the nitrogen
from boiling liquid air.
After the gases are passed over the catalyst, the pressure is reduced
somewhat and the mixture cooled. Fairly pure ammonia separates out
as an anhydrous liquid. It is ammonia in liquid form, without water.
The Cyanamide Process. The method of making ammonia at the
famous Muscle Shoals plant on the Tennessee River in Albania starts
with lime and coke in an electrically heated furnace. Calcium carbide is
produced.
CaO + 3C -4 CaC2 -fCOT (1)
lime coke calcium carbide
The calcium carbide is then placed in an electrically heated tank and
supplied with nitrogen from boiling liquid air. The lazy nitrogen is cap-
tured in a compound called calcium cyanamide. The pure compound is
a colorless substance, but it is blackened by the carbon that remains
mixed with it.
CaC2 -f N2 -4 CaCN2 + C (2)
The cyanamide may be used directly on the soil as a fertilizer, but
it can be made to produce cyanides when heated with coke and salt.
2NaCI + C + CaCN2 -> CaCI2 + 2NaCN
salt coke calcium calcium sodium
cyanamide chloride cyanide
Most of the cyanamide, however, is treated with steam under pressure
to form ammonia.
CaCNs + 3H2O -» CaCO3 4- 2IMH* (3)
cyanamide steam calcium ammonia
carbonate
THE BASIC HEAVY CHEMICALS
389
The ammonia in turn produces solid fertilizer when passed into sulfurio
or phosphoric acid (see page 290). The numbered equations (1), (2), and
(3) show the chemical changes in the cyanamide process.
Description of Ammonia. Once a person with a normal sense of
smell detects the pungent penetrating odor of ammonia, he is able to
recognize it again. Such a definite odor is said to be characteristic or
identifying. Small amounts of ammonia are detected also by the ability
of the gas to turn moist pink litmus paper blue.
Ammonia is colorless, either as a gas or a liquid. One liter of the gas
weighs 0.76 g, about one-half the
weight of air. Very large amounts of
ammonia dissolve in a relatively small
amount of water, 500 volumes to 1.
To show this experimentally let us fill
a round-bottomed flask with ammonia gas
and close the flask by a two-holed stopper
that has a medicine dropper full of water
through one hole and a long glass tube
tapered at the upper end through the
other. (See Fig. 22-11.) The flask is now
inverted and supported in such a fashion
that the outer end of the glass tube dips
into a vessel of water to which phenol-
phthalein has been added. The water is
squirted out from the medicine dropper.
Action follows immediately. The small
amount of water injected thus into the
flask dissolves so much ammonia that the
pressure within the flask is suddenly de-
Strong,
Round Bottom
Flask
Water with
Phenolphthalein
Solution
FIG. 22-11. — The ammonia foun-
tain experiment illustrates tho ex-
treme solubility of ammonia in water.
A similar experiment can be performed
with hydrogen chloride or sulfur
dioxide.
creased. The pressure of the air on the surface of the open vessel of water into
which the glass tube extends forces the liquid up the tube, making a miniature
geyser or fountain. The phenolphthalein turns bright pink when it reaches the
ammonium hydroxide formed in the flask.
Ammonia gas can be changed into a liquid rather simply by pressure.
The liquid boils again when the pressure is released, taking in heat. The
boiling point of ammonia at atmospheric pressure is — 33.5°C. Boiling
and condensing ammonia is the cycle used in the refrigerating system
for ice making, cooling meat counters in stores, cooling drinking water
in large buildings, and keeping entire buildings (food-storage warehouses)
cold.
How We Make Ammonia in the Laboratory. The commercial
methods of making ammonia need too much apparatus to be used in
most laboratories. We can obtain ammonia easily by boiling household
390
CHEMISTRY FOR OUR TIMES
ammonia. The dissolved gas leaves the solution when the temperature
is raised. Water-vapor molecules also leave with the ammonia gas, and
these are separated by some material that absorbs them but that does
not act on the ammonia. For this purpose, anhydrous calcium sulfate,
commercial Drierite, is one suitable material (see Fig. 22-12) ; soda-lime
mixture (NaOH and CaO), another.
Condenser
Clamp
NH3
FIG. 22-12. — Ammonium hydroxide decomposes into ammonia gas and water when
heated. If the vapors are dried, ammonia alone remains.
Larger amounts of ammonia may be produced easily by warming an
ammonium compound mixed with an alkali in a flask as in Fig. 22-13.
The alkali neutralizes the acid with which the ammonia has joined to
form the ammonium compound, leaving the free gas. Examples are
NH4CI -f NaOH -+ NaCI +
(NH4)2SO4 + Ca(OH)2 -» CaSO4
NH3|
2H2O
All ammonium compounds release ammonia gas when they are heated
with an alkali. The ammonia gas can be identified by its odor; therefore,
heating with an alkali is a means of testing a substance for the presence
of the ammonium ion (NHf).
THE BASIC HEAVY CHEMICALS
391
Chemical Actions of Ammonia. Ammonia gas dissolved in water
contains some ammonium hydroxide. It acts alkaline; ammonia is a base.
NH8 + H2O 1=5 NH4OH
OH~
As soon as the hydroxyl ions are all combined with grease, as they
might be, for example, when household ammonia is used for washing
NH
FIG. 22-13. — This is the apparatus for preparing and collecting a flask of dry ammonia
gas. Moisture from the generator is retained in the tube of drying agent.
windows, more ammonia acts with the water to produce additional
ammonium hydroxide. We can think of ammonium hydroxide as a good
source of hydroxyl ions (OH~) and at the same time as a mild base.
Of course, ammonia acts with acids, also; that is, it annexes protons
easily.. For example,
NH3
ammonia
HHHPp4
phosphoric
acid
NH4HHPO4
ammonium
dihydrogen
phosphate
Many metal ions become ammoniated readily. Silver (Ag+), copper
(Cu++), and mercury (Hg++) are examples. When ammonia water is
added to a solution of copper sulfate, a beautiful deep-blue color of the
tetrammine copper ion [CuCNHs)^* is formed.
[Cu(H,0)4]++
light bluo
4NH8
[Cu(NH,)4]++
rich deep blue
4H20
392
CHEMISTRY FOR OUR TIMES
Ammonia is oxidized to nitric acid (see page 362) with a heated
platinum wire screen for a catalyst.
NH8 + 2O2 -+ HNO, + H,O
In fact, when pure oxygen is bubbled through a solution of concentrated
ammonia, the mixture of gases emitted will explode when ignited.
The ammonia can be easily decomposed into its elements at moderate
temperature by using the proper catalyst.
2NH, -4 3H2 + N,
Hot magnesium will act with ammonia, releasing hydrogen,
2NH, + 3Mg -> Mg3N2 + 3H,
but a good oxidizing agent, heated copper oxide for example, removes
the hydrogen, freeing nitrogen.
2NH, + 3CuO -4 3H2O + 3Cu + N2
Ammonium Compounds. Most of the ammonium compounds are
white, resembling salt or sugar in appearance. Exceptions are those which
are colored because of a colored negative ion. Ammonium dichromate
[(NH4)2Cr207], for example, a strong oxidizing agent, is colored a brilliant
orange. Ammonium salts also decompose rather easily when heated, and
in most cases the mixed vapors above the heated materials cool and form
the ammonium compound again.
NH4CI ** NH8 + HCI
All ammonium salts dissolve well in water. These solutions have the
ammonium ion (NHf) in them and are acidic. A price list of the impor-
tant chemicals on the drug and chemical market lists 14 ammonium
compounds. Four of the more common are listed in the table below.
FOUR COMMON AMMONIUM COMPOUNDS
Name
Formula
Uses
Ammonium carbonate
(NH4)2COs
In smelling salts
Ammonium chloride ("sal ammoniac")
Ammonium nitrate
NH4C1
NH4NOi
In dry cells, as flux for
soldering
As fertilizer; in explosives
Ammonium sulfate
(NH4)2S04
and fireworks; to make
"laughing gas"
As fertilizer
SUMMARY
Sodium hydroxide, commercial lye, or caustic soda is prepared (1) by elec-
trolysis of common salt in water and (2) by interaction of calcium hydroxide
solution and sodium carbonate. Sodium hydroxide, a caustic substance, is corro-
sive to animal matter. It absorbs carbon dioxide, forming sodium carbonate. It is
THE BASIC HEAVY CHEMICALS 393
used in the manufacture of rayon, paper, and soap, for refining petroleum, and in
the treatment of textiles.
Potassium hydroxide is similar to sodium hydroxide. Sodium carbonate, soda
ash, sal soda, or washing soda (hydrated) is prepared by the Soivay process. The
raw materials used in the Soivay process are salt, water, carbon dioxide, and
ammonia. Sodium carbonate is used in the manufacture of soap, glass, and cleans-
ing powders. It is a neutralizer for acids.
Sodium hydrogen carbonate, baking soda, or sodium bicarbonate is prepared
by the Soivay process. It is used in baking powders, in cooking, in the soda-acid
fire extinguisher, and as a medicine.
The natural forms of calcium carbonate are found widely distributed on the
earth as limestone, marble, shells, calcite, and coral. Calcium carbonate neutral-
izes acids, forms lime when heated strongly, forms slag when heated with sand,
and forms limestone caves by action of soil water (weak carbonic acid).
Precipitated chalk is prepared by putting solutions of calcium chloride and
sodium carbonate together. The calcium carbonate precipitates. This insoluble
compound is used to make putty and tooth powder.
Lime, or quicklime (CaO, calcium oxide), is prepared by heating limestone in a
kiln. CaCOa — * CaO + C02. When slaked with water, lime evolves much heat
and forms slaked lime, or calcium hydroxide. A suspension of slightly soluble cal-
cium hydroxide in water, called milk of lime, is used in the manufacture of paper,
in making bleach powder, in making mortar and plaster, and for sweetening the
soil. The clear solution of calcium hydroxide, called limewater, is used to test for
presence of CO2 and in medicine.
Ammonia is formed naturally from the decay of proteins. It is a by-product of
the destructive distillation of soft coal. It is manufactured by direct synthesis,
by using the Haber method. N2 + 3H2 — » 2NH3. Any strong alkali and any
ammonium compound heated together produce ammonia. This is the common
laboratory method for its preparation. It is also manufactured synthetically by
the cyanamide process.
Ammonia is colorless, has a pungent odor, is very soluble in water, is easily
liquefied, and is about three-fifths as dense as air. Ammonia water is a solution
of ammonia in water. Some ammonium hydroxide forms in this solution. Ammonia
adds to acids, forming ammonium compounds, and it adds to some ions, forming
ammoniated complex ions. In the Ostwald synthesis, ammonia combines with
oxygen in the presence of platinum catalyst to form nitric acid. When heated,
ammonia decomposes into nitrogen and hydrogen.
Ammonium compounds decompose when heated, but the products of heating
recombine in some cases. Ammonium compounds are used for fertilizers and for a
variety of special purposes.
QUESTIONS
21. List three sources of ammonia.
22. How is ammonium chloride manufactured from ammonia? How is am-
monia manufactured from ammonium chloride?
23. In the synthesis of ammonia from its elements, what three factors are
controlled in order to increase the yield?
394 • CHEMISTRY FOR OUR TIMES
24. Write four equations for the Bosch-Haber process of producing ammonia,
including preparation of the elementary gases.
25. Write three equations showing the synthesis of ammonia by the cyanamide
process.
26. List five physical properties of ammonia.
27. In the ammonia-fountain experiment (page 389), a flat-bottomed flask,
used by mistake, broke explosively. What was the cause of the accident?
28. Write formula equations for reactions between the following substances:
(a) ammonium sulfate and sodium hydroxide; (b) ammonium chloride and potas-
sium hydroxide; (c) ammonium phosphate and calcium hydroxide; (d) ammonium
nitrate and lithium hydroxide.
29. State two uses for household ammonia.
30. Point out the importance of being able to manufacture ammonia syn-
thetically.
31. Write formula equations for the decomposition of the following compounds
when heat is applied: (a) ammonium chloride; (6) ammonium nitrate; (c) am-
monia; (d) sodium nitrate; (e) ammonium nitrite.
32. What is the penetrating odor that comes from a bottle of smelling salts?
Write an equation for the decomposition of the ammonium compound.
33. Compounds can be made in which a hydrogen atom of ammonia is sub-
stituted. One of these, hydroxylamine, has one atom of hydrogen in ammonia
replaced by the hydroxyl radical. Write the formula of (a) hydroxylamine;
(6) hydroxylammonium chloride; (c) hydroxylammonium sulfate.
MORE CHALLENGING QUESTIONS
34. Construct a model cell for the electrolysis of hot brine. Measure the elec-
trical input and the amount of chemicals produced; calculate the efficiency of
the cell.
35. Investigate the process for preparing mercerized cotton. Make some of
this cotton. Compare it for tensile strength with unmercerized thread of the same
size. Exhibit samples showing the cotton before and after treating.
36. Make a table, listing name, formula, and important uses of (a) caustic
soda; (b) potash lye; (c) sal soda; (d) ammonia water; (e) bicarbonate of soda;
(/) limestone; (g) quicklime; (h) milk of lime.
37. Clear crystalline caicite is notable for its property of double refraction.
Using the geometrical method, determine the indices of refraction for a sample
of crystalline caicite. Refer to a physics laboratory manual for the method.
38. Investigate the history of the Colosseum in Rome, Italy. For what pur-
pose was the building used? Of what material was it made? What became of
the stones taken from its walls after the building was abandoned?
UNITFIVE CHAPTER XXIII
THE SILICATE INDUSTRIES
The silicate industries are those which make bricks, cement, pottery,
china ware, glass, and similar products. These materials are quite common
in our homes and take an important part in everyday life. Silicate houses
are made of bricks held together by concrete mortar; windows are glass
made of transparent mixed silicates; sunrooms have special glass panes
made of high-silica glass that let in the sun's health-promoting ultra-
violet rays. The glass bricks that
are sometimes set into the walls
of buildings allow light to pene-
trate into an otherwise dark cor-
ner.
Walls of rooms are covered
with lime plaster that contains
much sand or silica in it. Base-
ment walls and sidewalks are con-
crete— more silicates. Glass is used
extensively within the house:
mirrors, light bulbs, and baking
dishes are all made of different
sorts of ^lass. Ordinary chinaware
is made from clay and glazed ; clay
is a complex silicate. Pottery for
tableware and ornamental vases
are also silicates. In the kitchen,
the enamelware pots and pans
have a silicate glass coating over steel, and a similar glazed surface is seen
on bathroom furnishings. Altogether, these serviceable silicate industries
provide practical and decorative articles that make life more enjoyable.
(Sec Fig. 23-2.)
The use of silicates is one of the earliest arts of mankind. Clay pottery
making is found among primitive peoples in many parts of the world.
Courtesy of Owens-Corning Fiberglas Corporation
FIG. 23-1. — Winding fine filaments of
glass onto a spool calls for workers with
steady hands. Glass fibers are newcomers
in the textile industry.
New Terms
infusorial, or diutomuccous, earth
feldspar
kaolin
biscuit ware
glass
water glass
395
396
CHEMISTRY FOR OUR TIMES
Writing on clay tablets was the ancient Assyrian way of keeping records.
Glassmaking has a long and fas-
cinating history. From our stand-
point, it is interesting to see how
each of these branches of the sil-
icate industries has profited by the
application of chemistry. One ex-
ample will serve as illustration:
Strong glass dishes have been
"available for many years, but such
dishes broke in hot water. Re-
cently, however, glass dishes have
been made in which the house-
Courtesy of Sterns Textile Manufacturing Company wife Can CVCn bake food in the
FIG. 23-2. — A lustrous bedspread shown
here was made from spun-glass fibers.
Careful examination of the picture will
show other articles made of glass that help
to make the room attractive.
oven. Furthermore, now we have
glass dishes that will withstand
an open flame on the stove top.
Other developments, such as flex-
ible glass, shatterproof glass, non-
expanding glass, tempered glass,
and bullet-resisting glass, are
either commonplace or are men-
tioned as coming developments.
Silica. The basis of the silicate
industries is silica. Chemically, the
substance is silicon dioxide (SiO2) ,
an inactive, water-insoluble com-
pound. This material is known to
everyone, for it is the white sand or
quartz rock found in nature. (See
Fig. 23-4.) Brown sand is silica
with impurities, usually iroif oxide,
in it. Mineral collectors recognize
many sorts of quartz and impure
silica. Among them are smoky
quartz, pink rose quartz, and pur-
ple amethyst. These may be found
in six-sided crystals, many beauti-
ful specimens of which are avail-
able. Silica is the most common
mineral in the earth's crust.
Semiprecious varieties of silica are agate, jasper, onyx, and opal as
well as amethyst. These possess beautiful colorings and when polished
are used for jewelry. (See Fig. 23-5.)
Courtesy of Corning Glass Works
FIG. 23-3. — Borosilicate glass, such as
Pyrex brand glassware, is one of the most
rugged types of glass. Here we see a strong
electrical insulator made of glass being
inspected.
THE SILICATE INDUSTRIES
397
Courtesy of The Travelers Insurance Company
FIG. 23-4. — Small grains of sand, such as these shown here under polarized light and
magnified fifty times, make "the pleasant land."
Courtesy of Journal of Chemical Education
Fio. 23-5.-»-This cut and polished opal shows bands and a mass of crystals in the center.
398 CHEMISTRY FOR OUR TIMES
Indians and other people used much silica, especially quartz and flint,
for chipping material from which to fashion stone knives, arrow points,
drills, and other tools. Many museums, as well as individuals, have
extensive collections of these interesting implements made of silica.
Sandstone is silica held together by some natural cementing mate-
rial. When some deposits of extremely fine silica are examined under the
microscope, it is apparent that they were once part of the skeletons of
Courtesy of General Electric Company
FIG. 23-6. — This 60-degree quartz prism shows almost perfect total reflection of the
cloth on the right of it.
tiny creatures. This material is called infusorial or diatomaceous earth.
It is used for adsorbing undesired colors from liquids and for a scouring
agent. One type of silver-polish cream is a suspension of fine infusorial
earth in a soapy gel.
The element silicon is the second most abundant in the earth's crust.
Some plants, straw and bamboo for example, have a small amount of
the oxide, or silica.
Pure silica (SiO2), called rock crystal or quartz, was once used exten-
sively in ornamental work, on lighting fixtures in formal ballrooms for
example. Today the chief use of high-quality quartz is in making optical
instruments and laboratory vessels. (See Fig. 23-6.) Modern torches can
readily melt this material at its rather high melting point, 1710°C, into
THE SILICATE INDUSTRIES 399
a highly transparent glass that transmits ultraviolet light. Laboratory
vessels made of fused quartz glass expand so little that they can be taken
from the heart of a flame and plunged suddenly into cold water without
cracking. Thin sheets of quartz crystal are used in controlling the fre-
quencies of radio transmitters and other electronic devices.
Silica (silicon dioxide) is the oxide of a semimetal. Chemically, carbon
dioxide resembles silicon dioxide in a general way, and carbonates have
a similarity to silicates. Silica will not act easily with most acids or
bases, but at high temperatures it joins oxides of metals.
AI2O8 + 3SiO2 -4 AI2(SiO8)s
Hydrofluoric acid corrodes it slowly.
4HF -f SiO2 -» SiF4T + 2H2O
Silica is not attacked by strong oxidizing agents. Only very strong
reducing agents will free the element silicon from its oxide. Carbon in an
electric furnace will do this (see page 251), or powdered magnesium.
2Mg + SiO2 -+ 2MgO + Si
The uses of sand in building and road construction are well known to
everyone. Good grades of white sand are used for making glass.
Soluble Silicates. When sand is heated with sodium carbonate or
potassium carbonate, a chemical action occurs.
SiO2 + Na2CO3 ->• Na2SiO8 +CO2|
sand sodium carbonate sodium metasilicate
"soda ash" "water glass"
The sodium metasilicate formed, after treatment with steam, dis-
solves readily in water. Prepared for the market, it is a sticky, thick sirup
called water glass. Soluble silicates are used to glue corrugated card-
board boxes together, to repair broken glass and pottery, and at home
to preserve eggs by filling the pores and thus preventing oxidation.
Cloth treated with water-glass solution becomes fireproof. Sodium silicate
solution is used as a water softener.
When an acid is added to water-glass solution, a thick jellylike paste
forms. This material is silica with more or less water loosely attached to
it. It is sometimes called silicic acid. When dried it is called silica gel, a
porous solid that is extensively used in refrigeration and in adsorbing
valuable vapors.
QUESTIONS
1. List 10 uses for glass.
2. List five products of silicate industries that are used at home.
3. What difference in composition distinguishes pure quartz from amethyst?
400 CHEMISTRY FOR OUR TIMES
4. What properties of flint caused primitive people to use it for making tools
and weapons?
5. What advantage has a windowpane of pure silica over one of common
quartz? What disadvantage?
6. Write formula equations for three different chemical reactions, each in-
volving silica.
7. What percentage of clay (H4Al2Si2O9) is silica?
8. Write an equation to represent (a) the action of hydrochloric acid on
sodium silicate solution; (6) the effect of strongly heating the silica-containing
product of reaction (a).
9. How can water glass be used so that money is saved on the family grocery
bill?
10. Write a formula equation for the action between (a) sodium hydroxide
and silica; (b) potassium carbonate and silica; (c) calcium carbonate and silica;
(d) aluminum oxide and silica.
Common Clay. Ordinary clay started as a hard rock called feldspar
(KAlSiaOg). Feldspar can be considered a compound made of potassium,
aluminum, and silicon oxides (K^O'AUO^GSiOa). Exposed to the weather,
feldspar decays by the action of water and carbon dioxide, permitting
its potassium oxide to become available for plant growth. The resulting
compound is clay (H4Al2Si209). Very pure clay is white and is called
kaolin, after the name of a Chinese emperor, Kao, who encouraged its
use in his realm for making chinaware. Brown clay has organic matter,
iron oxide, and sometimes sand mixed in with it.
Bricks. Red housebricks are usually made near a clay pit. The clay
is taken to the brickyard, where it is mixed with water, sand, and feld-
spar, unless these are already in the clay. The plastic mass is screened
and then pressed into molds of the proper shape. The molded blocks
of clay are placed on racks to dry. After drying, the bricks are
piled loosely over small tunnellike arches. When the pile is complete, it
is covered loosely with clay. Newer techniques stack the bricks in a
circular permanent kiln. Fires are burned in the arches or in the kiln, for
several days. The bricks lose water and melt a little (sinter) during the
firing, becoming honeycombed with tiny holes. Iron oxide (ferric) formed
during the firing accounts for the red color.
Many sorts of fancy bricks are made for special purposes. The compo-
sition of the mixture may be different or the temperature of the firing
altered. A higher temperature will melt the outside of the bricks, pro-
ducing a vitrified nonporous surface. A dimple way of getting a smooth,
water-shedding surface on clay products is to throw salt onto the fire
of the kiln when it is hot. The vapors of the salt deposit and react on the
THE SILICATE INDUSTRIES 4(H
outside of the ware, producing a glasslike coating. This is called a salt
glaze and is seen on jugs and earthenware.
Firebricks for lining furnaces may be made of nearly pure silica for
acidic linings and of magnesia (MgO) or alumina (A1203) for basic lining.
Some are also made of aluminum silicate.
Courtesy of General Ceramic* Company
Fig. 23-7. — Before the invention of paper, Babylonian businessmen used baked clay
tablets in baked clay envelopes for their records.
Roofing and drain tiles are made in a manner similar to bricks. Sewer
pipes are also made from clay, sometimes quite coarse. The surfaces of
these products are made nonporous by means of various glazes.
Pottery. Pottery is made from carefully selected clays that are mixed
with water and purified. The mixture may be used as a thick fluid that
is poured into plaster-of-Paris molds to form the ware. Another method
of forming the ware is to place a blank of stiffer clay on a revolving
potter's wheel and to shape it by a tool.
After drying, the ware is fired in a kiln. It comes out hard, light gray,
rough-surfaced, and porous. At this stage it is called biscuit ware. Next
it is glazed; that is, a glaze mixture, consisting for example of feldspar,
borax, lead oxide, crushed quartz, whiting, and clay, is suspended in
water and applied to the surface of the ware. Then the ware is fired again,
the glaze melting easily and giving the biscuit a glassy surface.
Let us melt some borax (Na2B407-10H20) in a loop on the end of clean platinum
or iron wire inserted in a glass handle. (See Fig. 23-10.) Let us then touch the edge
of the glassy bead thus formed in the loop to a small amount of manganese dioxide
and remelt the bead. When cool, a clear transparent purple bead is formed. The
oxide has dissolved in the glassy material and has colored it purple.
In a similar manner colors in pottery and glass are obtained. Some
402
CHEMISTRY FOR OUR TIMES
material, usually an oxide, is dissolved in the glass or the glaze. Cobalt
oxide produces blue; uranium, orange; and iron, red or green. Decora-
tions are put on either under or over the glaze and melted in. Transfer-
paper patterns or hand painting are both used.
m
Court t\t>t of General Ceramics Company
FIG. 23-S. Tli is piece of ancient Koman drain tile was once part of the famous
Appian Way, the road from Home to Brundisuin, now Brindisi. Thr road \\ -asb«>gun by
Appius Claudius Caecus about 312 B.C.
Courtesy of General Ceramic* Company
FIG. 23-9. — Until the job of making these vessels was completed, this gentleman
didn't rest as easily as he is shown here. These are the largest stoneware vessels ever
made. They arc us«'d for holding acids.
Tableware and Porcelain. Better quality dinner plates and other
dishes for the table are made from china clay, feldspar, and ground flint
mixed with water. This ware is shaped, dried, and "burned" to form the
biscuit ware in the manner employed for making pottery. The pattern
THE SILICATE INDUSTRIES
403
and the glaze are applied to the biscuit again
Dinnerware and porcelain are thus special
types of pottery.
Porcelain has a glasslike interior. The
clay mixture for its manufacture contains
a relatively large amount of feldspar. The
temperature of firing porcelain is higher
than that for ordinary dinnerware. Because
of the glasslike interior, porcelain allows
some light to pass through it. It is trans-
lucent, but not transparent like glass. Much
laboratory apparatus is made from "chem-
ical" porcelain. Porcelain was " discovered "
in Meissen, Germany, in 1709 in an at-
tempt to make better crucibles for the
alchemical transmutation of base metals
to gold, but porcelain had been made by
before.
as in the manner for pottery.
Pt
FIG. 23-10.— Melted borax
dissolves metallic oxides and
forms colored beads. A platinum
wire with a loop at the outer
end, mounted in a holder, is a
suitable' piece of apparatus for
making borax-bead tests.
the Chinese many centuries
Courtesy of Vernon KHn«
FIG. 23-11. — Designer Rockwell Kent has put scenes from the famous sea story,
"Moby Dick," onto a set of dinnerware.
A few years ago no satisfactory laboratory porcelain was made except
in central Europe. When by necessity the porcelain makers of the United
States were faced with a demand for this product, they studied and
404 CHEMISTRY FOR OUR TIMES
investigated. Eventually the Coors plant in Colorado produced a porce-
lain that is superior to the European in resistance to heat and chemi-
cals and in mechanical strength. Moreover, the quality of the American
product has been improved constantly.
The making of porcelain electrical insulators and spark-plug porcelain
are other specialized industries that have profited by the application of
chemical knowledge.
So many sorts of ceramic products are^possible that the field offers
great opportunity for the expression of artistic and decorative skill. The
variety of colors, designs, glazes, and clays is almost without end. Many
people adopt potterymaking as a hobby. Some have found the hobby
growing into an interesting and profitable business.
Enanielware. Enameled kitchenware has a glasslike coating over
steel. The coating is similar to the glaze applied to pottery, but more
problems are involved in producing satisfactory goods. A foremost con-
sideration is that the metal must be scrupulously clean. Then, the vitreous
enamel coating must expand at just the same rate as the metal. Also,
the coating must be applied evenly and have no holes.
The glaze is baked onto the metal base, as with pottery. Bathroom
sanitary ware is made in this way. Refrigerators, stoves, signs, and sinks
are only a few of the common articles coated with enamel. Dissolved
oxides or colloidal materials suspended in the glaze impart colors.
QUESTIONS
11. What element, valuable to plant growth, is made available through the
weathering of feldspar?
12. What is the cause of the coloration in brown sand? What treatment may
help whiten the sand?
13. Describe the process of making a common flowerpot.
14. Which of these products usually has a vitrified surface: roofing tile;
vinegar jug; laboratory porcelain crucible; water jug; flowerpot, sewer tile; drain
tile; enamelware; electrical porcelain; tableware?
15. What properties of porcelain make it useful as part of a spark plug?
16. List three compounds that should not be heated in laboratory porcelain
ware.
17. Glass stoppers of bottles containing sodium hydroxide or ammonium
hydroxide solution sometimes " freeze in" tightly. Account for this action.
18. Tell how to distinguish a paste diamond (glass) from rock crystal (quartz)
and also from a real diamond.
19. Glass could be manufactured more quickly and cheaply if the products
of the glass-molding machine could be cooled, racked, and packed immediately.
THE SILICATE INDUSTRIES
405
Instead, the products pass through a long lehr, cooling slowly. Why is the last
step in the process necessary?
20. Why is the use of chipped or cracked table chinaware inadvisable from a
health standpoint?
Portland Cement. Lime mortar (see page 384) "sets" only in air
with ample carbon dioxide. The search for a mortar that would harden
under water led John Smeaton of England in 1756 to discover the first
cement of modern times, Portland cement. Actually, he rediscovered a
cement similar to one that had been used centuries before by the Romans.
FIG. 23-12. — Portland cement starts as rock in a quarry.
Portland cement is made from a mixture of clay, or shale, and lime-
stone. Cement rock (which is equivalent to limestone and shale in one
stone) or slag may also be used. (See Fig. 23-12.) The raw material is
ground to a powder and introduced into the upper end of a rotating
kiln. This kiln is a nearly horizontal firebrick-lined cylinder, one end of
which is slightly raised and projects into the stack. (See Fig. 23-14.) It
is almost as long as a football field and so large in diameter that a tall
basketball center could run through it, holding his long arms up over
his head, without touching the top.
A fire hotter than that needed to melt steel (1425°C) melts the pow-
dered rock as it tumbles down the slowly turning tube. The rock melts
406
CHEMISTRY FOR OUR TIMES
Cement is usually made from limestone and cloy,
ihale or blast furnace slag; or marl and clay limt,iilico,
.and •alumina ore the mom constituents .qt cement..
At the blending bint the two kinds of 'raw materials
ore carefully proportioned by expert chemists" who let
the automatic scales to give the desired fixture. •
Instead of the materials being dried, in wet procest
plants water is added. Otherwise, operations are
essentially the same as in the dry process plants.
Samples are taken of the raw materials"oli frequent
Sta'ges and physical and chemical tests made to
insure a high grade product. This same expert
supervision t% maintained throughout the entire,
manufacturing process to insure quality. '
The cement industry Js the fourth largest monufocturmg user of
bituminous coal, and the largest consumer of putverlxed coal.
Oil or gas is used at some plants instead of coal.
The cement industry is the fourth largest shipper
of manufactured jnaterials. The cement produced
in a year would fill 725,000 freight cars.
Power demands for cement,
making are extremely heavy.
The cement industry ranks
tenth in power installed.
Returned sacks are cleaned, mended,
and tied. Then they ore -filled by a
machine which forces exactly
94 pounds of cement through a self*
closing valve in the bottom of the sack.'
CtMtKT STOKACt
__ _ « of gypsum Is
.ground' up with the clinker to control the rate
of hardening 'of the cement when used.
Courtesy of Portland Cement Association
FIG. 23-13. — The manufacture of cement — how rocks are converted into this versatile
material.
THE SILICATE INDUSTRIES
407
together, forming rough, gray clinkers of about the size of large peas.
In this form cement will keep indefinitely. The cement of commerce is
made by powdering the clinker and adding to it 2 or 3 per cent of gypsum,
to control the time needed for the cement to "set."
Courtesy of Portland Cement Association
FIG. 23-14. — The burner foreman
is about to inspect the hot end of a
Portland-cement kiln.
FIG. 23-15. — Norris Dam on the
Clinch River, Tennessee, is built of
reinforced concrete.
Courtesy of Portland Cement Association
FIG. 23-16. — The sewage treat HUM it.
plant at Huntington Beach, California,
has an exterior made chiefly from rein-
forced concrete. A progressive commun-
ity treats its sewage.
FIG. 23-17,— The Pennsylvania turn-
pike between Ilarrisburg and Pitts-
burgh is an excellent example of the
artistic and practical use of reinforced
concrete.
Chemically, Portland cement is a mixture of silicates of calcium,
aluminum, and a few other metals. Tricalcium silicate is the compound
moat desired in the cement for quick setting. Cement "sets" by the
addition of water only. Water attaches itself firmly to the powdered
cement and forms a hard material. The process is not completely under-
408 CHEMISTRY FOR OUR TIMES
stood, but evidence points to the formation of crystals by the reaction
with water as one important part. Colloidal material is present in the
"green/' freshly poured cement, probably formed by the action of the
water on silicates and aJuminates.
When cement is reheated with additional limestone in exact propor-
tions, a new cement is formed that has the property of high early strength.
It is quick setting and does not change much in volume when it "sets."
Such "doubly burned" cement is high in tricalcium silicate. It will stand
traffic 24 hours after being poured.
Cement two parts, sand three parts, and crushed stone six parts
mixed with water forms a satisfactory concrete. Its strength to with-
stand heavy loads and mechanical shocks is greatly improved by embed-
ding iron rods or wires in it. For this reason the cement for roads is
poured over a steel-rod mesh; floors, too, of a reinforced-concrete build-
ing, such as those in mftny modern schoolhouses, are a maze of steel bars
before the concrete is poured over them. The concrete must be kept
moist for several days, while gradually it increases in strength. (See Figs.
23-15, 16, and 17.)
QUESTIONS
21. Compare the setting of lime mortar with the setting of cement. Which
mortar would be used for laying up bricks that must later be covered with water?
22. What raw materials are needed for cementmaking?
23. Explain the necessity for embedding pipes of a refrigerating system in the
concrete at Boulder Dam when it was being built.
24. Distinguish Portland cement; concrete; sand; reinforced concrete.
26. List four important structures made, of reinforced concrete.
Glass. Chemists take a particular interest in glass. They use this
material extensively for their tools and vessels. It is light, strong, and
inactive chemically, and above all it is transparent. This fact, together
with its thousands of practical uses, accounts for its importance. Many
chemists are skilled glassworkers. They have practiced glassworking in
order to construct special equipment for their experiments.
Glass is so common that we probably cannot raise our eyes from this
page without seeing some.
No one knows who made the first glass; its story is lost in antiquity.
Without doubt glass was first noticed in the ashes of a very hot fire that
had been kindled on sand. Glass objects known to be over 5000 years
old have been found in Egyptian tombs.
Glassmaking in America started on the Atlantic seaboard where de-
posits of white sand and near-by stands of wood for fuel were located.
The center of glassmaking has since moved to certain regions of Ohio,
THE SILICATE INDUSTRIES 409
New York, lower New Jersey, and near-by states, because of the cheap
natural gas in this region. Carload after carload of window glass, bottles,
optical glass, colored glass, and even glass bricks roll away from these
glassworks daily — over 100 million dollars' worth a jear!
The Glass Furnace, The usual glass furnace is a large steel tank lined
with a special glass-resisting brick and heated by inexpensive fuel gas.
The raw materials are mixed and powdered: these consist of limestone,
sand, soda ash, salt cake (Na2S04), and a little carbon, although other
materials may be added for special types of glass. About an equal weight
of broken glass (cullet) is also added to aid melting. Most furnaces run
continuously until the lining wears out. Raw materials are placed in the
furnace at one end, and liquid glass is drawn out from the other. (See
Fig. 23-18.)
In glass of the ordinary type, silicates are formed in the furnace from
carbonates; the glass resulting is a fused mixture of silicates of sodium
and calcium with extra dissolved silica. This type is called lime-soda
glass. When it cools, it does not crystallize; it remains a liquid that
becomes more and more viscous, or thick, until it is essentially an amor-
phous solid.
The following equations show in part some of the chemical changes
that occur when a charge is melted in a glass furnace:
Na2CO3 + SiO2 -f Na2SiO3 + CO2t
CaCO3 -f SiO2 -» CaSiOs -f CO2 j
C + 2Na2SO4 4- 2SiO2 -» 2Na2SiO3 -f- 2SO2| -f CO2T
Window Class. Formerly window glass was blown either mechani-
cally or by the lungs into an elongated balloon. The ends of the balloon
were cut off, and the resulting cylinder was split lengthwise. Then, by
applying heat, the glass was flattened into a sheet. The outside circum-
ference of the cylinder was a little longer than the inside circumference,
and the flattened sheet formed was thus slightly irregular. These places
of irregular thickness cause distorted vision when a person looks through
this glass. We can notice such places in panes of window glass in all but
new buildings and those furnished with the more expensive plate glass.
An improved method of making window glass was made possible by
ingenious and persistent work. Today a wide ribbon of glass is drawn
from a furnace of molten glass just as paper may be pulled from a roll.
Attached to a bait rod that starts it, a flat band of glass passes over rolls
from the furnace through an annealing lehr, or oven, where it is cooled
gradually to avoid strains. Then it is cut into sheets automatically. The
demand for optically plane glass for automobile windshields and windows
has encouraged this development.
410
CHEMISTRY FOR OUR TIMES
Plate Glass. In one method of making plate glass, a huge ladleful
of the molten liquid is poured onto a flat-topped steel table, which has
a ridge along each side. A heavy iron roller flattens the plastic glass as
a rolling pin flattens piecrust. The thickness of the plate is determined
by the height of the ridges. When cool, the plate is removed and, set in
plaster of Paris, and about half of it (counting both sides) is ground away
by emery (AUOa). Then the plate is polished to a brilliant luster on both
Batch
(sand, soda, lime, tte.)
is Fed in Here
Batch is Continuously Melted into
Glass in this Furnace. Temperature
About 2650 F; Typical Capacity, 60
Tons per 24 Hours.
Feeder Delivers Gobs of Molten
Glass of Suitable Weight and Shape
to Forming Machine.
This Machioe Forms Gob
of Molten Glass into
Bottle or Jar
Stacker Loads Hot Ware on
Traveling Belt of Annealing Lent
Glassware is Cooled at a Controlled
Rate in this Annealing Lehr Otherwise
Stresses Set Up in Glass, Due to Rapid
Cooling, Would Result in Breakage.
Finished Ware to Packed
for Shipment Here.
Courtesy of Hartford Empire Company
FIG. 23-18. — This diagram shows the manufacture of hollow glassware by
automatic machinery. A picture of a machine that forms the ware is on the opposite
page.
sides by rouge (Fe203). The process is somewhat wasteful and expensive,
but a strong, clear, attractive glass is the result. This is the sort of glass
that is used for the show windows in most large stores. Plate glass is
now also made by a continuous-sheet process.
Glass Bottles and Jars. The making of glass containers is a mechani-
cal process and an exceedingly interesting one. Let us look at a bottle
containing some popular beverage and of a sort that is sold by the thou-
sands. The story of its making is told on the outside of the glass. An
automatic glass bottle-making machine has steel molds of the shape
desired. (See Fig. 23-19.) A gob of molten glass falls into the mold. It
is shaped and the inside blown hollow in two steps. We notice a thick
THE SILICATE INDUSTRIES
411
place in the wall about two-thirds
end of the first step in the mak-
ing. Then we note a slight ridge
around the bottleneck just below
the rim where the neck mold form
was brought up while the liquid
glass was pressed against it. A
similar ridge is found at the bot-
tom. Now we notice two vertical
ridges on each side. These show
where the molds opened while the
finished bottle was removed.
Then slowly the bottle passed
through an annealing lehr, or
oven, where it cooled gradually.
The resulting bottle, one of 0000
made that day from one machine,
is free of strains. Polarized light
is used to test for these strains.
Special Glass. Special types
of glass may be made in a clay pot.
These pots of liquid glass are
served by a team of workers, each
from the top. This place marks the
Courtesy Hartford Empire Company
FIG. 23-19. — A bottle- or jar-forming
iiuichine has four units, (lobs of liquid
glass slide down tubes to molds in the
center. A timing device for the automatic
operation is on the cylinders shown at the
bottom.
Courtesy of Corning Glass Works
FIG. 23-20.— Although much chemical apparatus is blown in molds, some pieces must
be blown "off hand/' This glass blower is shaping a retort.
412
CHEMISTRY FOR OUR TIMES
having special duties. A " gather" of glass is often removed on the end
of a blowpipe. Laboratory glass beakers and flasks, for example, are
blown in a mold, by lungs or compressed air, the glass rotating while it
is blown. We ma}' see spiral marks on this type of ware. (See Fig. 23-21 .)
Optical Glass. Every physics student has learned that a lens com-
posed of crown and flint glass will prevent chromatic aberration (color-
fringe error). Crown glass, like
the ordinary kind used for win-
dow panes, is a lime-soda glass.
Flint glass contains lead and po-
tassium silicates. Optical glass,
usually flint, is clear and brilliant;
it is used for making lenses, in-
cluding eyeglasses.
Courtesy of Corning Glaaa Works
FIG. 23-21. — In hand blowing a large
Pyrex brand cylinder, a tear-shaped gob of
glass is put into a mold for the final blowing
operation.
Colored Glass. Most sand
used in making glass contains iron.
Ferrous silicate, a green com-
pound, forms in the final glass.
This color may be noticed in cheap
glass bottles or in very old glass.
The green color is avoided, in
milk bottles for example, by in-
cluding some manganese dioxide
(Mn02) in the melt among the
raw materials. The iron is oxi-
dized, and light-yellow ferric sili-
cate is formed, rather than ferrous
compound. When glass containing manganese dioxide remains a long
time in bright sunshine, the purple permanganate ion (MnO^) forms, col-
oring the glass. The oxides that dissolve in and color glazes (see page 401)
produce the same effect in glass.
Collodial selenium added to the raw materials makes the red-colored
glass for taillights and signal lights, iron sulfide produces amber, and
chromic oxide makes glass green. Ruby and purple glass for stained glass
windows is made by using colloidal gold, the size of the gold particles
determining the color produced.
Low-expansion Glass. "Pyrex" brand glass is well-known for its
heat-resisting quality. It contains various percentages of aluminum oxide
(Al20s) and boric oxide (B20s) and a high percentage of silica (Si02).
Such borosilicate glass is used extensively for making kitchenware and
laboratory vessels. It has the ability to resist heat changes owing to its
small expansion coefficient.
THE SILICATE INDUSTRIES
413
Class and Thermometer Tubing. Glass tubing is made by forcing
a ring of liquid glass around a jet of compressed air, only very slight
variations being possible in the diameter of the bore (lengthwise hole).
(See Fig. 23-22.) Thermometer tubing is drawn from a shaped ball of
glass with a bubble inside; it has a very small bore.
Courli-su of Corning Glaus Work it
FIG. 23-22. — Not a piccolo player, but a skilled artisan in glass about to draw
out several yards of uniform thermometer tubing from the glass bubble on the end of
the blowpipe.
Safety Glass, Safety glass is a sandwich. Two sheets of glass are
sealed over a sheet made of a transparent plastic substance. The plastic
filling of the sandwich holds the pieces of glass together in case of break-
age. Many lives have been saved by this invention.
Tempered Glass. Tempered glass has a hard surface but a tough
flexible interior. Its ability to bend without breaking is remarkable.
Electric Light Bulbs. The bulbs for electric lights are blown from a
glass ribbon by automatic machines. A small disklike depression in the
ribbon is puffed out by the compressed air into the familiar pear-
shaped bulb. Thousands of bulbs can be made each day by a single
machine.
Glass Cloth. Glass fibers are produced by machine. They are very
fine and soft, resembling silk or wool. Since these fibers are obviously
fireproof and poor heat conductors when matted, they can be used for
insulating houses, refrigerators, and railroad cars. Some articles of fancy
414 CHEMISTRY FOR OUR TIMES
clothing are also made from glass fibers. It is not recommended, however,
that the cloth be worn next to the skin.
Fibers for glass cloth are made by spraying glass onto cooling trays.
These short fibers resemble staple rayon (see page 568), and they can be
spun and woven in much the same manner as any fibers.
"Vycor." For special laboratory uses there is now available a type
of glass that is 96 per cent silica. After the glass is shaped, the soluble com-
pounds of sodium, calcium, and other metals are dissolved by treatment
with acid. The glass is then dried and refired. In this process it shrinks
to the final dimensions. This new type of glass resists vigorous chemi-
cal actions well, expands very little, and has a very high softening
temperature.
Glass Blocks and Other Developments. Glass construction blocks
and glass linings for tanks and chemical apparatus are well known. Other
new developments in glass technology are coming onto the market
rapidly. They are the result of research, hard work, and patience. Each
new discovery opens up more possibilities for beginners, rather than
limiting the field. Many problems await complete solution. For example,
how can inexpensive window glass be made that will not give sharp
edges when it breaks and that at the same time will transmit practically
all the light that falls on it?
SUMMARY
Silica is a common name for the compound silicon dioxide (8102). Quartz is
silica in the shape of six-sided crystals, commonly colorless and transparent, but
also at times found in yellow, brown, purple, green, and other shades. White
sand is pure silica; brown sand, silica containing impurities. Flint is an impure
variety of quartz. Silicon is the second most abundant element in the earth's
crust, and its compound, silica, is a very common substance.
Silica is an inactive, water-insoluble compound. It has a high melting point
(about 1710°C), is transparent to ultraviolet light, and expands only slightly
with each degree increase in temperature.
At high temperatures silica joins aluminum oxide, sodium carbonate, and
calcium oxide, forming silicates. It reacts with hydrofluoric acid, forming silicon
tetrafluoride and water. It can be reduced to the element silicon by the reducing
agent carbon in an electric furnace.
Silica is used as an abrasive; it is used in mortar, concrete, and in glassmaking.
Quartz is used in making optical instruments, laboratory apparatus, and special-
ties such as radio crystals.
Soluble silicates include sodium and potassium silicate. Sodium silicate solu-
tion (water glass) is used as an adhesive, for fireproofing cloth, preserving
eggs, and for making silica gel.
Common clay is produced by weathering feldspar; feldspar is a compound of
potassium, aluminum, and silicon oxides.
White clay is kaolin, used for making chinaware. Bricks are baked clay.
THE SILICATE INDUSTRIES 415
Impervious coatings on bricks are obtained by melting the outside surfaces
(vitrifying) or by melting common salt onto the surface. Pottery is made from
mixed clay, molded and baked, forming biscuit ware. The glaze is then applied
and the ware fired again. Dissolved metallic oxides give colors. Tableware is a
special type of pottery made from clay, feldspar, and ground silica. The glaze
and pattern are applied as for pottery. Porcelain is pottery that is fired at a
higher temperature than ordinary dinnerware. Some porcelain is used for labora-
tory ware. Enamel ware is glass-coated ironware.
To form Portland cement, shale and limestone are heated in a rotary kiln,
forming a clinker; this is powdered and gypsum added to catalyze setting.
Cement sets with addition of water only. Concrete is made from cement, crushed
stone, and sand; sometimes it is reinforced with steel. .
Glass is made from sand, soda, and lime heated with culiet to aid in melting.
There are many special types of glass. Fabricating glass is accomplished by
making (1) sheets drawn or cast or (2) jars and bottles blown into molds. Colors
in glass are due to dissolved oxides or colloidal suspensions of metals. Borosilicate
glass has high silica and boric oxide content. Optical glass contains lead and
potassium silicates. Safety glass is (1) plate glass run onto wire reinforcement or
(2) glass sheets sandwiched with a plastic material between them.
QUESTIONS
26. List three transparent materials and one translucent material.
27. List four essential ingredients of a melt foir making glass.
28. Write equations for two reactions that occur in the glassmaking furnace.
29. Write formula equations for the reactions between (a) lead oxide and sand;
(6) barium carbonate and sand; (c) ferrous oxide and sand; (d) potassium sulfate
and sand.
30. Describe briefly three methods of making window glass. Which of the
three seems the most successful?
31. The most important glass articles imported into colonial America were
glass beads. For what purpose were they used?
32. Old glass in an automobile may break more readily than equivalent newer
glass. Account for the increase in brittleness of such glass with age.
33. What connection exists between colloid chemistry and glassmaking? *
34. Explain why glass manufactured from sodium carbonate and sand alone
would be unsuitable material for making window glass.
36. List five glass colors commonly seen, and tell how each is produced.
MORE CHALLENGING QUESTIONS
36. Read and make a report on (a) the novel Marietta, Maid of Venice,1 by
F. Marion Crawford; (6) plate glass, including pot furnaces; (c) cut glass; (d)
properties and uses of glass cloth; (e) early American glass.
1 The MacmUlan Company, New York, N. Y., 1919.
416 CHEMISTRY FOR OUR TIMES
37. Make a collection of colored glass. Perform tests to identify the coloring
agent in each sample.
38. Investigate types of cement other than Portland cement.
39. Obtain a sample of glass wool, and make a physical test of its heat-insulat-
ing property.
40. Secure several sorts of glass squares or prisms, and measure the index of
refraction of each.
UNIT FIVE CHAPTER XXIV
CHEMICAL CALCULATIONS
In the laboratory we try to answer many questions about substances.
Some of these questions ask, "What sort?7' The answers describe nature
to us. Here we find unsuspected beauty, orderliness, and reliability.
Equally interesting are the questions that ask, "How much?" The
answers to these questions show us another view of nature. Here we find
the strictest economy. Nothing is utterly destroyed. Matter is saved;
energy is saved; neither is lost.
The question "How much?" is asked in cooking, in making pictures,
in filling a doctor's prescription, and in adjusting the controls of a radio,
refrigerator, or stove. Satisfactory results depend upon the correct
answer.
In a similar manner the question "How much?" is asked in chemistry.
Here the answer is definite, and we can find' it by simple arithmetic. In
elementary chemistry laboratory, we may want to know how much of
reacting substances to put together and how much of each product to
expect. In industrial chemistry, the amounts of chemicals and of heat
used and produced are exceedingly important and may make one opera-
tion more profitable than another.
Let us start this chapter with a discussion of the full meaning of a
chemical equation.
The Complete Meaning of an Equation. Each formula for a sub-
stance that takes part in a chemical change represents a definite weight
of that substance. By CO2 we mean, not only one molecule of carbon
dioxide, but 44 parts by weight (C = 12, 2O = 32) of that substance.
The parts by weight are usually measured in grams for laboratory pur-
poses, but pounds, kilograms, or even tons may be used. Usually also,
CC>2 means 44 g of the gas (1 mole). Likewise, H2O signifies 18 g, or 1
mole, of water.
2H»O -4 2Hj -f Oj (balanced equation)
2 molea water — > 2 moles hydrogen + Imole oxygen (molar equation)
2 X 18 - 36 parts — » 4 parts by weight + 32 parts by weight (equation in terms of
by weight of water of hydrogen of oxygen weights represented)
36 g water -> 4 g hydrogen + 32 g oxygen (gram-molecular equation)
417
418
CHEMISTRY FOR OUR TIMES
In short,
2H2O
36 g
2H2 + O2
4 g + 32 g
Here we see illustrated the equality expressed by the chemical equa-
tion, for the weight of the substances entering into a chemical change is
equal to the weight of the products. In this case 36 g of water has been
decomposed into a total of 36 g of gases (4 + 32).
How to Find the Weight of a Substance in a Chemical Change.
We have just seen that 36 g of water produces 4 g of hydrogen and 32 g
of oxygen. It follows that 18 g of water would produce one-half as much
of each gas, namely, 2 g of hydrogen and 16 g of oxygen. One-tenth as
American r«,ro(- .... ; .. . mue
FIG. 24-1. — Industrial calculations involve carloads of materials. Mistakes are
costly. These tank cars are being loaded with petroleum products. Chemists sample the
fuel and determine its heat value when burned.
much, or 3.6 g of water, would form 0.4 g of hydrogen and 3.2 g of oxygen.
The weight relationships of the three substances are expressed by the
figures 36, 4, and 32. Any amount of water produces these gases in the
same proportion by weight. If 50 g of water should be decomposed into
elementary gases, the weight of gas formed in each case would be found
by a proportion.
60 g X Y (known and desired weights)
2H2O -» 2H2 + O2 (balanced equation)
36 g 4 g 32 g (formula weights)
_ CHEMICAL CALCULATIONS _ 419
If we assume that the formulas of the equation represent lines, we
can make a ratio (two equal fractions) from these figures as they stand.
Of course, we find the answer for the weight of each substance separately.
The weight of hydrogen formed is found thus:
36 # 4g
Solving for X,
X = 20%6 g = 5.56 g hydrogen. Ans.
Notice that units are cancelled out just like numbers and that the tin-
canceled unit goes with the answer. The weight of oxygen formed at
the same time is 50 g minus 5.56 g, or 44.44 g, or
= _
36/ 32 g
Solving for Y,
Y = lr>0%6 g = 44.44 g oxygen. Ans.
If we know the weight of any one substance in a chemical change,
either a substance entering into the change or a product of it, then it is
possible to find the weights of all other substances in the change, provided
that we know the balanced equation for the reaction. The general method
of finding the unknown weight of a substance in a chemical change when
the weight of one is given is as follows:
1. Write the complete balanced equation, taking great care that it is
correct. Every formula in the equation must be exactly right.
2. Write the given weight above the proper substance and an X above
the substance whose weight is to be found.
3. Underneath these substances put their formula weights, taken as
many times as the number before the formula for the substance indicates.
4. Make a proportion of these four quantities just as they stand in
space, calling the equation the line.
5. Solve for the unknown quantity X by clearing fractions and
dividing.
6. Express the answer in the correct units of measurement.
When aluminum is attacked by a solution of hydrogen chloride
(hydrochloric acid), aluminum chloride and hydrogen are formed. What
weight of aluminum is required to produce 534 g of aluminum chloride?
In solving this problem the six steps outlined are followed.
420 CHEMISTRY FOR OUR TIMES
(1)
2AI
+ 6HCI ->
2AICU + 3H2t
(2)
X
2AI
+ 6HCI -*
534«
2AICI8 -f 3H2
(3)
X
2AI
2 X 27 -
4- 6HCI -4
54 g
534 g
2AICU -h 3H»
2 X 133.5 - 267 g
(4)
X
534 v
54 g
267?
(5)
267AT =
534 X 54 g
(6)'
X =
108 g aluminum. Ans.
X may be placed on either side of the equation. Also, both the known
and the unknown substances may be represented on the same side of
the arrow.
As another example, a chemist has an order for 272 Ib of dry zinc
chloride. He is to make the compound by the action of zinc on hydro-
chloric acid, (a) How much zinc is needed, and (6) what weight of hydro-
gen chloride should be used?
(1) Zn +2HCI-* ZnCI2 + H2|
X 272 Ib
(2) Zn -|- 2HCI -> ZnCI2 -h H2
X 272 Ib
(3) Zn + 2HCI -> ZnC12 + H2
65 Ib 65 + (2 X 35.5) - 136
(4) _JL = 272JK
w 65 Ib 136 JB
(5) 136* = 272 X 65 Ib
(6) X = 130 Ib zinc. Ans. (a)
Y 272 Ib
(2) and (3) Zn -f 2HCI -» ZnCI2 -h H2
73 Ib 136 Ib
73 Ib " 136 X
(5) 136F = 272 X 73 Ib
(6) Y = 146 Ib hydrogen chloride. Ans. (b)
QUESTIONS
(Assume STP unless otherwise stated. In each problem use the correct units.
The answer should be expressed in the appropriate unit. Express weights in
grams and volumes in liters unless otherwise directed.)
{ 1600
1. A ton of coal is assumed to contain | - ™, pounds of carbon. What weight
(pounds) of carbon dioxide goes up the chimney when a ton of this coal is burned?
CHEMICAL CALCULATIONS
421
2. What weight (tons) of sulfur must be burned to produce \ K. ,°n of sulfur
lo tons
dioxide?
f 127 2
3. What weight of copper chloride is formed by burning jooi fi grams of
copper in chlorine?
(122 5
4. What weight of oxygen can be made from jo^y c grams of potassium
chlorate when the compound is heated?
f 269 2
6. How much of each of its elements is needed to produce | „„' ~ grams of
copper chloride by direct synthesis?
Courtesy of Corning Glass Work*
FIG. 24-2. — Good chemical technique requires skillful workmanship combined
with a knowledge of the properties of substances._These lamp workers produce appara-
tus with small tolerances for size error.
Weight -volume Relationships. Recall that C02 represents, not
only carbon dioxide, but a gram-molecular weight of that gas, or 1 mole.
The volume represented by 44 g of carbon dioxide is 22.4 liters at STP
(the gram-molecular volume). This is so because the gram-molecular
weight of any gas is the weight in grams of 22.4 liters of it at 0°C and
1 atm pressure (see page 148).
If we ask, "How much carbon dioxide gas by volume (liters) will be
422 CHEMISTRY FOR OUR TIMES
produced from 4.8 g of carbon?" the method of answering the question
is as follows:
4.8 g X
(1), (2), and (3) C + O2 -> CO*
12 g 22.4 liters
(5) and (6) X =
12 yg 22.4 liters
X 22.4 liters
^
carbon dioxide. Ans.
Instead of placing the gram-molecular weight of carbon dioxide under
the formula, the gram molecular volume, 22.4 liters, corresponding to
the molecular weight, is used. The portion of carbon dioxide produced
will have the same relationship to 22.4 liters as the gram weight of
carbon has to 12 grams, its gram-molecular weight. It is possible, there-
fore, to find the volume in liters at standard conditions of any gas in a
chemical change by using 22.4 liters in place of the molecular weight of
the gas.
If more than one gram molecular weight of the gas is used or pro-
duced, the 22.4 liters will be multiplied by that number. For example,
2H2 represents 44.8 liters of hydrogen, and 3C3H8 stands for 67.2, or
3 X 22.4, liters of propane gas.
What volume of oxygen at STP can be produced from 24.5 g of
potassium chlorate when the compound is heated?
X liters
24.5 * X liters
(1), (2), and (3) 2KCIO3 -> 2KCI -f 3O2 1
245 (gram formula weight) 3 X 22.4 - 6^
(grain-molecular
(4) 245jr = 67.2 litera
24.5 X 07.2 liters
(5) and (6) X =
245
= 6.72 liters oxygen. Ans.
QUESTIONS
{54
lft£ grams of mercury oxide.
(a) What weight of mercury did he produce? (6) What weight of oxygen gas was
formed? (c) What volume (liters at STP) did this gas occupy?
7. What volume of hydrogen gas can be liberated by the action of hydro-
chloric acid on i™ grams of aluminum?
CHEMICAL CALCULATIONS 423
(256
8. What volume of nitrogen gas is liberated when icio grams of ammo-
nium nitrite is heated? NH4N02 — > N2 + 2H2( k.
9. What weight of zinc must be burned to make 1 101 5 grams of zinc oxide?
(150
100 8rams
of hydrogen?
11. What volume of sulfur dioxide may be expected as a result of burning
/3200
14800 8rams °* su"ur*
12. In what volume ratio should the elementary gases be furnished when it is
desired to produce hydrogen chloride by direct union of the elements?
13. How many liters of hydrogen gas are needed to make j ^ liters of am-
monia gas by direct union of its elements?
14. What volume of each of the elementary gases can be made by the decom-
r /ISO r A 0
position of \ _4~ grams of water?
16. What weight of pure zinc will be needed by a chemist who is to prepare
f272
140K 8rams °^ zmc chloride by the reaction between zinc and hydrochloric acid?
16. What weight of plaster of Paris can be made from \ of gypsum?
I o tons
17. The weight when packed is marked on a package of washing soda crystals.
What percentage of loss in weight is permitted from such a package without cheat-
ing a customer?
1 2 5
18. A box of washing soda weighs \ ' pounds when packed. What is the least
I o.U
weight (pounds) it may have through loss of moisture only?
19. Write the equation for the burning of octane.
20. How many liters of chlorine can be produced by electrolysis of a solution
(585
1 170 8rams °f common sa^ in water?
Volume-volume Relationships. If in a problem two substances
are both gases, the same principle regarding liters applies except that in
this case the gram molecular volume, 22.4 liters, should be used with
both.
424 _ CHEMISTRY FOR OUR TIMES _
What volume of ammonia is needed to provide 60 liters of hydrogen?
X 60 liters
(1), (2), and (3) 2NH, -4 N2 + 3H,
(2 X 22.4) (3 X 22.4)
44.8 liters 67.2 liters
44.8 liters 67.2/
_ , ,., r 60 X 44.8 liters ..... . A
(5) and (6) A = - ^=-^ - = 40 liters ammonia. Ans.
07. &
It will be noted that the common factor 22.4 liters can be canceled
out; therefore, why not omit it altogether?
For example, what volume of nitrogen will be produced at the same
time the 60 liters of hydrogen are formed?
X 60 liters
(1), (2), and (3) 2NH3 -4 N2 + 3H2
(1 X 22.4) liters (3 X 22 4) liters
-
1 liter " 3/
60 X 1 liter
(5) and (6) X = - 5 - = 20 liters nitrogen. Ans.
o
Now it becomes clear why two volumes of hydrogen join one volume
of oxygen to form two volumes of water vapor (see page 85). In fact,
the gases concerned in a chemical change have the volume ratio of small
whole numbers. This principle is precisely that stated in Gay-Lussac's
law (see page 140) : The volumes of gases in a chemical change have the
volume ratio of small whole numbers, provided that all are measured
at the same temperature and pressure.
Obviously, the volumes can be read directly from the equation.
1CH4 + 2O2 -» 1CO2 4- 2H2O
1 volume methane 4~ 2 volumes oxygen yield 1 volume of carbon dioxide 4* 2 volumes of steam
All gases are assumed to be measured at the same temperature and
pressure. In this case the temperature has to be higher than 100°C.
A Practical Problem Using English Units. What is the amount of
salt (NaCl) needed to make salt cake (Na2S04)? Let us assume that
500 Ib of sodium hydrogen sulfate, 90 per cent pure, and salt (sodium
chloride), 98 per cent pure, are used.
The reacting part of the sodium hydrogen sulfate is 90 per cent of
500 Ib, or 0.90 X 500 Ib = 450 Ib. We can find the needed weight of
pure sodium chloride by the method already described (see page 419).
NaHSO4 + NaCl -> Na2SO4 + HCI t
120 Ib 58.5 Ib
Pound formula weights
X v 450 X 58.5 Ib 01ft,,, .. ,. ..
* -- 120 - " 219'4 lb Pure Bodmm Chlonde'
_ CHEMICAL CALCULATIONS 425
Since the salt used is only 98 per cent sodium chloride, we can find
the weight of salt needed (100 per cent) by dividing the answer above by
0.98 (98 parts per 100 parts).
lb = 223.9 Ib salt. Ans.
The answer may also be obtained in one operation.
0.90 X 500 >fe _ 0.98 AT
120 y& ~ 58.5 Ib
Solving for X,
X = 223.9 Ib salt. Ans.
SUMMARY
A formula indicates parts by weight of a compound. Equations also indicate
parts of weight of reaeting substances and products. Weight-weight problems, an
unknown weight of a reacting substance, are found by solving the proportion
_ X _ _ given weight (yjf _
Formula weight of unknown (g) formula weight of given substance ($
Any weight unit may be used.
Weight-volume problems are solved conveniently by using gram weights for
solids and 22.4 liters (STP) for each gram molecular weight of a gas. A typical
ratio is
X __ given volume of gas at STP
Formula weight of unknown (g) ~~ n X 22.4 liters
in which n = number of gram molecular volumes needed.
Problems of the volume-volume type are solved by using 22.4 liters for each
gram molecular weight of two or more gases. Also, in this sort of example the 22.4
liters cancels as a common factor, and the coefficients used in a balanced equation
express the volume relationships between gases. This is an example of applying
Gay-Lussac's law.
The equations above represent the weight relationships between pure ma-
terials. When percentages are involved, the mathematical equation should be
adjusted to take these into consideration.
QUESTIONS
21. How much oxygen (liters) is needed to burn -L. liters of methane?
22. When |fi0 liters of acetylene burns, what volume of oxygen is used? What
volume of carbon dioxide is formed?
23. What volume of oxygen is needed to burn |480 grams of magnesium?
446 CHEMISTRY FOR OUR TIMES
Assuming that the air is one-fifth oxygen, what volume of air is needed to supply
the oxygen? (Omit any chemical action involving nitrogen in this problem.)
{50
1 -^ liters of carbon monoxide?
What volume of carbon dioxide is produced? What volume of nitrogen remained
unchanged?
25. When 1800 liters of water gas. \ An , carbon monoxide, is burned,
& ' 142 per cent '
what volume of carbon dioxide is formed?
{r>^ O
' liters of carbon dioxide
are reduced?
27. When s -^ grams of calcium carbide, 96 per cent pure, is used with water
to make acetylene, what volume of the gas is formed?
f300
28. When \ ^^ gnims of limestone, 95 per cent pure calcium carbonate, is
louu
intensely heated, what weight of lime remains? What volume of gas is driven off?
UNIT
SIX
THE METALS
STEEL comes from a rusty rock that is mined in huge quantities.
The iron and steel industry is big business, dealing in tons and
shiploads and using equipment costing millions of dollars. As far as
usefulness goes, iron is far more valuable than gold.
Blast furnaces (1) are surrounded by stock piles of raw materials,
which they consume voraciously. Ore is located under the movable
bridge. The silolike structures are stoves for preheating air.
The blast furnace has an inclined track leading to the charging
"bell" on top of it. Melted pig iron from the blast furnace is carried
in a huge ladle and is poured into the open-hearth furnace (2). This
is the start of the process of steelmaking.
In the Bessemer process, air bubbling through melted pig iron in
the converter (3) refines pig iron into steel. The flame blasting from
the converter mouth is caused by being burned carbon in the pig
iron.
After steel has run from a furnace, the lighter slag (4) follows.
When the rod at the right of (4) is lifted, the liquid steel flows into
an ingot mold (5). A deoxidizier is added during the pouring process.
Crablike tongs (6) move the partly cooled ingot from the mold to a
gas-fired soaking pit of uniform temperature. The ingot is then ready
for the rolling mill, which squeezes the ingot to a bloom, billet, and
rod in succession. Picture (7) shows the making of wire from rod.
Courtesy of American Iron and Steel I institute
UNIT SIX CHAPTER XXV
IRON AND STEEL
Iron ore, coal that makes good coke, and limestone are three essentials
of an industrial nation. For economic reasons the sources of these three
materials must be located near each other if a country is to compete
in the world as a builder of heavy machinery, railroads, or automobiles.
We find that the heavy industries, in which iron and steel are made, are
located as a rule near the source of coal, for the brittle coke cannot be
hauled a great distance successfully.
Three regions in the world are outstanding in respect to these three
prime essentials. They are the Chicago-Ohio-Pittsburgh region in the
United States, the English Midlands, and the Ruhr Valley. Other regions
are of less importance from a standpoint of tonnage produced, but they
have possibilities of growth. They include the district around Birming-
ham, Alabama, and certain localities in the U.S.S.R., France, and possibly
China.
Among metals, iron is the giant. Copper, the second most important
metal, does not approach the world's tonnage of iron and steel. The
entire amount of pig iron, the first step in steelmaking, produced in the
world in any given year varies greatly. In 1937, world production of pig
iron was about 100 million metric tons of 2205 Ib each. The United States
produced about two-fifths of this amount. Germany, Great Britain, the
U.S.S.R., and France together produced almost all the rest.
The steel in an automobile is manufactured into motor, body, and
accessories. The price per pound of the completed car is about the same
as the purchaser pays for beefsteak, less than 50 cents a pound. In peace-
times enough automobiles are registered in the United States alone to
seat the entire population. Still the automobile industry, the largest
single user, consumed in normal years only about one-fifth of the steel
produced in this country. Automobile manufacturers have used as much
as 7 million tons of steel in a single year.
Other important industries that use immense amounts of steel are
New Terms
pyrite hematite blast furnace
magnetite casehardening reverberatory furnace
limonite nitriding converter
499
430 CHEMISTRY FOR OUR TIMES
railroads, building construction, farm and shop machinery making, con-
tainer manufacture (tin cans, drums for oil, chemicals, fats, etc.),
oil and gas industries. In 1942, during World War II, shipbuilding used
the greatest tonnage of steel, 16 per cent.
Iron Ores. Although less abundant in the earth's crust than alumi-
num, iron is a very common element. It is estimated that 4.7 per cent
of the earth's crust is iron. Iron is found in plants, animals, and the
human body, especially in the blood. The iron from the iron compounds
in a human body, collected together, would be enough to make a common
nail Millions of fragments of celestial dust, iron meteorites, fall on the
earth each year.
" Fool's gold," or pyrite (FeS2), is mined for its sulfur content, and
not for iron. One of the iron ores used in England is siderite (FeCOa).
About 5 per cent of all iron ores is the black magnetite (Fe3O4), a magnetic
material. Limonite (2Fe2O3*3H2O) is a yellow ore of some importance,
but by far the greatest amount of iron comes from hematite (Fe2O3),
which is similar in composition to ordinary red iron rust. Hematite is
found in a range of colors from red to red-brown. It is the coloring matter
in many natural rocks, in bricks, in red barn paint, and even in cosmetics.
The Indians used it for \var paint.
The most important ore deposit in the United States is the hematite
deposit a few miles from the western end of Lake Superior in the Mesabi
Range. After the overburden of loose earth is removed, the ore is dug out
of the open pit by huge power shovels. Here man has made one of the
mightiest scars on the face of the earth.
After a short haul by rail to the upper hike ports, Duluth and Superior, '
the ore is loaded by chute into ore boats. These lake steamers may
be completely loaded with 11,000 tons of ore in as short a time as 39
minutes. Once they start in the spring they run continually from mine
(upper lake) port to lower lake ports, Cleveland, Buffalo, Ashtabula, and
others. £nough ore must be accumulated during the .summer months to
supply the blast furnaces in the winter when ice locks the boats tightly
in the lake.
The Blast Furnace. The blast furnace serves to reduce iron ore to
metallic iron. It is built like a huge smokestack, about 90 ft high and
25 ft in diameter at the widest part, and is lined throughout with fire-
brick. This tubelike furnace flares out a little from the top, tapering
downward to provide proper flow of materials; it narrows in diameter
near the lower part to prevent slumping of the charge and to concentrate
the usable product. (See Fig. 25-1.)
The charges of limestone, coke, and ore are put in the top through
the "bell," a double trap-door arrangement that allows solids to enter
IRON AND STEEL
431
Courtesy of General Motors Corporation
FIG. 25-1. — Above is a diagram of a blast furnace in operation showing the bell, the
lining, and the ports for jets of hot air.
without much gas escaping. The solids descend slowly through the fur-
nace and meet the rising hot gases. Such an excess of hot carbon monoxide
is provided that the ore is reduced to metallic iron.
Fe2O3 -f 3CO -+ 2Fe + 3CO2
2Fe2O3 + SCO -f 4Fe + 7CO2 + C
If carbon alone is considered to be the reducing agent, the reduction is
described by this equation.
2Fe2O, + 3C -» 4Fe + 3CO2 T
The exact reactions in a blast furnace are more complicated than those
given in these equations, but they adequately represent the final result.
432
CHEMISTRY FOR OUR TIMES
The hot blast of air enters just below the widest part of the furnace.
Here coke burns with furious intensity.
C + O2 -» CO2
The excess hot coke in the upper reaches of the furnace changes
almost all the carbon dioxide into carbon monoxide
CO2 + C -* 2CO
Hence, the coke serves as both fuel and reducing agent. The iron, freed
from the ore, drops to the bottom of the furnace as a liquid, but not until
Courtesy of American Iron and Steel Institute
FIG. 25-2. — The man is watching glowing liquid pig iron flow from a blast furnace.
Above him may be seen the hot-air supply pipe that girdles the furnace.
it has absorbed carbon to saturation and other impurities to a lesser
extent.
The limestone, added as a flux or scavenger, combines with the un-
wanted but ever-present silica in the ore, forming a flux.
CaCO3 + SiO2
CO2|
This flux also drops to the bottom of the furnace and floats on the molten
iron. Both slag and liquid iron are drawn off at their respective levels
from time to time. (See Fig. 25-2.)
The hot gases leave the furnace through a big pipe, known as a "down-
comer," near the top of the furnace. After going through a dustcatcher,
they are used as fuel for engines that move materials into the furnace
IRON AND STEEL
433
and also for fuel in open-hearth furnaces. Most of these gases, however,
are burned in large stoves to preheat the air used in the blast furnace.
Usually four stoves, which are brick-lined towers through which the
air takes a tortuous path over white-hot firebrick, are needed with each
blast furnace.
Once started, the blast furnace operates continuously until the lining
needs repair.
FACTS ABOUT A BLAST FURNACE
Materials put i
n
Materials taken <
:>ut
Coke
c
Iron
Fe
Ore
Fe2O3(SiO2)
Slag
CaSiOa
Limestone
CaCOj
Gas
IN, 60%
CO 24%
Air
Nj, O2
C0216%
The U.S. Bureau of Mines Technical Paper 442 gives the following
facts about a day's operation of a 700-ton blast furnace:
Materials for each charge:
Mixed iron ores 24,500 Ib
Limestone 3,900
Coke 9,000
Total 37,400 Ib
139 charges in 24 hours = 5,200,000 Ib of solids
Air (at 17.6 Ib/sq in. and 1130°F) = 50,000 cu ft/min
or 4000 Ib/min for 24 hr = 5,800,000 Ib of air
QUESTIONS
1. List three essentials for making iron commercially.
2. The Kaiser interests built a blast furnace in southern California in 1942-
1943. Point out two reasons why such a project may be considered {ungoun(j
commercially under conditions other than wartime demands,
3. What part of the human body contains considerable amounts of iron?
From what source does the body obtain the needed iron?
4. The liver of a newborn calf contains a high percentage of iron. Milk is
very low in iron. After about 2 weeks the liver of the calf is low in its iron content.
From what source should the calf then begin to get its iron?
5. Considering the facts in the last question, is the higher market price for
calf liver over beef liver justified?
434 CHEMISTRY FOR OUR TIMES
6. Why is most soil brown?
7. In 1942, ore to the amount of 92,076,781 tons passed over the Great Lakes.
In World War I the tonnage was 65,000,000 for a similar time. Find the per-
centage of increase.
8. An ore ship holds 15,000 tons; a freight car, 70 tons. How many freight
cars are needed to carry the load from an ore ship?
9. A bucket lifts in 65 seconds an average of 15 tons of ore from ship hold to
freight car. How much time is required to unload a ship? Compare this answer
with the time required to load a ship.
10. Write equations for the reduction of both (1) hematite and (2) magnetite
by both (a) carbon; (6) carbon monoxide.
11. Why is the blast-furnace process a continuous one?
12. Air for the blast furnace is dried by refrigeration, (a) What becomes of
the moisture? (6) What harm would moisture do in a blast furnace?
13. Could a blast furnace operate with pure oxygen instead of air? If so,
what advantages or disadvantages would there be?
14. Calculate the amount (tons) of materials that must be stored to supply
a 700-ton blast furnace for four winter months.
16. Make a labeled diagram of a blast furnace, indicating (a) all substances
leaving the furnace; (6) all materials supplied to it.
16. What becomes of any aluminum oxide in the gangue of iron ore?
17. What component of the "downcomer" gas is useful for fuel? List three
other gases from a blast furnace that are not flammable.
Pig Iron. The liquid iron that runs from a blast furnace is about
92 per cent iron, 3.75 per cent carbon, 2.5 per cent silicon, and 0.05 per
cent phosphorus, with some sulfur, manganese, and a few other elements
in lesser amounts. It is conducted into a waiting preheated ladle, which
may hold 300 tons, mounted on a railroad car. The liquid may be (1)
sent to the steel mill for use in open-hearth furnaces or Bessemer con-
verters, (2) cast into bars, called pigs, of 40 to 100 Ib each, or (3) made
into wrought iron. The pigs of iron look like huge rusty loaves of coarse,
dark bread. (See Fig. 25-3.) As a common article of commerce they are
shipped to foundries in open freight cars.
Cast Iron. The crude product of the blast furnace is remelted with
a flux in foundries as one process in the manufacture of iron castings.
The liquid metal is poured into a prepared sand mold of a desired shape.
One of the crudest examples of this sort of work is seen in a sash weight,
the counterweight for a window. The supports for a pupil's schoolroom
desk and seat are usually made of cast iron. Radiators, furnaces, black
IRON AND STEEL
435
stoves, engine blocks, sewer pipes, some toy soldiers, and legs and bases
for machines in shops are made of cast iron. From these uses it can be
seen that cast iron is strong enough to withstand a steady load under
Courtesy of American Iron and Ktcd Institute
FIG. 25-3. — Pig iron, in addition to being used in the molten condition for making
steel, may he cast into "pigs.11 These are bought by foundries, which refine them into
east iron, or by steel plants that do not have their own blast furnaces.
compression. It does not resist tension or shocks well, however, and it is
quite apt to break if struck sharply. Cast iron rusts very slowly.
Cupola — »
cast iron
Reverberatory — >
wrought iron
16%
furnace
Bessemer /acid — >
steel 60,500,000 tons (in
1941)
Pig
converter!
iron
Klectric furnace 1.5% -
-> refined steel
(Open-hearth (acid
furnace (basic
— -> steel
I Crucible — » steel
Types of Iron Castings. When cast iron cools slowly, ordinary gray
iron castings form. Photomicrographs of this iron show the carbon
separated out in the form of large flakes of graphite. This explains the
weakness of cast iron to blows : it is honeycombed throughout with very
weak graphite flakes.
If iron castings are suddenly chilled after pouring, a white cast iron
436 CHEMISTRY FOR OUR TIMES
results. Such castings axe very hard, brittle, and strong. Often the excess
metal is removed by grinding to desired dimensions. The carbon in the
iron is in the form of the compound, iron carbide (FesC). It appears as
shiny, white streaks in photomicrographs. (See page 282.)
When white iron castings are heated to 1600°F, held at that high
temperature for several days, and then cooled slowly, malleable iron
castings are formed. These castings are not quite as strong as steel, but
they are easier to make to size and are cheaper. Like wrought iron they
can be bent, for the heat-treatment has decomposed the brittle iron
carbide. Malleable castings are used for pipe joints and parts of farm
machinery and locomotives. Photomicrographs reveal that most of the
carbon in malleable castings exists as fine particles, not as large flakes
as in ordinary gray iron castings.
Wrought Iron. When cast iron is heated and worked in a furnace
with iron ore and a suitable flux, practically all the impurities are re-
moved. The result is almost pure iron, except for inclusions of slag. The
furnace for making wrought iron has a low roof to reflect the heat down-
ward on the molten metal. The heat is supplied by burning fuel outside
the furnace and directing the hot products of combustion onto the melt.
Either by hand or by mechanical puddling, slag is stirred into the
iron; the resulting wrought iron has thus many fibers of slag running
through it. Wrought iron rusts very little because the glasslike slag pro-
tects the iron from corrosive influences.
Hardware on docks, anchors, chains, fancy fences, grilles, and orna-
mental ironwork that is used with the Spanish style of architecture are
made of wrought iron. Wrought iron, as the name suggests, was originally
wrought, or pounded, into shape, while hot, by the strength of the black-
smith's arm. Mild (low-carbon) steel is used for bridge lamps, plant
stands, and brackets today. Formerly they were made of wrought iron.
The steel is cheaper and practically equivalent to wrought iron for many
purposes.
The Age of Alloys. The importance of steel needs no demonstration
in modern times. We use it for ships, baking pans, power shovels, nails,
chicken wire, tractors, bridges, kitchen knives, and automobiles. But we
do not use the same kind of steel for all purposes. Everyone knows that
an automobile contains several kinds of steels — alloy steels, that is,
steels with other metals melted into them. These are improved steels,
adapting the metals better to the shocks and pulls they will receive in
service. So many alloys of steel and of other metals are on the market
today that the present era is sometimes called the age of alloys.
The increased cost 'per ton of steel for some alloying metals is shown
in the following table:
IRON AND STEEL 437
Vanadium . ...
For each 0.1%
$8.00
Tungsten
For each 10%
24.00
Chromium
For each 1.0%
2.30
Nickel
For each 1.0%
8.00
Obviously a great opportunity awaits workers who can produce these
needed alloying metals or the equivalent properties in steel at a lower
price, for thousands of tons of each are used every year.
Steel. Steel is essentially an alloy of iron and carbon, the amount
of carbon varying from 0.2 to 2.0 per cent. Other alloying elements
may be added to impart special properties.
There are two principal ways of making blast-furnace iron into
steel: they are the Bessemer and the open-hearth processes. The
open-hearth process is by far the more important of the two, for it makes
a satisfactory steel from pig iron that contains phosphorus.
Changing iron into steel is a process of purifying the iron; the impuri-
ties are burned out, forming oxides. The gaseous oxides can be readily
driven off, and the steelmaker endeavors to make the solid oxides form
into a slag that can be drained off. In the steelmaking process almost
all the impurities are removed. For practical purposes it is desirable to
have about 0.2 to 0.5 per cent of carbon in the finished steel, as well as
small amounts of silicon and manganese. Phosphorus and to a lesser
extent sulfur are considered undesirable impurities. The desired ele-
ments are added to liquid steel just before it is poured. Manganese, for
example, is added as an iron-manganese alloy. Not only does adding
manganese to the steel make a better quality steel than one lacking it,
but it makes the ingot more sound and improves the pouring and rolling
qualities.
Bessemer Steel. In 1847 William Kelly of Kentucky and in 1855
Henry Bessemer in England discovered independently an economical
method for changing pig iron into steel. The process today bears the
name of Bessemer, and the furnace is called the Bessemer converter.
(See Fig. 25-4.) Air is blown through liquid iron until the impurities that
act like a fuel are burned. Carbon burns readily and forms gases that
disappear in the blast of air. Sulfur is diminished by about 20 per cent,
but phosphorus not at all. Silicon and manganese are easily oxidized,
uniting to form a slag.
In modern practice a pear-shaped steel vessel is used in the Bessemer
process. This converter is mounted so that it may be emptied by tipping.
It is lined with silica firebrick (Si02 — acid Bessemer process) or with
dolomite (CaC03'MgC03— basic Bessemer process), depending on the
438
CHEMISTRY FOR OUR TIMES
impurities to be removed. The acid-lined converter is more widely used
in the United States.
About 12 tons, but not more than 20 tons, of liquid iron is poured
into the open converter. This vessel is then furnished with a blast of air
that enters through holes in the bottom. For about 20 minutes, long
yellow flames roar from the top of the converter. When the flames change
in character, becoming shorter and deeper brown in color, this indicates
that the burning is complete. The air is then turned off. The necessary
carbon and manganese are added, and the steel is poured out by tipping
the converter.
Although the Bessemer converter
still makes tremendous amounts of
steel, its relative importance decreased
before World War II in favor of the
slower, more versatile open-hearth
process.
Open-hearth Steel. An open-
hearth furnace is a firebrick-lined
chamber about as large as the first
floor of a small one-family dwelling
house. (See Fig. 25-5.) The roof is about
as high as the ceiling of the rooms.
The interior is lined with dolomite in
such a way that it forms a large basin
on the center of the floor. There are
several charging, or loading, doors along
one of the long walls. In the lower cen-
tral part of the opposite wall is the
pouring outlet, plugged with clay until
used. A large volume of preheated air and fuel gas, fuel oil, tar, or a
combination of two or more of these is blown in from one end of the
chamber, producing an intensely hot flame as they burn together over
the puddle of steel in the furnace. The hot products of combustion are led
through other chambers filled with checker-laid bricks before going up
the smokestack. These bricks become intensely hot. Every 15 minutes
the direction of the flow of gases is reversed, and the heated checker-laid
bricks warm the incoming gases.
The open-hearth furnace (see Fig. 25-5) is charged with pig iron
(sometimes solid, but more commonly liquid), rusty scrap steel, and a
suitable flux. After 11 to 12 hours the steel has formed. Most of the
phosphorus and some of the sulfur have been oxidized and passed into
the flux to form slag. The 100-ton charge is then tapped. A huge ladle
FIG. 25-4. — The Bessemer con-
verter is a device for changing iron
into steel by burning out a large
part of the carbon. The process is a
rapid and spectacular one.
IRON AND STEEL
439
OPEN-HEARTH FURNACE
Courtesy of General Motors Corporation
FIG. 25-5. — The open-hearth furnace has a huge puddle of liquid metal heated
from the top. The liquid metal is covered by a slag, which washes off undesirable
impurities. The direction of the air flow is reversed frequently.
receives the liquid steel. Other metals that alloy with iron are added if
necessary. The slag overflows into another ladle on one side.
The blast of the Bessemer converter and the tapping of an open-
hearth furnace are two of the most brilliant sights in modern industry.
Other
Comparison
Bessemer
Open-hearth
methods
Steel per charge
15-25 tons
100-200 tons
Charges per day (24 hr) .
30
2-
Steel per day (24 hr) ....
600 tons
300 tons
Lining
Usually silica, infre-
Usually dolomite,
quently dolomite
sometimes silica
Percentage of steel:
1900 ...
65.5
34.3
0.8
1935 ...
7.5
90.5
2.0
1941 . . .
8.0
83.0
9.0
Crucible Steel. Starting with a good grade of pig iron, high-quality
steel can be made by a careful hand process. The pig iron is melted in a
small crucible. If carbon is to be removed, selected iron ore is added. If
carbon is to be added, charcoal is put into the crucible. Alloying metals
may be added as needed. When the desired sort of steel is obtained, the
crucible is removed from the furnace. Crucible steel is used for some
440 CHEMISTRY FOR OUR TIMES
tools and watch springs. Only 6 tons in all of this steel was ordered in the
United States in 1940. It is more expensive than Bessemer steel.
The Electric Furnace. (See Fig. 14-9.) Scrap steel is remelted in an
electric-arc furnace. Three graphite electrodes carry an enormous surge
of electric current, the source of the heat, making a hot sparking arc,
flashing from one electrode to slag to metal to another electrode. From
1 to 25 tons of steel is made at each heat, depending on the size of the
furnace. In this controlled process the impurities in the steel are readily
converted into slag, for no hot oxidizing flame is present unless desired.
The liquid steel is removed from the furnace by tipping the entire vessel.
It is cast into strong, useful forms, such as frames for motors, pipe valves,
and castings for turbines. Electric-furnace steel may be rolled and forged
also. Nearly all steel used in airplanes is produced in this way.
QUESTIONS
18. What is the composition of pig iron?
19. How many 80-pound pigs make a 60-ton carload?
20. Distinguish white from gray cast iron in regard to carbon content.
21. What becomes of a sand mold after the iron has been poured into it?
22. What is a " pattern" (consult a dictionary)? Are patterns for cast iron
the same size as the finished casting?
23. Account for wrought iron's very slow rate of rusting.
24. Of what sort of iron should one make (a) horseshoes; (b) manhole tops
(for city streets); (c) fireplace andirons; (d) fireplace grates; (e) marine lanterns?
25. What is the increased cost per ton of steel containing 3 per cent chromium
and 2.2 per cent vanadium?
26. List three parts of an automobile for which special alloy steels are used
to enable them to withstand special types of forces.
27. Name two important methods of making pig iron into steel.
28. To what sort of pig iron is the Bessemer converter action well adapted?
29. Why is the lining of the Bessemer converter called acid and that of most
open-hearth furnaces called basic?
30. When the relatively cool air strikes the liquid iron in a Bessemer con-
verter, why does not the entire mass solidify?
31. Account for the sudden revival of interest in the Bessemer process in the
United States during World War II.
IRON AND STEEL
441
32. Explain this sentence: The open-hearth process is more versatile than the
Bessemer process.
33. About how many times more steel is made per charge in the open-hearth
furnace than in the Bessemer converter? About how many times faster is the
Bessemer process than the open-hearth?
34. What two compounds are formed in the slag when phosphorus-bearing
pig iron is refined in a basic open-hearth furnace?
35. Just at the time when a furnace is tapped or steel is poured, pieces of
aluminum are sometimes added. What useful purpose does the aluminum serve?
36. In the electric furnace, selected iron ore is sometimes added. What effect
has the addition of ore on the percentage of carbon in the resulting steel?
37. If scrap steel averaging 0.5 per cent carbon is used for charging an elec-
tric furnace, the final product may have higher percentage carbon. From what
source does the carbon come?
Processing Steel — Ingots. After steel is made by the open-hearth
or the Bessemer process, it is cast into ingots — huge, white-hot masses
'Hard
FIG. 25-6. — A wire becomes smaller in diameter and longer when it is drawn through a
die. Only ductile metals will undergo this treatment without breaking.
of solid metal. The liquid metal freezes or solidifies within the ingot mold
from the outside in. Obviously the ingot is not uniform and therefore
is unsuited to rolling. To take care of this difficulty, it is placed within
a large gas-fired furnace, called a soaking pit, until the temperature is
equalized throughout the metal. The ingot is then passed between rollers
in a machine, called a blooming mill, that squeezes and lengthens it.
This process is continued through several mills until the steel is rolled
into sheets, rods, rails, or beams. Wire is made by drawing a rod or
larger wire through a die of hard steel, a carbide, or even a diamond as
shown in Fig. 25-6.
Other methods of forming steel include melting and casting into
sand molds, drop-forging heated metal, cold-rolling, and cold-forming.
The Steel Catalogue. In modern shop practice, steel is designated
by a number system established by the Society of Automotive Engineers
(SAE). The digit that designates the type of steel and other information
about the steel are given in the following table:
442
CHEMISTRY FOR OUR TIMES
Principal element
Carbon :
High 0.75-1.4%
Medium 0.25-0.75 %. . . .
Low 0.05-0.25%.. .
Nickel
Nickel-chromium .
Molybdenum
Chromium
Chrome- vanadium
Tungsten
Silicon-manganese
SAE digit
2
3
4
5
6
7
9
Properties and uses
Tools, springs — generally heat-treated
Automobile axles, rails, car wheels —
sometimes heat-treated
Bridge girders, automobiles, ships,
buildings, nails
Rolled structural steel, boiler plates,
large castings
Stainless steel, cutlery — hard, tough,
shock resisting, corrosion resisting
Automobile parts, leaf springs, drive
shafts, bolts, gears
Axles, steering knuckles, gears, files,
axes, hammers, ball bearings
Casehardened parts — gears, springs,
tools
Tools for machining steels — retains
hardness when hot
Leaf and coil springs
Two examples of steel numbers will illustrate the system. One steel
number is 2 3 40. This is a nickel steel (observe the digit 2) with 3 per
cent nickel and 0.40 per cent carbon. Steel number 7 13 60 meets the
Courtesy of General Motors Corporation
FIG. 25-7. — Some of the properties of metals.
following specifications: tungsten steel (7) with 13 per cent tungsten and
0.60 per cent carbon. It can be seen that the last two or three figures tell
the carbon content in hundredths of 1 per cent. The second one or two
numbers give the percentage of the most important element in the steel.
IRON AND STEEL
443
The first digit of the number designates the type of steel as listed in the
table.
Alloy Steels. Many different elements are introduced into melted
steel to improve it for special uses. About 8 per cent of the steel in use
today is alloyed with some element in addition to carbon. Manganese
steel is considered an alloy only if above 1.65 per cent manganese.
An example of an alloy steel is high-speed tool steel of the following
composition:
COMPOSITION OF HIGH-SPEED STEEL
Carbon . . ...
C
0.5- 0 8%
Tungsten
W
12.0-20.0%
Chromium . .
(V
2.5- 5.0%
Vanadium
v
05-25%
Only about 1.5 per cent of all the alloy steel is of this sort.
High-speed steel is very hard after heat-treating. Moreover, it will
cut other steel and has the admirable quality of keeping its temper while
red-hot. These quick-cutting tools in
modern machines are an important
factor in today's mass production of
automobiles, airplanes, and household
appliances.
One type of stainless steel, com-
monly used as blades for knives and
metal for streamlined trains, contains
14 per cent chromium. This steel is
also used for making kitchen pots
and pans, food machinery, laundry
machinery, and other objects that
require strength, hardness, and rust
Brake Shoe
Freight Car
Wheel
FIG. 25-8. — Tough manganese steel
is used in the brake shoes that press
against the steel rim of each rotating
wheel to stop a train.
resistance. The most common stainless steel contains 18 per cent chro-
mium and 8 per cent nickel. It is nonmagnetic.
Armor plate is the 12 to 14 in.-thick metal wall, like a blister, about
the hull of a battleship. It contains 3.3 per cent nickel and 1 per cent
chromium, casehardened.
The brake shoes that rub on a train wheel to stop it (see Fig. 25-8)
must be made of tough steel. Manganese (14 per cent) gives the required
characteristics to this steel. Other uses for tough steel are the entering
prongs of a power shovel (manganese-nickel steel), the steel jaws of
rock crushers, and safes.
Almost every metal part of a modern automobile is made of a special
steel. The axles contain chromium, the springs chromium and vanadium,
444 CHEMISTRY FOR OUR TIMES
the engine block nickel, and the drive shaft molybdenum. Strong, light
wrenches used by mechanics are made of vanadium steel.
The one obstacle in the path of the wider use of alloy steels is their
cost. Nickel costs about $700 a ton; tungsten, $3,500. Of course, only a
relatively small amount of the alloying elements is present in a ton of
alloy steel, but alloy steels cost more than plain carbon steel (see page
437).
Heat-treating. Take a girl's hair clip, or " bobby pin," and straighten it.
Notice the springiness, or elasticity, of the wire. Now hold one end in a pair of
forceps, and heat the metal to redness. Let the wire cool slowly until room tem-
perature is reached again. Now, when the wire is bent, notice that the metal is
inelastic, lifeless. We say that it has lost its temper.
Again, let us heat a hair clip to redness and while it is still hot plunge it into a
jar of cold water. Now let us try to bend the steel. It snaps readily. In fact, a piece
H in. long can be broken in the fingers. It is as brittle as a clay pipestem.
If we wish to make steel suitable for a woodcutting chisel, we harden
the steel, containing 1.3 to 1.5 per cent carbon, preferably in the upper
part of the range 700 to 770°C, just as in the experiment with the hair
clip. Then we reheat it to a mild temperature and let it cool slowly. Some
hardness is subtracted and greater toughness imparted, and the steel is
said to be tempered. Heating to a higher temperature in the tempering
process subtracts more of the hardness, leaving the steel less brittle and
tougher.
To make a wood saw in which the steel is both tougher and more
flexible than that in the chisel, we select a steel of a lower percentage
carbon. It is hardened and then tempered at a higher temperature than
the chisel.
Heat-treating may increase the strength of steel as much as three-
fold, besides having a marked effect on the hardness of the steel. The
International Nickel Company reports that steel SAE 3140 (1 per cent
Ni, 0.40 per cent C) has tensile strength of almost 250,000 Ib per sq in.
when tempered at 400°F but only 105,000 Ib per sq in. when tempered
at 1300°F. An ordinary structural girder has tensile strength of 75,000
Ib per sq in.
Surface-treating Steel. When steel is packed in a carbonaceous
material (see page 510) and heated, carbon penetrates the steel a short
distance. The higher carbon alloy formed on the exterior of the piece gives
the steel a hard-wearing surface. A similar effect may be produced by
heating the steel in melted cyanide (KCN, for example). Steel so treated
is ideal for gears (see Fig. 25-9) and files that need a hard-wearing
surface and a tough interior. Steel treated in this way is said to be
casehardened.
IRON AND STEEL
445
atmos-
decom-
Special alloy steels may be hardened by heating them in an
phere of ammonia. This process is called nitriding. The ammonia
poses to form nitrogen and hydrogen.
2NH3 -4 2[N] + 3H2
The nitrogen unites with elements other than
iron, chiefly aluminum or vanadium in the
steel, forming nitrides. These compounds
give the steel a corrosion-resistant surface,
as well QS a hard one.
SUMMARY
Iron is the most important metal. The eco-
nomical commercial production of iron depends
on the nearness of coal, limestone, and ore to
each other and to markets.
Iron is widely distributed; it is found in most
soils, plants, and animal bodies. The principal
ores are Fe2O3, hematite; 2Fe208-3H20, iimonite;
FeCOa, siderite; Fe3O4, magnetite.
Commercial iron is produced in a blast fur-
nace. It contains about 5 to 8 per cent impuri-
ties, including carbon, manganese, sulfur,
phosphorus, and silicon. The blast furnace input
is coke, ore, limestone, and preheated air; the blast
furnace output is pig iron, slag, and gases. Iron oxides are reduced by hot carbon
monoxide or hot carbon in a blast furnace, and slag is formed by the reaction
between limestone and silica or silicates in ore.
Remelted pig iron is called cast iron; it may be gray, white, or malleable.
Iron is easily cast, has great strength to withstand steady force, but is brittle
to shocks. It is used for machine bases and some water pipes and for stove grates.
Wrought iron is pig iron heated on a bed of ore while the slag is puddled into
the mixture. Wrought iron is tough and malleable and rusts very slowly. It is
used for marine and ornamental hardware, some water pipes, and chains.
Steel is commercial iron purified by oxidizing the impurities. Steel is strong
and elastic; many alloys of steel are formed. It has a wide range of properties
available by alloying with various metals. Steel is used for automobiles, ships,
military purposes, railroads, and building construction.
In the Bessemer process heated air is blown through liquid iron in a pear-
shaped converter that has a perforated false bottom. Impurities are oxidized.
This is a rapid process of making steel, one that is good for iron low in sulfur
and phosphorus.
In the open-hearth process, fuel gases are burned over a puddle of steel and
slag. The impurities, including phosphorus, are burned out or go into slag. This
is a relatively slow process, but one carefully controlled and easily adapted to
special needs. An electric furnace refines steel. It has controlled conditions, it
removes sulfur, and it is adapted to making alloy steels.
Courtesy of General Motors Corpora-
tion
FIG. 25-9. — This cut sec-
tion of a case-hardened gear
tooth shows the extent of
penetration of carbon in the
hard-wearing exterior or case.
Case-hardened gears are used
in automobiles.
446 CHEMISTRY FOR OUR TIMES
The fabrication of steel is a big business. The steps are as follows: ingots cast;
equalized in temperature; rolled into sheets, rods, or rails; or cast into molds; or
forged by powerful hammers.
Steel is designated by an SAE number classification system in which the last
two (or three) digits represent the percentage of carbon.
Alloy steels develop special properties, such as toughness, hardness, resistance
to corrosion, and resistance to fatigue. Examples are stainless steel, 18 per cent
Cr, 8 per cent Ni; manganese steel, 14 per cent Mn for very tough steel; light
strong tools of steel may contain vanadium.
The properties of steel are controlled to a large measure by heat-treatment,
which regulates the relationship of the carbon to the iron, influences grain size
and structure, and controls other factors. Hardening is accomplished by sudden
cooling of hot steel. Tempering is done by reheating, but not to as high a tem-
perature as when hardened, and cooling slowly.
Surface treatment of steel may give a hard, wear-resisting surface. Case-
hardening, in effect, adds carbon to the outside portion of a steel object. Nitriding
converts the surface in part to metallic nitrides.
QUESTIONS
38. When white-hot steel is rolled between steel rollers in a mill, what
prevents the mill rolls from melting and sticking to the steel being processed?
39. Describe the steps needed to change open-hearth steel into plates for
battleship armor.
40. Describe the steps needed to change Bessemer steel into railroad rails.
41. A certain steel used for propeller shafts contains 3 per cent nickel and
0.4 per cent carbon. What is its SAE number?
42. Tell the composition of Bessemer screwstock, 1112; fatigue-resisting steel,
3335; rear-axle stock, 4140; stainless steel, 30905.
43. A modern battleship displaces 35,000 tons. Let us assume that 5 per cent
of its weight is armor plate. What weight of nickel is needed for this purpose
alone in constructing a battleship?
44. A hoe was used to tend a bonfir6. It became red-hot in the fire, and after-
ward it did not cut weeds as well. Explain.
45. Can nails that are collected from waste wood ashes be straightened and
used again successfully?
MORE CHALLENGING QUESTIONS
46. In manufacturing steel files, what treatment is given them so that they
will cut well?
47. An electric furnace operates about one-half the time during a 2-hour heat.
If 4000 amperes at 110 volts is drawn from the transformer, how many calories
(Cal) of heat are supplied by the current? (See top of next page.)
IRON AND STEEL 447
TJ /n ix °-239 /2 (amperes) R (ohms) / (sec) _ E (volts)
H (Cai) = -
48. A furnace contains 10 tons of steel containing 5 per cent manganese. What
weight of steel, 50 per cent manganese, should be added so that the final mixture
will contain 14 per cent manganese?
49. What alloy is used for (a) hacksaw blades; (6) high-speed cutting tools;
(c) leaf springs for trucks; (d) sewing needles?
50. Make a miniature of either a Bessemer converter or an open-hearth
furnace.
61. Report on the advertising of steel manufacturing companies in popular
magazines. Since these companies sell nothing directly to retail trade, often these
advertisements are sources of general information. Point out the messages from
several of the advertisements.
52. Investigate and report on "sponge iron."
UNIT SIX CHAPTER XXVI
THE LIGHT METALS
When Napoleon III (1808-1873), nephew of Napoleon Bonaparte,
dined in state, his guests had to be content to use gold forks. Napoleon
himself used an aluminum fork; only the great were privileged to use
such an expensive and light metal as aluminum.
The price of aluminum was $545 per pound in 1852. In 1862 one of
its first uses is recorded: the baby's rattle for the Princess Imperial of
France was made of aluminum. By that time the price of aluminum had
dropped to $16 per pound. A few years later the quantity of the metal
produced increased very markedly, and the price dropped continuously.
Today aluminum costs only about 15 cents per pound.
Public attention was drawn to aluminum in 1876 when the Washing-
ton Monument was capped with this metal. Recent inspection of the
cap showed the metal to be in good condition after more than 60 years
of exposure to the weather.
Napoleon's interest in aluminum was not mainly for eating utensils.
After dragging heavy iron military equipment over a great part of
Europe, the possibility of using a light but strong metal instead of iron
for military purposes was a welcome idea. Steel is 2.8 times denser than
aluminum.
In the development of the dirigible type of aircraft, Count Zeppelin
needed a strong light alloy. To meet this and other demands, an alloy
called duralumin, or dural, was developed in Germany. It contained
4.0 per cent copper, 0.5 per cent magnesium, 0.5 per cent manganese,
and the remaining 95 per cent commercial aluminum. The superior
strength of the alloy is attained by a novel method of heat-treatment.
The finished metal has approximately the strength of boiler steel, tensile
(pull-apart) strength 62,000 Ib per sq in., and about one-third its weight.
The making of duralumin increased the demand for magnesium. Then,
in an effort to make lighter, and yet strong, metals, experiments were
New Terms
duralumin bauxite cryolite
Hall process alumina magnesia
Thermit
449
450 CHEMISTRY FOR OUR TIMES
performed to find out the properties of magnesium and its alloys. The
aluminum alloys are about 1.6 times denser than magnesium alloys.
Alloys of both aluminum and magnesium are used extensively in the
manufacture of airplanes. The demand for them is extending to other
fields, also, where both lightness and moderate strength are required.
Thus a scientific and a military motive prompted the investigation
of the lighter metals. Both aluminum and magnesium are abundant; in
fact, aluminum is the most abundant of all the metals. No shortage of
raw materials for the production of magnesium is foreseen, for today they
are being extracted from sea water. It is interesting to note that a period
of over 50 years elapsed between the first isolation and the commercial
production of both aluminum and magnesium.
Aluminum
Aluminum's Infancy. The isolation of metallic aluminum was first
announced in 1825 by Hans Christian Oersted (1777-1851), a Danish
physicist and chemist. He replaced aluminum from its fused chloride by
the active metal potassium in the form of an amalgam.
AICI3 + 3K -> 3KCI + Al
The arrival of the new metal created no more interest than the arrival
of a new baby in a distant city. It was interesting only to those interested
in it.
Thirty years later (for new metals mature slowly) the supply of the
metal was large enough for it to venture into the Paris Exposition. There,
in 1855, was displayed a bar of the silvery metal made by chemical reduc-
tion, but by using sodium instead of potassium to act on the aluminum
chloride.
At Oberlin, Ohio. When Prof. Frank F. Jewett of Oberlin College
remarked in one of his lectures that the discoverer of a cheap method of
extracting aluminum from its ore would be a great benefactor to .man-
kind as well as the gainer of a fortune for himself, the thought captured
the imagination of his pupil, Charles Martin Hall (1863-1914). After
graduation, Hall went to work in the family woodshed with a homemade
apparatus, experimenting to meet the challenge. When he was only
twenty-two years old, after many discouragements he found a method
for extracting aluminum by using electricity.
HalFs successful method was the electrolysis of aluminum oxide dis-
solved in a bath of molten cryolite. He also discovered that the cathode
of the apparatus should be a carbon-lined container.
At almost the same time, in 1886, a young man in France, Paul Louis
Toussaint H6roult (1863-1914), discovered a method of making alu-
THE LIGHT METALS
451
minum. (See Fig. 26-1.) He applied
for a United States patent on his
process. Imagine his surprise to
learn that Hall had worked out
the identical process independ-
ently in the United States just
before him. These coincidence
twins, Hall and H6roult, born
the same year, might have become
bitter rivals. Instead, they coop-
erated. Incidentally, they died in
the same year.
Today a life-sized statue of
Charles Martin Hall, appropri-
ately enough cast in aluminum,
is located in the chemistry labo-
ratory of Oberlin College. (See
Fig. 26-2.) The young inventor
never forgot the college from
which his inspiration came. After
Prof. Jewett's prediction had been
fulfilled and fame and fortune
had come to him, he gave gen-
erously to the college.
Also Ran. A third competitor
in the race to make cheap alumi-
num deserves notice. He was an
American named Hamilton Y.
Castner. He reasoned that cheaper
sodium would make cheaper alu-
minum. He was correct. More-
over, in 1886 he developed a
process for making sodium cheaply
by electrolysis. Making aluminum
by the use of sodium is, however,
costlier than by the Hall-H6roult
process, and therefore the method
of Castner was abandoned.
Castner's experience was put to
good account, nevertheless, and
soon he was producing cheap
metallic sodium by the electro-
lysis of melted sodium hydroxide.
Courtesy of Aluminum Company of America
FIG. 26-1.— Paul Louis Toussaint H6-
roult (1863-1914) discovered the same com-
mercial method for extracting aluminum
as did Charles Hall. Compare Hall's and
HSroult's dates of birth and death.
Courtesy of Aluminum Company of America
FIG. 26-2.— Charles Martin Hall (1863-
1914) was the discoverer of a commercial
method for the extraction of aluminum.
His life-size statue in cast aluminum now
stands in the Severance Chemical Labora-
tory, Oberlin College, Oberlin, Ohio.
452
CHEMISTRY FOR OUR TIMES
Where Aluminum is Found. Aluminum is never found free in
nature. Consequently it was un-
known to peoples in ancient
civilizations. It is a metal associ-
ated with twentieth century life.
Its compounds, chiefly oxides and
silicates, are abundant. Common
clay (Al2O3-2SiO2-2H20), bauxite
(Al,Of3H,0), alunite (K,0-
3A12O3'4S03-6H20), and corun-
dum (AluOs) are well-known
aluminum compounds. Cryolite
(Na8AlF6), the "ice stone, " found
in Greenland, is important in the
making of aluminum.
Bauxite, the chief ore of alu-
minum, is produced in the United
States in Alabama, Arkansas, and
several other states. France,
Hungary, British and Dutch Guiana, and many other regions have good
supplies of bauxite. The mineral is mined both by the underground
tunneling and by the open-pit method.
Preparing Aluminum Ore. Crude bauxite is crushed, dried, and
treated with sodium hydroxide solution in a chemical purification process.
Courtesy of Aluminum Company of America
FIG. 26-3. — The original globules of
aluminum obtained by experimenter Hall
in his first successful electrolysis.
.Bus Bar
Electric
Insulation
Carbon—
Lining
Carbon
Anode
\ _
Frozen Crust
j Electrolyte
/and Alumin<
/\
/\
"-Collector
Plate
•Vi*£:v;Vf^
Courtesy of Aluminum Company of America
FIG. 26-4. — The electrolysis of alumina dissolved in fused cryolite takes place
in a carbon-lined steel cell. Carbon anodes hang into the cell. The metal is withdrawn
from the bottom at intervals.
THE LIGHT METALS
453
It is necessary to change the mineral into almost pure alumina (A^Os)
before using it in the production of aluminum. The chief reactions in the
process are as follows: (1) Dissolving crude bauxite in caustic soda.
AI(OH)3 -f NaOH -> NaAIO2 + 2H2O
(2) Precipitating aluminum hydroxide from the sodium aluminate solu-
tion by slow cooling.
+ 2H2O-4AI(OH)3| + NaOH
(3) Dehydrating the precipitate
by intense heat.
2AI(OH)3 -4 AI2O3 -f 3H2O
Making Aluminum. The
furnace for making aluminum
(see Fig. 26-4) is a rectangular
steel box or pot, lined with car-
bon, that serves as the cathode.
Molten cryolite (Na3AlF6) with a
little fluorspar (CaF2) is the elec-
trolyte; aluminum oxide (A1203)
is added from time to time as
needed. Anode rods of graphite
are suspended in the electrolyte.
When current is passed through
the electrolyte, liquid aluminum
(m.p. 660°C) collects at the bot-
tom of the furnace. The furnace is tapped daily for this metal. Oxygen is
deposited on the anodes, causing them to burn.
Courtesy of Aluminum Company of America
FIG. 26-5. — Molten aluminum from the
Hall cell is poured into ingot molds to
harden for shipment.
4 Ib bauxite (A12O3-3H2O) makes
2 Ib alumina (A12O3), which produces
1 Ib aluminum (Al)
Three-fourths of a pound of carbon electrode is also used up in the
process, and 12 kilowatt-hours (kw-hr) of electricity. Total production
of aluminum in the world in 1939 was about 650,000 metric tons of 2205 Ib
each. In 1943 the production of the metal in the United States alone was
over 2 billion pounds as a result of military demands.
The industry is one of the largest consumers of electricity. Aluminum-
extraction plants are usually located near a source of electricity from
water power.
Physical Properties of Aluminum. Aluminum is a silvery metal
that is light, ductile, and malleable. It can be hardened and strengthened
454
CHEMISTRY FOR OUR TIMES
Courtesy of Aluminum Company of America
FIG. '26-6. — Forging an aluminum-alloy
propeller blade is a convenient way of
rough-shaping the metal.
Courtesy of Aluminum Company of America
FIG. 26-7. — This workman is applying
metallic aluminum-foil insulation in a
home. Aluminum is a good reflector of
radiant heat; hence it acts as an insulator.
Aluminum is also a good conductor of heat.
by alloying with other metals. It
can be fabricated by rolling, draw-
ing, extruding, casting, forging
(see Fig. 26-G), and machine cut-
ting— in fact, by all known meth-
ods of metal working. It can be
welded electrically and by the
torch. It is an excellent conduc-
tor of both heat and electricity.
Aluminum exceeds copper, weight
for weight, as a conductor of elec-
tricity, but copper is a better
conductor size for size.
The density of aluminum is
168 Ib per cu ft. A cubic foot of
water weighs 62.4 Ib. We say that
the specific gravity of aluminum
1 (\Q
is g2^> or 2.7, its weight relative
to the weight of an equal volume
of water.
Pure aluminum melts at 660°C.
Its shiny surface is a good reflec-
tor of radiant heat. Hence alu-
minum foil is used in insulating
homes and mechanical refrigera-
tors. (See Fig. 26-7.) Aluminum is
nontoxic; and this fact, together
with its strength, lightness, and
durability, makes it an excellent
material for the construction of
cooking utensils.
Chemical Activity of Alu-
minum. Aluminum, when freed
of its oxide film, acts readily on
hot water, liberating hydrogen.
2AI +6H2O -+ 3H2T +2AI(OH),
To observe this action, scratch
aluminum with sandpaper while it is
under mercury. Keep the surface
of the aluminum away from air un-
til the hot air is added above the
mercury.
THE LIGHT METALS
455
Everyone knows, of course, that an aluminum kettle does not act
chemically on water boiling in it; that is, hot water does not seem to
attack aluminum. The explanation of the difference between this case
and the one above is that aluminum is protected from the corrosive action
of the water by a hard, tightly adhering skin, a film of aluminum oxide
(Al,08).
Automatic Crucible
Slag Basin
Riser
Thermit Collar
Section to be
Welded
Channel between Riser
and Pouring Gate
Pouring Gate
-Iron Plug or
Sand Core
Heating Gate
-Thermit Molding Material
Courtesy of Metal and Thermit Corporation
FIG. 26-8. — The arrangement of mold and crucible when a Thermit weld is being made.
Aluminum powder burns with a bright flash when it is tossed into
a flame.
4AI + 3O2 -» 2AI2O3
A dilute acid dissolves the oxide film on aluminum and readily attacks
the metal beneath. The action of hydrochloric acid on aluminum, liber-
ating hydrogen, may be considered typical.
2AI + 6HCI -> 2AICI3 + 3H2|
Sodium or potassium hydroxide solution, each a strong alkali, acts
vigorously with aluminum to produce hydrogen. The action is repre-
sented by the following equation:
2AI + 2NaOH + 2H2O -» 2NaAIO2 + 3H2T
The Goldschmidt Process. The strong affinity of aluminum for
oxygen is spectacularly illustrated by the vigorous reducing action of the
456
CHEMISTRY FOR OUR TIMES
metal. A mixture of powdered aluminum and iron oxide (Fe20s or Fe8O4)
is sold under the name of Thermit. When brought to a high enough tem-
perature, the mixture reacts violently, liberating so much heat in such a
short period of time that the iron formed is in a liquid state. (See Fig.
26-8.)
2AI + Fe2O3 -> AI2O3 + 2Fe (at 1650°C)
The liquid iron formed by this reaction can be run into properly
prepared molds to weld breaks in steel that are difficult to repair by any
other method. By adding other substances, an iron alloy of the correct
composition for the weld can be made.
Chromium and managanese are produced from their oxides by the
use of aluminum as a reducing agent. This process was discovered and
developed by the experimenter, Hans Goldschmidt (1861-1923).
Aluminum
Household
Iron and Steel
Excl. Machinery
8.7%
Automotive' Mlsc Service
9.7% H.1%
Courtesy of Dun and Bradstrcet, Inc.
FIG. 26-9. — Character of normal aluminum consumption.
Aluminum Alloys. Aluminum is alloyed with such metals as copper,
magnesium, silicon, zinc, manganese, and chromium. More than 30 dif-
ferent alloys are now in extensive commercial use. Duralumin (composi-
tion already given, page 449) is a strong aluminum alloy that obtains its
majfimum strength by heat-treating. An even stronger alloy, developed
in the United States and known as alloy No. 24S, is used extensively
in airplane construction.
Cooking utensils are commonly made from an alloy containing 1.25
per cent manganese and 98.75 per cent commercial aluminum.
Uses of Aluminum. In addition to cooking utensils and household
equipment such as vacuum cleaners, aluminum is extensively used in
transportation vehicles, such as aircraft, automobiles, trucks, and rail-
way cars; in architectural applications; and in thousands of manufactured
products.
Flake aluminum makes a good paint pigment either alone or mixed
with other pigments. Aluminum foil is used for candy wrapping, insula-
THE LIGHT METALS
457
Courtesy of Aluminum Company of America Courtesy of Aluminum Company of America
FIG. 26-10.-— Air transportation de- FIG. 26-11.— Window frames and
pends upon light, strong metals. sash made of aluminum alloy permit
wide vision.
tion in homes, boilers, and naval vessels. Aluminum wire and bus bars
are widely used in electrical work. Enough steel-cored aluminum cable
is used to girdle the globe at the equator twenty-four times.
QUESTIONS
1. What percentage of the earth's crust is estimated to be composed of
aluminum?
FIG. 26-12.— The 240-foot dredge FIG. 26-13.— This attractive
boom is made of structural aluminum giftware is made of aluminum
alloy. alloy.
Courtesy of Aluminum Company of America Courtety of Aluminum Company of America
458 CHEMISTRY FOR OUR TIMES
2. Why are many aluminum-producing factories located near river dams?
3. Aluminum, an abundant metal, was unknown to ancient peoples, while
gold, a rare metal, was well known. Explain this apparent contradiction.
4. Make a labeled diagram of the Hall electrolysis furnace for producing
aluminum.
5. In the preparation of aluminum by the Hail process, what purpose is
served by (a) alumina; (b) cryolite; (c) carbon?
6. Write equations for Castner's process: (a) electrolysis of fused sodium
hydroxide to form metallic sodium; (6) replacement of aluminum in aluminum
chloride by metallic sodium.
7. Why does the Hall process produce relatively pure aluminum?
8. Write formula equations for the action of aluminum hydroxide (a) with
sodium hydroxide solution; (b) when heated strongly; (c) when mixed with sul-
furic acid.
9. Four pounds of bauxite (Al2Os*3H20) eventually produces 1 pound of
metallic aluminum, indicating that aluminum is 25 per cent of bauxite, (a) What
is the actual percentage of aluminum in bauxite? (6) What is the percentage
effectiveness of the recovery of the metal from the ore?
10. What properties of aluminum account for its popularity for kitchen
utensils?
11. What properties of aluminum foil account for its effectiveness for insula-
tion?
•
12. A camper placed a bright, shiny aluminum frying pan over a charcoal
fire but could not get the pan warm enough to fry an egg. Then he dirtied the bot-
tom of the frying pan and had no more trouble in cooking. Explain.
13. How many kilowatt-hours of electricity are needed to produce 2 billion
pounds of aluminum?
14. How many times the specific gravity of aluminum is (a) mercury (13.6);
(b) iron (7.2)?
15. Write equations for the reactions of aluminum with (a) hydrochloric
acid; (b) dilute sulfuric acid; (c) sodium hydroxide solution; (d) oxygen; (e)
chlorine.
16. Write equations for the reactions of aluminum as a reducing agent on
(a) vanadium oxide (V^Os) ; (b) titanium dioxide (TiO2) ; (c) nickel oxide (NiO) :
(d) molybdenum oxide (MoOs); (e) silica (SiOz).
17. List two important aluminum alloys, and give their composition.
{204
^g pounds of alumina,
assuming that all the metal is recovered?
THE LIGHT METALS 459
19. What weight of pure alumina must be supplied to a Hall cell that pro-
duces •j0«n pounds of aluminum daily?
\&t\j
{48
-~ pounds. How many pounds of carbon were
consumed in its manufacture?
{g
grams of aluminum is con-
verted to aluminum nitride (A1N)?
22. What volume of ammonia must be decomposed in order to provide the
nitrogen needed for the preceding problem?
Magnesium
The Story of Magnesium. In 1808, Sir Humphry Davy first pre-
pared impure magnesium by electrolysis. In 1830 it was produced in a
purer form by replacing the metal from its chloride by the use of potas-
sium. For many years it remained a laboratory curiosity. Commercial
production of the metal developed first in Germany, then later in the
United States. For many years its chief use was in flash powders for
photographers .
Where Magnesium Is Found. Magnesium is the third most abun-
dant metal. Because, like aluminum, it is never found free in nature, it
is a metal associated with modern times.
Its compounds are very abundant. Perhaps the best-known compound
of magnesium is Epsom salts (MgS04-7H20), which is found in solution
in the waters of many mineral springs and even as the solid crystals in
salt deposits. The mineral carnallite (KCl-MgCl2'6H2O) is obtained from
the famous Stassfurt mines in Germany. This compound is used as a
source of magnesium. Magnesium compounds in sea water are used
today as a starting material in making magnesium metal.
Magnesite (MgCOs) and dolomite, or dolomitic limestone (MgCCV-
CaCO3), are found as huge mountain masses of rocks in the Alps and
elsewhere. Complex magnesium silicates include asbestos, a fibrous rock
used in insulation, and soapstone and talc, used for sinks and, when
ground, for talcum powder.
Preparation of Magnesium. Like aluminum, magnesium is pre-
pared commercially by electrolysis of a fused compound in the absence
of water. Anhydrous magnesium chloride from carnallite or from brine
is melted, and this liquid salt (m.p. 708°C) is the electrolyte. The metal
gathers at the cathode, where, while hot, it must be protected from con-
tact with the air. (See Fig. 26-14.) The change brought about by the
460
CHEMISTRY FOR OUR TIMES
electrolysis is
MgCI2 -» Mg + CUT
In another modern process, magnesite is heated to form magnesia.
MgCO3 -> MgO + CO2|
magnesite magnesia
The magnesia, mixed with carbon, is now heated to 2000°C in an electric-
arc furnace.
MgO + C ?=i Mgt + COT
The hot vapors containing magnesium and carbon monoxide are chilled
rapidly to 200°C in a blast of hydrogen or natural gas. The result is
Carbon
/Anode
Chlorine
Temperature
Above 650°C
Fused Magnesium
Chloride (with
KCI or NaCI)
<d~J Oil Burner
FIG. 26-14. — Magnesium is manufactured by electrolysis of fused magnesium chloride
in a cell.
magnesium dust, which can be purified by distillation at 750 to 950°C
under reduced pressure. The method is not without dangers, however,
and explosions have occurred.
The Pidgeon process is a recent method for producing magnesium.
A mixture of ferro-silicon alloy (75 per cent silicon) and dolomitic lime
(MgO and CaO) is heated to 1150°C in vacuo. The magnesium vapor,
liberated by the chemical reduction of the magnesium oxide, condenses
in stainless-steel condensers. While this process at present is more expen-
sive to operate than the electrolytic process, it has the advantage of
requiring only small installations.
The total production of magnesium was 2120 tons in 1935, 6250 tons
in 1940, 50,000 tons in 1941, and 290,000 tons in 1944.
Description of Magnesium. Magnesium is a remarkably light, sil-
very metal; its density is only 1.74 times that of water at 20°C. It melts
at 650°C.
THE LIGHT METALS
461
The Strongest Light Alloy. In the United States, the principal
magnesium alloys in use contain aluminum, zinc, and manganese. For
example, an alloy commonly used for extruded angles, I-beam sections,
and the like, has 6.5 per cent aluminum, 0.8 per cent zinc, and 0.2 per
cent manganese. When worked and heat-treated, it has a tensile strength
of 44,000 Ib per sq in. An alloy used for sand castings contains 6 per cent
aluminum, 3 per cent zinc, and 0.2 per cent manganese; its strength is
35,000 Ib per sq in.
Courtesy of The Dow Chemical Company
FIG. 26-15. — In the same manner that toothpaste is squirted from a tube, magnesium
alloy (Dowmetal) is extruded from the opening of this powerful machine.
Light magnesium alloys are used for typewriter and camera parts;
airplane parts; wheelbarrow, truck and bus bodies; and even for the
stratosphere flight gondola of the National Geographic Society-United
States Army Air Corps (1935). (See Fig. 26-16.)
Chemistry of Magnesium. Piles of magnesium chips or turnings
from a machine on which magnesium is being cut constitute a fire hazard,
for they may catch fire from the heat developed by friction at the cutting
tool in the machine. Such chips burn with a brilliant flash and intense
heat, forming a white powder. Magnesium confined in oxygen makes a
good photo-flash.
462
CHEMISTRY FOR OUR TIMES
Courtesy of the Dow 'Chemical Company
FIG. 26-16. — A gondola fabricated from magnesium alloy (Dowmetal) was used in a
famous stratosphere exploration ascension.
The white powder formed when magnesium burns is chiefly mag-
nesium oxide (MgO), magnesia, but some magnesium nitride (Mg3N2)
is also produced, for the hot metal combines with nitrogen as well as
with oxygen.
2Mg -f O2 -» 2MgO
3Mg + N2 -4 Mg3N2
An ordinary carbon dioxide type of fire extinguisher does not put out
a magnesium fire readily, for hot magnesium burns in carbon dioxide.
or possibly
2Mg
Mg
Courtesy of The Dow Chemical Company
FIG. 26-17. — Light, strong magnesium alloy (Dowmetal) is an ideal metal for
constructing featherweight safety goggles.
THE LIGHT METALS 463
Nor will water in relatively small amounts put out the fire; for steam
acts on the metal, or the metal will act slowly on hot water.
Mg + H2O -4 MgO + H2 1
MgO + H2O -4 Mg(OH)2
The surface of this active metal tarnishes slowly in air to form a white
covering. Salt water is a corroding agent, and most acids, even weak
Courtesy of The Dow Chemical Company
FIG. 26-18. — In fine motion picture cameras and projectors, a light, strong magnesium
alloy (Dowmetal) is used.
ones, act on magnesium with rapid evolution of hydrogen gas. Often
enough heat is produced to cause steam if the acid has water with it.
Mg + 2HCI -4 MgCI2 + H2|
Treatments with hot solutions containing chromates produce coatings
on the metal that help resist corrosion.
The Incendiary Bomb. Much attention has been drawn to the
metallic incendiary bomb used in warfare. A common type is the
1-kilogram (kg) (2.2-lb) magnesium bomb. (See Fig. 26-19.) This bomb is
detonated by a fuse (striking head) that explodes when the bomb lands.
This, in turn, ignites a small charge of Thermit, which sets the mag-
nesium on fire. Incendiary bombs of this sort have caused extensive
damage, especially if dropped from airplanes on buildings already
damaged.
The simplest manner of controlling metallic incendiary bombs that
have been ignited is to let them burn out without setting other fires. In
general, either a spray or a stream of water hastens the burning of the
464 CHEMISTRY FOR OUR TIMES ,
magnesium. At the same time the surroundings are kept wet, preventing
spreading of the fire.
Uses of Magnesium. In addition to uses already mentioned, metal-
lic magnesium is used extensively as an agent in chemical synthesis.
Organic compounds of magnesium, such as magnesium ethyl bromide
are easily made, and they are reactive. By using these
Three Steel Pins*
Safety-
Pin
Striking Priming
Head Composition
Aluminum and
-Body, 80% Magnesium
._ . . . UWVJT, W /O ITICIKIIC3IU
Iron Oxide (may also contajn
explosives)
FIG. 26-19. — The magnesium incendiary bomb is used in military operations for setting
fires.
so-called Grignard compounds, chemists have produced superior drugs,
dyes, and perfumes — some of the triumphs of modern chemical research.
QUESTIONS
23. What properties of magnesium account for its never being found free in
nature?
24. What is the percentage of magnesium in (a) magnesite; (b) dolomite; (c)
magnesia?
25. Give a use for each of the following: (a) asbestos; (b) magnesia; (c) dolo-
mite; (d) Epsom salts; (e) talc.
26. In the process of preparing magnesium from sea water (a) oyster shells arc
heated in a kiln; (b) the resulting lime is slaked; (c) the slaked lime is added to
sea water containing magnesium chloride, precipitating magnesium hydroxide;
(d) the precipitate is treated with hydrochloric acid ; (e) the resulting magnesium
chloride (after dehydration) is decomposed by electrolysis. Write equations for
the five chemical changes in the process.
27. In the ferro-silicon process for making magnesium, announced through
the Canadian National Research Council (a) dolomite is roasted; (b) the resulting
magnesia is treated with silicon (by means of ferro-silicon) and then distilled from
the mixture in vacua. Write equations for the two chemical changes in this process.
THE LIGHT METALS 465
28. Write equations for the action of magnesium on (a) hydrochloric acid;
(6) dilute suifuric acid; (c) oxygen; (d) carbon dioxide; (e) water; (/) nitrogen;
(g) chlorine.
29. Give four examples of uses for magnesium alloys.
30. (a) Why are magnesium fires so hard to extinguish? (6) What materials
are used to smother magnesium fires?
31. When magnesium chips are burning around a machine, which is the more
satisfactory fire extinguisher, sand or graphite?
{380
,,.- grams of an-
hydrous magnesium chloride?
33. What is the most satisfactory method of extinguishing a magnesium in-
cendiary bomb, assuming that it contains no further explosive?
34. What is the percentage composition of magnesium ethyl bromide?
35. Write the formulas for (a) magnesium methyl bromide; (6) magnesium
ethyl chloride. *
Beryllium
Properties of Beryllium. Any list of modern light metals should
include beryllium. This metal is found in the mineral beryl (3BeOAl203'-
6Si02). The metal, silver-gray, is 1.8 times as dense as water, melts at
1285°C, and is harder than glass. Its present high price, $15 a pound in
alloys, is due to two factors: (1) It is difficult to produce. (2) Only a
small percentage of this light element is found in its ores.
Uses of Beryllium, The chief use of beryllium is as an alloying ele-
ment. Springs made of copper alloyed with a little beryllium and nickel
may fail only after 20 billion flexings. This record is 10,000 times better
than that for a steel spring of equal size. Copper-beryllium alloy tools
are hard and never make a spark when dropped on stone or concrete.
Wrenches and other tools made of this alloy may be used safely in gaso-
line fumes and in the vapors of other flammable liquids, for no sparks
are produced when the metal is scratched or dropped.
Beryllium has uses in connection with the atomic bomb project.
SUMMARY
Aluminum is never found free in nature. Its compounds, including clay, are
abundant in the earth's crust. The chief commercial source is bauxite, a hydrated
oxide.
Aluminum is prepared from alumina by the Hall method. This consists of
electrolysis of purified alumina in molten cryolite. Carbon anodes and a carbon-
lined steel box as cathode are needed. The physical properties of aluminum are
466 CHEMISTRY FOR OUR TIMES
that it is light, silvery, ductile, malleable, easily alloyed, and a good conductor
of heat and electricity.
The chemical properties of aluminum are as follows: Pure aluminum is at-
tacked by water, but a protecting coating of aluminum oxide forms on the sur-
face. Aluminum burns, forming aluminum oxide. Aluminum is attacked by both
acids and alkalies. It is a powerful reducing agent, as in the Goldschmidt process.
Aluminum is used in light alloys for airplane, truck, train, and household
equipment. It is a pigment in some paints, and a reducing agent.
Magnesium was discovered by Sir Humphry Davy. It is never found free in
nature. Examples of compounds of magnesium are Epsom salts (MgSCh'TH^O)
and magnesium chloride (MgCU) in the Stassfurt deposits and in sea water.
Magnesifce (MgCO3) and dolomite (CaC03'MgCO3) are abundant. Magnesium
silicates include talc, asbestos, and soapstone.
Magnesium is prepared by electrolysis of molten magnesium chloride. Some
is made by reduction of magnesium oxide with carbon and rapid chilling and also
by reduction of magnesium oxide with ferro-silicon and distilling magnesium in
vacuo. The physical properties of magnesium are as follows: (1) It is a light, sil-
very metal and alloys well, forming light alloys of moderate strength. Its chem-
ical properties are that it tarnishes in air; burns readily in air, forming magnesium
oxide and a little nitride; reduc%s carbon dioxide when hot; joins nonmetals di-
rectly; and is readily attacked by acids.
Metallic incendiary bombs may contain magnesium ignited by Thermit. This
metal is contained in light alloys manufactured today. It is present in organic
magnesium compounds that are used in chemical synthesis.
Beryllium, a very light metal, has less than twice the density of water. It is a
silvery, hard metallic element, similar to magnesium chemically, and rather
expensive at present. It is useful in alloys that do not produce sparks and for
specialties such as springs.
QUESTIONS
36. What is the percentage of beryllium in beryl?
37. One of the richest sources of beryllium is bromellite (BeO). What weight
{50
2Q grams of this ore? Assume that all
the metal is recovered and that the ore is 100 per cent beryllium oxide.
38. What volume of carbon dioxide can be obtained at standard conditions
( QQP
when an acid is added to on £rams °f magnesium carbonate?
UNIT SIX CHAPTER XXVII
THE DENSER METALS
Lead
The symbol for lead, Pb, is taken from the Latin word plumbum..
Evidently, then, the plumber of today follows the trade of a long line
of leadworkers. Lead pipes were discovered in the ruins of Pompeii, and
Sink
Lead Pipe
To Sewer
Hard Solder
67% Pb
33% Sn
Water ^^—-^
Clean
Out
FIG. 27-1. — Using pads to protect his hands, a metal worker pours lead or solder onto
the pipe joint. As the metal cools, he fashions a bulgelike joint.
some of the famous Roman baths were supplied with water through lead
pipes, joined end to end by wiped joints. (See Fig. 27-1.)
The only important ore of lead is galena (PbS). This dense material
bronze
matte
blister copper
New Terms
Monel metal
cassiterite
galena
467
galvanized iron
powder metallurgy
468 CHEMISTRY FOR OUR TIMES
is often found in well-crystallized cubes that have purplish-gray shiny
surfaces and a metallic luster. Zinc sulfide (ZnS) and silver sulfide (Ag2S)
are at times associated with this ore.
The preliminary treatment of lead ore depends, of course, upon the
nature of the impurities present and their amount, but, in general, gravity
methods of concentration are used.
Production of Lead. About 2 million tons of lead is produced each
year in the world. Of this, one-fourth is made into paint pigments and
other compounds from which the lead is not recovered after use. The
United States leads the world by producing one-fourth of all the lead
mined; of this amount, one-third is produced in the state of Missouri.
The ore is concentrated, roasted, and blasted with air to remove
sulfur and then reduced by heating with carbon.
The equations that follow summarize the chemical changes in the
process :
2PbS + 3O2 -* 2PbO -f 2SO2
2PbO + C -* 2Pb + CO2 1
Properties of Lead. Lead as ordinarily seen is a dull-gray metal. A
piece freshly cut with a knife shines with a silvery, metallic luster, which
darkens after a short time, owing to the formation of a tarnish. Lead
melts at 327. 5°C and is 11.4 times as dense as water. Its tensile strength
is very low; in fact, under a strong pull it slowly "creeps." Also, its
ductility (ability to be drawn out into a wire) is poor.
Since lead linings are used in the chamber method of making sul-
furic acid (see page 351), it is obvious that lead withstands the attack of
this acid at the concentration (GO per cent) and temperature found in
the chambers. A protective coating of lead sulfate (PbS04) forms over
the lead. With higher concentration of sulfuric acid, this coating dis-
solves and therefore offers no protection against further corrosion. Weak
acids, even carbonic acid (H^COa), corrode lead. For this reason, lead is
not suitable for pipes for distilled water. When enough carbonic acid is
present, slow corrosion of the lead is produced. Lead pipes carrying
slightly alkaline drinking water are protected by a coating of lead car-
bonate, which is not soluble in mild alkali.
Lead Poisoning. The use of lead pipes for carrying slightly acid
drinking water is questionable, for lead compounds are poisonous. Lead
compounds are eliminated from the body so slowly that small amounts
taken internally accumulate until poisonous concentrations are reached.
This trouble may overtake painters and workers who handle tetraethyl-
leaded gasoline carelessly. The U.S. Public Health Service considers 0.36
part of lead per million parts of water definitely poisonous.
THE DENSER METALS 469
Chemical Actions of Lead. Molten lead gathers dross or scum on
its surface. By careful heating below 585°C, a red powder [red lead, or
minium (PbaC^)] is formed.
3Pb + 2O2 -» Pb3O4
This dense orange-red compound is the pigment used extensively for the
priming coat of paint over structural steel, as it offers good protection
against corrosion. In the laboratory it is a good oxidizing agent.
Above 585°C, yellow-brown litharge (PbO) is formed from lead or
from minium.
2Pb 4- O2 -» 2PbO
2Pb3O4 -> 6PbO -f O2
Some dilute weak acids, such as acetic acid, corrode lead, but hydro-
chloric and sulfuric acids do this very slowly. Lead chloride (PbCl2) and
lead sulfate (PbSO4) are compounds
insoluble in cold water. A coating of
either *of these substances on lead pro- nrn- stora e
tects the metal from further action. solder >^^^^^^^m Ba3o%es
Nitric acid (HNO3), a strong oxi- ° £^s^^mmmmh
dizing agent, attacks lead vigorously,
forming lead dioxide (PbO 2), a choco-
late-brown compound that is used in
storage batteries as the positive (+)
Cable
y-o Covering
Uses of Lead. Ill disk or cylindrical ' n%
form, lead is used for weighting dresses T, ^ c°urte;» of Dun & frad^' Inc-
, ' . . _ , . . , . I<IG. 27-2. — Character of normal lead
and fishing nets. Lead is also used to consumption.
make shot. For this purpose the metal
is alloyed with 0.5 per cent of arsenic to lower the melting point and
produce a harder shot.
Lead sheets line apparatus that must resist sulfuric acid. Some sky-
scrapers rest on lead blankets to help cushion shocks. Ornamental win-
dows are set in lead. Lead pipes are easy to install and are, as a rule,
satisfactory for drain pipes. The covering sheaths of underground elec-
tric wires or of cables are made of lead, sometimes alloyed with I per cent
of calcium or with other elements to harden them. Spongy, gray lead is
used for the negative ( — ) plate in storage batteries. "Leaded gasoline "
contains a lead compound, tetraethyl lead [(C2H5)4Pb], added to in-
crease the octane number (see page 538).
Lead alloys have many familiar uses, some of which are listed in the
table that follows.
470 CHEMISTRY FOR OUR TIMES
Name of alloy
Composition
Use
Solder (soft)
50 % Pb, 50 % Sn
Joining copper, brass, and
Type metal
80 % Pb, 20 % Sb
other metals together
Linotype slugs
Bearing metal (Frary metal)
98%Pb, 2%Ba
Antifriction bearings
QUESTIONS
1. What arc the name and formula of the chief lead ore?
2. Under what conditions are lead pipes (a) satisfactory for plumbing; (6)
unsatisfactory?
3. What is the percentage of lead in pure lead sulfide?
4. For what purpose is lead or a lead alloy used in each of the following: (a)
an automobile; (6) an airplane; (c) an electric motor; (d) a fish net; (e) draperies?
5. Account for the fact that satisfactory copper wires can be made finer than
a human hair but that lead wires as small as this cannot be drawn.
6. The use of lead pipes for conducting well water into a house, for drinking
purposes, should be questioned. Under what conditions are such pipes (a) safe;
(6) unsafe?
7. From what source do painters acquire the industrial disease called
"painter's colic"? Workers in what other industries may acquire the same
disease?
8. What useful property does antimony contribute to type metal?
9. Write formula equations for the chemical actions that take place under
the following conditions: (a) heating lead in air at a low temperature; (b) heating
lead in air at a high temperature ; (c) and (d) reducing each of the oxides formed
in (a) and (6) by carbon.
10. What weight of lead must be purchased if a manufacturer is to produce
10 tons of minium?
11. Which of the three oxides of lead contains the highest percentage of the
metal?
12. What weight of lead chromate precipitates when a solution containing
(993
\ **r» grams of lead nitrate is added to a sufficient amount of potassium chromate
looJ
solution (K2Cr04)? (Cr = 52.)
f 323 0
13. How much lead acetate was present when •{«'_, grams of lead chromate
1161.5
precipitated according to the equation,
2Pb(C2HsO2)2 + K2Cr2O7 + H2O -» 2PbCrO4 1 + 2KC2H8O2 + 2HC2H8O2?
THE DENSER METALS 41M
Tin
Tin is a bright, shiny metal familiar to all as the coating metal of
tin cans. Its symbol, Sn, comes from the Latin word stannum. This
metal has been known since ancient times; in fact, it is reported that one
of Caesar's reasons for invading the British Isles was to secure tin from
the mines of Cornwall. Tin was an article of commerce earned in ships
through the Mediterranean Sea and around the west coast of Europe by
ancient Phoenician traders.
The chief location of tin mines today is in the Malay States and the
East Indies. Metallic tin ingots are exported through the port of Singa-
pore. Other important deposits are found in Bolivia, South America, and
a plant to smelt Bolivian ore has been erected in Texas. Relatively
unimportant amounts of tin are produced in this country, although half
the world's supply of 200,000 tons annually is consumed here.
Tin Ore. Cassiterite (SnO2), or tinstone, is found in nature concen-
trated by the running water of streams, although sometimes it is mined
from veins in rocks. It is the chief tin ore. It is further concentrated by
flotation of the gangue, heated, and reduced with carbon.
SnO2 + C -» Sn -f CO2 1
The tin is then purified from other metals by applying heat. Tin
melts at 232°C, a temperature lower than the melting point of lead
(327. 5°C), and flows away from the impurities, which have a higher
melting point. Further purification can be made by electrolysis.
Properties of Tin. Although relatively soft, tin is harder than lead;
it is bright and shiny, but not ductile. Its melting point is lower than
that of most common metals. Its specific gravity is 7.3. Below 13°C tin
may be converted into an allotropic form, a gray powder. Some museum
specimens of tin, for example, break out with spots of this "tin disease"
when, as during a Russian winter, they are exposed to low temperatures
for a long time.
Tin at 100°C can be rolled into thin sheets, which in turn can be rolled
onto previously cleaned sheet steel. Tin may also be deposited electro-
lytically on sheet iron. From this coated metal, called tin plate, 20 million
blanks for tin cans are cut in a year. This use accounts for 40 per cent
of the tin imported into the United States. Tin costs more than ten times
as much per pound as lead, with recent tendencies upward from that
figure.
Chemical Actions of Tin. Tin acts slowly with acids. This metal is
in fact generally inactive, even less active than lead. Hot hydrochloric
acids acts on it steadily, liberating hydrogen.
472
CHEMISTRY FOR OUR TIMES
Sn + 2HCI
SnCI,
stannous chloride
Free chlorine will change both tin and stannous chloride to stannic
chloride, a compound in which tin is considered to have a combining
number of 4. The bond is covalent.
This action is one method by which
tin is recovered from scrap tin plate,
for chlorine attacks tin even more
readily than it does iron, the pro-
duct being so much more volatile.
Tin
Tin Plate
40.4%
Other 9.4%
Tin Oxide 1.7%-
Chemicals 1.8%' / f*
Type Metal 1.9% /
Tinning 3.1%
Collapsible Tubes 5.9%'
Courtesy of Dun & Bradstreet, Inc.
FIG. 27-3. — Character of * normal tin
consumption.
SnCI2 4- CI2
SnCI4
Bronze
6.8%
Babbitt
7.2%
Nitric acid and hot concentrated
sulfuric acid both act on tin; with
nitric acid, however, insoluble me-
tastannic acid (H2SnO2) forms.
Ordinary moist air and most fruit
and vegetable juices do not attack
tin.
Tin-can Chemistry. The protection of iron by a covering of sheet
tin is effective while the tin covering is complete. Practically, it is very
difficult to apply a coating of tin to iron, previously pickled free from
scale, without pinholes through the tin. When exposed to the weather,
Courtesy of Anaconda Copper Mining Company
FIG. 27-4. — Liquid zinc is poured from a ladle into flat molds. Most of this metal will be
used to protect iron.
THE DENSER METALS 473
iron is attacked more readily than tin. A little electric cell is formed in
which the iron is the negative ( — ) pole and tin is the positive ( + ) pole.
Iron dissolves in the action and forms, finally, red iron oxide (Fe2O3).
That is, tin, being less active then iron, is a good protection for iron
while the coating is unbroken. Once broken, as in the case of an old tin
can in a dump, the can quickly disintegrates. Notice that tin is below
iron in the replacement list (see page 89).
Uses of Tin. Pure " block tin" is used for making pipes to carry dis-
tilled water and slightly acid liquids (soda water for fountains in drug-
stores), for it resists their corrosive action. Long spans of tin pipe must be
supported by a trough of stronger material. Some collapsible tubes are
made of tin.
Tin is a component of some alloys. Solder has already been mentioned.
Pewter used for ornamental tableware, contains 75 per cent or more of
tin and the remainder lead. Commercial bronze has less than 19 per cent
tin and the rest copper. Sometimes zinc is put in bronze. The metal used
for bronze statuary and bells has about 10 per cent tin and the rest copper.
Tin foil, once used extensively for candy wrappers, is now replaced in
part by aluminum foil, waxed paper, or transparent sheet plastic material
because of the high expense of tin.
QUESTIONS
14. What is the chief ore of tin?
15. How is tin obtained from its ore?
16. The concentration of tin ore is sometimes called "reverse flotation."
Explain this term.
17. Give the composition of each of the following: (a) block tin; (6) solder;
(c) pewter; (d) shot; (e) bronze; (/) red lead; (g) a tin can; (h) tin foil; (i) litharge;
(j) galena.
18. Explain the theory of protecting sheet steel from corrosion by coating it
with tin. How does this work out practically?
19. A manufacturer of bronze tablets estimates that a memorial tablet will
weigh { pounds. What is the cost of the metals alone, assuming that copper
\^7o
costs 12 cents and tin 52 cents per pound?
20. Soldered gasoline cans were cached in the Arctic. Later the cans were
found open at the seams with the fuel gone, (a) Suggest a possible cause of this
disaster. (6) Tell how it could have been avoided.
21. Write formula equations for the actions of (a) tin with hydrochloric acid ;
(6) tin with chlorine; (c) tin hydroxide with hydrochloric acid.
22. Balance this equation (do not write in this book) :
SnCI2 + li + HCI -4 SnCU + HI
474 CHEMISTRY FOR OUR TIMES
23. What weight of tin can be recovered from I pounds of cassiterite that
VuUU
is 60 per cent tin oxide?
24. By the action of tin and hydrochloric acid, nitrobenzene (CbHsNCM is
reduced to aniline (CeH^NH^). Write arid balance the equation to represent this
change.
Zinc
Zinc is another metal that has been known since antiquity. In ancient
descriptions and uses it was sometimes confused with tin. A zinc-filled
bracelet has been discovered in the ruins of a city that was destroyed
about 500 B.C. Zinc, alloyed with copper, was also a component of brass
or bronze for weapons and tools in ancient times. Today everyone is
familiar with zinc as the blue-gray metal on the outside part of flashlight
cells. When free of tarnish, it has a bright luster.
Ores of Zinc. The most important ore of zinc is the sulfide ore (ZnS)
that is called zinc blende, sphalerite, or blackjack. It is shiny and dark
and a very attractive mineral when well crystallized. Smithsonite (ZnCO3)
is also found, and some zincite (ZnO). In New Jersey an ore called f rank-
Unite (ZnOFe203) is mined.
About 1.75 million tons of zinc was produced in 1939. Of this amount
the United States produced 28 per cent and Germany 13 per cent. Canada
and Poland were important producers, also. Half of the United States
supply came from the Joplin region of Missouri and adjacent states.
Obtaining Zinc. Today about three-fourths of the zinc is smelted by
the method already described (see page 279). The ore is concentrated
from the accompanying valuable lead sulfide (PbS) by froth flotation.
The sulfide or carbonate is roasted in air to form the oxide.
2ZnS -f- 3O2 ->> 2ZnO -f 2SO2
ZnCO3 -» ZnO -f CO2 1
The oxide is then reduced to metallic zinc. This, can be done by mixing
it with powdered coal and then heating.
ZnO -f- C -> Zn | + CO t
The zinc vaporizes in the operation and is condensed to recover the
metal.
In the Maier process, the impure zinc oxide is heated to 1000°C in a
tube in a reducing atmosphere of natural gas. The zinc distills over to
the condenser, where it deposits out 99.99 per cent pure. This process
is continuous and economical as well as producing a high-purity product.
Another way to get zinc from its oxide is to leach the oxide with dilute
sulfuric acid.
ZnO + H2SO4 -> ZnSO4 + H2O
THE DENSER METALS 475
The solution of zinc sulfate is then electrolyzed, and the zinc ions (Zn++)
plate out as zinc on the cathode ( — ). Electrolytic zinc has a purity of
99.999 per cent. It is better adapted than spelter (commercial zinc) for
making alloys and for certain other purposes. It costs about 4 cents
more per pound than spelter. Zinc may be refined by distillation or by
electrolysis.
Properties of Zinc. Zinc can be melted easily in the flame of a
Bunsen burner, for its melting point is 419.4°C. If liquid zinc is poured
slowly into a pail of water, mossy zinc results. The steam formed by the
contact of the hot drop of metal with the water expands the drop into
an irregular bubblelike shape. Mossy zinc is frequently used in the
laboratory to liberate hydrogen.
When heated between 120 and 150°C, zinc is malleable and easily
worked but between 200 and 300°C it becomes brittle. The density of
zinc, 7.14 g per ml, is about the same as that of iron. Its tensile strength
varies with treatment. Cast zinc has a tensile strength of 8000 to 14,000
Ib per sq in., while the tensile strength of drawn zinc varies between
22,000 and 40,000 Ib per sq in.
Chemistry of Zinc. Zinc resists corrosion well in the temperate
zone but not in the tropics. In moist air a coating of zinc basic carbonate
[ZnCO3'3Zn(OH)2] forms slowly. Acids, even dilute ones, attack zinc
readily, liberating hydrogen.
Impure zinc or zinc wrapped with a piece of copper wire reacts more
readily than pure zinc because the action is electrochemical, the action
being similar to that of an electric cell.
Zinc dissolves in alkaline solutions, but not as readily as aluminum.
It reacts with water in the presence of sodium hydroxide as follows:
Zn + (hot) NaOH + H2O -> NaHZnO, + H2|
sodium hydro-
gen zincate
It will replace all of the precious metals from their solutions and is
used to some extent for this purpose.
2AgNO3 + Zn -+ Zn(NO3)2 + 2Ag I
Uses of Zinc. Sheet zinc is used for roofing, valleys in roofs, weather-
stripping and, in general, for coverings that must resist weathering. Dry
cells use zinc for the outside can, which serves as a cathode ( — ). Cleaned
nails, hardware, sheet iron, and other iron articles are galvanized by
dipping them into molten zinc. This gives them a protective coating that
resists wear and rusting well. The ordinary galvanized water pail is a
good example of a sheet-iron utensil so protected. When it is new, the
crystals of zinc can usually be seen on its surface. Zinc is applied to iron
in several other ways. One of them, Sherardizing, covers the articles with
476
CHEMISTRY FOR OUR TIMES
powdered zinc and then melts the zinc onto the metal by the application
of heat.
Zinc is used in the Parkes process for separating silver or gold from
lead (see page 666) ; it dissolves the silver or gold but not the lead. Photo-
engravers use zinc for reproducing line drawings. Figure 27-1 in this book
and the cartoons in a school classbook are printed from an original zinc
plate. The tops of many glass preserving jars are made of zinc, a use
Zinc
Galvanizing
44%
Brass
Making
28%
Courtesy of Dun & Bradatreet, Inc.
FIG. 27-5. — Character of normal zinc
consumption.
that requires over 15,000 tons a year.
Brass, an alloy of copper 60 to 90
per cent and zinc 40 to 10 per cent, is
much used for pipes, hardware, cart-
ridge casings, and other purposes famil-
iar to all. Zinc-base-alloy, die-cast metal,
contains 2.5 to 3.5 per cent copper, 3.5
to 4.5 per cent aluminum, and the rest
zinc. This alloy when liquid can be
cast in permanent molds and gives
castings with fine details. Many auto-
mobile parts arc made in this way. An
ordinary computing gasoline pump,
such as is seen at filling stations, may
contain over 70 different parts made of zinc die-cast alloy. No sparks are
produced if the metal is accidentally hit.
QUESTIONS
26. Zinc occurs in what three sorts of ores?
26. Why is zinc not found free in nature, while copper is?
27. Show by a series of equations how zinc may be obtained (a) from zincite;
(b) from zinc blende; (c) from smithsonite.
28. What four metals are obtained from the Joplin, Missouri, region?
29. Make a labeled diagram of a cell in which zinc may be refined by elec-
trolysis.
(200
30. What volume of sulfur dioxide is produced when j ™ grains of zinc blende,
60 per cent zinc sulfide, is roasted in air?
f 390
31. What weight of zincite, 80 per cent zinc oxide, is needed to form JOOK
pounds of zinc?
32. When brass is melted, a white smoke arises from the crucible. What is the
chief component of this white smoke?
33. A demonstrator was showing the violent reaction of zinc with sulfur. He
mixed the powdered elements and set them afire. A portion of the reacting mixture
_ THE DENSER METALS _ 477
flew into unprotected supplies of zinc and of sulfur and set them afire, also. Write
equations for ail three burnings.
34. In what weight proportions should zinc and sulfur be mixed for maximum
violence of reaction?
35. What is the composition of (a) galvanized iron; (6) spelter; (c) zinc white;
(d) zinc ointment; (e) zinc stearate? [(d) and (e) are reference questions.]
36. State a use for each of the substances mentioned in the previous question.
37. What metals are present in each of these alloys: (a) brass; (6) bronze; (c)
nickel silver; (d) pewter; (e) type metal?
38. A cheap ladle made of zinc is placed in punch slightly acid with fruit juice.
What happens?
39. Balance this equation (do not write in this book):
Zn(OH)2 + NH4CI + NH3 -» Zn(NH3)4CI2 + H2O
40. (a) When \^ar grams of zinc is put into dilute hydrochloric acid, what
volume of hydrogen is liberated at STP? (6) What volume of hydrogen is gener-
ated if the pressure is J^Q millimeters and the temperature
Cadmium
Properties and Uses. When zinc is distilled, an impurity, cadmium,
distills over at a boiling point lower than that of zinc. Cadmium is a
metal that melts at 321°C and boils at 778°C. It is a little harder than
zinc and less active chemically.
Cadmium is applied by electroplating; we often see it on household
hardware, automobile wheel rims, and parts of typewriters. When thus
applied to steel, it gives a dense, silver-white, fibrous appearance. Its
most important use, however, is in alloys. These include a cadmium-
copper alloy for power and telephone wires and a low-melting alloy
(Wood's metal — parts by weight: bismuth 5, lead 2.5, tin 1.25, and
cadium 1.25; m.p. 65.5°C).
Cadmium is an important alternate metal for zinc. It resists corrosion
better than zinc. It will burn to form a brown oxide (CdO). Cadmium
sulfide (CdS) is widely used as a yellow pigment.
QUESTIONS
41. Distinguish cadmium from zinc in respect to (a) color; (b) boiling point;
(c) chemical activity.
42. Write equations for (a) burning cadmium in air; (6) passing hydrogen
sulfide through cadmium nitrate solution.
478 CHEMISTRY FOR OUR TIMES
43. What properties of cadmium make it a suitable metal for electroplating
over other metals?
44. Balance this equation (do not write in this book):
K2Cd(CN)4 + H2S -» KCN + HCN + CdS |
Copper
Early History of Copper. The Mediterranean island of Cyprus,
off the Greek coast, was a source of copper for the early peoples of that
region. They called copper the Cyprian metal. Eventually the same
name has reached us today through the Latin word cuprum.. In China,
Peru, and Asia Minor and in North America among the Indians, copper
was used by primitive man. Some articles preserved to us are copper
utensils, ornaments, weapons, and sacred figures.
The use of copper was so widespread that historians refer to the
period of the rise of mankind from savagery to a tool-using animal as
the bronze age — bronze age, rather than copper age, because copper
was often found naturally alloyed with other metals.
At Thebes in Egypt, on the Avails of Rekh-y-Re's tomb, were found
scenes of the casting of the metal for the large bronze doors for the
temple at Karnak.
In Italy, Benvenuto Cellini (1500-1571), an artist, cast in bronze
a heroic statue of Perseus, son of the Greek god Zeus.
After this extensive use in the early arts and crude industries, modern
science stepped into the picture. Scientific investigations show that not
only native copper, but also many low-grade sulfide ores are valuable
as sources of copper. An ore containing as little as 1 per cent of the metal
can be concentrated by froth flotation.
The properties of copper have been studied with care. This metal is
found to be the best practical conductor of electricity, ranking second to
silver. In 1882, when the world's first electrical power plant was opened
in New York, Thomas Alva Edison used about 125,000 Ib of copper in
its equipment. It supplied power for 5000 electric lamps in 1883 and a
year later for 11,000.
The spread of the use of copper for electrical purposes has been rapid.
Today this country, both above and below the surface, is enmeshed
with copper strands carrying power and messages, as if a million Lilli-
putian wires were binding the giant Gulliver, the United States.
Where Copper is Found. The chief copper-producing region, ac-
counting for about one-half the world's supply, is the United States,
with Chile, Canada, and Rhodesia in South Africa also important. In
this country the leading copper-producing states are Arizona, Utah
(famous for the large open-pit mine in Bingham Canyon), Montana,
THE DENSER METALS
479
Nevada, and Michigan, where on the Keweenaw Peninsula free copper
has been secured from the time of the early Indians and ever since.
Copper Ores. About one half of all the ores mined is chalcopyrite
(CuFeS2), and one fourth is chalcocite (Cu2S). All copper deposits
contain cuprite (Cu2O). The remaining fourth of the copper ores is chiefly
native copper with deep-green malachite [CuC03'Cu(OH)2] and blue
azurite [2(CuC03)-Cu(OII)2].
Copper Metallurgy. 1. Low-
grade ore, usually sulfide, is con-
centrated by several methods,
including froth flotation.
2. The ore is then roasted with
air available so that part of the
sulfide is changed to the oxide.
Cu2S + 2O2 ->• 2CuO -|- SO2
3. The roasted ore is heated
again in a large reverberatory
furnace to remove iron as a slag.
The resulting matte (Spanish for
"dull") is about 50 per cent
copper.
4. The matte is now placed in
a converter that resembles a
Bessemer converter. Here an air
blast completes the oxidation of
the sulfur and forms copper 98
per cent pure, which, because of
the gas bubbles that it contains, is called blister copper.
When certain types of ores are used, these last two steps (3 and 4)
can be more or less combined in a large reverberatory furnace. In this
case the ore contains both sulfides and oxides, which act on each other.
2Cu2O -I- Cu2S -> 6Cu -f SO2 1
Gold and silver are retained in the blister copper. The metal in this
form is cast into anode slabs, ready for electrolytic refining.
In the famous Minas de Rio Tinto, in Spain, which have produced
copper ever since the dawn of history, as well as in some United States
and South Africa locations, the copper is mined by leaching. The air
slowly oxidizes the ore to copper oxide. A liquid, sometimes sulfuric acid
(H2SO4), trickles slowly through the pile of ore. Copper dissolves, and
copper ions (Cu** ) are formed. These are recovered as copper either by
electroplating or by replacement when scrap iron is added.
CU++ + Fe -* Cu + Fe++
Courtesy of Anaconda Copp< V / Company
FIG. 27-6. — A miner prepares to attack
a vein of copper ore with a compressed-air
gun.
480
CHEMISTRY FOR OUR TIMES
Refining Copper. Slabs of blister copper as large as the top of an
office desk are hung in a tank of copper sulfate (CuSO4) solution con-
taining some sulfuric acid. These are anodes (+) that are to be refined.
Suspended between these slabs are sheets of pure copper cathodes ( — ).
A regulated current surges between them and through the solu-
tion. The Cu++ ions are deposited from the solution onto the cathode. The
solution is in turn resupplied by copper dissolved from the anode.
This process continues until the anode is quite thin. Zinc, iron, and
lead impurities go into the electrolyte. Gold and silver drop out of
the anode and collect as a slime in
the bottom of the tank. This sludge,
an important source of precious
metals, is sometimes of sufficient
value to pay cost of the refining
process. The expense for the elec-
trical energy is important in this
process. Copper deposits at the
rate of 0.3294 milligram (mg) per
ampere per sec. Electrolytically
deposited copper may be 99.98 per
cent pure. Copper conducts elec-
tricity without much loss from
energy changed to heat, but as
little as 0.3 per cent arsenic lowers
the conductivity 14 per cent. If
the electrical resistance of a strand
of silver wire is taken as standard
at 1.0 for a given size and tem-
perature, then that of copper is
1.05.
Courtesy of Anaconda Copper Mining Company
FIG. 27-7. — Refined copper is cast into
cakes before being sent to market.
Physical Properties. Copper is the only red-colored metal. It is soft,
ductile, and malleable under most conditions. Cold-working the metal
increases its hardness. This process of increasing the hardness of copper
by working the metal when cold has given rise to the story that the
ancients were able to temper copper and that the art has since become
lost. White1 states, " Copper tools and weapons used by the American
Indians were hardened by cold work and not by any lost or secret
process."
Modern workers have copper tools, made of an alloy of copper and
beryllium, that not only give no sparks, as iron alloys do, but also are
harder than any copper tool known to antiquity.
1 A. H. WHITE, Engineering Materials, p. 228, McGraw-Hill Book Company, Inc.,
New York, 1939.
THE DENSER METALS
481
Copper is 8.9 times as dense as water. It melts at 1083°C. Its ductility
is so great that copper wires can be made that are finer than a human
hair. The tensile strength of a specimen depends on its previous history.
When annealed, or softened by heating, its strength is about 36,000 Ib
per sq in. for large wire. When cold-drawn, the same size has a strength
of 49,000 Ib per sq in.
Chemical Properties of Copper. The resistance of copper to
atmospheric corrosion is well known. A bright-red coating of oxide (Cu20)
forms, especially in moist air or under salt water, but this slowly turns
to an attractive, dull-green "patina." Drainpipes for rain water also
sometimes acquire a green coating. This coating is considered to make
bronze statues more attractive as they age. The composition of the green
material is now known to be the basic sulfate [CuSO4'Cu(OH)2] or the
basic copper chloride.
When copper is heated in air, a black coating of cupric oxide (CuO)
forms. 2Cu + 02 -» 2CuO. Some
of the red cuprous oxide (Cu20)
also forms.
Copper joins readily with sulfur.
Under ordinary conditions of plac-
ing copper in sulfur vapor the ac-
tion forms cuprous sulfide.
Thin sheets of copper placed in
Copper
chlorine burst into flame spontane-
ously. Hydrochloric acid cleans the
oxide film from its surface but fails
to attack the metal since copper is
less active than hydrogen. The
same applies to dilute sulfuric acid,
but hot concentrated sulfuric acid oxidizes and dissolves copper.
Buildings
11%
Automobiles
10%
Courtesy of Dun & Bradstreet, Inc.
FIG. 27-8. — Character of normal copper
consumption.
Cu + 2H2SO4 -» CuSO4 + 2H2O + SO2 1
Concentrated nitric acid acts on copper, producing dense, poisonous,
brown fumes of nitrogen dioxide gas.
Cu + 4HNO3 -> Cu(NO3)2 + 2NO2T + 2H2O
With dilute nitric acid the decomposition of the nitric acid is less vigorous,
forming nitric oxide (NO) in the solution, which oxidizes as soon as it
comes in contact with the air.
3Cu + SHNOs
2NO + O2
3Cu(N08)2+2NOT + 4KUO
2NO,
482
CHEMISTRY FOR OUR TIMES
Notice that, in every case given of attack by an acid on copper, no
hydrogen is liberated. In this respect copper differs from the more active
metals, such as zinc, cadmium, and iron.
Uses of Copper. Copper shingles make a lasting and attrac-
tive roof. Ships sheathed with copper below the water line resist the
attack of barnacles and other marine creatures. Copper and sometimes
cuprous oxide are ingredients of many antifouling paints used on the
bottom of both wooden and steel
boats.
The chief use of copper is for
making wire and other electrical
equipment. Almost three-quarters
of the annual production of the
metal, over 2 million tons, is used
directly as the metal. A large
steamship requires immense
amounts of copper for condenser
tubes and other purposes. Over 3
million pounds of copper was used
in building the "Queen Mary."
The average automobile contains
about 45 Ib of copper, most of it
in the radiator. Electrified rail-
roads require great tonnages of
copper.
At home, copper is used for
roofing gutters, flashings, and
conductor pipes. Copper tubing
may be used for plumbing. In
other forms copper is used for
screening, lightning rods, heating coils, and hot- water storage tanks. These
are in addition to the electrical and hardware equipment of the home.
The famous Statue of Liberty (Liberty Enlightening the World),
located on Bedloe Island in New York harbor, is made of sheet copper
riveted together. (See Fig. 27-9.)
Copper Alloys. Brass, the most important alloy of copper, has
already been mentioned under the topic of zinc (see page 476). Bronze
contains copper and tin, sometimes with zinc added. It is used for statues,
ornamental work, hardware, and memorial tablets. Its permanence and
beauty are well known. Today all United States coins contain copper
in the alloy, silver coins having 10 per cent copper. Sixteen-carat (k)
gold is one-third copper, added for hardening.
FIG. 27-1.). This rare old photograph
shows the operation of putting the copper
garment on the Statue of Liberty.
THE DENSER METALS 483
Tests for Copper. The red color of copper is usually sufficiently dis-
tinctive to identify the metal. Sulfur tarnishes it black, and nitric acid
forms a blue solution of copper nitrate. Copper compounds form a deep-
blue solution when ammonia water is added in excess. The blue color is
that of the complex ion [Cu(NH3)4]++. When a nail is added to a solu-
tion of a copper compound, a red precipitate of copper is formed.
Cu ++ + Fe -» Fe++ + Cu
Copper in Printing. If we wish to prepare a picture for publication
in a book, a copperplate is made. The printing of class pictures in a class-
book, for example, is done from a copper half-tone. The metal is treated
on the surface with a photo-sensitive coating. After being exposed through
a half-tone screen and treated, it is etched with acid. The resulting high
and low spots, some taking ink and others not, are capable of printing
a picture.
The actual printing of a book such as this one is done from copper
electrotypes, or " electros'7 (see page 480). The type (see page 470), line
cuts (see page 476), and half-tones are assembled in a printer's form,
pressed into wax, the wax dusted with graphite (carbon), and electro-
plated with copper. The resulting copper shell, properly mounted, forms
the printing surface.
QUESTIONS
45. Write the symbols for these elements: copper; gold; silver; lead; tin;
antimony; mercury. From what language are the symbols derived? Account for
their common origin.
46. Cite references to the use of copper or brass in ancient classic or religious
writings, such as Caesar's Commentaries, Vergil's Aeneid, or the Bible.
47. What is the chief use of copper?
48. A beautiful, polished, green semiprecious stone is a copper ore. What is
its probable composition?
49. What treatment is given to copper suifide ore (a) in order to concentrate
it; (b) in order to remove the sulfur?
50. What is the percentage of copper in the following ores: (a) chalcopyrite,
2 per cent CuFeS2; (b) chaicocite, 1 per cent Cu2$?
51. Write formula equations for (a) action of zinc on copper sulfate solution;
(I)) union of copper with sulfur; (c) union of copper with phosphorus; (d) action
of cuprous oxide and hydrochloric acid.
52. What fact about copper probably gave rise to the legend that copper could
be tempered?
484 CHEMISTRY FOR OUR TIMES
63. Write the formula equations for the action of copper oxide (CuO) on (a)
dilute nitric acid; (6) dilute sulfuric acid; (c) concentrated sulfuric acid; (d) dilute
hydrochloric acid.
54. Write equations for the action of copper, if any, on the acids mentioned
in the previous question.
55. What properties of copper make it a suitable material for shingles? State
a disadvantage of copper shingles.
56. Compare copper-tubing plumbing with threaded and jointed iron piping
in a home in respect to (a) convenience in installation; (6) cost of material; (c)
resistance to corrosion.
57. What weight of copper is needed to make 200 class rings, weighing
•L grams each |12-carat gold?
58. (a) How can metallic copper be identified? (6) How can copper ions in
solution be identified?
69. For what purpose is copper used in each of the following industries:
(a) fishing; (b) plumbing; (c) printing; (d) electroplating; (e) furniture making;
(/) farming: (g) automobile making?
60. (a) Why should copper kitchen utensils be kept bright? (6) Why are cop-
per utensils sometimes tin-lined?
61. A common method to prepare steel for marking is to wash it over with
copper sulfate solution. What change is thus made on the steel so that it shows
scratches readily? Write an equation in ionic form for the reaction.
{/»o />
05 4 grams of copper is dis-
solved in dilute nitric acid?
Nickel
Nickel Ores. About 90 per cent of the world's nickel comes from Sud-
bury, Ontario, Canada. The sulfide ore found there contains copper, iron,
and cobalt in addition to nickel and may be made directly into the Ni-Cu
alloy, Monel metal. Some nickel is found in New Caledonia. The United
States produces very little.
Nickel is obtained from its ore by a complicated process. It is roasted,
treated in a converter that resembles a Bessemer converter, freed of
copper, purified by use of carbon monoxide in the Mond propess, and
finally refined by electrolysis.
Properties of Nickel. Refined nickel is sometimes 99.95 per cent
pure. It is a silvery-white metal. Its density, 8.9 g per ml, is a little more
than that of iron. It melts at 1450°C. Nickel is malleable, ductile, and
somewhat magnetic. Its tensile strength is about 70,000 Ib per sq in.
THE DENSER METALS
485
All Other
17%
Brass Mills
6%
Iron Foundries -
6%
Electroplaters
Supplies
8%
Steel Mills
63%
Courtesy of Dun & Bradstreet, Inc.
27-10. — Character of normal nickel
consumption.
Nickel rusts very slowly. It is less active than iron. It liberates hydro-
gen from dilute acids very slowly and resists the attack of hot alkaline
solutions. Nitric acid dissolves nickel, forming nickel nitrate. Carbon
monoxide combines directly with the metal, forming nickel carbonyl
[Ni(CO)J.
Uses of Nickel. About two-thirds of all the nickel produced is used
with steel in nickel-steel alloys. In Nickel
general, the addition of nickel to
steel improves many of the desir-
able qualities of the steel, includ-
ing tensile strength. The SAE
handbook recommends nickel
steel 2345 (3 per cent Ni) for
structural purposes where great
strength is desired, as for pro-
peller or axle shafts. Nickel is
used extensively as an electroplate FlG-
over plumbing fixtures and on
automobiles, bicycles, and small machine parts, for it combines resistance
to corrosion with pleasing appearance.
Nickel Alloys. Monel metal, a trade-marked alloy, contains 60 to
72 per cent nickel with copper and some iron and manganese. It is used
for covering table tops and cabinets in dining cars and large kitchens
and for many purposes that require a noncorrosive, nonpoisonous, shiny
metal for food-handling equipment. Monel metal has a slightly red color,
from the copper in it.
Invar (63.8 per cent Fe, 36 per cent Ni, 0.2 per cent C) is an alloy
that changes size very little with changes in temperature. It is used for
precision instruments, measuring tapes, airplane-engine parts, and pen-
dulum rods. The seal-in wire in electric light bulbs is an alloy of this
type. It has a core of 45 per cent nickel and 55 per cent iron covered with
a copper sheath that comprises one-fifth the volume of the entire wire.
It has the same expansion characteristics as glass to which it adheres
in a vacuum-tight seal. The entire lighting industry depends on the use
of this alloy.
The wire in an electric toaster, flatiron, or similar heating device
gets red-hot but does not burn or corrode readily in the air. This wire
is frequently made of nichrome, an alloy of 75 per cent nickel, 11 per cent
chromium, 12 per cent iron, and 2 per cent manganese.
Permalloy, 80 per cent nickel with 20 per cent iron, shows great
magnetic permeability when small electric currents are near it. It is used
in magnetic apparatus, telephone cables, and other electrical equipment.
486 CHEMISTRY FOR OUR TIMES
Nickel-silver, formerly called German silver, has copper 57 per cent,
zinc 19 per cent, and nickel 24 per cent. This alloy is bright, shiny,
weather resistant, and hard. It is the base metal for silver-plated
tableware.
A nickel coin is a sort of Monel metal. It contains only one-fourth
nickel; the rest is copper.
Wartime Coinage. The composition of United States coins was
affected by wartime conditions in the metal market. "Nickels,'1 formerly
75 per cent copper and 25 per cent nickel, were changed to 56 per cent
copper, 35 per cent silver, and 9 per cent manganese. These alloys have
almost identical colors.
Wartime pennies were of zinc-coated steel. Other pennies are a bronze
that contains 2.5 per cent tin and 2.5 per cent zinc with copper. Silver
coinage contains 10 per cent copper as formerly.
Powder Metallurgy. A technique of forming useful shapes from
high-melting or very hard metals has become important recently. The
metal is prepared as an extremely fine powder by reduction of oxides or
by spraying. Then it is packed into a mold under pressure and brought
to the sintering1 point, thereupon taking the form of the mold. Some
pieces are allowed to remain very porous. They absorb oil and serve as
"oilless" bearings, as they require no further oiling.
Many laboratories use powerful Alnico magnets. These are made
from a mixture of the powders of iron, aluminum, nickel, and cobalt
molded into shape by powder metallurgy technique. This method permits
us (1) to produce alloys otherwise impossible to make, (2) to mold intri-
cate shapes cheaply, and (3) to fabricate high-melting tungsten, tantalum,
and molybdenum that cannot be melted and cast.
SUMMARY
Lead has been known and used since ancient times. It is found chiefly in the
ore galena (PbS). The ore is roasted and blasted with air to remove sulfur, then
reduced with carbon.
The physical properties of lead are as follows: It is a dense, soft, silvery metal.
It can be melted readily.
Its chemical properties are as follows: It tarnishes quickly on the surface, but
slowly thereafter. It is not rapidly attacked by strong acids or alkalies, but it
is readily corroded by some weak acids and by concentrated nitric acid. Its com-
pounds are poisonous to the body. Lead forms oxides when heated in air.
Minium, or red lead (Pb8O4), forms below 585°C.
Litharge (PbO) forms above 585°C.
1 Sintering is a process by which some materials are brought to a coherent mass by
heating, but not by completely melting.
THE DENSER METALS 487
Lead dioxide (Pb02) forms when nitric acid is used with lead.
Lead is used for lining chemical apparatus, for making weather-resisting
sheathing, for storage batteries, and for sinkers. It is also used in alloys, including
solder (with Sn), shot (with As), and type metal (with Sb). A lead compound,
tetraethyl lead, raises the octane number of gasoline. Many other compounds
are important.
Tin was also known to ancient peoples; it is found chiefly in the ore cas-
siterite (SnCh). The metal is easily prepared by reducing the oxide with carbon.
It is then refined by remelting and electrolysis.
The physical properties of tin are as follows: It has a soft, silvery, bright,
metallic luster and a relatively low melting point. It changes into a powdery form
at a low temperature.
Its chemical properties are as follows: It is attacked by strong acids but
resists corrosion by weak acids and the atmosphere. It protects iron well while
the coating is unbroken.
Tin is used for block tin pipes, collapsible tubes, and tin-foil wrappings. Tin
alloys include solder (with Pb), bronze (with Cu), and pewter (with Pb or Sb).
Zinc is also a metal known and used since ancient times, but it was some-
times confused with tin. The ores of zinc are zinc blende (ZnS), zincite (ZnO),
smithsonite (ZnCOa), and franklinite (ZnOFe203).
The metallurgy of zinc is relatively simple. (1) Roasting in air and reducing
with coal produce zinc from the sulfide or carbonate. (2) Leaching zinc oxide
with sulfuric acid produces zinc sulfate; the metal is obtained on the cathode by
electrolysis of solution of zinc sulfate. (3) Zinc is refined by electrolysis or by
distillation in a vapor of natural gas.
The physical properties of zinc are as follows: It is bluish gray; it has a metallic
luster; its melting point is 419.4°C; it is malleable between 200 and 300°C; its
density is about the same as that of iron.
Its chemical properties are as follows: It corrodes slowly in air, forming a
gray tarnish. It is a fairly active metal. It burns in air and is attacked readily
by acids. It dissolves slowly in strong alkalies.
Zinc is used as the cathode in dry cells; for galvanizing steel; as sheet metal
for protective coverings; for recovering other metals; for making jar tops; for
making alloys, especially brass (with Cu).
Cadmium occurs in ores with zinc and is similar to it chemically. It has a
lower melting point than zinc and is less active chemically. It is used in the form
of electroplated coating and for making low-melting alloys.
Copper has been known and used extensively since before the dawn of written
history. It is found both free and combined, as oxides and sulfides chiefly.
The metallurgy of copper is complicated. Copper ores are usually concen-
trated by froth flotation. Roasting removes part of the sulfur. Iron is removed
as slag in a reverberatory furnace, forming matte. Matte is converted in a blast
furnace to blister copper. Blister copper is refined by electrolysis. Leaching and
replacement methods are also used with some ores.
The physical properties of copper are as follows: It is a pink-colored metal,
soft, ductile, and malleable, that hardens when cold-worked. It is an excellent
conductor of heat and electricity.
488 CHEMISTRY FOR OUR TIMES
Its chemical properties are as follows: It corrodes in air very slowly. It joins
sulfur and chlorine directly. It is attacked by concentrated sulfuric acid and by
nitric acid. It does not replace hydrogen from nonoxidizing acids.
Copper is used extensively as an electrical conductor; for making pipes;
for weather-resisting parts of houses; and for making electrotypes and half tones
in printing. Copper alloys include brass (with Zn) and bronze (with Sn). Copper
is alloyed with gold and silver to harden those metals. Compounds of copper
are used extensively as fungicides.
Nickel occurs chiefly as suifide ores in the Sudbury region, Canada. In its
metallurgy, nickel is freed of sulfur, purified by use of carbon monoxide, and
refined by electrolysis.
Nickel is a silver white metal, strong, ductile, and malleable. It corrodes very
slowly and is attacked by nitric acid and by carbon monoxide.
Nickel is used as an electroplating metal for covering other metals with
bright, wear- and tarnish-resisting surfaces. Alloys of nickel with steel are used
for many purposes; a popular alloy of nickel and copper is Monel metal. Other
alloys include nichrome (with Cr), permalloy (with Fe), nickel silver (with Cu and
Zn), and stainless steel (with Cr and Fe).
QUESTIONS
63. What is the chief source of nickel?
64. What is the chief use of nickel?
66. What is the composition of steel No. 2345?
66. What properties make Monel metal a popular covering for shelves in
large kitchens?
67. How does the junkman aid in conserving natural resources?
68. Investigate the uses to which Alnico magnets are put.
69. For what purposes were the composition of nickels and composition of
pennies altered during World War II? What specific requirements had to be met
by the replacement alloys selected?
70. What chemical industry depends upon the catalytic properties of finely
divided nickel?
MORE CHALLENGING PROBLEMS AND QUESTIONS
71. A copper coin liberated | ' liters of sulfur dioxide under standard con-
15.60
ditions when it was dissolved in concentrated sulfuric acid. What weight of copper
was in the coin?
72. A 2-gram sample of brass precipitates < ' grams of copper suifide (CuS)
after it has been dissolved and the solution saturated with hydrogen suifide.
What is the percentage composition of the brass?
THE DENSER METALS 489
73. What is the difference between hard solder, soft solder, and silver solder?
What is the composition of electric fuse wire?
74. (a) Lye is dissolved in water and placed in (1) a galvanized iron pail; (2) a
tin can; (3) an aluminum pan. Write equations for any reactions that may take
place. (6) If the lye solution stays in a metal vessel exposed to air, what change in
composition takes place? Write the equation for the reaction, (c) Does this change
affect the usefulness of the lye in neutralizing acids? Write equations to show the
effect of hydrochloric acid on the lye both before and after the lye has been stand-
ing exposed to air.
UNIT SIX CHAPTER XXVIII
CORROSION— HARMFUL OR
HELPFUL
When men produce iron by placing iron ore in a blast furnace and
heating it with coke and limestone, they are reversing a process of nature.
Iron is an active metal that rusts easily. Most iron found in nature occurs
as iron oxide. The blast-furnace process reduces, or deoxidizes, the iron
ore. Consequently unprotected iron, attacked by water, oxygen, and
carbon dioxide together in the air, tends to produce iron ore again.
The rusting of iron articles represents an enormous waste of the energy
used in their production, as well as a loss of the articles themselves.
Everyone agrees that such waste should be avoided. As a result, increas-
ing attention is being given today to the cause and prevention of rusting,
or corrosion.
Another way to consider the matter is to say that iron is at the top
of a hill and iron ore is at the bottom. Iron can roll toward the bottom
of the hill, becoming iron ore, and do work on the way. But to get iron
up to the top of the hill (from iron ore to iron) requires the heat from
fiercely burning coke. At the top, the level of potential energy is high,
and work must therefore be done to reach that position. In going down,
the changing of iron to iron oxide is accomplished by a change of chemical
energy to heat : indeed, the rusting of iron is accomplished by the evolu-
tion of measurable quantities of heat.
We shall now consider (1) the reasons why metals, chiefly iron, cor-
rode; and (2) how to stop rusting or, better, how to prevent rusting from
starting.
Iron Rusting. Experiments show that under water all forms of iron-
cast, wrought, and steel — rust at the same rate. In air, under identical
conditions, steel rusts fastest of the three; cast iron and wrought iron
rust much more slowly.
New Terms
corrosion reduction vehicle
passive iron electron transfer white lead
oxidation depolarizer
491
492
CHEMISTRY FOR OUR TIMES
Experiments also show that, unless moisture and oxygen both are
present, the rusting of iron in air is very slow. The presence of sulfur
dioxide hastens the process. The end compound formed by ordinary
rusting of iron is hydrated ferric oxide (Fe2O3'3H20) or ferric hydroxide
[Fe(OH)3
To Stack
To Tank
Sensitive
Electrical Meter
S Pi<*
Iron
Fe~
- - Weak
-" Acid
Copper
Cu
IN PRACTICAL LIFE IN LABORATORY
FIG, 28-1. — When iron and copper are connected in contact with slightly corroding
liquid, the iron soon becomes pitted with corrosion.
Two-metal Corrosion. A heating coil made of copper is connected
to a water-supply system that uses iron pipes. (See Fig. 28-1.) After a
relatively short while in service, a
leak is noticed at the joint between
the copper and iron pipes. Examina-
tion of the leak shows that the iron
pipe is badly corroded, or " eaten
away."
The explanation of this corrosion
is that, when two unlike metals are
in contact with each other in the
presence of even very dilute salt solu-
tions, the more active metal is at-
tacked to a slight degree. The active
metal in this case is iron. A little
electric cell is set up. (See Fig. 28-2.)
Iron is the cathode, or fuel, for the
cell. Copper is the anode and is un-
corroded. Impure water is the weak
electrolyte. Any hydrogen that tends
Zn— >
•*— Cu
e
===
^
e
i
:
=~=-:=
ZnS04
CuS04
— .
e
•4-
e
**•
e
e
CuVCu"
e
„
e
e
e
ZnS04
CuS04
Courtesy of Journal of Chemical Education
FIG. 28-2. — The mechanism of cell
action. Notice that electrons leave the
less active metal (Zn) and that this
metal goes into solution as ions (Zn++).
to accumulate and to stop the electrochemical action is oxidized to water
by the oxygen dissolved in the water. Thus the iron pipe rusts.
CORROSION-HARMFUL OR HELPFUL 493
This sort of corrosion may be expected where any two unlike metals
are in contact with the same corroding liquid. Salt water acts faster than
fresh water as a corroding liquid. Consequently, ship's fittings are readily
subject to two-metal corrosion wherever ttfro-metal joints have been
used in their equipment.
An experimental study of common industrial metals and alloys
exposed to common water, salt water, weak acids, and weak alkalies has
been made. An activity list based on these experiments is given below.
The most active materials come first. Those grouped together have little
action on each other. Obviously, the further separated in the list, the
more rapid the corrosion of the upper one of a pair of metals is expected
to be.
ELECTROCHEMICAL SERIES OF THE IMPORTANT
INDUSTRIAL METALS*
— Easily corroded
Magnesium, aluminum, duralumin
Zinc, cadmium
Iron, chrome-iron (active), chrome-nickel-iron (active)
Solder, tin, lead
Nickel, braSvS, nickel-copper, copper
Chrome-nickel-iron (passive), chrome-iron (passive)
Silver solder
Silver, platinum, gold
4- Slowly corroded
* McKAY, R. J. and R. WORTHINGTON, Corrosion Resistance of Metals and Alloys, Rcinhold Publish-
ing Corporation, New York, 1937.
Acid Corrosion. We have learned that aluminum, magnesium, zinc,
iron, and lead are easily attacked by dilute acids, forming hydrogen. For
example, in terms of ions,
Fe + 2H+ -+ Fe++ + H2|
This action is greatly hastened if oxygen is present to change the
hydrogen into water as fast as it forms. The oxygen in this case is called
a depolarizer, for an accumulation of hydrogen on the metal tends to
stop the action of the acid.
In general, the rate of corrosion of iron becomes rapid if the acidity
(see page 225) of the corroding liquid is as high as pH 4 and if a good
supply of oxygen is on hand to act as a depolarizer. If the supply of
oxygen is low, the evolution of hydrogen starts at pH 5, but the rate of
corrosion is very much slower than when oxygen is abundant. Thus we
see that the amount of dissolved oxygen is an important factor in deter-
mining the rate of corrosion of iron in very dilute acids.
Concentration Effects. Assume that the same piece of iron is in
contact with impure ordinary water. (See Fig. 28-3.) At one region the
water has plenty of dissolved oxygen, but at another region for some
494
CHEMISTRY FOR OUR TIMES
reason the water lacks dissolved oxygen. This difference in concentration
of dissolved oxygen is cause enough for corrosion to take place. The area
at which the oxygen is lacking becomes the anode (+) in a tiny elec-
trolytic cell. The aerated iron becomes the cathode ( — ). The rust formed
is porous and rich in available dissolved oxygen, and therefore deep
pitting is produced. Many iron pipes that corrode in soil or cinders are
attacked because an oxygen concentration cell forms.
Oxygen-
absorbing"
Agent
Much
Corrosion
Little
Corrosion
sMuch
Dissolved
Oxygen
FIG. 28-3. — An oxygen concentration cell. The two electrodes differ in the amount
of dissolved oxygen in the electrolyte at each.
_ Sensitive
Electric Meter
Dilute
Salt Water-
Solution
U-Shaped Glass
Tube Containing
Salt Water
Concentrated
Salt Water
Solution
Slower Rusting More Rusting Here
FIG. 28-4. — An electric cell may be set up when identical electrodes are used — one is
placed in a solution, the other in a similar solution, differing only in concentration.
Another possible cause of corrosion can be seen from an experiment. Two
iron nails are placed in separate beakers. One contains a dilute salt solution, the
other a concentrated salt solution. The beakers are connected by an inverted
U-shaped tube of salt water that serves as a bridge or liquid connection between
the beakers. The two nails are connected by iron wires to a sensitive electrical
meter. (See Fig. 28-4.) A slight movement of the meter needle shows that a cur-
rent is flowing, or that more electrons are being liberated on one nail than on the
other. The nail in the concentrated salt solution corrodes faster.
Electrolysis. The earth is a storehouse of electrons. Feeble stray
electric currents from numerous sources are continually surging under
and on the surface of the earth.
CORROSION-HARMFUL OR HELPFUL 495
Let us assume that a long pipe line is buried in the earth. At one damp
spot many stray earth electrons come to it. The iron of the pipe carries
these electrons in the pipe through a length of dry nonconducting soil.
At the next wet spot the electrons leave the pipe. At this spot the pipe
is the anode of an electroplating cell, or the electrode that is eaten away.
Serious corrosion may result where the electrons leave the pipe. (See
Fig. 28-5.)
c
^ Anode (+) Cathode (-) '
FIG. 28-5. — Stray-current corrosion. Where does the underground pipe corrode?
Other Causes of Corrosion. When alloys are made hurriedly, they
are sometimes not uniform in composition. This may be true of Bessemer
steel in which the added manganese has not had time to distribute itself
evenly. Irregularity in composition causes the steel to corrode more
readily. Duralumin corrodes more readily than aluminum alone, possibly
owing to irregularities in its composition. Lack of uniform composition
is equivalent to a two-metal cell.
Metals under stress corrode more readily than those without any
force acting on them. This is especially true of metals that have been
cold-worked. A small crack in a tightly fastened nut becomes a serious
failure if the atmosphere is moist and somewhat corroding. The effect
is something like crumbling the keystone in an arch.
Sometimes lubricants may cause corrosion. If the oils present break
down into fatty acids (see page 560) or if petroleum oils are improperly
refined so that acid remains in them, these acids may attack metals,
especially lead (see page 469.)
Prevention of Corrosion. 1. The obvious method of stopping corro-
sion is to protect the metal. Painting is used extensively for this purpose.
The linseed- or tung-oil " vehicle " of the paint carries a pigment, or
"body," to aid in its covering power. When oxidized, or " dried," the
496
CHEMISTRY FOR OUR TIMES
oil forms a horny impervious coating over the metal, effective as long as
it is unbroken.
2. Electroplating (see page 240) iron with other metals less active
chemically has been discussed. Nickel, cadmium, chromium, silver, and
even brass are among the metals applied by electroplating.
Courtesy of Armour Research Foundation
FIG 28-6. — Chemist L. E. Anderson demonstrates corrosion-testing apparatus that was
designed at a research chemical laboratory.
3. Mechanically applied metal coatings are also used. A cleaned base
metal may be dipped in molten protective metal, or the protective metal
may be warmed and rolled onto sheet iron or aluminum. Gold-filled
jewelry has merely a gold coating. Tin, lead, and zinc are used for rolling
onto steel, forming a sandwich of the steel between two waferlike sheets
of protecting metal.
4. Enamels or porcelain surfaces applied to iron are well known.
Kitchen utensils of enamelware have a baked, glasslike coating.
5. Another way to avoid corrosion is to make a corrosion-resisting
alloy of the iron. Even 0.2 per cent of copper in steel increases its corrosion
resistance greatly. Stainless steels, which must contain 12 per cent of
chromium or more (see page 443), are known to all. The common type
of stainless steel contains 18 per cent chromium and 8 per cent nickel.
CORROSION— HARMFUL OR HELPFUL
497
Surface-treating Steel. Ordinary brown rust is porous and flaky.
It does not protect the iron beneath. In fact, rust adsorbs acidic gases
and moisture, hastening more cor-
rosion. If the surface of steel
could be treated so that a tough
inactive oxide coating was formed,
then ordinary rust could not gain
a foothold.
Several metals furnish exam-
ples of self-protection by tough
oxide films. Aluminum is protected
by a tough layer of aluminum ox-
ide (A1203); and magnesium, al-
loyed with about 5 per cent
of other metals, resists weather
well and corrodes no faster than
aluminum.
When hot iron acts on steam,
a protective film (FeaC^) is
formed.
3Fe + 4H2O
Fe3O4
Courtesy of Aluminum Company of Americu,
FIG., 28-7. — A strong aluminum-alloy
mast reduces dead weight on the sailing
Dipping steel into hot phos- yacht "Rainbow." Aluminum alloys are
phoric acid (H3PO4) also produces available that resist salt-water spray
j • • •• ,• corrosion.
a good corrosion-resisting coating.
This treatment is often given to steel that is to be sprayed with lacquer
or enamel. The coating bonds well with modern steel finishes, such as those
applied to automobile bodies and
household machines.
Tacks, razor blades, and small
firearms are sometimes blued. This
corrosion-resisting finish is applied
by heating the metal with bone
black.
Passive Iron, When iron is
immersed in concentrated nitric
acid, it is made unreactive, or
passive. That is, the iron no longer
acts chemically like ordinary iron
but is attacked much less by
common chemicals, resembling
lead chemically more than iron. Passive iron will not replace copper
from copper sulfate solution. Chlorides destroy the passive state, and
Courtesy of D. W. Haering & Company, Inc.
' FIG. 28-8. — This scale deposit was found
in a 12-in. steam line 400 ft. from the boilers
in a 29-story building. Corrosion can take
place on both sides of a metal pipe.
498 CHEMISTRY FOR OUR TIMES
the chromate ion (CrO7~) preserves the passive condition. Investi-
gators claim that razor blades become dull because of a slight rusting
on the cutting edges. A blade kept between shaves in a solution of sodium
chromate (Na2CrO4) will keep its cutting edge for a long time, for the
passive condition of the steel prevents rusting.
Strangely enough, if the oxygen concentration of a solution that
normally corrodes iron is kept high, the passive condition is preserved —
just the reverse of ordinary corrosion.
In stainless steels containing over 12 per cent chromium, the iron is in
the passive state. The steels remain stainless just as long as the iron
remains in the passive condition. When the oxygen supply is low in a
corroding liquid, stainless steels rust. Pitting occurs because the active
form and the passive form of the same metal act as if they were two
different metals (see table, page 493).
QUESTIONS
1. Bicycle handle bars are usually made of steel plated with nickel. Many
water pails are made from sheet steel and galvanized by dipping them into molten
zinc. Explain how each coating protects the steel.
2. Give an example of an article that has lost its usefulness owing to cor-
rosion.
3. Which of the two metals in contact corrodes the more rapidly in each of
the following examples: (a) On a seagoing boat a phosphor-bronze propeller shaft
has a steel guide. (6) An iron water pipe is connected directly to a copper water
tank, (c) Aluminum and silver (in contact) are heated in a weakly alkaline
solution for the purpose of cleaning tarnish from the silver, (d) Carbon and zinc
are in contact with ammonium chloride in a dry cell, (e) Sulfuric acid from a
storage battery sprays on both steel and copper. (/) A dentist using a steel instru-
ment touches a silver rilling in a tooth that is moist with saliva.
4. Point out how the nature of the surface corrosion of iron differs from that
of aluminum.
6. Why must steel be perfectly clean before an enamel coating is applied
to it?
6. Point out the effect of high content of dissolved oxygen on the rate of
corrosion of ordinary iron as compared with the rate of corrosion of stainless
steel otherwise under the same conditions.
7. What is one important reason for razor blades becoming dull while stand-
ing? How may they be kept sharp?
8. A successful antifreeze liquid must not corrode three materials. Name
them.
9. An airplane made of magnesium-aluminum alloys makes a crash landing
CORROSION-HARMFUL OR HELPFUL
499
in a swamp that contains slightly acid water. If the airplane cannot be removed
for several days, what damage does the metal undergo?
10. If an organic (carbon compound) antifreeze liquid is used in an auto-
mobile radiator, sodium chromate must not be used for an antirusting agent.
Explain.
11. Why is calcium chloride considered to be an unsatisfactory antifreeze
material?
Helpful Corrosion. Owing to improvements in modern metallurgy,
many metals can be made almost 100 per cent pure. They are suitable
and often economical starting materials for making compounds (salts)
of the metals.
Copper, burned in chlorine, effectively corrodes and produces copper
chloride of high purity.
Cu + CI2 -» CuCl2
Tin on scrap tin plate (tin coated on iron) is recovered in the form
of the compound stannic chloride (SnCl4) by treating the metal at fairly
low temperatures with chlorine.
Sn + 2CI2 -4 SnCU
This process is controlled in such a manner that very little of the iron
is attacked.
About one-fourth of all the lead produced is deliberately corroded in
the manufacture of white lead [approxi- _
mate formula Pb(OH)2-2(PbCO8)], or
basic lead carbonate, the most impor-
tant white pigment in paints. The
Dutch process of making white lead
uses earthenware crocks (see Fig. 28-9)
that have a reservoir in the bottom
containing 500 ml of 28 per cent acetic
acid (H«C2H302). Perforated lead disks,
called buckles, are piled on shoulders
in the crocks. The perforations in the
disks are so arranged that the circula-
tion of acetic acid fumes, moisture, and
carbon dioxide cannot be shut off. The
crocks fill a room in layers. Ferment-
ing tanbark from a leather tannery is
strewed between each layer. With this
~ " — Fermenting Tan-bark
- Perforated
— Lead
— Discs
•or Buckles
$v Acetic Acid -"-
FIG. 28-9. — When lead is cor-
roded in a warm, moist atmosphere
containing carbon dioxide, white
lead forms. White lead is used in
many types of paints.
combination of carbonic and acetic acids in the warmth from the fermen-
tation, the lead corrodes to form a white powder, the basis of much of
the outside white house paint used today.
500
CHEMISTRY FOR OUR TIMES
F" ' '!- \^ ;;,, >V '! |f ,f bv',\ jW^nt'rtwtesi W*h
,
^-^:v7^;.'i|
; ; .'flwiitad^Mbes^e^;1 ..A
i iijj^withfiWuH.H1;^
anrf ifee wafer wwirraWt1 ' \ ' I
wilh CNo'rt ®t*c09atp. |" "1
f^ege steel tubw aresWl j
^jewtw^^rwyw*,11.?
Courtesy of D. W. Haering & Company, Inc.
FIG. 28-10. — The effect of the use of a chemical inhibitor in preventing corrosion is
clearly shown in this display.
CORROSION — HARMFUL OR HELPFUL 501
Thus we see that corrosion is helpful in two cases,
1. When it forms a protective coating over the metal
2. When useful compounds of the metals are formed.
An Ounce of Prevention. Further examples of how to prevent corro-
sion are interesting.
The water in the cooling system of an automobile flows from the
bronze radiator to the iron water jacket of the motor. In the summer,
corrosion may be prevented by Adding 1 oz of sodium or potassium
chromate (K2CrO4) to the water. This renders the iron passive. Borax
(Na2B4O7) and trisodium phosphate (Na8P04) also work well for the
same purpose, but not for the same reason; they render the solution
alkaline, which reduces the rate of corrosion.
Antifreeze preparations also contain an inhibitor to prevent corrosion
in the cooling system. In this case the inhibitor must be soluble in the
antifreeze fluid. Organic compounds, such as sodium chrome glucosate,
ethanol amine, and quinoline ethiodide, are used.
To remove rust from a file, dip it in 6JV1 hydrochloric acid (dilute
HC1 of the laboratory) to which aniline (C6H6NH2) has been added. The
rust dissolves but not the steel, for the aniline acts as an inhibitor. The
use of such a preparation to clean out rusty plumbing or to clean steel
before electroplating is suggested.
Corrosion in steam boilers is prevented £y suitable water treatment.
Salt-water corrosion of magnesium alloys used in the construction of
certain seaplanes is prevented by a selenium coating. Pure aluminum
coated on aluminum alloys has a similar effect.
Compounds of the Metals. Many useful compounds of 'the metals
are in everyday use. Everyone has heard of Epsom salts or hydrated mag-
nesium sulfate (MgSO4-7H20), blue vitriol or hydrated copper sulfate
(CuSO4*5H20), and bichloride of mercury or corrosive sublimate (HgCl2).
Some of these compounds, especially salt (NaCl), are found in nature.
Others are made by treating the metal, metal oxide, hydroxide, or car-
bonate with the proper acid. For example, Epsom salts can be made by
treating magnesium carbonate (MgCOs) with sulfuric acid.
MgCO3 -f H2SO4 -4 MgSO4 -f H2CO8
The solution is filtered from the excess of magnesium carbonate that
should be used and the salt crystallized from the clear solution.
In making magnesium from sea water, magnesium hydroxide
[Mg(OH)2] is obtained by treating the sea water with a solution of slaked
1 See Appendix. 6N hydrochloric acid may be made by adding 516 ml of concen-
trated (36 per cent) hydrochloric acid to enough water to make 1 liter.
502
CHEMISTRY FOR OUR TIMES
lime [Ca(OH) J.
MgCI2 + Ca(OH)2 -4 Mg(OH)2| + CaCI2
in sea water slaked lime a precipitate left in solution
The less soluble magnesium hydroxide precipitates and is retained by a
filter cloth, removed, and treated with hydrochloric acid to convert it
to the chloride.
Mg(OH)2 + 2HCI -> MgCI2 + 2H2O
A solution of magnesium chloride free from the other metal ions originally
present in sea water results. This, when evaporated, dried, and fused,
is used in the electrolysis cell to obtain metallic magnesium.
Courtesy of Pennsylvania Salt Manufacturing Company
FIG. 28-11. — Deliberate corrosion produces useful compounds. Above, scrap iron
is lowered into hot hydrochloric acid as the first step in manufacturing ferric chloride.
The tank is lined with acid-resisting bricks.
The making of both soluble and insoluble metal salts has already been
discussed (see page 226). These general methods should be reviewed at
this point. A list of the more useful metal compounds together with their
common names, formulas, and uses is given for reference in the Appendix.
Oxidation-reduction. When iron rusts, a compound of iron is
formed. The action may be represented imperfectly by the equation
4F°e + 3O2 4- 6H2O ->> 2(Fe2O3-3H2O)
A similar corrosion is seen in the slower oxidation of zinc,
0
2Zn
O2 -4 2ZnO
CORROSION-HARMRUL OR HELPFUL 503
or the tarnish on household silverware,
2Ag + S -4 Ag2S.
An examination of the metal (or sulfur) in each of these examples of
corrosion shows that the element changes its combining number. A gain
in the combining number is evident. More accurately, a loss of electrons
has taken place. The oxygen or sulfur in these examples has gained elec-
trons and is reduced from 0° to 0 — . In fact, all examples of so-called
oxidation come under this classification. Oxygen is not necessary — merely
an increase in the combining number of the metal. The equations follow-
ing show more cases of oxidation and reduction. Let us examine with
care the change in the combining number of the various elements. We
also observe that as oxidation occurs other atoms are undergoing a
decrease in combining number. This process is called reduction.
o 4-4- o + J H2 -4 H (oxidation)
Hj + CuO -4 Cu + H2O I ^ o
V Cu -4 Cu (reduction)
1+4-4- 0
Fe -4 Fe (reduction)
+4- +4-4-4-
C -4 C (oxidation)
Just as borrowing and lending are two different aspects of the same
transaction, so oxidation and reduction are two aspects of the same
chemical process. We have just noticed that oxidation increases the
combining number of a metal. Reduction, on the other hand, means a
decrease in the combining number of a metal or nonmetal. More explicitly,
since oxidation is a loss of electrons, then reduction is a gain of electrons.
The whole process is oxidation-reduction.
In each of the following examples oxidation and reduction can be dis-
tinguished by noting the change in the combining number :
+±+ o f+f o (loss of 3e~ per atom of Al)
Fe2O3 + 2AI -4 AI2O8 + 2Fe (gain of 3e~ per atom of Fe)
+++ (, ++ (loss of 2e~ from each atom of metallic
2FeCl» + Fe -4 3FeCI2 iron)
(gain of le~ per atom of Fe in FeCl3)
In short, oxidation-reduction actions are simply those chemical actions
in which an electron transfer takes place. Balancing such equations
involves making the electron transfer balance.
SUMMARY
The corrosion of iron and other metals causes great economic loss. Under
water, all forms of iron rust at the same rate. In moist air, steel rusts faster than
504 CHEMISTRY FOR OUR TIMES
cast iron or wrought iron. Local conditions, such as the presence of mild acid,
may greatly hasten the rusting of iron. !
1. Corrosion takes place when two different metals are in contact in a corro-
sive liquid. The more active metal dissolves. An activity list of commercial metals
and alloys is available.
2. In acid corrosion, the extent of corrosion depends in a measure on the
amount of dissolved oxygen available. Dissolved oxygen acts as a depolarizer,
changing hydrogen to water.
3. In concentration corrosion, the differing concentrations of the same elec-
trolyte in contact with a metal cause corrosion at the area in contact with the
more concentrated part or parts.
4. In electrolysis, the stray electric currents set up electrochemical cells in
which the anode is corroded.
5. Less frequent causes of corrosion include lack of uniform composition of
alloys, presence of strains, and presence of acids developed by breakdown of
lubricants.
Corrosion is prevented by
1. Painting. A horny coating of oxidized oil containing pigments increases
wear and attractiveness.
2. Electroplating. A corrosion-resisting metal is deposited electrically over a
less resistant base.
3. Mechanically applied coatings. A surface coating of one metal is applied
on another. Examples are galvanized iron or tin plate.
4. Surfacing with enamel or porcelain. An enamel or porcelain glasslike sur-
face is melted onto metal.
5. Surface treating. Oxide films form naturally on aluminum. Other types
of films are formed by chemical treatment, as in the case of iron. Insoluble oxide
films resist further corrosion.
6. Passive metal. The passive condition of the metal is developed. In the
case of iron, the passive condition is preserved by the chromate ion and destroyed
by the chloride ion.
Corrosion may be helpful in the following respects:
1. Some surface corrosion protects the metal beneath from further attack.
Red-brown iron rust, however, is flaky and porous and does not act in this way.
Black magnetic iron oxide (FeaO^ protects iron, and aluminum oxide (AhOa) is
an effective covering agent for aluminum.
2. Preparation of certain compounds, notably white lead, is accomplished by
means of corroding the metal.
Compounds of metals may be formed as a result of corrosion. Many metallic
compounds are used extensively, such as common salt (NaCl), blue vitriol
(CuSO4'5H2O), and Epsom salts (MgSO4'7H2O) and some are the source of the
metal.
Oxidation-reduction reactions comprise a common type of chemical change.
They are electron-transfer reactions that involve a change in combining number
(valence). The element that is oxidized has a higher combining number due to
loss of electrons. The element that is reduced has a lower combining number
due to gain of electrons. Oxidation-reduction equations may be balanced con-
veniently by considering the electron transfer.
CORROSION— HARMFUL OR HELPFUL 505
QUESTIONS
12. Point out two examples of useful corrosion.
13. The addition of either potassium chromate or trisodium phosphate solu-
tion to the cooling water of an automobile radiator retards the rate of rusting.
Explain the action of each.
14. Show by formula equations how to make (a) copper chloride (CuCl2) in
five different ways; (6) copper nitrate in five different ways.
15. Define oxidation-reduction in terms of (a) combining-number change;
(6) electron transfer.
16. Show that the burning of carbon is an oxidation-reduction process.
17. Illustrate oxidation-reduction by showing combining-number changes in
each of the following equations (do not write in this book):
(a) ZnO + C -» Zn -f CO T
(6) SnO2 -f C ~> Sn -f CO2 T
(c) 2FeCI2 + CI2 -4 2FeCI8
(d) CO2 -f C -* 2CO
(e) SnCI2 + 2HgCI2 -4 SnCU + Hg2CI2i
18. When metals corrode, do they gain or lose weight?
19. Describe the Dutch process for corroding lead, using a labeled diagram.
UNIT
SEVEN
THE CHEMISTRY OF CARBON
COMPOUNDS
L)GS are made into pulp, and pulp is made into paper. The process
is both mechanical and chemical The number of uses for paper
is increasing, and more and more varieties of paper are coming into
daily use.
Logs are piled along a river (1), where they await the spring
thaw for transportation to the pulp mill. Log jams are broken up
by blasting with dynamite.
In the pulp mill (2), logs are barked and prepared to be cut
into chips. When wood chips' are cooked with chemicals in the
digester (3), pulp is produced. The lignin, or natural binder in the
wood, is destroyed, and a mass of fibers remains. This wood pulp
is carried through the bleacher (4) with a huge volume of water.
The beaters, tublike machines (5), are used to prepare a uniform
suspension of pulp in water. The portable platforms are loaded
with sheets of pulp.
The Fourdrinier papermaking machine is over 200 ft long. It
converts a uniform soup of pulp and water into a continuous sheet
of paper. On the left of (6) is shown a portion of the drier rolls.
Finished paper is counted, inspected, and packed (7) for shipment.
Courtesy of Hammermill Paper Company
UNIT SEVEN CHAPTER XXIX
THE NATURE OF CARBON
COMPOUNDS
A story is told about an organic chemist who, having a headache,
sought relief at a drugstore. He explained his need to the clerk in this
manner: "I'd like to buy some tablets of acetylsalicylic acid."
"Oh," replied the clerk, "you mean aspirin."
"That's it," responded the chemist. "I can never remember that
name."
One reason why chemists give such strange, long names to organic
compounds is because there are so many of them. The organic compounds,
compounds of carbon, almost half a million in all, are ten times as num-
erous as the inorganic compounds, that is, compounds of all the rest of
the 95 chemical elements. This great number, however, should not
discourage the beginner. Learning about a few organic compounds will
serve to give a general view of the entire field, for it is possible to classify
organic compounds into groups, thus simplifying study.
As the term implies, organic compounds were once considered to be
produced only through mysterious forces by living organisms. This view
is not held today, for many organic compounds are made in laboratories
without the use of materials directly connected with living creatures or
plants. Organic chemistry is the study of compounds of carbon with
hydrogen, nitrogen, sulfur, phosphorus, oxygen, the halogens, and rela-
tively few other elements.
Comparison of Organic and Inorganic Compounds. 1. Like-
nesses. All previously learned laws describe the behavior of both organic
and inorganic compounds. The law of conservation of matter (see page
29), Gay-Lussac's law of volumes (see page 140), and Dalton's law of
multiple proportions (see page 143) all hold true in both fields. Heat
New Terms
organic wood alcohol denatured alcohol
inorganic grain alcohol structural formula
unsaturated enzyme double bond
carboxyl group diastase
509
510 CHEMISTRY FOR OUR TIMES
speeds up the rate of reaction, and the effect of a catalyst is the same
where both types of compounds are involved. Valence (combining-
number) rules hold for both, but fewer ionic compounds are encountered
among the organic group.
2. Differences. 1. All organic compounds have carbon as a con-
stituent. Examples are sugar (C^H^On) and alcohol (C2H6OH).
Aside from carbon dioxide, carbon monoxide, and carbonates very
few compounds that contain carbon are classified as inorganic.
2. In organic compounds, carbon shows a tendency to form long
chains of atoms. Other elements do not show this property to any
great extent.
3. We are aware that sodium hydroxide (NaOH) is a polar, saltlike
solid compound which when melted or in solution conducts electricity
well (see page 245). We explain this by saying that the compound is
made of ions which dissociate easily and that its chief valence bond is
of the ionic or electrovalent type; that is, an electron has actually been
transferred from the sodium atom to the hydroxyl group (OH~)..
Alcohol (C2H6OH), on the other hand, is a volatile, mobile liquid, a
carbon compound containing the hydroxyl group ( — OH) that does not
conduct electricity. We explain this by saying that the compound is not
made of ions ; and neither alone nor in water solution does it dissociate to
produce conducting solutions. The hydroxyl group is attached to one of
the carbons of the ethyl group (C2H5 — ) by means of a shared pair of
electrons, a covalent bond (see page 191).
4. Chemical reactions in inorganic chemistry, when ionic, are fre-
quently rapid. In organic chemistry hours and sometimes days are re-
quired for the completion of a given chemical process. Organic reactions
frequently go in steps or stages. Only a very few of them are rapid.
5. A great number of inorganic compounds like salt (NaCl) dissolve
in water. Very few organic compounds dissolve well in water. Compounds
like sugar (C^H^On), alcohol, and glycerol are exceptions. Organic
compounds do dissolve readily in organic solvents, such as benzene
(CeHe), ether [(C2Hs)20], and acetone [(CH,)2CO].
6. The structure (arrangement of atoms in the molecule) of most
organic compounds is well established, but the structure of inorganic
compounds is more difficult to determine. Up to the present, relatively
few have been completely worked out.
Series of Compounds. Let us consider hydrocarbons. These are com-
pounds of carbon and hydrogen only. The simplest is methane (CH4).
In this*formula carbon has valence 4 and hydrogen 1. The next two
members of the methane series of compounds are ethane (C2H6) and
propane (CaH8); many others in the series are known (see page 535).
THE NATURE OF CARBON COMPOUNDS 511
Hydrocarbon
Derived radical
Molecular formula
Structural formula
Formula
Structural formula
H
H
i
i
CH4
H-C- H
CH,-
H-C-
i
i
methane
H
methyl radical
H
H H
H H
C2Hf, or
i i
C2H6- or
i i
CH3-CH3
H-C-C- H
CH3-CH2-
H-C- C-
i i
i i
ethane
H H
ethyl radical
H H
H H H
H H H
C3H8 or
i i i
C3H7- or
i i i
CH3 - CH2 - GH3
H- C- C-C- H
GH3 - CH2 - CH2 —
H-C-C-C-
i i i
i i i
H H H
normal propyl
H H H
propane
normal propane
radical
H
i
CH3
H- C
i \
CH-
H CH"
CH3
i /
H- C
Lso-propyl
radical
H
Organic Radicals. Radicals with valence 1 may be considered to be
related to a series of hydrocarbons by the removal of a single hydrogen
atom, as shown in the table. Thus the methyl radical (CH3 — ) is related
to methane (CH4), the ethyl radical (C2H6 — ), to ethane (C2H6), and so
on. The beginner should write these formulas out both as given here and
in the structural form given in the table, checking to see that each carbon
atom possesses four bonds, each hydrogen atom one, and each oxygen
atom (if present) two.
We can now see how to represent the formula for methyl chloride, a
compound sometimes used as a refrigerant. It is methyl (CH3 — ) chloride
( — Cl), or CH3C1. Again, ethyl bromide, an important material in
synthesis, is ethyl (C2H6 — ) bromide ( — Br), or C2H5Br. Their structural
formulas are
H
H-C-C!
i
H
methyl chloride
H H
H-C-C- Br
i i
H H
ethyl bromide
Carbon to Carbon to Carbon. Important and easily noticeable
from the structural formulas already given is the fact that carbon atoms
512
CHEMISTRY FOR OUR TIMES
Courtesy oj Celluloid Corporation
Cotton bolls Staple cotton
Cotton seed before removing linters Cotton seed after removing linters
Linters before purification Chemical cotton
FIG. 29-l.—The organic chemist views cotton as a source of cellulose and of oil. Cotton
can be made into nitrocellulose, a material of extensive uses.
join together by means of covalent bonds. In the examples given, chains
of carbon atoms are formed. Such chains may be either straight or
branched. Here are the structural formulas of two octanes, omitting the
hydrogen:
THE NATURE OF CARBON COMPOUNDS 513
-c-
i i i i i i i i i i i i i i i
-c-c-c-c-c-c-c-c- -c-c-c-c-c-c-c-
I I I I I I I I I I I I I I I
normal octano an iflo-octano
Again, owing to the chain-forming tendency of carbon, the atoms may
take the form of a ring. An example is cyclopropane, which is now an
important anesthetic.
H
H H C
\ / t *
C H-C C-H
H- C - C- H H-C C-H
s \ \ 4
H H C
H
cyclopropane benzene
Benzene (C6H6) is an important ring compound in which some of the
carbon atoms are attached doubly to each other. The derived radical,
CeHs — , valence 1, is called the phenyl radical. Thus, phenyl (CeH6 — )
iodide (—1) is C6H5I.
Saturated and Unsaturated Compounds. Let us consider three
different compounds of hydrogen and carbon that contain two atoms of
carbon: ethane (C2H6), ethylene (C2H4), and acetylene (C2H2). A satis-
factory way to account for the formulas is seen by the structural diagrams
for these compounds.
H H H H
it ii
H-C-C-H H-C=C-H H-CaC-H
H H
ethane
(single bond) (double bond) (triple bond)
ethane ethylene acetylene
' "juble bon<"
In ethane the carbon to carbon linkage is a single bond; in ethylene
the linkage is a double bond; and in acetylene it is a triple bond. This
situation fs explained in terms of electrons. Each line in the bond repre-
sents a pair of shared electrons. There are thus two shared pairs of
electrons in the carbon-to-carbon bond in ethylene and three pairs in
acetylene.
The existence of double and triple bonds is supported by the labora-
tory fact that compounds thought to contain them are ready to add
chemically at the point where the bond occurs in the compound. For
example,
C,H4 + Br« -4 C2H4Br2 l
514 _ CHEMISTRY FOR OUR TIMES
or
H H H H
H-C-C-H+Br-Br-+H-C-C-H
i i
Br Br
or
CH* * CH2 + Br - Br -> CH2Br - CH2Br
ethylene -j- bromine — * ethylene dibroinide
Acetylene adds bromine even more readily than does ethylene and takes
double the amount.
Such compounds as ethylene or acetylene that contain double bonds
or triple bonds are called unsaturated compounds. They are important
especially in rubber, petroleum, and plastic chemistry.
Helpful Comparisons. We have seen that the radicals CH3 —
(methyl) and C2H6 — (ethyl) have combining numbers of 1. Comparing
their position in compounds, as in CH8C1 (methyl chloride), with HC1
(hydrochloric acid), we see that the methyl radical is in the place corre-
sponding to the hydrogen alone. Thus, at least for the purpose of writing
formulas, the organic radicals mentioned may be considered similar to
hydrogen.
The hydrocarbon methane, CH3 — H, usually written CH4, corre-
sponds to H — H, molecular hydrogen. The compound CH3 — OH is called
methyl alcohol and corresponds to H — OH, water, which is also a hy-
droxyl compound.
/ ..... CIK
/ Oxides are known in organic chemistry; dimethyl oxide, J)O, is
CH/
H\
an example. They are called ethers and correspond to water /O con-
W
sidered as an oxide, in which both the hydrogen atoms have been replaced
by an organic radical.
The formulas for the so-called carboxylic acids all contain the group
0
II
— COOH (better — C — 0 — H), called the carboxyl group, containing
an ionizable hydrogen atom. Methyl (CH3 — ) carboxylate ( — COOH), or
CH3COOH, is called acetic acid. One common method of representing
this compound is H*C2H302. The position of the replaceable hydro-
gen atom is shown by the formulas for sodium acetate, Na'C2H302,
0
CH,COONa, or CHs— C— 0— Na.
The three hydrogen atoms of the methyl radical are not ionizable.
THE NATURE OF CARBON COMPOUNDS 515
Organic "Neutralization." The chemical action called neutraliza-
tion has been shown to be merely the transfer of a proton (see page 222).
H2O-H+ + OH-
and
NHj
acid
OH-
baae
H2O
NH3
un-ionized
product
- H2O
H2O
water
In the previous paragraph we saw that the compound corresponding
to a hydroxide is an alcohol. Now we can make the comparison.
CH3COOH + CH3OH -> CH3COO- CH3 + H2O
organic acid alcohol an ester, un- water
ionized product
Thus ester formation, or esterification, corresponds closely to neu-
tralization; esters are organic compounds that may be considered to be
derived from an organic acid (or sometimes a mineral acid) with the
replaceable hydrogen atom(s) replaced by an organic radical. Natural
fats, oils, and waxes are mixtures of esters.
To summarize, a tabulation of the comparisons may be made.
Inorganic compounds
Organic compounds
Ionized
Un-ionized
Positive part .
Hydride. ...
Hydroxide . .
Oxide
Na4
Na^H
Na4OH
NaV-
Na^U
Na<
Na^b
H-
H- H
H - OH (water)
H
\
O
/
H
H
\
S
/
H
H- Cl
CH3-
CH3- H (CH4), methane
CH3 - OH, methyl alcohol
CH3
\
O, dimethyl ether
CH/
CH3
\
S, dimethyl thioether
CH3'
CH3COO - H, acetic acid
CH3COO~Na\ sodium acetate
CH3CO - OCH3, methyl acetate
Sulfide
Acid
Salt
Na+CI~
Kster
O
II
Other Organic Groups. In addition to the carboxyl group, — C — OH,
H
I
which is found in all carboxylic acids, the group — C=O is found in all
aldehydes, and the group yC=0 is found in all ketones.
516
CHEMISTRY FOR OUR TIMES
Alcohols. Chemically, alcohols are similar to water (HOH), except
that the first hydrogen in the formula is replaced by an organic radical.
Thus the simplest alcohol is meth-
yl alcohol, or methanol (CH3OH),
commonly called wood alcohol.
Wood Alcohol, or Methanol.
Wood alcohol obtained its name
because it is among the volatile
materials driven off when wood is
heated. Formerly it was obtained
in quantity by the destructive dis-
tillation of wood. It is made syn-
thetically, 100 per cent pure, by
passing carbon monoxide and hy-
drogen from water gas over a
catalyst.
CO
(ZnO.CraOa)
2H2 - > CH3OH
Methanol, a colorless liquid
that boils at 64.5°C, has about
four-fifths the density of water. It
mixes completely with water. It
vaporizes easily, the fumes being
poisonous. If it is taken internally,
such disastrous effects are pro-
duced on the optic nerve that
blindness may result. It may even
cause death.
The compound is used as an
antifreeze in automobile radiators and as a solvent for gums, as in shellac
and varnishes; it is also used in some types of denatured alcohol and in
making formaldehyde.
Courtesy of American Forest Products Industries, Inc.
FIG. 29-2. — Trees are a source of resins,
lignin, and cellulose. This tree has been
tapped for turpentine.
ClIAKAC TKIUSTIC GROUPS FOR SOME CLASSES
OF ORGANIC COMPOUNDS
Carboxylic acids
0
-C-OH
Aldehydes
H
-C*O
Ketones
%C-O
f
Obviously, preparations of this sort- are not beverages. Drinking
them may produce fatal consequences. Like most organic compounds,
THE NATURE OF CARBON COMPOUNDS 517
"wood spirits " burn.
2CH3OH + 3O2 -4 2CO2 + 4H2O
When a warmed piece of heated platinum or copper is held in a mix-
ture of methanol vapor and air, the oxidation is partial, and the vapor
of the formaldehyde produced is very irritating to the eyes.
H
CH8OH + [O]
H - C « O + H2O
formaldehyde
When this experiment is carried out, the odor of formaldehyde will recall
that of the solution in which biological specimens, frogs, for example,
are preserved. Formaldehyde is also used extensively in making Bakelite
and urea plastics.
Courtesy of Rural Credits Department, Pierre, S.D.
FIG. 29-3. — Starch, oil, and cellulose, all organic compounds, are obtained from corn.
Grain Alcohol. Grain alcohol, or Cologne-spirits, received its name
from its source. When grain sprouts or germinates, catalysts from the
plant, called enzymes as a group, change the insoluble stored starch to
soluble sugar, an available food for the growing plant. The enzyme in
this case is called diastase, and the preparation of sprouting grain is
called a malt.
diastase
(C6H10O6)x + *H2O > sCi2H22On
starch from malt maltose (malt sugar)
In the presence of the enzyme maltose, the maltose is converted into
glucose.
Ci2H22On H- H2O -> 2C«H12O6
maltose glucose
518
CHEMISTRY FOR OUR TIMES
The glucose is now fermented by yeast, single-celled plants that con-
tain many enzymes, zymase being used in this case.
alcoholic fermentation
2C2H5OH + 2CO2T
(glucose) zymase from yeast
Much of the alcohol made today comes from alcoholic fermentation of
the sugar left in molasses after the crystallization of cane sugar (sucrose).
sugar (sucrose)
H2O
invertase in yeast
(a mixture of glucose
and fructose)
This process is easily demonstrated in the laboratory by adding yeast to
a mixture of molasses and water and allowing it to remain in a warm
FIG. 29-4. — The alcoholic fermentation of sugar solution by yeast goes on when
this apparatus is kept in a warm place. Alcohol, produced in the large flask, can be
recovered by fractional distillation. The limewater turns milky, proving the production
of carbon dioxide as a by-product — for no carbon dioxide from the air can enter the
apparatus through the soda-lime tube.
place. The fermentation stops when a concentration of about 14 per cent
alcohol is reached (see Fig. 29-4). The alcohol may be separated from
the mixture by distillation. This, on a small scale, parallels the commercial
method. The product is called ethyl alcohol or, better, ethanol (C2H5OH)
or just alcohol.
What Is Pure Alcohol? Pure alcohol, 100 per cent, called absolute
alcohol, is used for special laboratory and industrial purposes. It is a
colorless liquid, boiling at 78.5°C«and freezing at the low temperature of
— 112°C. It vaporizes readily at room temperature and has a pleasant
odor. Alcohol has a strong tendency to absorb water, with which it
mixes in all proportions.
THE NATURE OF CARBON COMPOUNDS 519
Commonly, alcohol is 95 per Cent pure. The 5 per cent of water
represents the water vapor that distills over when alcohol is distilled at
78°C with water. No matter whether one starts with a mixture that is
stronger or weaker than 95 per cent, the vapor always has the same
composition, 95 per cent alcohol, if water is present. (The vapor pressure
of water at 78°C is 327 mm.)
Alcohol can be partly oxidized in the presence of a catalyst to form
acetic acid. This happens when hard cider changes to vinegar in the pres-
ence of u mother of vinegar/ ' which contains Bacillus aceti. Unfiltered
vinegar contains visible amounts of the cloudy "mother" that supplies
the enzyme vinegar oxidase.
C2H6OH + O2 BaeMu§ ) H2O + CHgCOOH
aceti
Uses of Alcohol. Alcohol is an excellent fuel, for it burns without
soot. " Canned heat" is a jelly containing alcohol. Alcohol is used to some
extent as a motor-vehicle fuel, but in most places its price is too high to
compete with gasoline.
It is the most widely used solvent except water. The following com-
mon commodities contain alcohol: vanilla extract (37 per cent alcohol),
peppermint extract (90 per cent), perfume (70 per cent), hair tonic
(73 per cent), mouthwash (38 to 25 per cenfc), aftershave lotion (50 per
cent). The concentrations given all represent information obtained from
labels.
Alcohol is extensively used as an antifreeze liquid and for sterilizing.
It is widely employed in the preparation of other compounds. Ether, for
example, is made by dehydrating alcohol by means of sulfuric acid.
CsHiOlH
1 --' (cone. HiSOO
1 H2O + (C2H5)2O
CiH,|OHj
alcohol, 2 parts ether
At a higher temperature, the same process forms ethylene (C2H4).
A Compound with Social Significance. The effect of alcohol on
the body depends on the amount drunk, the state of health of the
person, and other factors. Hence no absolute statements can be made.
In general, however, a small quantity causes deadening of some nerves,
allowing blood to rush to the surface of the body, imparting a feeling of
warmth, but actually chilling the body. The heart beats a little faster
at first but later drops below the normal rate. Hence the use of alcohol
as a stimulant is questionable. Social restraints, called inhibitions, appar-
ently are removed as larger quantities are imbibed, and more nerves are
paralyzed, causing intoxication (poisoning). If continued use of alcoholic
520
CHEMISTRY FOR OUR TIMES
beverages increases the amount of alcohol in the blood stream to 3 oz,
alcohol is fatal. Even }^ pt of whiskey (16 oz), 100 proof (50 per cent
alcohol), contains 8 oz of alcohol. Alcoholic poisoning is more frequently
a contributing if not a direct cause of death than many people realize.
Alcohol slows the " reaction time," important in avoiding or causing
automobile or industrial accidents. Many experiments have been con-
ducted to determine the effect of alcoholic beverages on efficiency. The
results point out that- alcohol must
be regarded as a narcotic.
Some authorities consider the
use of alcohol, along with war, as
a great handicap upon human
progress. Alcohol has not an alto-
gether black record, however. In
some cases its stimulating action
has saved lives. The use of bever-
ages with slight alcoholic content
instead of water is undoubtedly
necessary in countries where the
water supply is unreliable. In
America, however, where reliable
water supplies are common, no
reason exists for drinking alcoholic
beverages as a sanitary precaution.
Denatured Alcohol. Govern-
ments have found alcoholic bever-
ages a convenient source of
revenue. If, for example, the cost
of 1 gal of 95 per cent alcohol
is $6, only about 40 cents or
less is the actual cost of the
material. The rest is chiefly tax. But as we have seen there are many
uses for alcohol other than that as a beverage. With these commercial
uses the government should have no desire to interfere. Commercial
alcohol may be sold tax-free if it is denatured, that is, has substances
added to it which cannot be removed easily by distillation or any other
means. These substances render the alcohol a direct, violent poison. A
number of combinations of denaturants are permitted; the industrial
user chooses the type of added impurity that will interfere least with the
intended application. Radiator alcohol often contain pyridine (CsHUN),
a disagreeable-smelling compound, or methyl alcohol (CH3OH) as de-
naturants. Rubbing alcohol is a mixture of denatured alcohol, water, and
isopropyl alcohol [(CH3)2CHOH].
Courtesy of E. I. du Pont de Nemours & Company,
Inc.
FIG. 29-5. — Neoprene is being poured
from polymerization kettles, one step in
the processing of a type of synthetic rub-
ber. Neoprene is an organic chemical.
THE NATURE OF CARBON COMPOUNDS 521
Other Alcohols. Propyl alcohol (C8H7OH -iso) is used in medicine.
Butyl alcohol (C^gOH) is used in making esters for solvents. Both may
he made by catalytically reducing the corresponding acid or by special
fermentations.
In addition to the alcohols having just one hydroxyl group some
important dihydroxy and trihydroxy alcohols are known. Ethylene glycol
[C2H4(OH)2] is widely used as a nonevaporating antifreeze. Glycerol
[C3H6(OH)8, glycerin], a by-product from soapmaking (see page 603),
is a sirupy liquid of high boiling point used for the making of explosives,
toilet creams, and rubber-stamp pads. It absorbs moisture from the air.
The compound commonly called carbolic acid is really an alcohol,
phenol (C6H5OH). This compound is extensively used for making Bake-
lite plastic and as a vigorous antiseptic. It has an acid reaction — hence
the name carbolic acid. Hundreds of other alcohols are known.
SUMMARY
Organic compounds are similar to covalent inorganic compounds in all funda-
mental essentials. The term " organic compounds " includes only certain com-
pounds of carbon. In organic compounds the carbon often shows a tendency to
form chains or rings. These compounds are seldom dissociated owing to covalent
(electronic-pair sharing) bonds. They react relatively slowly. Few are soluble in
water; organic compounds are better solvents for organic compounds. ("Like
dissolves like.") Structural formulas are helpful in Classifying organic compounds.
Hydrocarbons are compounds of hydrogen and carbon only. Methane (CH4)
is related to methyl radical (CH3 — ). Ethane (C2H6) is related to ethyl radical
(C2H5 — ). Many hydrocarbons exist in chain and ring forms. Some hydrocarbons
have two or three covalent bonds between adjoining carbon atoms. These are
called double or triple bonds and are points of chemical activity of the molecule.
Organic compounds are classed according to groups and may be compared
with inorganic compounds of similar structure. Organic reactions are somewhat
similar to inorganic reactions; for example, ester formation is often compared with
neutralization, although many differences between the reactions are prominent.
Typical organic groups include:
Oarboxyl .... .
O
ii
- C- O- H
Typical of organic acids
Aldehyde
H
- C«O
Typical of aldehydes
Ketone
\
CaO
Typical of ketones
Hydroxyl
/
- O- H
Typical of alcohols
Methanol, or wood alcohol, is prepared from destructive distillation of wood.
An impure product results. Synthetic methanol, 100 per cent pure, is prepared
from carbon monoxide and hydrogen.
522 CHEMISTRY FOR OUR TIMES
Methanol is a poisonous, colorless liquid. It has low boiling and freezing points.
It is an excellent solvent for gums. It burns readily and oxidizes partly, to form
formaldehyde in the presence of platinum catalyst.
Methanol is used as a solvent in shellac and to make formaldehyde; also, it is
an effective antifreeze.
Ethanol, or grain alcohol, is prepared from grain by the change of starch to
sugar by the enzymes diastase and maltase. The glucose formed is then fermented
to alcohol and carbon dioxide by use of the enzyme zymase from yeast. Alcohol
is separated from the ferment by fractional distillation.
Ethanoi is a colorless, pleasant-smelling liquid. It is an excellent solvent, ab-
sorbs water readily, and mixes with it in all proportions. It burns in air. Dilute
solutions of ethanol can be oxidized to acetic acid, as in the manufacture of vine-
gar. It reacts with acids and a great variety of organic compounds.
Ethanol is used as a fuel and an antifreeze. It is also used as a solvent in medi-
cines, tinctures, extracts, and spirits. It is a component of all alcoholic beverages.
It has a part in the preparation of ether, synthetic rubber, explosives, and many
other compounds.
QUESTIONS
1. Tabulate the compounds represented by the following formulas in two
groups, organic and inorganic: CH4; SiH4; CO.; Na2CO8; HCHO; H-C2H3O2;
MgC03; NaHC03; CC14; CH3OH.
2. Contrast organic with inorganic compounds in four ways.
3. Name three elements that are very important in organic compounds.
4. Contrast in two respects the behavior of inorganic arid organic; compounds
toward water.
5. Butane has the formula C4Hio. Write the formula for the butyl radical.
What is its valence?
6. Write the structural formula for (a) normal (straight-chain) butane; (6)
iso- (branched-chain) butane.
7. Write the formula for (a) ethyl nitrate; (6) methyl bromide; (c) iso-
propyl chloride; (d) ethyl acetate; (e) dimethyl sulfate.
8. In what three ways can two carbon atoms be joined together? What does
each type of bonding represent in terms of electrons?
9. Make a "dot" diagram showing electrons in the outermost orbits of each
atom in (a) ethane; (6) ethylene; (c) acetylene.
10. Write the formula for (a) acetic acid; (b) sodium acetate; (c) calcium
acetate. Also, write the structural formulas for these compounds.
11. What evidence shows that acetic acid possesses hydrogen atoms with two
differing sorts of chemical activity?
THE NATURE OF CARBON COMPOUNDS 523
12. List three different classes of organic compounds, and opposite each write
its corresponding inorganic compound.
13. Write formula equations for the reaction of acetic acid with (a) sodium
hydroxide solution; (6) calcium hydroxide solution; (c) methyl alcohol; (d) ethyl
alcohol; (e) propyi alcohol.
14. Write the structural formula for the characteristic group of elements
found in all (a) aldehydes; (6) ketones; (c) organic acids; (d) alcohols.
16. Point out the difference between burning methyl alcohol and oxidizing
it in the presence of platinum as a catalyst.
16. Which produces the greater lowering of freezing point when added to a
liter of water, 100 grams of methyl alcohol or 100 grams of ethyl alcohol? Give a
reason for your answer.
17. Tell how to distinguish methyl alcohol from ethyl alcohol and from a mix-
ture of the two.
18. Formaldehyde solution is a good preservative for biological specimens.
Why is it riot used for preserving foods, such as meats and fish?
19. Name two by-products of bakeries that are usually wasted.
20. Tell the steps in changing starch to alcohol. Include three equations.
21. Distinguish absolute alcohol from denatured alcohol and from ordinary
grain alcohol.
22. List two disadvantages of alcohol for motor fuel, as compared with gaso-
line.
23. For what purpose is alcohol used in many "patent" medicines?
24. When ether is prepared from alcohol, how is the formation of ethylene
retarded?
f540
25. What weight of alcohol can be produced from j^n grams of glucose?
( 1 flOP
26. What volume of carbon dioxide at STP is formed when lio^o grams of
sucrose ferment?
27. What is the percentage composition of methyl alcohol?
28. A gas is composed of 40 per cent carbon, 6.7 per cent hydrogen, and the
balance oxygen. The weight of 200 ml of it at STP is 0.27 gram. Find its correct
molecular formula.
29. In what volume proportions should air and methyl alcohol vapor be
mixed when formaldehyde is to be produced by aid of a catalyst?
524 CHEMISTRY FOR OUR TIMES
30. Account for the fact that repeated distillation of 95 per cent alcohol fails
to lower the percentage of water that it contains.
31. What volume of liquid alcohol is needed to produce a liter of diethyl
ether? The density of ether is 0.71 gram per milliliter and that of alcohol 0.79
gram per miililiter.
UNIT SEVEN CHAPTER XXX
OUR FUELS
If we watch a fire of soft coal burning, we see tongues of flame spurt
from the lumps of coal from time to time. These jets of flame are caused
by burning gas that escapes from the coal while it is being -roasted in the
fire.
From this observation comes the suggestion that the making of this
flammable gas might be separated ^H§Ve burning. This indeed can
Water Pipe
Packed Loosely with Rubber
Soft Coak Connector
Cap
Wing Top
Bunsen Burner
Two-Holed
Rubber Stopper
Coal Ga
Water
FIG. 30-1. — This working model brings the gas works into the laboratory. The
destructive distillation of coal is carried on conveniently on a small scale in a capped
water pipe provided with an opening for the escape of volatile products.
be done if we place the coal in an oven, airtight except for an outlet,
and then apply heat outside the oven. The heated coal gives off gases.
The gases can be carried away in pipes, purified, and used at a distance
from the place where it was made.
Making a miniature gasworks is a simple and instructive experiment. A piece
of iron water pipe is fitted with a cap at one end and a tapered fitting at the other,
(See Fig. 30-1.) The pipe is filled loosely with soft coal. The tapered fitting is
attached by a rubber tube to a glass tube inserted through a stopper in a bottle,
destructive distillation
producer gas
natural gas
water gas
New Terms
hydrocarbon
octane number
lignite
525
bituminous coal
Btu
methane series
526
CHEMISTRY FOR OUR TIMES
which serves as a scrubber. The glass tube dips just below the surface of the
water in the bottle. This scrubber apparatus is thus simply a bottle fitted with a
two-holed stopper. The glass delivery tube is in one of these holes, and a jet
shaped like the glass part of a medicine dropper is in the other.
When we apply heat to the iron water pipe, the coal inside decomposes. The
products formed by this process of heating coal shut off from the air are different
from the coal. Any such decomposition carried out by applying heat to material
shut off from the air is called destructive distillation.
In commercial practice the oven is called a retort. If all or part of
the vapors from the heated coal are allowed to escape directly into the
( 'nn,{> .N :•/ nf Koppfrs Company, Inc.
FIG. 30-2. — By-products from soft coal distillation come through (he off-take main
(central pipe) to the by-product plant (right). Coke-pushing machine is also shown.
air and there burned, the retort is called a beehive coke oven, named from
its general shape. Beehive coke ovens waste valuable by-products from
the coal; they are an extravagant means for making coke to supply the
hungry mouths of the nation's blast furnaces. Modern practice saves
the vapors that come from the heated coal.
Gaseous Fuels
By-product Coke Ovens. A vertical wall of coal about 14 ft high
and 8 in. thick is poured into a section of a multiple retort. The walls of
the retort are kept hot by burning cheap fuel gas between adjacent
retorts. Vapors escape from the coal for perhaps 18 hours. The solid
OUR FUELS 527
material that remains behind after the heating is coke — a porous, gray
substance, chiefly carbon. It is used for blast furnace and foundry fuel,
as a reducing agent, and for heating homes.
Coal Tar and Coal Gas. The hot vapors that are drawn off a by-
product coke oven are passed through water and further cooled to con-
dense tar. Some coal tar floats on the water; the soluble portions of the
coal gas, chiefly ammonia (NH3), remain dissolved in the water. A little
of the ammonia joins the water to form ammonium hydroxide.
NH3 + HOH -> NHrOH-
This solution is then run into sulfuric acid until the ammonium sulfate
crystals form.
2NH4OH + H2S04 -f 2H2O + (NH4)f SO; ~
The crystals are washed and whirled dry in the basket of a centrifugal
machine.
The tar is used as a binder in making roads, or it may be subjected to
further distillation and treatment to make coal-tar products (see page
581).
Coal gas, chiefly hydrogen and methane with some carbon monoxide
and nitrogen, is purified to free it from several objectionable impurities.
Then it serves as a household and industrial* fuel.
A ton of coal might produce 10,000 cu ft of gas with 537 Btu1 heat
value per cubic foot, 10 gal of tar, and 25 Ib of ammonium sulfate and
leave ^4 ton of coke in the retort after the distillation.
Opportunities for Improving Coal Distillation. Experts in the
destructive distillation of coal agree that the process is far from perfect.
For example, most coke ovens are intermittent; only a few are con-
tinuous. As a rule, continuous processes are preferred for commercial
operations.
When the red-hot coke is pushed out of the oven with a single stroke
of a powerful ram, the coke burns furiously while it is being carried in a
steel car to an enormous showerbath. This is a startling and wasteful
wight. Some work has been done toward eliminating this obvious loss,
but more is needed.
Changing the temperature at which coal is distilled results in a
definite change in the products, favoring liquid oils and less tar. Here
again possibilities of development in the future are indicated.
Water Gas. To make water gas, a firebrick-lined cylinder, called a
generator, which is as large as a squatty farm silo, is well filled with
coke or hard coal. A fire is made within the cylinder and forced to furious
1 Btu means British thermal unit. This is the quantity of heat needed to raise the
temperature of one pound of water through one degree Fahrenheit.
528
CHEMISTRY FOR OUR TIMES
intensity (1400°C) by powerful motor-driven fans. Then the air draft is
shut off and steam sent through the glowing coals. The steam is reduced
by the hot carbon, liberating carbon monoxide and hydrogen gases.
The mixture is known as water gas. H20 + C — > CO + H2. This
chemical action takes in heat (endothermic), and after 3 minutes the
coke has cooled to 1000°C, necessitating sending more air through the
coals for 2 minutes, to brighten the fire. While the air is reviving the fire,
the gasmaking machine sends a bright glare into the sky, a brilliant sight
at night. Thus the process of making water gas is one of alternately
heating coal red-hot in air and then sending steam through it.
Smokestack — Jj I
Steam
Generator .. Carburetor Superheater
FIG. 30-3. — The water-gas machine is composed of three principal parts: generator,
carburetor, and superheater.
Straight water gas does not meet the legal heat requirements for fuel
gas of most states. Oil gas, therefore, is added to it. This is made by
spraying oil onto hot checker-bricks in a second cylinder, the carburetor,
through which the hot blast from the generator is passed. When the
oil strikes this very warm region, it " cracks " (see page 537), and most
of it remains in the form of a stable, permanent gas mixed with the water
gas by the time it has passed over another checker-brick-lined heating
chamber, the superheater. (See Fig. 30-3.)
Not only has water gas higher heat value when enriched with oil gas,
but the flame of burning is changed from pale blue, as seen when hydrogen
or carbon monoxide burns, to a light-giving, or luminous, sooty flame.
This gas is purified as coal gas is.
Water gas is interesting to us because it illustrates how coke can be
made into gas, even after coming from the coke oven. The process, a
convenient one, is often run to supplement coke-oven gas at times of
peak loads.
OUR FUELS 529
Steam may be introduced into coke ovens or into producer-gas ma-
chines (see page 526). The mixture of carbon monoxide and hydrogen
produced by the water-gas machine is tW starting material for making
synthetic alcohol and other valuable synthetic chemicals.
QUESTIONS
1. Name four products of the destructive distillation of bituminous coal,.
2. In what way are beehive coke ovens wasteful?
3. What product is formed when cooled coke-oven gas is run through hydro-
chloric acid?
4. What weight of coal must be distilled daily in order to supply the needs
of a city that consumes 12 million cubic feet of gas per day?
6. What weight of ammonia is available from a ton of coal if 25 pounds of
ammonium sulfate is made from it? HINT: Find the percentage of ammonia in
ammonium sulfate.
6. Explain why the process of making water gas is an intermittent one.
7. In the water-gas-making machine, what purpose is served by (a) the
generator; (6) the carburetor; (c) the superheater?
8. What products are formed when water gas burns?
*
9. Assuming that no time is lost in adding fuel and that water gas is made
by a machine at the rate of 500 cubic feet per minute, what is the daily output of
the machine
10. The gas from a water-gas machine is immediately passed through a large
tank containing water. State two changes brought about by this treatment.
Producer Gas. Another gas that is used as a fuel is producer gas.
To manufacture it, a revolving cylindrical tank as large as a railroad car,
lined with firebrick, is used. A cheap fuel, coke for example, is burned
inside, while air is sent through the bottom of the deep fuel bed. The
nitrogen of the air passes through it unchanged, but the oxygen at the
bottom of the bed joins carbon to form carbon dioxide. C + 02 — > CO2.
The carbon dioxide rises and is reduced by hot carbon to carbon monoxide.
C02 + C -> 2CO.
Often steam is put into the machine also, adding hydrogen to the
mixture of fuel gases. C + H20 — > CO + H2. Thus producer gas con-
tains nitrogen, carbon monoxide, and hydrogen.
Producer gas is always made for definite direct use. It may be used
to heat coke ovens, to run gas (not gasoline) engines, or for industrial
fuel. It is too poisonous for use in homes, and its fuel value is low.
Natural Gas. Some borings into the earth produce flammable gas,
which is chiefly methane (CH4). Oil wells are usually gas wells, also.
530 CHEMISTRY FOR OUR TIMES
The "wet" gas, as taken from wells, sometimes contains a little vapor of
gasoline. This vapor is absorbed in oil or condensed and saved. The
gases that do not condense to form liquids are used directly for fuel.
Natural gas is being made wherever leaves and vegetable matter
decay. It can be found by stirring the mud at the bottom of a pond.
In certain places, sometimes thousands of feet below the surface, great
quantities of such gas are imprisoned in pores of the earth's rocks.
Special Gases. Blast furnaces for making iron produce such great
excess of carbon monoxide that the gas can be burned. This gas is a
lean fuel, but it will provide power for engines that move materials
around the furnaces.
Compressed gas in strong steel tanks is used extensively for fuel.
This gas comes chiefly from petroleum refineries and natural gasoline
plants as a by-product, and it is comprised of compounds of carbon and
hydrogen only. Such compounds are called hydrocarbons. The gas may
be propane (C3H8), butane (C4Hi0), and possibly pentane (CfJIl2), or a
mixture of these. It is used for fuel for trucks, for industrial heating, and
for household fuel gas in the country.
Acetylene. When water is added to calcium carbide, a colorless gas
called acetylene (C2H2) is evolved. This gas, 92.3 per cent carbon, burns
with so sooty a flame that a special type of burner must be used when it
is burned to produce light.
CaC2 + 2H2O -4 Ca(OH)2 + C2H2|
calcium carbide water slaked lime acetylene
Acetylene is a hydrocarbon gas, exceptionally high in heat value.
It is used in the oxyacetylene torch to produce a heat so intense that it
melts steel. It decomposes easily when warmed, liberating heat (exo-
thermic reaction). We may represent this change as
»
C2H2 -4 2C + Hj (+ heat)
Three results follow from thin fact. (1) Acetylene can* be used as a source
of pure carbon with hydrogen, as a by-product. (2) The heat of burning
is added to the heat of decomposition, a very hot flame being thus pro-
duced. The equation that represents the complete burning of acetylene
is 2C2H2 + 5O2 -» 4CO2 + 2H20 (+ heat). (3) Acetylene cannot safely
be compressed and stored in tanks directly, for it may explode. There is
no danger of explosion if the tanks contain asbestos soaked with acetone.
Acetylene has many uses an a gas for lighting or for heat. It is also
the starting material for making some synthetic rubber and some plastics.
Gas Flames. The fact that a handful of fuel gas can be ignited and
the burning gas carried in the hands (see Fig. 30-4) illustrates clearly
OUR FUELS
531
that flames come from burning gas. Solids glow when they burn, as does
burning charcoal; flames from solids or liquids, however, are produced
A
landfut of Gas at A
Light it at B, and Return it
to A, Lighting Gas There
Air Holes
Closed
Combustion of
Hydrogen and
Carbon
Region of
Decomposition
Unburned
Gas
A B
FIG. 30-4. — While this experiment illustrates the hard way to save a match, it also
clearly shows that flames are produced from substances burning in the gaseous state.
When solids burn, they glow.
only if the substances (1) are changed to vapor by heat, (2) give off gas
by destructive distillation, or (3) form
gas by chemical action. Alcohol in a
spirit lamp burns with a flame be-
cause the liquid alcohol is changed to
gaseous form by the heat of the burn-
ing. A piece of wood burns with flame
because the vapors of wood alcohol
and other substances formed by de-
structive distillation are burning.
Coke or charcoal may burn with a
flame when the oxygen of the air forms
carbon monoxide, which in turn burns.
Bunsen's Gas Burner. The Bun-
sen burner, invented by Robert Wil-
helm Bunsen (1811-1899), is in general
a most satisfactory gas burner. It is
simply a vertical tube. At one end are
a small opening to admit the gas and
an adjustable opening for air; at the
other end the gas and air mixture
burns. A gas range at home has many
small Bunsen burners.
When adjusted correctly, a Bunsen burner flame consists of two dis-
Fio. 30-5.— The Bunsen burner is
the type commonly used in labora-
tories that are supplied with fuel gas.
53J CHEMISTRY FOR OUR TIMES
tinct cones. The inner cone consists of unburned gas, surrounded by a
darker region. In the second cone, decomposition of hydrocarbons takes
place. Surrounding the latter cone, the hot decomposed material meets
the oxygen of the air. Here vigorous burning takes place in a third region,
which is visible only under favorable light. (See Fig. 30-5.)
If the supply of air is limited, the carbon formed by decomposition
glows, forming a yellow, sooty flame. Such a luminous, or light-giving,
flame is much cooler than the blue Bunsen flame. If blown about by a
breeze, the hot carbon may not burn when it reaches the outer edge of
the flame but forms smoke instead.
QUESTIONS
11. Some producer-gas machines are made in such a way that the surround-
ings are almost entirely open to the outdoor air. Of what benefit is this arrange-
ment to the workers?
12. Why is producer gas considered a "lean" gas?
13. Name the chief constituent of natural fuel gas.
14. Do all natural gases burn?
16. Describe a method for securing gas for cooking in regions removed from
city gas mains.
16. Write equations for (a) producing acetylene from "carbide"; (6) burning
acetylene.
17. What percentage of acetylene is hydrogen?
18. Account for the very high temperature produced in the oxyacetylene
torch.
19. In attempting to synthesize acetylene from coke and hydrogen, does the
expected reaction absorb heat, or does it give out heat?
20. A match head can be held unburned in the lower central part of a Bunsen
burner flame. Account for the low temperature in this region.
Liquid Fuels
Motor Fuels. An ordinary automobile engine uses gasoline for fuel.
In the carburetor the gasoline is forced into a fine spray that evaporates
easily when it is mixed with a large amount of air. The vapor mixture
thus formed is then drawn into the automobile cylinders. Here the fuel-
air mixture is compressed and set on fire by sparks from spark plugs.
The burning or exploding fuel in the cylinder expands, forcing the piston
downward. The downward movement of the piston is transmitted to the
rotary movement of the wheels. All this takes place very quickly.
Fuel requirements for modern motors, namely, a cheap liquid that
OUR FUELS
533
will vaporize readily and burn violently when mixed with air, are at
present met by only two common substances, gasoline and alcohol.
Sources of Gasoline. Gasoline is produced (1) by the distillation of
petroleum, (2) by "cracking" of oils, (3) by absorbing the gasoline vapors
from- natural gas (see page 530),
(4) by combining hydrogen with
low-grade coal or oil, (5) by "poly-
merizing" small molecules into
clusters. Gasoline is such an im-
portant fuel that its story is inter-
esting to us all.
Petroleum. The liquid re-
mains of animal and vegetable life
of ages past are stored in cracks
and pores of some rocks. This
dark, ill-smelling liquid is called
petroleum. In most places petro-
leum is found far below the sur-
face of the earth, but in a few
instances it occurs fairly close to
or even on the surface. The first
oil well was sunk by Col. Edwin
L. Drake in Titusville, Pennsyl-
vania, in 1859. He struck oil 70 ft
below the surface. Today in some
wells oil must rise from great
depths — the deepest well is 3
miles deep. Deposits of petroleum-
like material on the surface of the
Courtesy of American Petroleum Institute
FIG. 30-6.— This oil-well drilling crew
is inserting a "knuckle-joint" into the well
hole to begin directional drilling. Direc-
tional drilling is a technological advance
that increases immeasurably the nation's
oil reserves. -
earth are different from petroleum bel<>\\ the surface. We have, for
example, the asphalt "lake" in Trinidad and the La Brea tar pits in Los
Angeles, California.
How Petroleum Is Obtained. Oil-well drilling is a specialized occu-
pation. Except in the case of "wildcat" wells, location of the place to be
drilled is established by scientific experimenting with earth vibrations
and by othef methods. A derrick is set up to lift the heavy tools and
pipes. In one type of drilling a diamond-studded collar is revolved by a
powerful motor. This hard cutting tool on the end of a long steel stem
cuts its way through the hardest rock. When seams of the rock are cut,
they may allow oil or water to seep into the hole. To prevent this, the
liole'niust be lined with cement. Bentonite clay in colloidal form is often
used as a drilling mud to aid in removing rock chips (see Fig. 15-10).
534
CHEMISTRY FOR OUR TIMES
So highly developed is the art of well drilling that holes, many thou-
sands of feet deep and sometimes at an angle, are pierced in rocks. A
derrick on the seashore may start a hole directionally drilled a quarter
of mile out under the sea, (See Fig. 30-7.)
Oil is found in many places. The principal oil-producing states in the
United States are Texas, California, Oklahoma, Illinois, and Louisiana.
Paraffin-base oils in important quantities come from the vast mid-con-
tinent and Pennsylvania fields. Asphalt-base oils come from the Texas
Gulf coastal region. The United States leads in the production of petro-
Coui-u*!i «>/ JS > udt i -Triangle
FIG. 30-7. — Shown here is a score of petroleum wells drilled in the ocean.
leum. Large supplies are produced in the U.S.S.R., Venezuela, Iraq, the
Netherlands East Indies, Rumania, Mexico, and elsewhere.
Oils from different wells may be very different. Petroleum is sometimes
found together with much natural gas. Other oil wells produce very little
or no natural gas. Some petroleum leaves a thick tarlike remainder when
it is refined and is therefore called asphalt-base. Other oils produce much
paraffin when refined. These are the paraffin-base oils. Many of the
Russian oils are naphthene-base. Some oils are mixed-base.
What Petroleum Is. Petroleum is a mixture of hundreds of com-
pounds of carbon and hydrogen, called hydrocarbons. Some compounds
in petroleum are members of the methane series of hydrocarbons.
OUR FUELS 535
i i i i i i M M M H H M
-C-C-C-C-C-C- :C:C:C:C:C:C:
111111 H H H H H H
Chemists have made diagrams to show the arrangement of the atoms
in the hydrocarbons. These show clearly that carbon has valence 4 and
that a carbon atom shows marked ability to join with other carbon
atoms. The carbon-hydrogen bond is of the covalent type, the electron
pair of the bond serving jointly to fill the outer orbit of both the hydrogen
and the carbon atoms.
H H H H H H
H:C:H H:C:C:H H:C:C:C:H
H H H H H H
methane (CHi) ethane (CaH«) propane
The Importance of Arrangement. Three letters, T, R, and A, for
example, may be arranged in several ways, as A R T, TAR, or R A T.
Just so in chemistry we find that different arrangements of the same
atoms within a molecule make different molecules.
We can make diagrams of two sorts of butane (C4Hi0) known in the
laboratory. One, called normal butane, has a straight chain of carbon
atoms and a boiling point of — 0.6°C; the other, called isobutane, has a
branched chain of carbon atoms and a boiling point — 10.2°C. These
two compounds are almost alike, except for the arrangement of atoms
within the molecule. They are called isomers.
H H
H H H H H H [ C '
H:C:C:C:C:H H:C:C ' ' £j
H H H H H ' 'c '*
H'' ' H
normal butane (CJIio) isobutane (CiHio)
When there are more carbon atoms in the molecule of a hydrocarbon,
the number of isomers increases. Seventy-five different decanes (Ci0H22)
are possible.
To make the situation even more complicated, many other classes of
hydrocarbons are known. Some are related to benzene (C6H6), a cyclic
compound in which the carbon atoms are arranged in a ring; others are
related to ethylene (C2H4), a compound in which a " double-bond " or
"unsaturated" linkage is known between the carbon atoms.
H H
H .. .. H
C»C C::C
H " " H
H H
536
CHEMISTRY FOR OUR TIMES
Courtesy of Atlantic Refining Com pan./
FIG. 30-8. — A close-up and an air view of modern petroleum refineries.
OUR FUELS 537
Two pairs of electrons shared between two atoms is called a double
bond.
Chemically, a mixture of normal and isomeric compounds, saturated
and unsaturated, cyclic, branched, and straight
•• •• chains of carbon atoms, but all hydrocarbons,
H : C ' :'C ' : C : H is petroleum. Moreover, petroleum is a mixture
H . £ '' Q . H °f liquid hydrocarbons that contains solid and
•" c : : ' C : ' gaseous hydrocarbons all dissolved in each other.
H H Usually, the liquid hydrocarbons contain 4 to 10
ncycUchify^^^ an(^ more G3>r^on atoms per molecule, the gases
fewer, and the semi-solids even more.
How Petroleum Is Prepared for Use. The first "coal oil" was bot-
tled and sold, to the accompaniment of a banjo entertainer, as a cure-all,
good for man and beast. Later, the chief use of petroleum was for making
kerosene for lighting when burned in coal-oil lamps.
Today petroleum is in most cases piped directly to a refinery. (See
Fig. 30-8.) Many methods of refining are used, but let us assume that a
maximum yield of gasoline, the product most used, is desired.
The petroleum is heated in a huge boiler called a still. The vapors are
cooled and condensed within pipes. The part boiling between 104 and
436°F is the gasoline fraction. This fraction is kept separate from the
next higher range of boiling points, 437 to 572°F, the kerosene fraction.
At a higher range of temperatures, fuel oils, light lubricating oils, heavy
lubricating oils, and paraffin or asphalt are vaporized. Petroleum coke is
left in the retort. This process of separating a liquid according to range
of boiling points is called fractional distillation.
We should notice carefully that benzene, sometimes called benzol, is
a definite compound (C6H6) obtained from the fractional distillation of
coal tar. Benzine, on the other hand, is a mixture of hydrocarbons ob-
tained from the fractional distillation of petroleum. The term benzine
is rapidly becoming obsolete in the petroleum industry. It is principally
a drugstore product used in dry cleaning. This product is more volatile
than gasoline.
The various fractions must now be refined, or purified from assorted
foreign substances that are present in the original petroleum. This is
done in several ways. One method washes the fraction with concentrated
sulfuric acid, sodium hydroxide solution, and water in turn. Sulfur may
be removed by sodium plumbite (Na2Pb02). The purified fraction is now
redistilled, and the gasoline so prepared is ready for the market as
" straight-run" gasoline.
Cracking. The fuel-oil fractions are sent to another part of the plant,
where they are heated under pressure. As a result of this treatment the
538 CHEMISTRY FOR OUR TIMES
hydrocarbon molecules split, or "crack," into fragments, or simpler mole-
cules, that correspond to the more volatile compounds.
One possibility illustrates in general the chemical change accomplished.
CioHa2 — f C?Hi6 -f- CgH«
decane heptane propene
at ordinary saturated saturated gas,
temperatures kerosene- gasoline- unsaturated
like liquid like liquid
The fractions used for cracking stock, however, usually have more than
10 carbon atoms. Almost any breakdown of the higher boiling-point
hydrocarbons is possible, but the process is controlled to produce the
NITROGLYCERINE BLACK
3200 B.T.U. POWDER
1850 BJ.U.
25°°
Courtesy of General Motors Corporation
FIG. 30-9. — Gasoline is one of the most powerful packages of energy.
greatest possible amount of gasoline. The cracking process has greatly
extended the yield of gasoline from petroleum.
The portion of the oil that resists cracking is sold for fuel oil. The
unsaturated compounds may be used to make plastics, alcohols, synthetic
rubber, or other by-products, but they can also be used to make gasoline.
Polymer Gasoline. The process of making gasoline from small mole-
cules is just, the reverse of cracking. The joining of small molecules to
make larger ones is a process called polymerization. This can be accom-
plished by the help of catalysts. The difficulty is to stop the molecules
from joining when gasoline has been formed. Hydrocarbon molecules that
continue to join may form gums when the gasoline is stored.
Gasolines made in the several different ways are blended and then
offered for sale.
Octane Number. The most important fact about a gasoline today is
its octane number. This number is a measure of its "knock" rating. A
high octane number, 72 for example, indicates high antiknock gasoline.
Straight-run gasoline, composed of straight-chain saturated hydrocarbons,
knocks easily. Its octane number is low. Branched-chain or ring hydro-
carbons have much higher octane numbers. Hence certain oils are natu-
rally high in antiknock value, while others are naturally low.
The octane number of a gasoline is improved (1) by the method of
OUR FUELS
539
refining, (2) by blending, and (3) by the use of inhibitors (negative
catalysts).
The inhibitor most used is tetraethyl lead [Pb(C2H5)4], a compound
that together with ethylene dibromide (C2H4Br2) and a dye constitutes
the " Ethyl fluid" that is added to many gasolines. In the motor, the
carbon and hydrogen parts of these molecules burn. Lead bromide (PbBr2)
forms. At the high temperature of the motor, this is a gas; it is exhausted
through the tail pipe of the car.
I
1
Courtesy of Ethyl Corporation
FIG. 30-10. — A compression ratio of five to one is shown here. Note that the piston
at the bottom of cylinder (1) encloses five times as much volume as it does when at the
top of cylinder (2).
Motor Knock. Effective use of gasoline in an automobile engine re-
quires that the gasoline-vapor-air mixture be highly compressed before
it is exploded. The compression ratio in modern engines may be 7 or
8 to 1 (see Fig. 30-10), and many gasolines knock badly when they are
compressed to such a high extent and exploded.
In order to prevent knocks, gasoline with octane rating 70 to 80 or
over must be used if the compression ratio is high. The required octane
rating depends on the design of the engine as well as the compression
ratio. For airplane engines, gasoline with octane values 100 or over may
be demanded. Such demands require skill and economy in all steps of
the petroleum industry. Small wonder that about one-half of the chemists
in the United States are employed by oil industries. "Triptane," a power-
ful aviation gasoline, is a fuel that has a very high knock rating.
The cause of knocking is interesting. The spark from the spark plug
sets the gasoline-air mixture on fire at one spot in the cylinder. If this
mixture burns steadily and smoothly, it will deliver steady power to the
piston, owing to the expansive force of the hot gases formed by the burning.
If, on the other hand, the gasoline-air mixture burns too rapidly or ex-
540
CHEMISTRY FOR OUR TIMES
plodes, the gases expand faster than the piston can move, and the motor
"knocks."
A badly knocking motor gives poor power, wastes fuel, and is under
extra strain. It may be compared to hitting a stone wall with a baseball
bat. The stone wall pushes back with as much force as the bat pushes
forward. The power of the stroke is wasted. A smoothly running motor
may be compared to striking a ball with a baseball bat with a "follow-
through" swing. The full power of the stroke is used in driving the ball.
Technically speaking, pure iso-octane
CH3 CH3
(CH3-C-CH2-CH-CH,,
CH3
2-2-4 trimethylpentane) is rated as 100 in octane number, for it burns
nicely under high compression. Normal heptane
(CH3- CH2- CH2- CH2- CH2- CH2- CH3),
with no branched-chain structure, knocks badly under compression.
Gasoline, when compressed and ignited, that causes knocks to exactly
Courtesy of Ethyl Corporation
FIG. 30-11. — Octane number, and the effect on octane number of adding a catalyst.
the same extent as a mixture of 72 per cent iso-octane and 28 per cent
normal heptane is given a 72 octane rating.
Oil Resources. In spite of the great amount of oil that has already
been used, the total volume used is only a small fraction of the total
OUR FUELS 541
supply. Also, in recent years we havd discovered extensive oil reserves,
although some existing fields have been exhausted. Improved methods
enable us to reach oil at a lower depth than could be reached a few years
ago. Forcing the natural gas back into the wells has extended the "life"
of oil wells. Drawing the oil out at a slow rather than at a rapid rate has
also increased total yield.
On the other hand, we are certain that the oil supply of the world is
limited. We cannot get all the oil from any well. Some oil we cannot
reach. The cost of getting oil is slowly becoming higher.
From these facts we can reasonably conclude that (1) we should con-
serve oil, that is, we should use it carefully, without waste; (2) we should
extend the use of oil, for example, by adding hydrogen and reclaiming
used oil wherever economically possible; and (3) we should develop
petroleum substitutes.
The Burning of Gasoline. Gasoline burns easily. It vaporizes
readily. It forms an explosive gasoline-air mixture at ordinary tempera-
tures.
THE BURNING OF GASOLINE
in an automobile cylinder
[Gasoline assumed to be octane (CgHis)]
Exhaust tail-pipe gases
1 . When air is abundant and flame is free,
carbon dioxide steam
2C8H18 + 25O2 -» 16CO2 + 18H2O
2. When air is abundant, hot flame strikes water-cooled cylinder wall,
Carbon monoxide
(poison) steam
2C8Hi8 + 17O2 -4 16CO + 18H2O
3. When air is limited and flame strikes cooled metal,
Carbon steam
2C8H18 + 9O2 -4 16C + 18H2O
Carbon dioxide is 7.7 per cent and poisonous carbon monoxide 7.1 per
cent by volume of the exhaust from an average car.
Gasoline Substitutes. A liquid substitute for gasoline is alcohol.
It burns with abundant heat, vaporizing readily. Moreover, it can easily
be made from a number of annual crops — sugar cane, corn, or potatoes,
for example. In peacetime, however, most of it, is made by fermenting
the sugar in commercial molasses, although synthetic methods are im-
portant also.
CeHioOi + H2O -4 2C2H5OH -f 2CO2 1
sugar alcohol carbon dioxide
Two disadvantages of this liquid may be mentioned: alcohol absorbs
water readily, taking it even from the air; and at present, in the United
States, it costs more than gasoline. Also, the entire alcohol production ia
542 CHEMISTRY FOR OUR TIMES
only about 3 per cent of the volume of gasoline used. In spite of these
objections, alcohol-gasoline mixtures are used for motor fuel in other
countries where alcohol may not cost more or where its use may be
subsidized.
The countries where gasoline is scarce furnish us with a preview of
the fuels that cars and buses will use when petroleum is almost gone.
Some gasolineless cars use compressed fuel gas in large clumsy tanks.
Others carry little gas generators, using coal or wood for fuel. Such cars
travel a much shorter distance with a lot more bother than a car with
a tank full of gasoline. They also lack power on hills.
Dangers with Gasoline. Three facts should be remembered about the
use of gasoline. (1) Gasoline-vapor-air mixtures are explosive. Such ex-
plosive mixtures are always formed when gasoline is used for cleaning
or when a tank is being filled with gasoline. (2) Gasoline with tetraethyl
lead (leaded gasoline) is poisonous. The poison may be absorbed through
the skin. (3) The fumes from gasoline make some persons ill.
Lubricating Oil. Oil from the higher boiling fractions of petroleum
is an important lubricant. Waxes may be removed by chilling and filter-
ing, and other impurities are sometimes extracted by solvents. It is
interesting to note that most lubricating oils used today are far better
than are needed for the purpose of automobile lubrication.
Tests show that oil in service under differing conditions oxidizes
slowly and becomes diluted by gasoline that "blows" by the piston rings.
The oxidized oil is a satisfactory lubricant, and the gasoline evaporates
through a " breather." In fact, after 2000 miles of service, oil is found to
change less than 2 per cent in all its important properties. "Studies
of used oil show that a good oil retains its lubricating qualities much
longer than was formerly supposed, although the point at which it be-
comes unfit for use cannot be accurately determined — at the present
time."1
Under some conditions lubricating oil used in a car may be all right
at the end of 2000 miles or more; under others, such as driving in a
dust storm, it may be unfit for use after 300 miles. The demands of
the modern car on lubricating oil are severe, and oil may deteriorate
rapidly. No hydrocarbon can withstand excessive heat without decom-
position. It is good insurance in case of doubt to change oil rather than
to have expensive repair bills.
Smoke. Incomplete burning (see page 541) forms carbon, a black
soot that clouds the sky of some manufacturing cities. Smoke smudges
1 HOLMES, EDWARD O. JR., "The Changes in the Physical and Chemical Charac-
teristics of Lubricating Oil with Use," Report of the N.E.A. of Chemistry Teachers,
vol. 42, No. 3, March, 1941.
OUR FUELS 543
everything— curtains, clothes, buildings, and people. Worst of all, it is
an unnecessary and preventable waste.
To avoid smoke, burn it up. This may be done by (1) keeping the
fire hot enough, (2) supplying enough air, and (3) being sure that fuel
and air are well mixed.
Tobacco smoke (the visible part) is not a gas as some people assume,
but a collection of tiny solid particles, formed by the incomplete burning
of the tobacco.
QUESTIONS
21. State the requirements for a liquid automobile fuel.
22. What is petroleum with respect to composition?
23. Petroleum Facts and Figures, 1941, published by the American Petroleum
Institute, lists the 1940 use of petroleum in barrels in the United States (times
100,000) as: motor fuel, 5900; light fuel oil, 1640; heavy fuel oil, 3360; kerosene,
690; lubricants, 246; other products, 1364. What percentage of the total does
each use represent?
24. In 1940 the United States had 390,000 producing oil wells; in 1917, it
had 197,000. What is the per cent increase? Was the increase in petroleum produc-
tion necessarily the same percentage?
26. Total world production of petroleum in 1940 was 2,146,105 thousand bar-
rels. Outside the United States, 794,258 thousand barrels were produced. What
percentage of the world's supply was produced in the United States?
26. Make a diagram showing the arrangement of carbon and hydrogen atoms
and bonding electrons in normal (straight-chain) pentane (C5Hi2).
27. Distinguish destructive distillation from fractional distillation.
28. Show two possible structural arrangements for isomers of pentane.
29. Contrast "cracking" hydrocarbons with "polymerizing" them.
30. What is the meaning of 80 octane number as applied to gasoline?
31. Point out three ways by which the existing supply of petroleum is being
extended.
32. For what reason are lead compounds added to gasoline?
33. Production of 150 octane number gasoline is now possible. What does
this figure mean in respect to the standard scale?
34. What causes a motor to knock?
35. What is the real source of the motive power of a gasoline engine?
36. Why are the exhaust fumes from any gasoline engine always poisonous?
37. Point out the hazard of keeping containers oi gasoline in a garage.
544 CHEMISTRY FOR OUR TIMES
"You'll Never Know What Hit You." This ominous title ap-
peared on a warning against the danger of carbon monoxide in closed
garages. Slight amounts of carbon monoxide cause a headache. Larger
amounts produce quick unconsciousness, followed by death. The gas is
colorless and odorless so it gives absolutely no warning to its victims.
The only way to guard against it is by knowledge and intelligent actions.
To balance the comfort and service of fires to mankind, we must pay
the price of continual watchfulness. Out of control, fires destroy property
and people. The product of normal burning, carbon dioxide, may suffo-
cate persons. The product of improper burning, carbon monoxide, is an
insidious danger.
Carbon Monoxide. When carbon monoxide is to be made, a well-
ventilated fume hood must be used. The gas should not be prepared in
Courtesy of The Travelers Insurance Company
FIG. 30-12. — A closed cab and a leaky exhaust pipe may mean death from carbon
monoxide.
an ordinary room. To make carbon monoxide, formic acid is heated to
boiling and concentrated sulfuric acid .allowed to enter slowly. The acid
is dehydrated.
(cone. HiSO*)
H.COOH > H2o + co T
formic acid
The production of the gas industrially has already been described (see
page 529).
Carbon monoxide burns easily in air, with a blue flame.
2CO + O2 -4 2CO2
As we have learned, it is found in many fuel-gas mixtures.
Carbon monoxide can take oxygen from hot oxides, also. It is an
excellent reducing agent. In the laboratory we can easily show this by
its action on hot copper oxide or lead oxide.
'PbO 4- CO -* Pb 4- COa
OUR FUELS
545
Industrially, it is used to make our iron from the ore,
Fe2O8 -f 3CO -+ 2Fe -f 3CO2
to refine nickel, and to make wood alcohol (CH3OH) and phosgene
(COC1,).
3/UCfi GfL
\
Courtesy of The Travelers Insurance Company
Fio. 30-13. — In this portable carbon monoxide detector, the sample is first freed
of carbon dioxide (6). Then the carbon monoxide is oxidized to carbon dioxide (c) and
absorbed in strontium hydroxide solution to which an indicator is added (d). Twenty
pump strokes will decolorize 20 ml of solution if CO in the sample is 100 parts per
million.
546
CHEMISTRY FOR OUR TIMES
Asbestos
Pneumatic Trough
Hot HCOOH
FIG. 30-14. — Carbon monoxide may be prepared in the laboratory and its proper-
ties demonstrated by using the apparatus shown above. Complete ventilation ^s
essential.
Solid Fuels
Fossil Fuel. Many of the same processes that have gone on in the
past on the earth are going on today. The formation of coal is one ex-
ample. In swampy places plant and animal matter became decayed and
matted together. Peat was formed. This can be dried and used for fuel,
but it is not satisfactory for industrial uses. In some places layers of
peat became covered by soil and rocks. The pressure of the material
on top made it lose water and gases and change in chemical nature.
Brown coal, or lignite, was the result. Increased pressure gradually
changed the lignite to soft, or bituminous, coal. Special conditions of
high pressure produced the hard, or anthracite, coal. An authority esti-
mates that 20 ft of plant accumulations forms 3 ft of peat, and in turn,
1 ft of coal. The material in a seam of coal 1 ft thick thus represents the
accumulation of plant matter for about 300 years.
Our coal supply has a limit. When we use it, we are drawing on our
capital stock of the sunshine of other ages. Although we have a large
supply, it follows that we should use coal with care and not waste it.
Nature of Coal. Plant stalks, fibers, and wood are composed chiefly
of cellulose, a compound that has the formula (CeHioOb)*. When plant
tissue is changed into coal, it loses water, carbon dioxide, and methane
(CH4). The coal formed contains less oxygen and hydrogen and a rela-
tively larger amount of carbon as we go from lignite to bituminous to
anthracite.
Coal is a mixture of compounds. Most of these compounds are able
OUR FUELS
547
to join with oxygen and form carbon dioxide and water vapor. In addi-
tion, all the mineral matter that was present in the original plants is
left in the coal and remains as ashes when coal is burned. Sulfur, an
unwanted impurity, is frequently found in coal.
COMPOSITION AND FUEL VALUE OF THE SOLID FUELS*
Fuel
Carbon,
%
Hydrogen,
%
Oxygen,
%
Relative
fuel value
Cellulose
44 5
6.2
49.3
7.5
Wood . . .
50 0
6.0
44.0
7.4
Peat
60 0
5 9
34.1
9.9
Lignite coal
67.0
5.2
27.8
11.7
Bituminous coal
Anthracite qpal ....
88.4
94.1
5.6
3.4
6.0
2.5
14.9
15.7
* Adapted from Alexander Findlay, Chemistry in the Service of Man, 5th ed., Chap. V, Fuels and
Illuminants, Longmans, Green and Company, New York, 1939,
Use of Coal. Coal is one of the great raw materials of industry. If we
trudge about the grounds of a large manufacturing company or power
plant, we observe large coal piles — ample proof of the need for coal.
' '
FIG. 30-15. — These men are mining a seam of coal.
Much of our coal is wasted. Indeed, great need exists for studying
the best ways of using coal effectively. In a modern steam power plant,
548
CHEMISTRY FOR OUR TIMES
the supply of coal represents two-thirds of that which started from the
mine. About one-third is wasted or lost in mining and transportation.
Two-thirds of the part burned in the fires of the boilers is wasted, and
often less than 4 per cent is changed into useful work. A small steam
locomotive is one of the most ingenious machines for wasting coal ever
devised by man.
The most effective way of heating with coal is by the use of carefully
designed grates or by burning it as a powder. Anthracite coal is entirely
a fuel coal. Lignite is not used
extensively, although when our
bet ter grades of coal are exhausted,
more use may be made of this sort
of fuel.
Smokeless Fuel. By outlaw-
ing it, the city of St. Louis, in
1940, eliminated the smoke nui-
sance, which in the past often made
it necessary to turn on automobile
headlights during the daytime.
Outlawing smoke was economic-
ally possible because of the Cur-
ran-Kn<>\\ Ics process of producing
smokeless fuels from the inferior
Illinois coals, which, though cheap
and plentiful, burned with an ap-
palling evolution of soot. This was
accomplished after extensive re-
search into the methods of making
coke that would give full heat at
a fuel-bed temperature below the
melting point of the slag. The im-
proved coke costs the St. Louis
fuel consumer no more, and the
benefits to health and cleanliness are tremendous.
This is one example of how citizens can apply the advances of scien-
tific research if they keep informed and are interested.
Charcoal. When wood is heated in a closed retort, or destructively
distilled, interesting changes occur. A choking, smoky vapor arises. The
wood becomes black and porous charcoal. The vapors are condensed by
passing them through pipes cooled by running water. Wood alcohol
(CH3OH), acetic acid (HC2H3O2), acetone [(CH3)2CO], and water are
found in the condensed vapors.
Courtesy of A . , mpany, Inc.
FIG. 30-16. — Coke is shown here being
pushed from by-product ovens after the
"burn" has been completed. From this
point, the coke will go to the quencher.
OUR FUELS 549
Charcoal is a good household fuel since it burns readily, without
smoke, and leaves little ash. Carefully made charcoal sticks are used by
artists. Charcoal absorbs gases, sometimes undesirable ones. Decayed
animal matter is made a bit more approachable when sprinkled with
charcoal. Activated charcoal is made from carefully selected vegetable
matter and is used in military and industrial gas masks.
Charcoal is frequently made without collecting the vapors. Piles of
wood are placed in a pit and covered with sod. The whole mass is set on
Photo by Philip Acqitariv*
FIG. 30-17. — This is a rural method of making charcoal. A volcanolike heap of wood
is covered with sod. Then it is set afire, burning partially in limited air. A heap of char-
coal remains when the sod is removed.
fire. Owing to lack of air the burning is incomplete, and the wood becomes
changed into charcoal. Charcoal "burning" was done in the European
forests in King Arthur's day and is carried on today in the same way.
(See Fig. 30-17.)
SUMMARY
Among gaseous fuels, coal gas, the product of destructive distillation of bitu-
minous coal, consists chiefly of methane and hydrogen. Destructive distillation
is the process of heating a material in a closed retort in the absence of air and
condensing the vapors formed. Water gas is made by an intermittent process.
Steam is blown through hot coke, an endothermic change taking place. The result-
ing mixture of hydrogen and carbon monoxide is enriched with oil gas and the
mixture stabilized by passing it over hot bricks. Water gas is the starting point
550 CHEMISTRY FOR OUR TIMES
for synthetic chemicals. Producer gas is made by passing air slowly through a
deep bed of burning coal or coke. It consists . chiefly of nitrogen and carbon
monoxide and is a "lean" fuel and an inexpensive one. Natural gas is fuel from
the earth, chiefly methane. Blast furnaces and oil refineries produce fuel gases as
by-products.
Acetylene is prepared by the action of calcium carbide With water. It is a color-
less gas that decomposes when heated and burns in oxygen with enough heat to
melt steel. Acetylene is used as an illuminating gas because it burns with a sooty
flame, as fuel for the oxyacetylene torch, and as a starting compound for syn-
thetic chemicals.
Flames are burning gases. The Bunsen burner burns a mixture of -gas and air,
producing a luminous flame if the air holes are closed and a nonluminous flame
when a mixture of air and gas is burned.
Among liquid fuels, petroleum, a natural mixture of hydrocarbons, is obtained
by drilling into the earth. Fractional distillation separates petroleum according
to a range of boiling points into fractions some of which are gasoline, kerosene,
fuel oil, lubricating oil, and paraffin. Refining consists of removing unwanted
impurities from petroleum fractions.
Sources of gasoline are (1) straight-run distillation, (2) " cracking" heavier
hydrocarbons into smaller molecules, (3) condensing vapors from natural gas,
(4) hydrogenation of lignite, and (5) polymerization of low molecular-weight
hydrocarbons.
Hydrocarbons are compounds of hydrogen and carbon only. The simplest is
methane, (CH4). Some hydrocarbons are straight-chain compounds, some have
branched chains, ancj others have a ringlike structure. Isomere are compounds
having the same number of atoms arid same molecular weight but differing in
arrangement of atoms within the molecule.
The octane number is a rating of the knock performance of gasoline when
compressed and ignited in an engine. High octane number (80 to 100) means
that a gasoline will burn smoothly when compressed. The octane number can
Be raised by addition of lead tetraethyl and other inhibitors.
The petroleum supply is limited, although resources are extensive. Gasoline
is very high in available energy. Burning gasoline evolves heat, which expands
the gaseous contents of an automobile cylinder, pushing the piston down. Poison-
ous carbon monoxide is always formed by burning gasoline in an automobile
engine.
Gasoline substitutes include alcohol and fuel gases. Wood gas from a generator
carried with the vehicle is sometimes used.
Smoke represents unburned fuel. It can be avoided by (1) maintaining a high
temperature in the fire, (2) a sufficient supply of air, and (3) adequate mixing of
air and fuel.
Carbon monoxide is prepared by incomplete burning of carbon or carbon
compounds, by reduction of carbon dioxide with hot carbon, and by action of hot
formic acid on concentrated sulfuric acid. It is a colorless, odorless gas at room
conditions. It is extremely poisonous, burns with a pale blue flame, and is an
excellent reducing agent. It is used as an industrial fuel and as a reducing agent for
metallic oxides. It is used to make methyl alcohol and to refine nickel.
•OUR FUELS 551
Among solid fuels, coal, the vegetable matter of past ages, is found in ex-
tensive deposits in many different types. Coal is used as a fuel, to make coke,
and to make coal gas. It is the main source of industrial energy.
Charcoal is made from wood by destructive distillation or by partial burning.
It is used for fuel, for a reducing agent, and for adsorbing gases.
QUESTIONS
38. What part does the concentrated sulfuric acid play in the preparation of
carbon monoxide from formic acid?
39. List three physical properties of carbon monoxide.
40. Write formula equations for (a) burning of carbon monoxide; (6) re-
duction of carbon dioxide by hot carbon; (c) reduction of ferric oxide (FejOj)
by carbon monoxide; (d) reduction of magnetic iron oxide (Fe3O4) by carbon
monoxide.
41. What percentage of nickel carbonyl [Ni(CO)4] is due to carbon monoxide?
42. Distinguish three types of coal from each other.
43. What evidence shows the origin of coal?
i$8
per ton or an-
$5
f$14
thracite coal at •{ _„ per ton?
l$o
45. Coal ashes are sometimes spread on the soil. Do they have fertilizing
value?
46. What advantage has the by-product method of making charcoal over the
old method? Why is the old method still used?
UNIT SEVEN CHAPTER XXXI
PLANT AND ANIMAL CHEMISTRY
Acids
Picture an alchemist gathering ants. A supply of these creatures is
obtained and crushed in a mortar with a pestle, and the carcasses are
extracted with water. The resulting liquid is found to taste sour, and it
is given the appropriate name formic acid (H — COOH) (ant acid from
the Latin formica, meaning "ant"). In fact, this is the acid injected
into the flesh by nettles, bees, mosquitoes, wasps, and hornets that
"sting." A synthetic ant bite may be enjoyed by dipping a needle in a
solution of formic acid and thrusting it into the flesh. If a less personal
observation of swelling is desired, the needle may be pricked into pre-
pared gelatin instead of the flesh.
All organic acids that contain the carboxyl group may be recognized
0
by —COOH* or, better, — C— O— -H*. Irf the case of formic acid the
remaining valence bond on the carbon atom is attached to a hydrogen
O
atom by a covalent bond, H — C — 0 — H*. The replaceable hydrogen
atom is starred (*).
Formic Acid (H — COOH*). Formic acid is the simplest of all the
organic acids. When pure, it is a colorless liquid that has a sharp odor
and taste, boils at 100.5°C, and is 1.22 times as dense as water. It dis-
solves in water in all proportions.
Formic acid can be made by heating oxalic acid [(COOH) 2] dissolved
in glycerol [C8H6(OH)8].
(COOH)s -+ CO2 + HCOOH*
oxalic acid formic acid
When heated, formic acid decomposes into carbon monoxide and
steam.
HCOOH -» CO + H20
The acid is a good reducing agent.
New Terms
formic acid ketone fat
aldehyde ester anesthetic
hormone
553
554
CHEMISTRY FOR OUR TIMES
Acetic Acid (CH3COOII*). The best-known organic acid is acetic
acid (CH3 — COOH), since 4 to 10 per cent of it is found in vinegar.
H
Acetic acid may be considered to be related to methane H — C — H by re-
H
H
placing one of the hydrogen atoms by a carboxyl group. H — C — COOH*.
H
Vinegar forms when hard cider (which contains alcohol) oxidizes in
air in the presence of certain bac-
teria (see page 519).
C2hUOH + O2 -f
alcohol from air
CHa-COOH* 4- H20
acetic acid
The change is slow when the cider
is stored in barrels but relatively
rapid when the hard cider is
sprayed into air or allowed to
trickle over wood shavings in a
tower through which a current of
air is flowing.
Acetic acid may also be pre-
pared from acetylene in the pres-
ence of catalysts by the following
synthesis :
C2H2
acetylene
2CH3CHO
02
from air
CH3CHO
acetaldehyde
-» 2CH3COOH
acetic acid
Glacial acetic acid (100 per
Courtesy of V. 8. For e*t Service
FIG. 31-l.-Plant chemistry is illus- cent) * so called because of the
trated by this stand of longleaf pine being icelike crystals that form from
turpentined at Georgetown, S.C. the pure liquid at 16.7°C. Both the
sharp odor and the sour taste of a dilute solution of this liquid are observed
in vinegar, which contains in addition some flavoring and coloring
materials derived from the original fruit.
Acetic acid is a weak acid when compared with hydrochloric but
relatively strong when compared with most organic acids. It dissociates
CH3COOH
CHaCOO- + H+
acetate ion
extensively enough to react with zinc and other active metals, carbonates,
PLANT AND ANIMAL CHEMISTRY
555
and hydroxides. It combines with alcohols in the presence of a dehydrat-
ing agent (concentrated H 28(1)4) to form esters.
CHjCOOH + HOCH, -» CHaCOOCH, + H2O
acetic acid methanol methyl acetate
Acetic acid is used to make acetates, such as sodium acetate
(CH8COONaorNaC2H302)andlead acetate or sugar of lead[Pb(C2H802)2].
Other Organic Acids. Other organic acids are known. Many re-
freshing soft drinks (soda water) contain citric acid or tartaric acid. Sour
fruit or berries contain acids, or salts of organic acids.. In fact, some
acids contain more than one carboxyl group per molecule. More infor-
mation about carboxylic acids is contained in the following table:
SOME COMMON ORGANIC ACIDS
Acid Name
Formula
Remarks
Formic
Acetic
H-COOH
CHa-COOH
Trace in honey — acts as a preservative
Synthetic vinegar made from acetic acid
Propionic ... .
Butyric. . .
Palmitic
CiH»-COOH
CaH7-COOH
Ci6H8l-COOH
(4 %) and water — lacks flavor
Also called propanoic acid
Found in rancid butter and in Limburger
cheese
Found as esters of glycerol in fats or oils
Stearic
Ci7HJ6-COOH
Used to make cold, vanishing, shaving, and
Oleic . .
C,7Haa-COOH
latherless shaving creams
Its glyceryl ester found in oils. "Unsatur-
Linoleic
Oxalic
OnH.i-COOH
COOH
ated," can add hydrogen
Found in linseed and cottonseed oil as esters.
More unsaturated than oleic. Adds oxygen
from air readily; also adds hydrogen
Found as potassium salt in sorrel. Has two
Tartaric
COOH
COOH
carboxyl groups. Poisonous. Used as bleach-
ing agent
Potassium hydrogen tartrate (C^^eKH);
Citric
HCOH
HCOH
COOH
CH2— COOH
HO-^C— COOH
CH»— COOH
insoluble in alcohol and deposits inside wine
casks. Crude deposit called "argols," re-
fined, "cream of tartar"
Found in many fruits and berries. In lemons,
6%. Many uses of citrates. Magnesium
citrate used in medicine as a purgative
QUESTIONS
1. Write the formula for the radical found in ail organic acids. Indicate the
replaceable hydrogen atom.
2. Write the formula for (a) formic acid; (6) sodium formate; (c) calcium
formate; (d) methyl formate.
556 CHEMISTRY FOR OUR TIMES
3. Write the formula for (a) oxalic acid; (6) sodium oxalate; (c) calcium
oxalate; (d) dimethyl oxalate; (e) methyl ethyl oxalate.
4. Name three organic acids, and tell the natural source of each.
5. Write an equation for the complete burning of (a) formic acid; (b) acetic
acid; (e) oxalic acid.
6. By equations show the change of (a) oxalic acid to formic acid; (6) alcohol
to acetic acid; (c) acetaidehyde to acetic acid; (d) acetic acid to sodium acetate;
(e) acetic acid to lead acetate.
7. Name two industries in which the flavor of vinegar is important.
8. On standing in air, grape juice changes to wine, and in turn the wine
changes to wine vinegar. Write two equations to represent these changes.
9. Write formulas for the (1) sodium and (2) calcium salts of (a) propionic
acid; (6) butyric acid; (c) palmitic acid.
10. (a) Tartar emetic is potassium antimony! tarjrate. Write its formula. (6)
Rochelle salts is the sodium potassium salt of tartaric acid. Write the structural
formula.
11. Point out an essential difference between acetic, oxalic, and citric acids.
12. What weight of sodium hydroxide is needed to neutralize |«QQ grams of
vinegar, 10 per cent acetic acid?
13. When \ -^ grams of dilute vinegar, 6 per cent acetic acid, is run onto an
excess of sodium hydrogen carbonate, what volume of carbon dioxide gas at STP
is liberated?
14. What difference, if any, would there be in the volume of carbon dioxide
produced if sodium carbonate was used in the previous problem instead of sodium
hydrogen carbonate?
15. Write equations for the complete neutralization by potassium hydroxide
of (a) acetic acid; (6) formic acid; (c) oxalic acid; (d) tartaric acid; (e) citric acid.
Aldehydes
Formaldehyde. Aldehydes are so called because they can be made
from alcohol deAydrogenated. They all contain the characteristic group-
O
I!
ing — C — H, or — CHO. Aldehydes represent an intermediate stage of
oxidation between an alcohol and an acid. This can be seen from the
following series of chemical changes, which show the steps in the oxidar
tion of methyl alcohol:
PLANT AND ANIMAL CHEMISTRY 557
CH.OH + [O] -» HCHO + H,0
methanol formaldehyde
HCHO + [O] -» HCOOH
formaldehyde formic acid
Some aldehydes are fragrant and give characteristic odors to so-
called " essential " oils, as cinnamic aldehyde in oil of cinnamon, and
benzaldehyde (CeHsCHO) in oil of bitter almonds.
Formaldehyde is made by the oxidation of methyl alcohol vapor by
oxygen of the air in the presence of hot copper that has oxide on its sur-
face. The equation for the reaction is the first of the two given above.
The product of the reaction is a gas, irritating to the eyes. A solution of
the gas dissolved in water to 37 per cent strength is called "formalin."
Formaldehyde is used for making resins (Bakelite, for example) and
dyes. It is a good disinfectant. The solution is used to harden gelatin in
photographic processes and by a similar action to preserve biological
specimens.
Formaldehyde readily changes into a solid form called paraformalde-
hyde. This change is explained by assuming that formaldehyde is poly-
merized, that is, that the solid contains a multiple molecule composed
of a number of units each having the simple formula HCHO. Formalde-
hyde gas is easily released from the solid form for use as a disinfectant
and preservative. "Paraform candles" are burned for this purpose.
QUESTIONS
16. Point out the difference between the characteristic groups in aldehydes
and in organic acids.
17. What product is formed (a) by oxidation of an aldehyde; (6) by reduction?
18. Balance this equation: (Do not unite in this book.)
HCHO + NH, -> (CH,)6N4 + H2O
hexamethylenetetramine
19. What weight of methanol must be used in order to fill an order for i ,. tons
of formaldehyde?
20. Formaldehyde is one ingredient of embalming fluid. What purpose does
the formaldehyde serve in this mixture?
21. List three uses for formaldehyde.
Ketones
Acetone. Another class of organic compounds is called ketones and
has the characteristic group yC = 0.
The most important member of this group of compounds is acetone
[(CH3)2CO], or dimethyl ketone. Acetone is a colorless liquid with a
penetrating pleasant odor, boiling at 56°C. It is a good solvent for resins,
gums, and varnishes, including fingernail lacquer. It is used for making
558
CHEMISTRY FOR OUR TIMES
chloroform (CHC13) and iodoform (CHI3). Like wood alcohol, acetone
was formerly made from distilling wood. Today both methanol and
acetone are made synthetically.
QUESTIONS
22. Write formulas for (a) diethyl ketone; (b) dimethyl ketone; (c) methyl
ethyl ketone; (d) chloroform; (e) iodoform.
23. For what purpose is acetone used in lacquers?
24. Write an equation for the burning of acetone.
25. What weight of dry calcium acetate is needed to produce j - liters of liquid
acetone (density 0.79 grains per milliliter) ? The equation for the reaction is
heated
Ca(C2H802)2
(CH,),CO -h CaC03
Courtesy of Commercial Solvents Corporation
FIG. 31-2. — Animal chemistry is illustrated by these rabbits lined up in stanchions
in a penicillin factory. The rabbits are used for pyrogen tests. They are not injured, the
same rabbits being used several times.
Ethers
Ether. Ethers correspond to organic oxides. For example, the com-
mon ether is diethyl oxide [(C2H6)20]. Note the difference between the
characteristic grouping in an ether (=0) and that in a ketone (=C=O).
Ether is made by treating alcohol with concentrated sulfuric acid
PLANT AND ANIMAL CHEMISTRY 559
as a drying agent in the presence of an aluminum compound as a catalyst.
2C2H5OH -> (CjHOfO -f H2O
ethanol ether
Ether is a liquid that boils at 34.5°C and evaporates quickly at room
temperature. The vapor is flammable and is explosive when mixed with
air. Ether has an advantage over chloroform (CHCls) as a general an-
esthetic because its effects are more easily controlled. However, it has
several disadvantages as an anesthetic, and its use is giving way to more
desirable ones.
Ether is an excellent solvent. Natural fats and waxes are often ex-
tracted from plants by dissolving them in ether, evaporating and recover-
ing the ether, and leaving the plant product.
QUESTIONS
26. Write the formula for (a) dimethyl ether; (b) diethyl ether; (c) methyl
ethyl ether.
27. To what class of compounds does each of the following belong?
(a) CH, (c) CH3 (e) C2H6
\ \ \
c«o c«o c*o
H HO H
(6) CH, (d) CH3 * (/) CH3
C*O H-C-OH O
/ / /
CsHy H C2Hs
28. Why is ether sometimes used to remove spots from clothing? What dan-
ger accompanies its use?
29. State one advantage and one disadvantage of the use of ether for anes-
thesia.
30. Write an equation for the preparation of dimethyl ether.
{1480
37Q grams of common
ether?
Esters
Ethyl Acetate. We have already seen (see page 555) that esters can
be made from an acid and an alcohol by the removal of water.
When small amounts of ethanol and acetic acid are heated in a test tube with
a few drops of concentrated sulfuric acid, a pleasant, "fruity" odor of ethyl ace-
tate, an ester, can be noticed.
CH,COOH + HOCaHft -4 CH,COOCtH» + H,O
acetic ethanol ethyl acetate
acid
560
CHEMISTRY FOR OUR TIMES
By substituting different acids or alcohols in the above general reaction, a
large number of esters can be made. For example, the popular wintergreen flavor-
ing, identical with that found in the checkerberry plant, can be made in the
laboratory by the action of salicylic acid and methanol.
C«H4(OH)COOH + HOCH, -» C«H4(OH)COOCH, + H2O
salicylic acid methanol methyl salicylate
or oil of wintergreen
The natural odors and flavors in fruits and flowers are due chiefly
to esters. In some cases the identical plant product may be prepared
synthetically, but in many others the perfumes of flowers are delicate
mixtures of several scents. To imitate these requires the blending skill
of a perfumer.
Esters, such as butyl acetate and ethyl acetate, are excellent solvents
for the gums in lacquer finishes that are sprayed onto automobiles. These
solvents evaporate quickly, leaving a tough coating. Esters of high
molecular weight are used as internal lubricants, or plasticizers, in rubber
and plastic products. Common fats are esters of the alcohol glycerol
[C3H6(OH),].
Name
Formula
Remarks
Esters of simple alcohols
Iso-amyl acetate
CHaCOOCsHn
C.H7COOC,H8
CH,COOC8Hi7
Called "banana oil"
Odor resembles that of pineapples
Odor resembles that of oranges
Ethyl butyrate
Octyl acetate
Esters of glycerol — fats
Glyceryl butyrate
(C,H7COO).C,H,
(Ci7H»COO),C,H,
(C,7H,,COO),CaH6
In butter (5 %)
In beef suet and mutton tallow
In olive oil (72 %)
Glyceryi stearate
Glyceryl oleate
Fats. Fats are mixtures of the glycerol esters of the higher molecular
weight acids of the formic acid series or esters formed from a combina-
tion of them. Esters commonly found are those of stearic, oleic, and
palmitic acids. All fats and oils, regardless of natural source, are
combinations of relatively simple parts. Because the esters of the acids
mentioned are found in fats, the acids themselves are called the "fatty
acids."
A fat can be made in the same general way in which an ester is pro-
duced. An alcohol (glycerol) and a fatty acid are brought together in the
presence of a dehydrating agent.
C,H6(OH)a
glycerol
(C17H,6COO),C8H5 -f 3H,0
glyceryl etearate
stearic acid
Notice that glycerol, a fnhydroxy alcohol, requires three molecules of
_ PLANT AND ANIMAL CHEMISTRY 561
the fatty acid for complete reaction. This equation may look complicated,
but the learner who tries writing it our for himself will see that no new
principles are involved, merely new and larger radicals.
Decomposing Fats. A supply of glycerol (glycerin) can be made for
explosives by the action of steam on fat. This reaction is the reverse of
the one showed in the preceding paragraph.
3H6 + 3HOH -+ C3H5(OH)8 + 3CuH3iCOOH
glyceryl palmitate steam glycerol palmitic acid
Esters also act with solutions of sodium or potassium hydroxide to form
soaps or soaplike metallic salts. If a fat is treated with lye (NaOH) solu-
tion, the products are a sodium soap and glycerol. (See page 603.)
QUESTIONS
32. What is the percentage composition of ethyl acetate?
33. The formulas C4H8O2 and CH8COOC2H8 both Represent ethyl acetate.
Why is the second preferred?
34. Write equations for the preparation of the following, each from its ap-
propriate organic acid and alcohol: (a) ethyl acetate; (b) methyl acetate; (c)
methyl salicylate; (d) ethyl salicylate; (e) isoamyl acetate.
35. What is a plasticizer?
*
36. Define the general terms ether; ester; aldehyde; ketone; carboxylic acid;
alcohol.
37. Most fats contain esters derived from what alcohol?
38. In what respect does the composition of glycerol differ from the composi-
tion of ordinary alcohol?
39. Palmitic acid has the formula CuHiiCOOH. Write the formula for (a)
ethyl palmitate; (6) glyceryl palmitate; (c) sodium palmitate; (d) calcium
palmitate.
40. Name two solvents for fat.
41. When butter turns rancid, an evil-smelling acid is formed by the decom-
position of glyceryl butyrate (butterfat). Write the formula for this acid.
42. Write the formula of a fat, showing the glyceryl, stearate, oleate, and
palmitate radicals all in one molecule.
43. What product made from fat is useful for (a) military purposes; (6) house-
hold purposes?
Waxes
Waxes, like fats, are esters, but they are esters of alcohols containing
one hydroxyl group. One of the most extensively used waxes in furniture
and floor polishes is carnauba wax, obtained from the fcoating on certain
Brazilian palm leaves. It contains myricyl cerotate (
562
CHEMISTRY FOR OUR TIMES
an ester. Beeswax contains another ester, myricyl palmitate
(C15HaiCOOC3iHfl3).
While these formulas look large, they represent nature.
QUESTIONS
44. Distinguish in general the composition of a wax from that of a fat.
45. Write an equation to show the reaction produced by treating beeswax
with lye.
46. What is the percentage of carbon in beeswax?
47. Give two uses for beeswax and one for carnauba wax.
Enzymes and Hormones
Enzymes. Let us stir one-half a yeast cake into a little warm water in a bottle,
then fill the bottle with a solution of hydrogen peroxide, cover it with a glass
plate, and immediately invert and place it mouth downward in a pan of water so
Oxygen.
Yeast
Warm Water
Hydrogen Peroxide
FIG. 31-3. — Enzyme at work is illustrated by this experiment. Yeast enzymes readily
liberate oxygen from hydrogen peroxide.
that the mouth is below the water in the pan. (See Fig. 31-3.) The yeast cake con-
tains catalysts produced by the living yeast plants that decompose the hydrogen
peroxfde.
2H2O2 -4 2H2O + O2 T
The oxygen produced collects in the upper part of the bottle and expels the reac-
tion mixture.
Such catalysts from living sources are called enzymes. Many useful
and interesting changes are aided by enzymes. "Most life processes are
accomplished in the presence of enzymes. The oxidation of food in the
cells of animals can occur at rapid rates at body temperature only be-
cause enzymes serve as catalysts for the very complicated processes."1
We have seen that the enzyme in malt called diastase assists the
change of starch to sugar (maltose) (see page 597). An enzyme in yeast
called zymase catalyzes the oxidation of glucose to alcohol (see page 518).
Another enzyme in yeast called invertase catalyzes the hydrolysis of
sucrose into simple sugars.
H2O
C12H«OU
sucrose
C«H,2O«
glucose
fructose
Erie Ball, Harvard University,
PLANT AND ANIMAL CHEMISTRY 563
It is well known that a cracker held in the mouth tastes sweet after
a while.
A more convincing test may be made by boiling a chewed and unchewed
cracker respectively with Benedict's solution. The former reduces the copper
salt dissolved in Benedict's solution to a pink precipitate of cuprous oxide
(Cu20), showing that a reducing sugar has been formed from the starch of the
cracker. The unchewed cracker gives no evidence of sugar.
The change of starch to sugar in the mouth is carried on with the
aid of ptyalin, an enzyme in saliva. Other changes aided by enzymes occur
throughout the digestive system.
Hormones. The processes within the body itself are controlled by
small amounts of chemical regulators in the blood stream called hormones.
These chemical compounds are produced in the "ductless glands " in
specialized organs of the body. In the neck the thyroid gland produces
the hormone thyroxine, controlling growth. Thyroxine contains iodine,
an element that must be supplied in small amounts for normal health.
The adrenal glands produce the hormone adrenalin, which causes blood
vessels to contract, heart to speed up, sugar to be released from the liver
ready for fuel, and the body to be prepared generally for emergencies.
Other hormones control the process of normal reproduction. Lack or
excess of a hormone results in disturbance to growth or health. The
study of hormones has been made by doctors and chemists jointly, and
many human ills have been corrected by the knowledge gained about
them and their action. The use of the hormone insulin has removed the
terror of diabetes.
The following steps in a study of this sort are typical of modern
chemical research: (1) study of the subject in general by experimentation
and observation of healthful and diseased conditions; (2) collection of the
active principle (hormone in this case) from natural sources; (3) purifica-
tion of the substance, analysis, and investigation of the structure (ar-
rangement of atoms within the molecule) ; (4) laboratory synthesis of a
compound identical with the natural one; (5) synthesis of compounds
similar to the natural one in the hope of "improving on nature. "
Obviously, such a study requires years of patient work and challenges
the skill of many trained workers to make even the tiniest advance into
the unknown.
SUMMARY
0
All organic acids contain the caboxyl radical — C — 0 — H. Formic acid, the
simplest organic acid, is prepared by heating oxalic acid. It decomposes when
heated, forming carbon monoxide and water.
Acetic acid is formed by the oxidation of alcohol, as in vinegar making. It is
also synthesized from acetylene, water, and oxygen. Acetic acid is a weak acid,
564 CHEMISTRY FOR OUR TIMES
that is, it dissociates slightly in water solution; it reacts with active metals,
hydroxides, alcohols; it is used in the manufacture of vinegar, insecticides, and
plastics.
Many other organic acids are known. Some occur in nature either as the acid
itself or as salts of the acid. Included among the well-known organic acids are
oxalic acid, tartaric acid, and citric acid.
0
All aldehydes contain the — C — H group. Formaldehyde (ECHO), simplest of
all aldehydes, is a gas at room temperature. It is made by the oxidation of methyl
alcohol. Formaldehyde is soluble in water and is irritating to the eyes. It is used
as a disinfectant and preservative and to make synthetic resins. Some aldehydes
are found in nature as natural flavoring agents.
All ketones contain the =C=O group. Acetone, an excellent solvent for gums
and resins, is the best known compound in this class.
All ethers contain the =0 group. Ordinary ether is diethyl ether. It is pre-
pared by the dehydration of alcohol. It is a low-boiling liquid, is flammable, and
is an excellent solvent for waxes, gums, and grease. It is also used as an anesthetic.
Esters are made from acid and alcohol by removal of water. They are found
in nature in fruits and flowers. Fats are esters, chiefly of stearic, oleic, and palmi-
tic acids with glycerol. They may be decomposed (hydrolyzed) by steam into the
corresponding fatty acid and glycerol. Fats treated with lye form soap and
glycerol (saponification).
Waxes are esters of monohydroxy alcohols of high molecular weight. Car-
nauba wax is used for furniture and automobile polish. Beeswax has many
uses.
Enzymes are catalysts, produced in living organisms, that promote definite
chemical changes. Examples are as follows: Diastase in malt changes starch to
sugar. Invertase in yeast changes sucrose to simple sugars. Ptyalin in saliva
changes starch to sugar.
Hormdnes are chemical regulators of the body. The normal processes of the
body are controlled by small amounts of chemical substances secreted into the
blood from glands.
Hormones have been studied according to the steps characteristic of chemical
research, as follows: (1) extensive, accurate observation of the problem; (2) iso-
lating the natural material relating to the problem from impurities found with it
in nature; (3) analysis of the purified natural compound; (4) synthesis of the active
principle, including preparation of similar compounds.
QUESTIONS
48. Name two enzymes found in the body and one outside the body. Tell
where .each is produced and the purpose each serves.
49. Give an example of cooperative research between chemists and doctors of
medicine.
60. Indigo dye, formerly made from plants, is now manufactured in fac-
tories. How do the five steps of chemical research apply to this example?
UNIT SEVEN CHAPTER XXXII
CELLULOSE AND PLASTICS
We start the day by rising from a bed on which cellulose in cotton is
some part of the bed clothing. Our own clothing consists in part at least
of cotton or rayon cellulose garments. At breakfast time we may read
the news from a cellulose wood-pulp newspaper while sitting on a cellulose
chair. Throughout the day paper in numerous forms — in books, letters,
business blanks, wrappings — is an accepted part of life. Our vegetable
food contains some cellulose. We enjoy radio programs from a radio
contained in a cellulose-filled plastic case. Burning wood cellulose warms
the hearth of our cellulose house.
Cellulose. The stalks of plants, wood, cotton, and linen are chiefly
cellulose. From cellulose is manufactured paper, explosives, and rayon.
Obviously, a large part of the vegetable world is cellulose (CeHioOs)*.
A large part of the activity of mankind Is concerned with oxidation.
Food is oxidized to secure energy for the body; wood, coal, and oil are
burned (oxidized) for warmth and power. The vegetable world, however,
reverses this process. By the process of photosynthesis carbon dioxide
and water are changed to starch and cellulose in the presence of sunlight,
the sun's energy thus being trapped.
Because man makes extensive demands on the vegetable world, both
present and past, the problem of supply is a pressing one. Reforestation,
for example, is necessary to ensure a continuous supply of paper and
other cellulose products.
Properties of Cellulose (CeHioOe)*. Filter paper used in the chem-
ical laboratory is almost pure cellulose. It burns leaving no solid re-
mainder if pure and only a small amount of mineral matter as ash present
in the original wood if impure.
A solution of zinc chloride (ZnClj) or of copper hydroxide [Cu(OH»)2]
in ammonia water (NH3 in H20) acts on cellulose to form a colloidal
New Terms
thermosetting cellulose vulcanize
resin latex
565
566 _ CHEMISTRY FOR OUR TIMES _
dispersion.1 When cellulose is soaked in lye (NaOH) and treated with
carbon disulfide (CS2), orange crumbs of cellulose xanthate form. The
last two actions mentioned are the basis of manufacture of two different
types of rayon.
Nitric acid (HNOa) in the presence of concentrated sulfuric acid a$
a dehydrating agent adds nitrate groups ( — NO 3) to cellulose, forming
cellulose nitrate.
C24H4oO2o -f 10HNO3 -4 C24H3opio(NO8)io -f 10H2O
cellulose nitric acid cellulose nitrate
nitrated highly (12.8 %)
The extent of nitration determines the number of nitrate groups added
and the use of the product. Highly nitrated cellulose is used for explosives;
less highly nitrated cellulose is used for lacquers, celluloid, and coatings
for cloth that make it resemble leather.
When cooked with acid under pressure, cellulose slowly changes to
starch.
(HCl)
(CeHioO*)* + zH2O - » zCeHnO*
catalyst
Pulp. Pulp is made chiefly from rags or wood, although many cellu-
lose fibers such as straw or grasses may be used. Cooking the fibrous
material with steam, usually with added chemicals, produces a uniform
cream of cellulose fibers.
Mechanical pulp is simply ground wood containing lignin and other
materials present in the original log. Paper, such as newsprint, made from
mechanical pulp can be identified because it turns yellow with a water
solution of aniline (C6H6NH2), while chemical pulp shows no color change
with the same treatment.
Chemical pulp is made by cooking clean wood chips with lye (NaOH)
or with calcium hydrogen sulfite [Ca(HS03)2] with an excess of sulfur
dioxide (SO2). Kraft pulp is made by using sodium sulfate (Na2S04)
and lye. Other special pulps, such as that produced from southern pine,
require additional chemical processes.
Much pulp is used in the manufacture of paper (commonly a mill
makes fibers into finished paper, using its own pulp), but other uses of
pulp are important. Pulp is used to manufacture rayon, to make ex-
plosives, and as a filler.
Paper. The art o^ papermaking consists in catching a uniform felt of
fibers on a screen, removing the water, and pressing the resulting mat
into a sheet. A sheet of paper so made would resemble blotting paper,
unsized, unfilled, and absorbent. Binders, such as rosin soap, and fillers,
1 A simplified preparation of Schweitzer's reagent A. Breslau, Journal of Chemical
Education, vol. 19, No. 8, August, 1942.
CELLULOSE AND PLASTICS 567
such as clay or barite (BaSO^, are added so that ink will not run. Fine
papers may be coated with casein or with gelatin.
Making paper by hand can be carried out with simple equipment con-
sisting of a fine-mesh wire screen mounted on a frame, a bucket of pulp
suspension, and a warm flatiron.
Careful examination of a baker's ordinary cardboard pie plate will
show the method of manufacture. Notice on one side the marks of the
wire screen to which a rather irregular mat of fibers was drawn by suction.
Making sheets of paper by machine depends on doing the job con-
tinuously and rapidly. An even fall of pulp, often bleached and dyed,
suspended in water is fed onto one end of a wire screen arranged as an
endless belt. The water drains through the screen at first; then it is
forcibly drawn through by suction. The weak, wet mat of fibers is trans-
ferred to a felt blanket arranged as another endless belt that supports
it through drying and pressing rollers. After drying, the paper gain&
enough strength to go by itself through the rest of the machine to the
calender rolls that compress the sheet. Sometimes finishes are added, or
special treatment is given the surface.
Rayon. Rayon started as an imitation of silk, but today's product has
long left behind the imitation stage of development. Under the name
rayon, the fiber has created a growing market for itself, second only to
that for cotton. The success of this synthetic fiber is an outstanding
example of the results of scientific research applied to a practical problem.
Rayon today is made by three principal processes: (1) cupram-
monium, (2) acetate, and (3) viscose. The last-named method produces
about four-fifths of the supply.
A Robot Silkworm. Sheets of cellulose pulp, resembling large sheets
of thick blotting paper, are soaked in a solution of lye (NaOH). The
product is treated with carbon disulfide (CS2), forming orange-colored
crumbs called cellulose xanthate (yellow cellulose). This colored mate-
rial dissolves in more lye solution, forming a clear, sirupy liquid called
viscose. After aging, viscose is squirted through a nozzle called a spin-
neret made of acid-resisting metal. Through it are drilled 10 to 150 tiny
holes in a space much smaller than the surface of a dime. The number of
holes depends somewhat on their size; their size, in turn, determines the
diameter of the fibers produced.
On one side of the spinneret is viscose sirup under pressure. On the
other is a solution containing chiefly 10 per cent sulfuric acid (H2SO4).
During the first half second in the coagulating bath, the cellulose is
reprecipitated as a strong, lustrous fiber. It is then washed, dried, and
reeled. About 40 ft per sec of continuous, strong, many-stranded fibers
is produced.
568
CHEMISTRY FOR OUR TIMES
Variations on a Theme. Many variations of this process produce
interesting and novel effects. Flat and ribbonlike, rayon resembles straw
for hats. Flat and very thin, it appears as Cellophane. Coarse fibers can
be made stiff, resembling horsehair. Much of the " horsehair " used today
for forming the shoulders of suit coats never grew in a stable.
Courtesy of E. I. du Pont de Nemours & Company, Inc.
FIG. 32-la. — Steeping press — sheets of
cellulose.
FIG. 32-16. — Shredding machines.
Courtesy of E. 1. au Pont de Nemours cfc Company, Inc.
FIG. 32-lc. — Blending disulphide with FIG. 32-ld. — Filtering the spinning
crumbs in churn. solution.
Rayon cut into short lengths (staple fiber), carded, spun, and woven
has many loose ends in the yarn. When woven or knit into cloth, this
staple rayon makes a desirable fabric unlike silk or cotton with qualities
all its own.
Cellulose can also be coagulated around crystals of soluble salts in
CELLULOSE AND PLASTICS 569
such a manner that it resembles natural sponges. Cellulose sponges have
the same uses as the marine product, and some advantages.
Many Farm By-products Are Available. An enormous amount of
cornstalks, wheat straw, and cane as well as other cellulose-containing
material is grown each year. Only a relatively small amount is used for
Courtesy of E. I. du Pont de Nemours & Company, Inc.
FIG. 32-2a. — Spinning machine. FIG. 32-26. — Close-up of spinneret.
Courtesy of B. I. du Pont de Nemours & Company, Inc.
FIG. 32-2c. — Bobbins of rayon. FIG. 32-2d. — Winding from bobbins.
paper and wallboard. Investigation of other uses for these farm by-
products has gone forward, and much information has been gathered.
But thus far only a start has been made. Many unexplored possibilities
are waiting in this field of investigation.
QUESTIONS
1. Answer the following questions referring to the formula for cellulose
(CeHioOs)*. (a) What is the proportion of hydrogen to oxygen by weight? (6) In
570 CHEMISTRY FOR OUR TIMES
what other well-known compound is the same proportion found? (c) What is the
meaning of the £? (d) What is the simplest formula weight?
2. Contrast the relationship of mankind to cellulose with the relationship of
plants to cellulose.
3* Name five products of forests.
4. List three solvents for cellulose.
5. Write an equation for the nitration of cellulose to one-half the extent
shown in the equation on page 566.
6. After cellulose has been cooked with hydrochloric acid to form starch,
how can the catalyst be removed?
7. For what purpose is rag pulp used?
8. Why are knots removed before logs are made into pulp?
9. Examine the paper in a dollar bill. What is unusual about it?
10. What is the essential difference among blotting paper, writing paper, arid
magazine-cover paper?
11. List three uses of pulp other than the making of paper.
12. What use is made of old newspapers?
13. Find out how paper is prepared for the following uses: diplomas; butter
wrapping; tissue for cold-cream removal; bread wrapping (waxed); postage
stamps (reference question).
14. How is corrugated cardboard made?
15. List the principal steps in making rayon by the viscose process.
16. Why could not successful spinnerets for making rayon be made from steel?
aluminum? zinc? gold? lead?
17. List three chemicals that must be shipped continuously to a viscose-
process fayon factory.
18. Compare the composition of silk with that of rayon.
19. In what respect, if any, is rayon better than silk for hoisery? less desir-
able?
20. Describe the method for producing staple rayon fibers.
21. When rayon burns, which does it resemble most, burning cotton, silk, or
wool?
22. When viewed under a microscope, which fiber does rayon resemble most
closely, cotton, silk, or wool? Find out by examining samples if possible.
CELLULOSE AND PLASTICS 571
Plastics
What Are Plastics Like? The mud pies of childhood are plastics.
Soft, yielding, and easily molded under one condition, they harden and
stiffen under another, taking a more or less permanent form. More useful,
dinner plates are made in a similar manner from plastic clays.
Rubber, glass, and celluloid are all plastic materials. In recent years
the field has been extended to include light and transparent plastic
materials of such novel design and striking uses that it has stirred the
popular imagination. While the total tonnage of plastics used is low
compared with the tonnage of copper, for example, the very rapid increase
in the use of plastics for ornaments and electrical devices and as a sub-
stitute for metals and rubber calls particular attention to the synthetic
plastic industry, chemistry's lusty youngster.
Plastics may be divided into two groups. A plastic material that be-
haves as clay does, hardening when heated, is called thermosetting. Others
are thermoplastic, flowing when warmed.
The Plastic Age. In the days of the glorious development of organic
chemistry by von Bayer and Fischer in Germany, numerous new com-
pounds were made. Series of compounds were studied and the properties
of the carboxyl, aldehyde, and other groupings of elements systematically
worked out. In this period of masterly development, definite compounds,
liquids or crystalline solids, were sought. Whenever a combination of
chemicals produced a pasty or tarry mass inside the apparatus, the fact
was noted and regretted and the product put aside as an error. Progress
was sought in another direction. Today's strides in the fields of plastics
have, in some cases, been based on these " mistakes " of the past.
Another factor in the modern picture that did not exist 50 years ago
is that organic chemicals can be prepared in carload lots, and cheaply.
For example, starting with lime (CaO), coal, and water as raw materials,
it is possible to operate a chemical factory that produces a 2-in. steadily
flowing stream of acetic acid (CH3COOH). Examples of carload-lot
production of organic chemicals of high purity and at relatively low cost
are increasing daily.
Synthetic plastics were introduced in 1855 when Alexander Parkes,
in England, produced cellulose nitrate (see page 566). This was not much
used until 1868, when Hyatt, in the United States, developed celluloid
by adding camphor as a plasticizer to cellulose nitrate. Hyatt was seeking
a substitute for ivory for making billiard balls and piano keys.
Bakelite. In 1909 Dr. Leo Hendrik Baekeland, in America, seeking a
substitute for shellac, produced the first phenolic resin by putting to-
gether phenol (C6H6OH) and formaldehyde (HCHO). A resin is a hard
572
CHEMISTRY FOR OUR TIMES
gumlike substance. Cherry, pine, and other trees produce natural resins.
Shellac is also a natural resin, but from an oriental insect. The rosin used
on violin bows is a natural resin. Bakelite, this synthetic phenol-formalde-
hyde resin, may be filled or extended by adding wood flour or other inac-
tive substances, coloring matter included; thus many varieties are
produced. Many other synthetic resins have been prepared that have
properties and uses not found in natural resins.
For making caps for collapsible tubes, cylinder-shaped pills composed
of a mixture of resin,fc filler, and coloring matter are placed in a steel
Courtesy of /Copper* Company, Inc.
FIG. 32-3. — These phenolic plastic products came originally from coal tar. Coal tar was
once thrown away as a messy nuisance.
mold that is heated with steam under heavy pressure. After a short
molding period the plastic has flowed into the form of the steel mold,
producing a useful shape of a material that is hard, inactive chemically,
and insoluble in water. Thus are made distributor heads for automobiles,
buttons, and piccolos.
Plastics from Natural Sources. 1. Nitrocellulose is a good example
of a plastic from a natural raw material, cotton. Brush backs, combs,
and still and motion-picture films are well-known articles made of cellu-
lose nitrate, or pyroxylin. Unfortunately, the product is explosively
flammable and must not be brought near flames.
2. Safety film for motion pictures at home is made with the almost
nonflammable cellulose acetate. Fibers of this 'plastic form a type of
rayon yarn called " acetate. " In thin, transparent sheets, usually coated,
CELLULOSE' AND PLASTICS
573
it is well known for wrapping merchandise. Over 10 million pounds per
year of cellulose acetate is used for this purpose alone. Acetate cloth is
soluble in acetone [(CH3)2CO], and spots on dresses made of it must not
be removed with fingernail-polish remover.
3. Lignin, 25 per cent of wood, the natural gum that binds wood
fibers together into the form of lumber, is a natural plastic. Growing
interest is given to conserving and using this material, formerly wasted.
Its use is limited because of its dark color, but its cost is low.
Courtesy of E. I. du Pont de Nemours & Company,
Inc.
Courtesy of U.S. National Archives
FIG. 32-4. FIG. 32-5.
FIG. 32-4. — Out of an inexhaustible source of raw materials — coal, air, and water —
chemists in recent years hav^ been producing new and vitally important products for
modern life. Among these are textiles, dyes, antifreeze solutions, perfume bases, and
plastics. Cast "Lucite," methyl methacrylate resin, shown here is an important exam-
ple of this last group of chemical products.
FIG. 32-5. — The art of preserving ancient valuable documents uses modern plas-
tic envelopes to good advantage.
4. Protein, or nitrogen-containing, plastics include those made from
casein, a by-product of skimmed milk. This plastic is cheap, but it is
difficult to mold. An interesting woollike fiber has been made from this
raw material. Unlike the staple rayon imitation pf wool, the fiber actually
resembles wool in its chemical composition. Corn gluten (zein) and
soybeans (soya) are also used as sources of protein plastics. Automobile
steering wheels, for example, can be made from soybean plastic.
Rubber, another plastic from natural sources, will be considered
separately.
Synthetic Plastics. Purely synthetic plastics are of two types:
(1) the condensation type; (2) the polymerization type.
1. Condensation products are thermosetting. They involve a chemical
reaction in which water is separated. Included in this classification are
phenol-formaldehyde resins, phenol-furfural (from oat hulls), urear—
574
CHEMISTRY FOR OUR TIMES
[CO(NH2)2]-formaIdehyde, and "glyptal" resins, which are made from
glycerol [C3Hft(OH)8] and phthalic anhydride (C6H4C203).
PLASTICS
Trade
names
Uses
Chemical type
X molecules of
Luc He or
i'lexiglas
Light conductor for
surgical instruments,
nosepieces for air-
craft
t
Methyl-methacrylate
CH*=C— CO— CH3
CH3
Styron
Vinylite ....
In low-temperature
safety glass
Suspenders and belts,
phonograph records,
Vinyon textiles
Styrene (polystyrene)
Copolymer of vinyl
chloride and vinyl
acetate
CHt=CH— C6HB
CH2=OHC1
and
CH2=CH— OOCCH,
Light, decorative plastics that color well are very popular for dinner-
ware as a substitute for or alternate to glass. These are urea-f orrnaldehyde
condensation plastics. The reaction between glycerol and phthalic
anhydride, which forms the glyp-
tal resins, corresponds to the form-
ing of an ester (see page 559). As
a coating on cloth the resin is an
excellent insulator; it is therefore
used in transformer windings and
also, when dissolved, as gum in
paints.
2. Polymerization compounds
are formed mainly by the self-ad-
dition of unsaturated (see page
513) compounds into large clus-
ters. The molecular grouping may
be compared roughly to shaking
fishhooks together in a box. When
one is lifted out a number of others
cling to it.
Nylon. Nylon is a class name
for a group of compounds known
chemically as polyamides. Its ori-
gin from air, water, and coal il-
lustrates its synthetic nature.
Many chemical changes and
processes are necessary between
Courtesy 6) E. I. du Pont de Nemours & Company,
Inc. ^
FIG. 32-6.— At Seaford, Delaware, the
Nylon polymer appears first when it is
extruded in ribbon form on this huge cast-
ing wheel, called "Moby Dick" by the
employees. The polymer is first seen as a
molten mass, but quickly solidifies and
resembles ivory. In later operations it is
chopped, melted, and extruded again as
filaments.
CELLULOSE AND PLASTICS
575
these simple raw materials and the finished product. Nylon resembles
silk both in its lustrous appearance and in its proteinlike nature.
It is a definite polymerized substance in the form of a giant molecule
containing the — N=N — bond. 'This product was first applied to the
manufacture of bristles and later to that of hosiery and other wearing
apparel. It dyes readily, resists wear, and in many properties is superior
Courtesy of E. I. du Pont de Nemours A Company, Inc.
FIG. 32-7. — Winding Nylon yarn onto cones is a mechanical step in the process of
making Nylon garments. The insert shows finished dyed Nylon hosiery packaged in
Cellophane, a cellulose-type plastic material.
to "natural silk. It is thermoplastic and can be remelted and reworked.
Its production, development, and marketing are examples of the triumph
of American synthetic chemistry.
Many Plastics Have Been Developed. The number of plastics avail-
able today is well over 300 in the United States alone, and other coun-
tries have an imposing list of similar or identical products under various
trade names. We should understand that each of these materials has a
different set of properties, making certain plastics more or less suited to
particular uses than others. In searching through the list of the properties
of plastics, users can find readily those with high resistance to electric
576 CHEMISTRY FOR OUR TIMES
sparks, resistance to acids, resistance to water and air corrosion, and
insolubility in water and In a great number of other solvents. The plastic
most suited to a given need is the typ^e with the desired properties that
can be furnished at the least cost. Hence both chemical and economic
knowledge are needed.
QUESTIONS
23. In general, contrast thermosetting resins with thermoplastic resins.
24. From which type of resin can the scrap trimmings be reworked?
25. A certain eyeglasses frame softens in hot water, permitting adjustments.
Of which type of plastics is it made?
26. List an article made of plastic material that is used at home today but
was unknqwn 25 years ago.
27. Some transparent acrylic resins conduct light around corners. Explain
how this is possible.
28. Some transparent resins transmit light a little better than does glass.
Why are they not used more extensively for eyeglasses?
29. What raw material is needed to make (a) Bakeiite; (6) celluloid; (c)
pyroxylin; (d) Cellophane?
30. Why should nylon garments not be pressed with a very hot flatiron?
31. What property of nylon makes it desirable for parachute shroud ropes?
32. What factors should be considered before deciding upon a certain plastic
substance for manufacturing ash trays? Umbrella handles?
»
33. What type of plastic is suitable for making (a) dress-belt slides; (6) tooth-
brush handles; (c) men's belts; (d) binder in safety glass; (e) electrical plugs?
The Story of Rubber. When Columbus visited the New World, he
noticed that the native children were playing with balls that bounced.
These bouncing balls, masses of gum from the rubber tree, were so inter-
esting and novel that he took a few back to Europe. Three hundred
years later, Joseph Priestley discovered that rubber could be used to rub
out pencil marks and gave the substance its name. The Scotsman, Mac-
intosh, first daubed rubber on cloth to make a water-resisting raincoat,
and Dunlop in England wrapped a rubber tube around a wheel to make
the first rubber tire.
But Macintosh's raincoat was so stiff in cold weather that it would
stand alone and so sticky in warm weather that it adhered to everything
it touched. The overcoming of these undesirable properties of rubber
was accomplished in 1839 at Woburn, Massachusetts by Charles Good-
year, who, while experimenting with a rubber-sulfur mixture, accidentally
let some of it spill and become intensely heated on his kitchen stove.
CELLULOSE AND PLASTICS
577
From testing this sample he discovered that rubber so heated with sulfur,
or vulcanized, stretches and snaps and has the desirable properties by
which we recognize rubber today.
Making Rubber from Latex. Latex from the (Hevea) rubber tree
is the chief source of rubber. Guayule, desert rabbit bush, and many
Courtesy of E. I. du Pont dc Nemours & Company, Inc.
FIG. 32-8. — This shows the final milling operation on Neoprene, a chloroprene
rubber. Articles made of Neoprene not only possess similar strength, resilience,
abrasion resistance, and elasticity as rubber products, but also resist the deteriorating
effects of oils, heat, sunlight, chemicals, ozone, and aging.
other plants produce a latex juice from which a rubberlike hydrocarbon
can be obtained, but in smaller amounts or mixed with unwanted plant
materials. The Hevea latex is coagulated, for example, by adding acetic
acid, and then the rubber is " compounded" with sulfur, zinc oxide,
carbon black, and a number of other materials. These substances, when
vulcanized into the rubber, produce a stable, elastic product, resistant
to wear and oxidation. •
Most of the 2 million tons of rubber per year (1939) used in the United
States went into the making of tires.
Synthetic Rubber. Rubber is essentially a polymer of the simple
hydrocarbon, isoprene (CsHg), which has double bonds.
CH2-C-CH»CH2
CH,
578 CHEMISTRY FOR OUR TIMES
This compound is closely related to butadiene (CH2=CH — CH— CH2),
the compound that is the basis for a number of the synthetic rubbers.
Butadiene can be synthesized from acetylene (C2H2) with sodium as a
catalyst to polymerize it — hence the name Bu na. Introducing chlorine
into the rubber molecule gives other properties that are useful. Unsatu-
rated compounds from petroleum are also used as starting materials for
synthetic rubber. These simple compounds are always polymerized to
make the long molecules that give rubber its stretching properties.
Some types of synthetic rubber are superior to natural rubber in
resistance to oxidation, especially ozonation, and for this reason are used
for insulation on wires leading to spark plugs in gasoline engines. Some
synthetic rubbers are also less soluble in oils and other organic solvents and
swell very little in gasoline. The hose from a gasoline pump is lined with
one type of synthetic rubber, Neoprene. (See Fig. 32-8.) In recent develop-
ments useful products have been obtained when synthetic rubber is
polymerized with other synthetic plastics.
SUMMARY
Cellulose is the chief constituent of woody stalks of plants. It is made by
photosynthesis by plants, a reduction process in the presence of sunlight. Ex-
amples of substances chiefly cellulose are cotton, wood, paper, and linen. Cellulose
is soluble in zinc chloride solution, ammoniacal copper hydroxide, and sodium
hydroxide solution. Cellulose burns; it is acted on by nitric acid in the presence of
a strong dehydrating agent, such as concentrated sulfuric acid, and is hydrolyzed
in presence of hydrochloric acid, forming starch.
Pulp is & suspension of fibers, usually cellulose fibers. Pulp for coarse paper
may be made mechanically by grinding or chemically by cooking wood chips in
lye solution, sodium hydrogen sulfite solution, or sodium sulfate in the presence of
lye. Pulp is used to make paper, rayon, and explosives and as a filler in plastics.
Paper is made from an even suspension of pulp, dried and pressed. Most
paper is produced by a continuous mechanical process.
Most rayon is cellulose, dissolved and reprecipitated in the form of filaments.
The viscose process is the most important. Rayon is the second most important
fiber. The rayon-making process is versatile, permitting many variations.
Plastics is a general term given to materials that can be made to liquefy
under heat and pressure and to take some useful form in a mold. Commercially,
plastics are classed as thermoplastic and thermosetting. Thermoplastic materials
liquefy when heated and "set" when cooled. Thermosetting materials take final
fflrm when heated. Well-known plastics include
Celluloid — made from nitrocellulose and camphor
Bakelite — made from phenol and formaldehyde
Nitrocellulose-pyroxylin — for photographic films, brush backs, and combs
Cellulose acetate — for transparent wrapping material and safety films
Lignin plastics — raw material from wood, dark-colored
Protein plastics — made from soybeans, corn, and skimmed milk
Some synthetic plastics are transparent, brightly colored, electrical insulating
• Courtesy of The Goodyear Tire & Rubber Company
FIG. 32-9. — Fabric impregnated with synthetic rubber is wound onto a drum in the
first stage of making an automobile tire casing.
Courtesy of Tht
Tire A Kufrher Company
FIG. 32-l(X — This finished tire carcass is made of a synthetic rubberlike elastomer.
Crude elastomer, a product of polymerization, is seen in front of the tire.
579
580 CHEMISTRY FOR OUR TIMES
materials with a wide range of variation of properties among themselves. Promi-
nent among them are the acrylic, styrene, and vinyl type of resins. Synthetic
resins are used for impregnating cloth and wood, for making varnish, and for
molding into decorative and useful devices.
Nylon is a thermoplastic resin, containing nitrogen. It is adapted to the
manufacture of bristles and of strong, lustrous fabrics and is used for hosiery
and clothing.
Rubber is a hydrocarbon found in several plants, but especially in the Hevea
rubber tree. Rubber is vulcanized by heating it with sulfur and is compounded
with carbon black, zinc white, and other fillers, including catalysts. It is used
chiefly for making tires, but hundreds of other uses are important.
Synthetic rubber, made from unsaturated hydrocarbons by polymerization,
has properties similar to those of natural rubber, but differing in important
respects.
QUESTIONS
34. What is suggested by the following trade names: (a) Buna rubber (cata-
lyst); (b) LanitaZ (country); (c) Awm'pol (country); (d) Thiokol rubber (element);
(e) rayon?
35. Write an equation for the burning of isoprene.
36. Does rubber oxidize faster when stretched? Give evidence for your
answer.
37. Which is more elastic, steel or rubber?
> 38. Why cannot rubber be used successfully for insulation on wires leading
to spark plugs on cars?
39. Point out the difference between
H CH8 H H i
it ii
-c-c - c-c-'
I
H H J
and
H Cl H H n
iiii
-C- C-C-C-
I I
H H J
natural rubber Neoprene
40. Name a use for which some synthetic rubbers are better adapted than
natural rubber.
41. Name a use for natural rubber for which synthetic rubbers are not suitable.
42. Name three uses for reclaimed rubber.
43. (a) What filler in a tire notably increases the resistance of rubber to
abrasion? (b) What filler in rubber tires produces white side walls? (c) What
filler produces red rubber for inner tubes? (d) What is done to preserve tires not
yet placed in service?
44. Is it possible for a tire to catch fire and burn while in service on the road?
UNIT SEVEN CHAPTER XXXIII
COAL.TAR CHEMISTRY
Following a suggestion of his instructor, August Wilhelm von Hof-
mann, William Henry Perkin, a seventeen-year-old English schoolboy,
in 1856 began trying to make quinine, an important drug, the synthesis
of which was accomplished 87 years later. During his experiments Perkin
noticed that a colored substance was formed. The colored substance
appeared when he used impure aniline (CeHsNH^) as a starting material.
Was this new substance useful as a dye? If so, he had made the first
dye that did not come from a natural source.
Later, Perkin (1838-1907) showed that this compound, called mauve,
was a successful dye and that others like it could be made in a similar
manner. This discovery was destined' to change the lives of countless
people and to unlock the secret of cheap dyes, royal colors for the cloth-
ing of everyone. So extensively did this one discovery influence life that
some writers call the years that first felt the effects of Perkin's discoveries
the mauve decade.
While Perkin sought a drug, he found a dye. The formation of the
dye was partly accidental, for it involved an impurity in his chemicals.
Also, without the help of von Hofmann, who solved the chemical riddle,
very likely the discovery would have been delayed. Nevertheless, we
honor the discoverer of this first coal-tar dye because he noticed and
because he followed up his discovery.
Perkin continued his work, and 10 years after the first discovery
he succeeded in making alizarin, a widely used dye. It is interesting to
note that this discovery was made also at the same time by two German
investigators. Hundreds of chemists are employed* today making dyes
similar to those made by Perkin and investigating the worth of new ones.
Coal Tar. When coal is heated in a closed oven (see Figs. 33-2, 33-3)
or retort, the baked coal gives off three easily separated products, namely,
(1) coal gas, (2) ammonia, and (3) coal tar. Coke (4) remains in the retort.
New Terms
coal tar phenol benzene ring
benzene naphthalene TNT
toluene
581
582 CHEMISTRY FOR OUR TIMES
Coal tar was always a trouble to the early gasmakers. There was no
way to use it. The demand for road tar did not exist. Nor was anything
known about coal-tar dyes or other derivatives. Consequently, much
tar was allowed to flow onto near-by rivers. When the thick, black tar
was discharged onto a river, the ill-smelling material was distributed down
the stream, adding to the unpopularity of the gasworks. The crowning
Courtesy of Weatinohouse Electric Corporation
FIG. 33-1. — This young lady, a student at Girls' Commercial High School, Brooklyn,
X.Y., used coal-tar dyes to color plastic materials.
insult to nature soon followed. Tar on the water shut off the supply of
oxygen. Soon the fish died, and they smelled worse than the tar, thus
firmly establishing the odorous reputation of the gasworks.
The Tar Chemist. The solution to this unhappy problem was found
through chemistry. Pointed out by Perkin's experiments, the way was
found to use part of the coal tar by changing it into a dye.
Today coal tar is redistilled. The material is placed in a retort and
heated. As the temperature is raised, different compounds or mixtures
of compounds distill out. These are separated in order of increasing boiling
points. This process, as we have previously learned, is called fractional
COAL-TAR CHEMISTRY
583
Courtesy of Koppvrts Company, Inc.
FIG. 33-2. — Volatile, valuaMc by-products go up in smoke in the old-style beehive
coke ovens. These ovens are being replaced by modern by-product ovens.
Courtesy of Koppers Company, Inc.
FIG. 33-3. — This general view shows by-product coke ovens at Weirton, W. Va.
Two Hundred Thousand Products. The 10 gal of tar that come
from a ton of coal yield about
3.5 Ib of benzene (C6H6) and toluene (C6H6CH3)
1. 25 Ib of phenol (C6H6OH)
6 Ib of naphthalene (Ci0H8)
0.625 Ib of anthracene (CuHio)
Only approximately 10 Ib of products per ton of coal may seem unim-
584 _ CHEMISTRY FOR OUR TIMES _
portant, but two facts show otherwise: (1) Over 40 million tons of coal
is made into coke each year. (2) Chemists have made over 200,000 different
compounds from these five starting substances. From these, over 3000
compounds are manufactured regularly for commercial purposes. They
include dyes, medicines, explosives, plastics, and photographic chemicals.
Benzene. The liquid portion of coal tar contains benzene (CJHe).
This colorless liquid was discovered by Michael Faraday in 1825. Benzene
boils at 79.6°C and is a good solvent for many organic substances. It is
very flammable, burning with a smoky flame. It is a possible substitute
for gasoline to a limited extent, but it is too expensive to use on a large
scale. The vapors are harmful to breathe.
The Chemical Bird Cage. The formula of benzene as visualized by
Friedrich August Kekul6 (1829-1896) seems best explained by assuming
that the carbon atoms are arranged in a ring with double bonds (two
pairs of shared electrons) alternating with single bonds. This bird-cage-
like structure for benzene is often abbreviated as a simple hexagon. Each
angle indicates a carbon atom attached to a hydrogen atom unless an-
other symbol is placed there.
H
H-C C- H
n <
H-C C- H
* «•
C
i
H
Kekul6 formula for simplified formula for
benzene (C«He) benzene (CeHe)
The lack of chemical activity of benzene suggests that the unsaturated
double bonds are different in some way from those in typical unsaturated
compounds like ethylene (C2H4). For example, benzene adds chlorine or
bromine only with difficulty to form a number of products — monochloro-
benzene (CeHBCl), dichlorobenzene (C6H4Cl2), and trichlorobenzene
(CeHaCU). More important, nitric acid with concentrated sulfuric acid
forms nitrobenzene (CgHsNC^) (page 566). By reduction with hydrogen
(tin and hydrochloric acid), aniline (CcHsNH^) is formed. Aniline is
the starting point for making medicines and hundreds of dyes. For
example, acetanilide (CHsCONHCeHs), a useful but dangerous medicine,
is made by combining acetic acid with aniline.
Toluene. Toluene (CeHsCHa), a coal-tar product, is a colorless liquid
that boils at 110.8°C. Chemical treatment makes toluepe into ben zoic acid
(C0H5COOH), the sodium salt of which, sodium benzoate (C6HBCOONa),
is a preservative. It is used to keep cider sweet and in some brands of
COAL-TAR CHEMISTRY
585
tomato catchup to prevent fermentation. Other useful compounds made
from toluene include dyes and saccharine, a very sweet substitute for
sugar in special diets.
Toluene is made from petroleum as well as from coal tar. One plant
in the United States has a capacity of 10 million gallons of toluene from
petroleum each year. Most of this toluene was nitrated, forming TNT.
Phenol. Phenol (C6H6OH), or carbolic acid, a "pink slush/' has a
definite pungent penetrating odor, which may be noticed in a popular
Courtesy of Koppers Company, Inc.
FIG. 33-4. — Useful products from coal tar include dyes and medicinals,
brand of red-colored soap. The crystals melt at 100.5°C. The compound
alone is dangerously corrosive to the flesh, but in dilute solutions it is
useful as an antiseptic. The germ-killing ability of other antiseptics is
rated in terms of a "phenol coefficient."
Phenol is combined with formaldehyde to make plastics (see page 573),
such as Bakelite, from which telephone sets are molded. Printing inks,
aspirin, medicines, and dyes are all made from this versatile compound
as a starting point.
Naphthalene. Naphthalene (Ci0H8) crystals are white. They have a
penetrating odor and give out a vapor that repels clothes moths. Thus
this compound is used for mothballs. At 80°C the crystals melt to form
a colorless liquid that boils at 218°C. Naphthalene, like anthracene
586 CHEMISTRY FOR OUR TIMES
(CiiHio), is used as a starting substance from which many beautiful
dyes are made. From naphthalene, vitamin K is synthesized.
A Long List of Coal Products. Valuable services are also available
from other chemicals derived from coal tar. A solution of ammonium
thiocyanate (NH4CNS) is used in the laboratory to test for the presence
of ferric ions (Fe"1"1"4"), for a deep-red coloration appears when they arc
mixed. This same compound is also used in fly sprays.
Pyridine (C5H5N), a compound resembling benzene in structure ex-
cept that one carbon atom with its attached hydrogen is replaced by
nitrogen in the ring, j^ a poisonous liquid usually possessing a strong
disagreeable odor due to impurities. It is used often to denature alcohol.
It is the starting substance for the manufacture of some of the newer
drugs, waterproofing agents, and rubber-curirig accelerators.
So the ugly duckling of the gas works has grown, developed, and pros-
pered with healing in its wings and colors gayer than those of the peacock.
SUMMARY
Destructive distillation of bituminous coal yields coal gas, ammonia, coal
tar, and coke. Coal tar, fractionally distilled, yields benzene, toluene, naphtha-
lene, anthracene, phenol, and other products known as coal-tar compounds.
Benzene is a compound that structurally contains a ring of carbon atoms. It
is a clear liquid that burns and is a good solvent for many organic compounds.
When acted upon by concentrated nitric acid in the presence of concentrated
sulfuric acid, it changes to nitrobenzene. This may be reduced to form aniline, a
compound used to make dyes and medicines.
Toluene, after several chemical changes, forms TNT, henzoic acid, or dyes.
In addition to being made from coal tar, toluene is also made in large quantities
from petroleum.
Pure phenol is a white crystalline solid with jfn aromatic odor. It is used as an
antiseptic and for making Bakelite, aspirin, and dyes.
Naphthalene is a white crystalline solid. It is used for moth balls and in the
preparation of dyes and vitamin K.
QUESTIONS
1. What is mauve? (Use a dictionary.)
2. Classify the products of the destructive distillation of coal as solid, liquid,
or gaseous.
3. List three uses for coal tar.
4. Describe the process of fractional distillation.
5. About how much phenol per year would be available in the United States
if all were to be recovered?
6. Wtiat reason have we for representing benzene as C6H6 rather than by
its simplest molecular formula CH?
COAL. TAR CHEMISTRY 587
7. Write equations for the reaction of benzene with three different substances.
8. Trace the steps from coal tar to acetanilide; to TNT.
9. Trace the steps from coal to a plastic case for a telephone hand set.
10. Write equations for the burning of (a) naphthalene; (6) anthracene;
(c) phenol; (d) benzoic acid.
11. Write equations for the reaction of benzoic acid with (a) sodium hydroxide;
(6) methyl alcohol; (c) phenol.
12. What is the percentage of carbon in naphthalene? Predict the nature of
the flame from burning naphthalene. If possible, test the prediction by burning
a little of the compound.
13. List five useful common substances that are derived (or one constituent
that is derived) from coal tar.
14. Tell how to prove that iron is present in spinach.
15. List the names and formulas of four substances, other than water, that
are sometimes put into automobile radiators.
16. Prepare a biographical account of one of the following chemists : William
Henry Perkin, Johann Friedrich Wilhelm Adolf von Baeyer, Victor Meyer, Emil
Fischer, Paul Ehrlich, Justus von Liebig. (Reference questions.)
UNIT
EIGHT
CHEMISTRY AND HUMAN
PROBLEMS
DAIRY farming is one of the oldest industries. {As you read the
following, see pictures (1) to (7) on this and the next page.}
Picture (1) shows milk being changed into clothing. The cheese-
making industry also uses milk. The milk is coagulated, usually
with rennet. The coagulated casein, or curd, is gathered on wire
strainers (2). The liquid that remains is called whey. The rubber'
like curd (3) contains nearly all the milk's fat, casein, calcium
compounds, other minerals, and vitamin A.
Dried crumbs of casein are put in trays, treated with bacteria
to develop flavors, and compressed into cylinders (4). The cheese
is set aside to "cure." The finished product (5) is high in protein
value.
All dairy processes must be carried out with the utmost
cleanliness, for bacteria multiply rapidly in milk. After use,
the equipment (6) is flushed with steam and a hypdchlorite
solution.
Constant inspection and control are exercised in well-equipped
dairies. The percentage of butterfat, the total solids, the specific
gravity, and the bacteria count are investigated. This technician
(7) is shown using the analytical balance.
Photos courtesy of National Dairy Council and Connecticut Dairy and Food Council
UNIT EIGHT CHAPTER XXXIV
FOOD AND CLOTHING
In addition to improving mankind's answer fco the three fundamental
needs for food, clothing, and shelter, chemistry applied to natural prod-
ucts improves them and makes them more adapted for service. Natural
drugs extracted from roots and the bark of plants are effective in many
instances, but the drugs prepared synthetically, without using the plant,
are still more suitable for medicines, for these compounds often comprise
the active principle of the drug without undesirable impurities.
One of the most remarkable series of chemical changes is going
on all the time inside the body of any living person. Food is being changed
into tissues, repairs are being made to injuries, and growth is being pro-
vided to the young. Some of the food is stored, other parts are built into
specialized tissue, and still other parts act as a control of the entire
process.
Functions of Food. If a person lies perfectly still for a long period
of time and except for shallow breathing does not move, he still needs
food. The purpose of such food is to maintain the temperature of the
body.
Additional food is needed to provide the energy for muscular exer-
cise, and it is evident from experience that the amount of exercise regu-
lates to a great measure the quantity of food required. If excess food is
eaten, it may be stored as fat. Further — witness the traditional appetite of
growing boys — food is needed for new growth as well as for repair in
case of injury.
Today we know that food has a fourth function, namely, keeping
the body in good health through the regulatory action of the vitamins
and other important components. Even though satisfying food is eaten,
a person may suffer from malnutrition due to lack of these important
regulators.
New Terms
nutrient invert sugar pasteurization
vitamin rayon centrifuge
bone black
591
59J CHEMISTRY FOR OUR TIMES
Nutrients. For purposes of study, food is classified as carbohydrates,
proteins, and fats.
Carbohydrates are compounds of carbon, hydrogen, and oxygen,
the last two elements usually being present in the proportions 2 to 1,
the same as in water. They include sugars and starches. They are fuel
foods only, but by conversion to fat in the body they may be stored.
Proteins are complex compounds containing carbon, hydrogen,
nitrogen, and oxygen. Some proteins also contain phosphorus, sulfur,
iron, manganese, and other elements. Lean meat, egg white, and milk
curds are rich in protein. During the last century the brilliant studies of
Emil Fischer (1852-1919), of Germany, advanced our knowledge of
sugars and proteins more than the work of any other person. He was
awarded the first Nobel prize in chemistry. Proteins are needed for
growth and repair, but proteins are also used by the body for fuel.
Fats are well known to everyone. They are an important fuel food.
We have seen that fats are esters of glyceroland fatty acids (see page 560).
Oils are essentially the same as fats, but as food they are a little more
easily digested.
A complete food analysis includes consideration of water, minerals,
and vitamins, also. These are accessory to the three main factors in the
diet.
Analysis of Food. Let us analyze milk for the presence of the various food
nutrients. The scum on boiled milk is removed and treated with concentrated
nitric acid (HNOa). A yellow color is produced, which is deepened by addition of
ammonia water (NH4OH). This is a test for protein.
A sample of milk is tested with a few drops of iodine solution. The absence of
a blue color indicates that no starch is present.
Another portion of the milk is boiled with an equal volume of Benedict's solu-
tion. A red precipitate of cuprous oxide (Cu20) indicates the presence of a kind of
sugar in the milk, lactose (Ci2H22Oii).
A small crucible is half filled with milk, and the contents are heated gently.
After water has boiled away, the remaining solid matter when heated strongly
chars and burns. Finally, after ignition over a hot flame, a white ash is left. This
is the mineral matter — in this case chiefly compounds of calcium and phosphorus.
Vitamins in milk can be detected by feeding it to animals who have
been fed previously on a diet entirely lacking in the particular vitamins
and noting their almost immediate improvement in health if the par-
ticular vitamins are present. Other tests for vitamins are available, but
the techniques are too elaborate for an elementary discussion.
Food Measurements. Experiments have proved that the heat pro-
duced by food is the same whether the food is burned in the body or in a
calorimeter. The unit of heat used in food measurement is the Calorie
(large calorie, Cal), or kilocalorie (Kcal), 1000 times the small calorie
FOOD AND CLOTHING
593
(see page 102). Carbohydrates and proteins produce about 4 Cal per
g or 1800 Cal per Ib. Fats yield about 9 Cal per g or 4100 Cal per Ib.
Food Requirements. The average grown person needs about 1 g of
protein per kilogram of body weight per day. This amount increases
gradually down the age scale to 3.5 g per kg of body weight for children
three years old.
The total calorie value of food required by the average adult is
about 2400 per day. This amount varies considerably with age, occupa-
tion, state of health, climate, and other factors. Many persons seem to
thrive on a diet lower in protein and less in amount than the figures
given here. These values were suggested by a committee of food specialists.
Courtesy of Merck and Company, Inc.
FIG. 34-1. — This picture would have been impossible to take one generation ago.
The crystals are vitamin Bi, thiamin hydrochloride. No vitamin has gained such
widespread adoption as a pure compound as BI.
Vitamins. Before definite information was known about vitamins,
seafaring men knew that long voyages without fresh vegetables would
produce scurvy among the crew. The British Navy discovered that a
small ration of tomato or lime juice would prevent or cure this disease.
Doctors discovered that cod-liver oil would greatly help cure or prevent
rickets, a disease that weakens the bones in children. These and other
facts were gradually accumulated, but about 1907 feeding experiments
definitely proved that certain substances, other than the main nutrients
and mineral substances, were essential in a complete diet. These sub-
stances, necessary in only the tiniest amounts, were called vitamins, and
are designated by letters.
Vitamin A is made in the body from the yellow coloring matter in
carrots (carotene) and in leafy vegetables, by hydrolysis. Dairy products
and fish-liver oils are rich sources. It is fat-soluble but not water-soluble.
594
CHEMISTRY FOR OUR TIMES
Vitamin A promotes normal
growth in children, prevents eye
diseases and " night blindness/'
and helps the body resist infec-
tions.
Vitamin B is now known to be
composed of several vitamins. We
have isolated and identified BI
from the B complex. (See Fig.
34-1.) This is called thiamin; it
is found in vegetables and in the
coarser parts of the germs of
grains. These rougher parts of
grains are removed in the process-
ing of foods, as, for example, in
making white wheat flour. Knowl-
edge of nutrition has increased a
demand for whole-grain cereal
products and for adding vitamin
BI to bread. This was done on a
nation-wide scale in England dur-
ing World War II and also ex-
tensively in America. This vitamin
is not stored in the body, and a
sufficient amoun^ should be taken in with the food each day. Without
vitamin BI, beriberi results. (See Fig. 34-2.)
Vitamin B2 or riboflavin, was formerly known as vitamin G. It pro-
motes growth and a healthy condition of the skin.
Vitamin B5 or niacin, nicotinic acid, is a preventive for pellagra, a
disease that has for symptoms nervous disorders, skin eruptions, and
upset digestion. B5 is found in meat, milk, and yeast.
Included in the B complex are pyridoxin (B6), pantothenic acid
(B8), and adenylic acids (B8) and other substances that are now being
investigated.
Vitamin C, ascorbic or cevitamic acid, is present in abundance in the
juices of citrus fruits, in tomatoes, in green peppers, and in less amounts
in many other foods. It is easily destroyed by heating and air. Vitamin C
prevents scurvy or its beginnings, among the symptoms of which are
bleeding gums and loosening of the teeth. Some experimental animals,
such as rats, can manufacture their own vitamin C from other materials
in their food. Human beings evidently cannot do this but must rely on
fresh fruits and vegetables for their supply of vitamin C.
Vitamin D, the sunshine vitamin, is also known to consist of at least
Courtesy of Merck and Company, Inc.
FIG. 34-2. — The sick rat shown at the
top is suffering from a diet lacking in vita-
min BI. Lack of food containing BI caused
this polyneuritic condition. Below we see
the same rat completely and speedily •
cured by adding vitamin BI to his diet.
FOOD AND CLOTHING 595
10 separate compound*, all of which may be considered together for our
purposes. Lack of this vitamin causes rickets, a bone disease. The sun
shining on the skin develops vitamin D in the body. Likewise, the sun
shining on small plants and animals in the sea causes them to develop
this compound. They in turn become food for fish who store vitamin D
in their livers. Fish-liver oils are rich sources of this vitamin.
Passing some materials under artificial sunshine, rich in ultraviolet
light, produces in them the equivalent of vitamin D. This treatment
produces irradiated food. Viosterol, a vitamin D concentrate, is made by
artificially irradiating ergosterol, a substance extracted from yeast.
This process parallels the production of vitamin D in the human body.
Vitamin E is found in wheat germs, lettuce, lean meat, milk, egg yolks,
and other foods. This vitamin is known to be important for the process of
normal reproduction in rats, but its place in human nutrition is not
established. Without a sufficient supply of this vitamin in the diet of
the mother, the young rats may be born dead and usually in advance of
normal schedule. Apparently no general lack of this vitamin exists in
human beings.
Vitamin K, now known to consist of Ki and K2, is important because
it hastens the clotting of blood. This has been a great help after surgical
operations, and already it is standard practice in hospitals to give a
small amount of it to newborn infants, who cdnnot make it for themselves
during the first few days of their life. The result has been the saving of
many infants from death by internal bleeding and giving others a better
start.
The Vitamin Search. The story of the vitamins is not merely a list-
ing of the vitamins by letters and recording their sources and purposes,
important as this knowledge is to everyone preparing meals. Behind each
story is a drama of intensive and exhaustive search: rooms full of rats
and other experimental animals, each being fed specialized diets, and
the results being recorded accurately and painstakingly; chemists working
with 2 tons of rice bran to isolate a sample of 0.005 gram (454 g in each
pound and 2000 Ib in each ton) ; the complex structure of the organic
compound being accurately determined by using so skillfull a technique
that a sample scarcely visible is large enough ; finally, the identical vitamin
being synthesized in the laboratory. Later comes commercial production
of* the vitamin, even by the ton. These or similar chapters are part of
the story of each vitamin. The entire knowledge of vitamins is scarcely
30 years old, and the field is rapidly developing. Eight vitamins have
already been synthesized, and six of them are available as pure chemical
compounds, commercially manufactured.
Good Health with a Balanced Diet. With so much knowledge
available about vitamins, how can we maintain good health without
596 CHEMISTRY FOR OUR TIMES
using expensive vitamin concentrates? The best answer seems to be to
eat a balanced diet. This means a diet containing the proper amounts
of carbohydrates, proteins, fats, and mineral matter. If we include in this
diet fresh fruits and vegetables, some dairy products, whole grains, and,
if possible, although not necessary, some meat or fish, we need not fear
any of the so-called " deficiency " diseases that come from lack of vitamins.
Courtesy of Merck and Company, Inc.
FIG. 34-3. — This chemist is isolating vitamin Bi.
Sugar. One of the most important carbohydrate foods is common
table sugar, or sucrose (C^H^On). The chief sources of this compound
are sugar cane and sugar beets. Each contains about 18 per cent jpy
weight of sugar, but about twice as much tonnage of sugar is obtained
from cane as from beet. Let us follow sugar from the cane until it appears
on our table in the form of pure white crystals.
The cane is trimmed to the stalk only and crushed to remove the
juice. The remaining pulp, or bagasse, is used to make Celotex wall-
board. The juice is partly purified by adding lime, which precipitates
some impurities, and then it is filtered. The filtrate is evaporated by
FOOD AND CLOTHING 597
boiling it at a reduced temperature in vacuum pans. The resulting slush
of crystals is freed from the mother liquor, or molasses, by centrifuging.
The crystals, known as raw sugar, are brown with an unpleasant taste
and a slight odor.
The second stage in the preparation of white sugar for the table is
accomplished at a refinery. The raw sugar is dissolved and passed through
activated charcoal or bone black. This process removes the color and
odor from the sugar. The solution is again evaporated under reduced
pressure, and the crystals are separated. This time they are glistening,
white, uniform crystals.
Inverting Sugar. When some forms of soft candy are made, a little
vinegar is added to cane sugar and the mixture heated. In the presence
of acid the sucrose combines with water and forms two simpler sugars,
isomers (see page 535), not as sweet as sucrose and not crystallizing
so readily. They therefore make a smooth, noncrystalline candy.
C12H22On + H2O > C9H1206 + C6H12O6
sucrose gin rose, or fructose, or
grape sugar fruit sugar
invert sugar
The mixture is called invert sugar. Cane sugar does not reduce Benedict's
solution, but invert sugar does.
When sugar is heated slowly, caramel, a popular flavoring material,
forms.
Other Sugars. Milk sugar, or lactose (C^H^On), is the natural
sweetening agent in milk, in which it occurs to the extent of about 5 per
cent. When milk sours, lactose changes to lactic acid by bacterial action.
Ci2H22On -f H2O -> 4C3H6p3 (CH3CHOHCOOH)
lactose lactic acid
The acid coagulates the colloidal casein into a curd. The souring of milk
can be greatly delayed by pasteurization, that is, by heating and
maintaining it at a temperature of 143°F for 33 minutes or, in the new
process, at 160°F for 15 seconds. Lactose reduces Benedict's solution.
Maple sugar is sucrose plus certain flavoring materials that are present
in the sap of the sugar maple tree.
Corn sugar, or corn sirup, is glucose (C6Hi206) made from starch.
It is used in candy- and jam making because it does not crystallize easily.
Honey contains this sugar, and many of its commercial uses depend upon
its slow crystallization property.
Starch (CeHioOs)*. Let us shred a small potato into water, using a kitchen
grater, and then strain the mixture through a piece of cotton cloth to remove
fibrous material, collecting the cloudy filtrate in a transparent vessel. In a short
time, a white deposit settles at the bottom. Now let us pour, or decant, the liquid
598 CHEMISTRY FOR OUR TIMES
above the white material into a test tube and add a drop of iodine solution to the
residue. The iodine produces a dark-blue color, showing that the white material
is starch;
Potatoes contain only 15 per cent starch, but corn contains 65 per
cent. Different sorts of starch can be distinguished from each other by
comparing under a microscope the tiny grains or flakes of starch with
samples from a known source. Each kind has its characteristic appearance.
Starch is used for laundry purposes to stiffen cloths and to give a luster
to ironed articles; to make glucose, alcohol, and dextrin; and as a food.
Dextrin, which is familiar to all in the form of the gum on envelope
flaps and postage stamps, is made by heating starch slowly.
Glucose is made from starch by boiling it in a sealed vessel with
acid,
(HCl)
(CeHioO*)* + xH2O > xC6Hl2O6
starch glucose
and neutralizing the excess acid. Commercial glucose made in this man-
ner contains also some dextrin and maltose (Ci2H22On) (see page 597).
Preserving Foods. One of the most inconspicuous, yet important,
contributions to the art of living comfortably is our ability to preserve
foods. Sealing sterile food in an airtight container is widely practiced at
home and in factories. Refrigerated food is transported by steamship,
railroad, and truck from producing centers to markets. Quick-frozen
foods have such tiny ice crystals that the cell walls of the food are not
broken. This preserves freshness and flavor until the food is prepared
for serving. Jams keep well because of the high sugar content. Drying,
salting, pickling, smoking, and similar methods of preserving foods are
among the older means that were developed before refrigeration and
are still used extensively today.
Chemical preservatives may be used in some cases. Sodium benzoate,
a compound derived from coal tar, is used for this purpose, but in a
limited amount. Foods containing preservatives are so marked on the
label, a provision of the Pure Food and Drug Act.
QUESTIONS
1. Suggest some foods that a person should eat if he wishes to gain weight
quickly.
2. Suggest some foods that a person should eat if she wishes to lose weight.
3. A knowledge of food chemistry is important to persons in what occupa-
tions?
4. What is wrong with a diet consisting of purified fats, purified carbohy-
drates, and purified proteins?
5. Distinguish a hydrocarbon from a carbohydrate.
FOOD AND CLOTHING 599
6. What element is always present in protein foods that is not present in
carbohydrate or fAts?
7. What function of protein food cannot be duplicated by carbohydrates or
fats?
8. Trace the course of a nitrogen atom from Chile saltpeter to muscle tissue
in an animal.
9. Trace the course of a carbon atom from carbon dioxide in the air to fat
tissue in the human body.
10. How can you prove that an apple contains (a) water; (6) sugar; (c)
minerals?
11. Assuming that you need 1.5 grams of protein per kilogram (2.2 pounds)
of body weight, what is your daily protein requirement?
12. Which in general of the following is richer in vitamins: (a) white (unforti-
fied) or dark bread; (6) white or yellow turnips; (c) bleached or green celery; (d)
green-leaf or head lettuce?
13. What proof have we that vitamins are necessary supplementary foods?
14. Name three occupations in which a knowledge of vitamins is important.
16. Aviators defending the coast of England at night were supplied with car-
rots and urged to eat them. How do carrots help aviators?
16. In processing grains most of the coarse bran is removed, the vitamin con-
tent of the resulting flour being low. People seem to like white bread, but they
should not be deprived of vitamins normally present in grain. How has the baking
industry met this problem?
17. Do the conclusions reached from experiments carried out on diets for
animals always hold true for diets for human beings?
18.» How may a person be sure that his diet is adequate in respect to vitamins?
19. Explain how the diet of a person depends upon climate. Give examples.
20. What special food value has each of the following: (a) fish livers; (b) calf
liver; (c) sea food in general; (d) citrus fruits; (e) spinach; (/) bananas; (g) beans;
(h) coffee; (i) soybeans?
21. Give the names and formulas for four carbohydrates.
22. Describe a test to determine the presence of sugar in a body fluid.
23. Why is toast more digestible than bread?
24. Why is pasteurization of beverage milk desirable?
25. What change is brought about in candymaking when sugar is heated with
vinegar?
600 CHEMISTRY FOR OUR TIMES
26. What change is brought about in the final product by "pulling" molasses
taffy (with buttered fingers)?
27. A 100-gram sample of milk contains 1.6 per cent lactose. What weight of
lactic acid is present in the sample when all the sugar has fermented?
28. Corn products for sweetening are on the market. Among them are Dyno
sugar and Karo sirup, both light and dark, (a) From what part of the corn are
these sugars made? (6) What is the composition of Dyno (see box)? (c) What is
the difference in composition between dark and light Karo sirup? (d) Name a
purpose for which Karo sirup is better adapted than sucrose.
29. What purpose does lactose in milk serve?
30. Why are men's shirt collars starched? What use is made of the starch in
corn flakes?
31. Some children hide crusts under their plates. What makes crusts different
from the rest of the bread? How do crusts compare in taste with the rest of the
bread? Why do some children dislike them? What is zwiebach?
32. In home canning, what precaution should be taken before sealing the
jars to prevent spoilage?
33. Which is probably the better product of each of the following: (a) tomato
catchup with or without preservative; (b) frozen or chilled imported beef; (c)
pasteurized or raw milk; (d) oleomargarine or butter; (e) sprayed or unsprayed
apples? In answering the question tell " better for what" and "why."
Clothing
Let us take a mass of cotton fibers, such as absorbent cotton or a boll from the
cotton plant. By combing, the fibers can be laid parallel, and by twisting and
drawing them out a thread can be spun. The thread can then be knitted or woven
into cloth.
This simple experiment illustrates the mechanical processes necessary
in making cloth. Chemical processes consist in bleaching, dyeing, and
finishing the cloth and testing the fabric in the various stages of its
manufacture.
Cotton. Cotton is by far the most important fiber. In chemical com-
position it is chiefly cellulose, like wood. When viewed under the micro-
scope, cotton fibers appear similar to flat, twisted ribbons. They burn
somewhat like paper, and are unaffected by most dilute chemicals.
Cotton is used chemically for the manufacture of nitrocellulose. The seeds
of the plant yield meal for cattle food and cottonseed oil.
Rayon. Although the production of rayon is only a fraction of that of
cotton, the industry is growing rapidly. Rayon is regenerated cellulose,
made by dissolving cellulose and reprecipitating it in the form of smooth,
continuous fibers. This has already been described (see page 567). Rayon
FOOD AND CLOTHING
fibers can be distinguished from cotton fibers by viewing them under
the microscope, where they appear as round tubes or rods. Viscose rayon,
the most common type, burns like paper. Acetate rayon (cellulose acetate)
can readily be distinguished from the viscose type in that acetate dis-
solves readily in acetone [(CH8)2CO] and viscose does not.
Wool. Animal hair is protein in nature, containing the elements car-
bon, hydrogen, oxygen, nitrogen, and sulfur. Wool viewed under mag-
nification shows overlapping scales similar to miniature shingles on each
rodlike fiber. This is an identifying characteristic. Wool burns like hair,
with an unpleasant odor. Dilute alkalies dissolve it, and Concentrated
nitric acid turns it yellow.
Synthetic Wool. Protein matter in the casein of milk, in fish, and in
soybean meal has been used successfully to produce synthetic wool.
The process of manufacture is quite similar to the making of rayon.
The regenerated protein is kinky, like wool, and an excellent heat insula-
tor. Some of it is called Lanital.
Silk. Silk, the wrapping of the cocoon of the silkworm, is also a protein
product. It resembles rayon when viewed under the microscope but
differs from it in chemical nature. In fact, silk responds to chemical tests
in almost the same way as wool, but its generjil smooth, lustrous appear-
ance when magnified readily distinguishes it from wool.
SUMMARY
The functions of food are to supply heat, to give energy for muscular move-
ment, to provide for growth and repair of tissues, and to control general health.
The nutrients are carbohydrates, proteins, and fats. Carbohydrates include
starches and sugars. They are compounds of carbon, hydrogen, and oxygen, the
latter two in the proportion of two hydrogen atoms to one oxygen. Proteins are
organic nitrogen-containing compounds. Fats are esters of glyceroi with fatty
acids. Minerals, vitamins, and water are also essential in a balanced diet.
Nutrients are identified by the following laboratory tests: (1) Starches turn
iodine solution blue. (2) Some sugars form a brick-red precipitate of cuprous oxide
when boiled with Benedict's solution. (3) Proteins form a yellow color with the
addition of concentrated nitric acid. The color turns darker orange when mois-
tened with ammonia water. (4) Fats make a grease spot on unglazed paper. (5)
Minerals remain as ash when the food is ignited.
Food measurement is similar to fuel measurement, for food heat values are
measured in calories. Food requirements of persons differ, depending upon many
factors.
Vitamins are compounds that are essential in small amounts for the main-
taining of good health. Lack of a sufficient supply causes a " deficiency" disease,
such as scurvy, rickets, or beriberi. Although the amount required is small, the
supply may be insufficient unless the diet is correct. The Jiuman body can manu-
602 CHEMISTRY FOR OUR TIMES
facture some vitamin D in sunlight. Several of the vitamins are now identified as
definite chemical compounds and are manufactured synthetically.
Sucrose, or common table sugar, is found in plants, especially sugar cane, sugar
beet, and (the sap of) the sugar maple tree. Sugar cane is crushed and the ex-
tracted juice evaporated under vacuum, forming raw sugar, which is separated
from molasses in centrifugal machines. Refining sugar consists in dissolving raw
sugar and passing the solution through adsorbing agents, including carbon char.
The resulting clear liquid is evaporated under reduced pressure, and the crystals
are dried by whirling them in the perforated basket of a centrifugal machine.
Sucrose boiled with a little acid forms glucose and fructose, two isomers that
do not crystallize readily. Heating sucrose gently forms caramel.
Lactose, milk sugar, is found in milk. It changes into lactic acid when milk
sours.
Starch, found in many plants, may be identified by its characteristic tiny
grains or flakes. It is used for laundry purposes and food. It is also used to make
alcohol, glucose by hydrolysis, and gum dextrin by gentle heating.
Cotton is a plant fiber, chiefly cellulose. Rayon is regenerated cellulose. Wool
is a protein animal fiber. Synthetic wool, made from skimmed milk and other
materials, resembles wool in both general appearance and protein nature. Silk is
animal fiber of high strength and pleasing luster.
QUESTIONS
34. Define warp; woof.
35. Name a type of fabric that has threads woven in three different directions
at right angles to each other.
36. Which fibers when burning smell like burning paper? Which like burning
hair?
SPECIAL REPORTS
1. Prepare a report on the process of obtaining sugar from beets.
2. What is a polariseope? What are its uses?
3. What difference in vulcanization causes the differences between hard rub-
ber arid elastic rubber? Which lasts longer? Is there a chemical reason for this?
4. Types of synthetic rubber produced commerically in the United States are
Buna S (GRS), Buna N, Neoprene, Butyl rubber, and Thiokol. Write an account
of the development and manufacture of one or more of these.
5. Prepare a report on the obtaining, preserving, coagulating, compounding,
and vulcanizing of natural rubber.
UNIT EIGHT CHAPTER XXXV
CHEMISTRY FOR CLEANLINESS,
HEALTH, AND BEAUTY
Two centuries ago a householder who wished to make soap had to
save waste kitchen fats and wood ashes. The wood ashes were soaked in
water and strained. The more or less clean solution of potash was then
boiled with the fat and a rather soft soap obtained.
Today's soap is hard, pleasantly scented, and in soft water an effec-
tive cleansing agent. It keeps well, dissolves at a moderate rate, and pro-
vides an alkaline colloidal suspension of suds. This condition is excellent
for emulsifying grease and hence for cleansing.
Soap. Ordinary soap is a sodium salt of a fatty acid of higher formula
weight, such as sodium stearate (CiyHasCOONa). Mixed also with this
compound are the more soluble sodium oleate and palmitate, for no
natural fat is derived entirely from one fatty acid. Potassium soaps are
in general more soluble than sodium soaps. They are made by using some
potassium hydroxide (KOH) in place of the corresponding sodium
hydroxide. Such a product would be used for a shaving soap.
Soapmaking. Soap for the market is made in huge kettles, which in
some instances are capable of holding as much as several carloads of
fiaished soap in a single batch. (See Fig. 35-1.) First the kettle is filled
with a mixture of fat and lye solution. Steam is bubbled through the
contents for about 4 hours, which cooks and stirs the mixture. The fol-
lowing reaction, called saponification, takes place:
(Ci7H86COO)3C3H6 -f 3NaOH -» 3C17H36COONa -f C3H6(OH)3
fat lye soap glycerin
glyceryl ester of sodium sodium glycerol
stearic acid hydroxide stearate
The soap formed floats in the kettle like a huge curd. It is coagulated
from the colloidal condition by adding common salt. Then, after removal
New Terms
soft water insulin hydrolysis
hard water adrenalin antiseptic
saponify
603
604
CHEMISTRY FOR OUR TIMES
from the kettle and hardening, it is mixed in a crutching machine,
molded into blocks, and cut into slabs and cakes.
The glycerol is recovered by frac-
tionally distilling it from the liquid
mixture that remains.
Millions of pounds of soap are used
each year in processing Buna S syn-
thetic rubber. The soap acts as an
emulsifying agent in the formation of
a synthetic latex.
Kinds of Soap. Fundamentally
all soaps are made by treating fats
and oils with a base. The product may
be varied, however, by using different
raw materials and finishing processes
and additional materials. Soap will
float if tiny air bubbles are beaten in-
to it during the finishing processes.
When the materials are dissolved in
alcohol, transparent soap is obtained.
Castile soap is a variety of soap that
is made from olive oil. Scouring soaps
have finely ground abrasives incorpo-
rated in the cake, while scouring
powders have some soap included with
the scouring agent together with sodi-
um carbonate and trisodium phos-
phate, which serve as builders, or
agents to make the soap act more rrfj)-
idly. A great variety of perfumes and
antiseptics are included with different
sorts of soaps. Rosin is usually added
to the fat in the making of laundry
soap. The rosin reacts with the lye in
the same manner as the fat does. The
sodium rosinate formed is fairly sol-
uble and aicte in suds making.
Courtesy of Colgate-Palmolive-Peet Company
FIG. 35-1. — This commercial soap-
making kettle extends through three
floors of the building.
Soap chips can be made by running a thin sheet of liquid soap onto
a refrigerated cylinder, or drum, and scraping off the soap in small broken
pieces as a continuous process. Soap granules are dried, thick, miniature
soap bubbles. Soap powder is made by spraying soap and sodium car-
bonate solution into a drying room. The soap powder, bound together by
the sal soda crystals (Na2C03'10H2O), collects on the floor of the drier.
CHEMISTRY FOR CLEANLINESS
605
Chemical Actions with Soap. Soap is an ionized salt with an organic
radical ion and a sodium ion. At one end of the organic radical is a long
chain of nonpolar carbon atoms;
at the other, a polar carboxyl rad-
ical. The positive sodium ion is
largely free in the solution, as in
all sodium salts. The solubility of
soap in both organic and inorganic
compounds is explained in part by
its dual nature.
Soap in acid solutions forms a
curdy precipitate of a fatty acid,
a very weak acid.
HCI
stearic acid
Metallic ions other than sodi-
um or potassium form a curdy
precipitate of the soap and of
metal that separates as a scum.
This happens with the calcium
and magnesium ions that are
present in hard water*
2Ci7H36COONa + CaCI2 -»
2NaCI + (C17H36COO)2Ca
insoluble calcium soap
i
THese " metallic soaps " are
useless for cleaning. In fact, they
are a decided hindrance to good
washing. They precipitate and col-
lect in the fiber of the cloth,
shedding water and forming a
gummy mass. Cloth washed in
hard water does not take dye
evenly, and hair washed in hard
water looks dull unless rinsed free
of this precipitate. A scum of precipitate together with the attached dirt
forms an unpleasant-looking ring around the washbasin when hard water
is used for washing.
Courtesy of Manhattan Soap Company
FIG. 35-2. — This scene in a soap
factory shows a stage in the preparation
of soap into bars for retail trade.
606 _ CHEMISTRY FOR OUR TIMES _
Metallic Soaps. Calcium soap, although undesirable in washing, is
suitable as a lubricant for some purposes. Other metallic soaps have
special uses. Zinc stearate is used in antichafing powder, and copper
oleate impregnated in marine ropes makes them resistant to fouling by
marine growth.
QUESTIONS
1. Describe how soap aids in removing particles of solids from hands ; from
clothes.
2. How can soap be tested to determine whether sodium hydroxide or
potassium hydroxide was used in its manufacture?
3. How can soap be tested for excess lye?
4. What type of fat is used in making (a) sodium stearate; (&) sodium oleate;
(c) sodium palmitate?
5. Write the equations for (a) the hydrolysis of glyceryi palmitate
(CisHsiCOC^sCsHc; (6) for its saponification. Write similar equations for the
hydrolysis and saponification of glyceryi oleate (CirHa
6. Some soap manufacturers claim that their products contain olive and
palm oils. In what sense is this true?
7. From what is "tar" soap made?
8. What is the purpose of adding "builders" to soap powder? How do they
act?
9. Describe from start to finish the process of making a cake of white floating
soap.
10. In wartime, housewives are urged to turn in waste kitchen fats. To what
use are these fats put?
11. Write the formula equation for the saponification of glyceryi stearate
with lye.
12. Write the formula equation for the interaction of soap solution (use
sodium stearate) with solutions of (a) Ca(HC08)2; (b) Na2S04; (c) HOI; (d)
MgS04; (e) FeCl3; (/) alum.
Soft and Hard Water. Soap lathers readily in rain water or other
soft water where no metallic ions are present to react with the soap.
Hard water, on the other hand, reacts with soap and wastes it, inter-
feres seriously with cleansing, and forms a deposit or scale in boilers.
(See Fig. 35-3.) Hard water contains the ions of calcium or magnesium.
If hard water can be softened by simple boiling, the hardness is said to
be temporary. Otherwise, the hardness is called permanent, and chemical
treatment is needed to soften it.
CHEMISTRY FOR CLEANLINESS
607
Temporary Hardness. A certain family uses water from a well.
Hot water for domestic use is obtained by heating the well water in a
large kettle. Every few days, a collar-shaped ring of white solid crust is
taken out of the kettle. This crust effervesces when acid is added, and
the gas liberated turns clear limewater milky. Here is a typical case in
which temporary hard water is used. Let us assume that calcium bicar-
bonate was dissolved in the well
water. This compound decom-
poses when heated.
Ca(HCO3)2 ->
CaCO3 1 + H.O + CO2 T
This method of softening tempo-
rary hard water is too expensive
for city-wide scale usage. For ur-
ban use a carefully controlled
amount of slaked lime is added
to the water.
Ca(HCO3)2 + Ca(OH)2 -4
2CaCO3| -f 2H2O
This precipitate is allowed to set-
tle in huge basins, and the clear
softened water is run off and after
being filtered is piped to the con-
sumer.
Courtesy of The Travelers Insurance Company
FIG. 35-3. — This steel boiler tube was
completely filled with hard scale from hard
water.
Permanent Hardness. Per-
manent hardness is usually due
to the presence of calcium and
magnesium salts other than the hydrogen carbonates. Many methods
are used for softening permanent hard water. Most of them depend on
the exchanging of calcium ions in the water for sodium ions from the
softening agent. The sodium ions in the water do not react with soap,
which is itself a sodium compound. For example, washing soda is a
widely used water softener in water purification installations.
CaCI2
Na2CO3 -» 2NaCI + CaCO3
Borax (Na2B407'10H20), trisodium phosphate (Na8P04), and ammonia
water (NH4OH) are all used for the same purpose. Soap, too, is a water
softener, but an expensive one.
In another type of water-softening process, zeolite clay may be used
or, better, commercially manufactured artificial clays, such as Permutit,
that resemble the natural sodium aluminum silicates. We shall represent
608
CHEMISTRY FOR OUR TIMES
the complex zeolite radical by Ze, in the equation.
Na2£e + MgCI2 j=± MgZe j + 2NaCI
The hard water is run into a tank containing the zeolite grains. Here the
water exchanges its calcium and magnesium ions for sodium ions by
reaction with the clay, which retains its granular form. After a period
of service, the clay is reactivated by soaking it in 10 per cent salt water.
This causes the reverse action to occur. The resulting magnesium and cal-
cium compounds are flushed out,
and the softener is ready for
further service.
Sodium "metaphosphate,"
marketed under the trade name
of Calgon, and sodium tetra-
phosphate in solution have the
ability to lock calcium or mag-
nesium ions in the form of a
complex ion so tightly that they
will not react with soap. These
compounds are marketed widely
for washing dishes in machines
without leaving streaks and for
washing clothes without leaving
gray patches.
Ion-exchange Resins. A
way to render water almost
chemically pure without distil-
lation has been found and put in-
to practical service in industries
that formerly required the more
expensive distilled water. In
this process the raw water is slowly run successively through two tanks
of synthetic resins. In the first tank the metallic ions, such as calcium
and magnesium, are exchanged for hydrogen ions, rendering the water
acid. In the second tank the acid is absorbed, removing not only the
hydrogen ions but sulfate, chloride, and nitrate ions as well. The resin
in the first tank is regenerated by an acid, and that in the second tank
by soda ash (Na2CO3) solution. The treated water, since it contains
neither positive nor negative ions, compares favorably with once-distilled
water in purity.
Suds in Hard Cold Water, Salt-water soap contains much of the
soluble potassium salts of the fatty acids. It is derived chiefly from coco-
nut oil. In spite of the fact that such soap can make suds in very hard
water because it is very soluble, an unwanted scum forms.
•"he Travelers Insurance Company
FIG. cio-4. — After a correct water softener
is determined, its actual performance in a
boiler is studied in these model boilers. The
heating is done electrically by a wire coiled
around the tube that is backed by a sheet of
asbestos.
_ CHEMISTRY FOR CLEANLINESS _ 609
Newer detergents make suds in any sort of water, regardless of dis-
solved mineral compounds. One that is widely used and marketed under
the name of Dreft or in solution for shampoo as Drene is essentially the
sodium salt of a sulfonated alcohol of high formula weight, sodium lauryl
sulfate, with a chain of 12 carbon atoms (ttCi2H2oO'S02-ONa). Though
expensive compared with soap, these compounds serve as wetting agents
in cleansing cloth preparatory to dyeing, in cleaning metals preparatory
to drawing or plating, and in numerous special cases where their cost is
easily justified. Dreft solution, for example, gives a tough film of foamy
suds even in ice-cold, hard water.
Hydrolysis. A certain school cafeteria has the problem of washing
greasy dishes. The manager would like to change the grease on the dishes
to soap, that is, wishes to saponify it and use the soap formed in this
manner for cleaning the dishes. He selects trisodium phosphate as a
compound that will do this. The pll value (see page 225) of a molar
solution of trisodium phosphate (13.8) is almost that of a molar solution
of sodium hydroxide (13.9), and it is much easier to handle. The explana-
tion of the action of this compound as a base is found in its reaction with
very hot water in the washing machine.
NaaPO4 4- HOH -» Na2HPO4 4- NaOH (formula equation)
PO- - - 4. HOH -* HPOr - + OH- (ionic equation)
Such an action of a dissolved salt on the ions of water is called hydrolysis
(see page 232). Sodium carbonate can also be used for the same purpose.
Na2CO3 -f HOH -4 NaHCO3 4- NaOH (formula equation)
COr " 4- HOH -> HCOr 4- OH~ (ionic equation)
The explanation of hydrolysis involves reactions between ions and water.
Let us consider a solution of sodium acetate (NaC2H3O2), a salt that may
be considered to have been formed by interaction of the strong base,
sodium hydroxide (NaOH), and the weak acid, acetic acid (H-C2H3O2).
Four ions are present in the solution, namely, Na+, C2H3O2~, H+, and
OH~. The latter two are originally present in small amount from the
water that dissociates very slightly. The Na+ and OH~" ions do not tend
to join together, but the H+ and C2H30^~ ions do join to form the slightly
dissociated molecule called acetic acid (H-C2H3O2). This leaves effec-
tively Na+ and OH~ ions in solution. When we test a solution of sodium
acetate with litmus paper, we find that its solution turns the red color
to blue.
These actions may be summarized as follow:
NaC,H,02 *± Na+ 4-
HOH *=t OH- 4- H+
strong weak
hydroxide acid
610 _ CHEMISTRY FOR OUR TIMES
More simply,
r + H20 -4 HC2H802 + OH-
Salts like copper sulfate (CuSC^) and zinc chloride (ZnCl2) in solution
hydrolyze and produce solutions containing excess hydrogen ions. Again
this is due to the action of water on the dissolved ions. Each of these com-
pounds may be considered to be derived from a weakly dissociated
hydroxide and a strong acid.
Cu^ + HOH -4 (CuOH)+ -f H+
Compounds like aluminum sulfide (A12S3) that may be considered
derived from both a weak hydroxide and a weak acid hydrolyze vigor-
ously. In this case hydrogen sulfide gas is liberated.
AI2S3-h6HOH -4 2AI(OH)3l -f 3H2St
In solutions of compounds like common salt (NaCl) and potassium
nitrate (KN03), none of the ions change the pH of the solution. They act
neutral to litmus. The pH value of sodium chloride solution, for example,
is the same as that for pure water, namely, 7.
Dry Cleaning. Everyone knows that woolen suits cannot be washed
satisfactorily in water. Cleaning greasy overalls and woolen garments is
accomplished by "dry cleaning/' in which a fluid is used but the fluid
does not mat down the cloth as water does. The cleaning fluid is a frac-
tion from petroleum resembling gasoline or some chlorinated organic
compound. The fluid, to which a special soap is added, is passed through
the garments, removing grease and dirt, until it comes through clear.
The garment^ are then ventilated and pressed. The fluid is recovered,
passed through a bed of adsorbing material like activated charcoal, and
then rectified, or distilled, for re-use.
Cleaning Metals. Let us recall that metals can be cleansed of oxide
films by acids, by fluxing with zinc chloride (ZnCl2) or ammonium chloride
(NH4C1), or by fluxing in such a fashion that the oxide forms a slag
(see page 279). Clean metal surfaces are necessary for many operations
that are performed on metals, such as plating, etching, photo-engraving,
and drawing into wire. When a hot alkali solution is used for washing a
metal free from grease, the addition of a small amount of one of the newer
detergents for a wetting agent is often helpful.
QUESTIONS
13. What is the effect of treating hard water with sodium hexametaphosphate
(in slight excess) and then adding soap solution?
14. Write equations for softening temporary hard water (a) by boiling; (b) by
adding sodium carbonate; (c) by adding hydrated lime.
16. Write equations for softening two sorts of permanent hard water by
adding sodium carbonate.
CHEMISTRY FOR CLEANLINESS 611
16. How can all the salts in hard water be removed without resorting to
distillation?
17. What methods for obtaining drinking water are available to shipwrecked
sailors afloat on a rubber raft?
18. How can suds be produced in hard water without removal of the dissolved
salts?
19. From what materials are such commercial products as Dreft and Drene
compounded?
20. What would be the most effective way of softening hard well water for a
country home?
21. Define and illustrate hydrolysis of a salt.
22. Woolen clothes cannot be washed successfully with hot soapy water.
How may they be cleansed?
23. Visit a dry-cleaning establishment, and write a report on the procedure
for cleaning one's school clothes and recovery of the cleaning fluids. What com-
pounds are used in the process?
24. Why is glycerol considered to be an alcohol? How is it obtained com-
mercially?
26. Why do solutions of washing powders have an alkaline reaction?
26. How does the process of removing a grease spot with soap and water
differ from that of removing it with gasoline?
27. What substances are formed when fats are hydrolyzed?
28. From what is silver polish made, and how does it accomplish the cleaning?
29. How can silver be cleaned "electrolytically"?
30. Why is rosin sometimes used as a flux in soldering copper wire?
31. Compile a list of soldering fluxes and the metals on which they are used.
Health
Antiseptics. A number of chemical compounds are used for killing
germs. If the surface of the skin is washed with a little 70 per cent grain
alcohol (ethanol, C2H5OH), the region is perfectly sterile. Surgical instru-
ments may be sterilized by steaming them under pressure. Mercury
(mercuric, valence II) chloride (HgCl2) in solution with ammonium
chloride (NH4C1) is a powerful antiseptic; but since it is very poisonous,
care must be exercised in its use. Tincture of iodine (I2), hydrogen peroxide
(H2O2), and boric acid (H3BO3) are all well-known antiseptic agents.
Each has its special uses. Phenol (carbolic acid, C6H5OH) is a useful
germ killer.
612 CHEMISTRY FOR OUR TIMES
In addition to general antiseptics, special compounds are available to
attack fungus growths or infections of the body. Gentian-violet dye is
used to combat impetigo, and ammoniated mercury ointment subdues
infections. Copper naphthenate is a recently discovered remedy for
ringworm and " athlete's foot." It is also used to prevent mildew on
tents.
Medicines. No internal antiseptic has yet been found. Any com-
pound strong enough to kill bacteria will also kill the corpuscles in the
blood or injure tissue. Recently, however, certain compounds called the
"sulfa compounds " as a group have been found to be most useful in
medicine. They seem to attack germs in the body in such a fashion that
the white corpuscles can kill them rapidly. Almost daily we hear about
seemingly impossible cures from pneumonia and meningitis by use of
sulfathiazol, sulfanilamide, sulfapyridine, or a related compound. Sul-
fadiazene is useful in intestinal disorders. The use of these compounds in
powder form has gone far in the prevention of gangrene infections in
wounds and overcoming other infections in the body caused by dangerous
streptococcus bacteria.
Penicillin, an extract obtained from the mold Penicillium notatum, is
another modern medicine that has produced remarkable cures for infec-
tions of the blood stream. The material was first described by Dr. Alex-
ander Fleming in 1929. Today many difficulties connected with its
production on a large scale have been overcome, and this important
medicine has been added to the lifesaving resources available to the
doctor. ~~ " "
In addition, certain chemical agents are specific for definite ills.
Ehrlich's six hundred and sixth experiment in the preparation of arsenical
medicines resulted in salvarsan, which destroys the bacterial cause of the
dread disease syphilis. Tetrachloroethane is used to "worm" dogs.
Experiments with the digestion of carbohydrates and the function
of the pancreas in this connection led Banting and Macleod to the dis-
covery of insulin, a hormone required in digestion produced by the
pancreas. When this substance was purified and isolated, a specific remedy
for diabetes was obtained. Diabetes is now listed among those diseases
which are almost conquered, and this by the application of chemistry.
Space does not permit more than a suggestion or two to bear out
the point that both organic compounds, such as aspirin, and inorganic
compounds, such as sodium hydrogen carbonate (bicarbonate of soda,
NaHC03) and magnesium hydroxide [milk of magnesia, Mg(OH)2l, play
an important part as medicines that help us maintain or regain health.
Physiological Chemistry. A great number of experiments are in
progress that deal with the application of chemistry to the functioning
CHEMISTRY FOR CLEANLINESS
613
of the human body both in sickness and in health. The processes of
digestion, respiration, growth, and recovery from disease are all studied
with the greatest care. The effects of various medicines are watched in
clinical chemistry, starting with animal experimentation.
One method of proceeding is to extract some of the active principle.
This process is often a long, expensive one, for some substances like
hormones and vitamins are present in the body in only the tiniest amounts.
Dr. John J. Abel, an American investigator, prepared adrenalin, an
extract obtained from tiny glands that are located on top of the kidneys.
He was the first to obtain a hormone in crystalline form as a pure sub-
stance. This compound, manufactured synthetically, is now available to
doctors as a medicine, epinephrine, and as such has been the means of
Courtesy of H. J. Heinz Company
FIG. 35-5. — These compounds are undesirable when used as preservatives in food.
saving many lives. It has the. combination of properties of stopping
bleeding and being a heart stimulant at the same time.
Beauty
History of Cosmetics. Studies of Egyptian mummies reveal that
the art of using cosmetics was well advanced as early as 4000 B.C. We
have positive evidence that Roman ladies used stibnite (antimony black,
Sb2S8) to darken lashes. Perfumes were first used to cover objectionable
odors by their overpowering fragrance, but modern usage of perfumes
in most cases is more delicate and subtle. In Elizabethan times a mascu-
line parliament of England passed a decree making it unlawful for women
to use cosmetics for the purpose of concealing their true age. Today
beauty aids are available to men and women in all walks of life at mod-
erate prices, due in part to modern methods of machine production.
614 CHEMISTRY FOR OUR TIMES
The cosmetic business today grosses over 2 billion dollars a year, and
reputable manufacturers employ chemists to check the quality of raw
materials as well as to supervise their manufacture.
Powder. Talcum powder is chiefly ground rock talc (Mg3Si4Oii'H20)
with a suitable scent added. Face powder contains zinc white (ZnO)
or titanium dioxide (TiO2) for covering, kaolin clay for adhesion to the
skin, precipitated chalk (CaCO3) for absorbing perspiration, and talc
for a slippery texture. In. addition, more or less coloring matter and per-
fumes are added. Many variations of these ingredients are available.
Face Creams. Tests show that as a skin cleanser no superior substi-
tute has been found for soap and water. In fact, frequent washing with
soap and water is one of our best and simplest ways to keep well and aid
in personal attractiveness. Soap has a slight antiseptic action. For most
satisfactory results, users of face creams are advised to wash the face
first. Creams cleanse and lubricate the skin.
Cold creams are a stable emulsion of (I) an oil (olive, mineral) and
(2) a waxy material (beeswax, lanolin) in (3) water stabilized by (4)
an emulsifier (borax, Na2B4O7); (5) a perfume is added. These ingredients
are simple and inexpensive. Indeed, a most satisfactory face cream can
be made at home by using no more complicated apparatus than an ordi-
nary double boiler and an eggbeater (see Appendix).
Vanishing creams are chiefly emulsions of potassium soaps. They
correspond very closely to brushless shaving-cream preparations.
The variations possible in face creams are countless. Hence many
varieties are on the market. None, however, will feed the body through the
skin, which is an organ of excretion. Some creams are represented as
bleaching, while others are alleged to remove freckles. Some of these
preparations, especially bleaching creams, may contain mercury com-
pounds. These should be used with the greatest caution, if at all; for
mercury compounds are poisonous, and their use may result in dis-
figuring the face and marring beauty.
Lipstick. The basis of lipstick is a thick, waxy face cream, perfumed
and colored. The fire-engine red color is obtained by the use of dyes.
Irritation of the lips may develop if poisonous dyes, such as certain
aniline dyes, are used.
Nail Polish. The original nail polish consisted of a mildly abrasive
powder like talcum powder. Fingernails buffed on a chamois pad using
this powder take on a smooth, satinlike polish. This method of polishing
nails is still effective.
Many persons today prefer to coat the nails with a quick-drying
lacquer, which dries with shiny Surface and which has the added feature
of the choice of a great variety of colors. The result of such paint jobs
CHEMISTRY FOR CLEANLINESS 615
depends largely on the skill of the artist. Lacquer solvent or acetone
[(CHa^CO] will remove lacquer polish from the fingernails.
Dentifrices. Most dentifrices consist of a mild abrasive like precipi-
tated chalk (CaCO8), a little soap or soaplike material, such as the sodium
salt of a sulfonated higher alcohol, and a pleasant flavoring. Other than
convenience, no particular advantage can be claimed for the dentifrice
in either the powder or the paste form. The purpose of a dentifrice is
to clean and polish the teeth. A preparation that aids in doing this with-
out injury to the teeth has fulfilled its purpose. Clean teeth are more
attractive to look at than discolored or dirty ones. No relationship
between the brushing of teeth and absence of tooth decay has been
proved.
A dentifrice containing an abrasive as hard as pumice, which is-
harder than some of the exposed parts of the teeth, should be avoided.
Sodium peroxyborate (perborate^ NaBOa'4H20) in tooth powder may
produce gingivitis, an irritated condition of the gums. Such inexpensive
materials as salt, bicarbonate of soda, and precipitated chalk, plus a
little flavoring, make a satisfactory, yet very inexpensive, homemade
dentifrice. If the user prefers to froth at the mouth, he adds powdered
soap.
Composition of Cosmetic Products. The composition of typical
lotions, mascaras, rouges, toilet waters, perfumes, after-shave astringents?
hair tonics, bleaches, depilatories, and styptic pencils can readily be
found in standard reference books. There is no mystery about their
ingredients. None can do anything more helpful for the user than to
cause him or her to think of the impression being made on others by his
or her personal appearance.
It is interesting to note that the use of cosmetics is, to a measure, to
imitate the glow and natural radiant beauty of youth reflecting wholesome
living. Those who possess these characteristics have little need for arti-
ficial aid.
SUMMARY
Soap is an important emulsifying agent for cleansing. It may be made at home
by boiling fats with alkali and also may be made commercially in huge kettles
from various fats and oils by reaction with either sodium or potassium hydrox-
ides. An important by-product is glycerol (glycerin). Soap, which contains
builders to make it a better cleansing agent, is packaged as cakes, flakes, or
powder. Chemically, soap is a salt of a fatty acid; sodium and potassium soaps are
soluble, but calcium and magnesium soaps are insoluble.
Mineral salts in "hard water" precipitate calcium and magnesium compounds
by reaction with soap. "Soft water" lathers freely. Temporary hard water is sof-
tened by boiling. Permanent hard water must be treated chemically to remove
minerals that react with soap to form a precipitate.
616 CHEMISTRY FOR OUR TIMES
The newer detergents are not like soap; they are important in the processing
of fabrics and metals, but they serve as cleansing agents even in hard, water.
Hydrolysis is the reaction of ions of dissolved salts with water.
Salts of a strong base and a weak acid form alkaline solutions as a result of
hydrolysis; and salts of a strong acid and a weak base form acid solutions. Salts
of a strong acid and a strong base are neutral in solution. For example, NasPO*
produces an alkaline solution in water by hydrolysis and aids in the removal of
grease.
Dry cleaning involves the use of grease solvents like carbon tetrachloride and
certain hydrocarbons, with various special soaps added to aid removal of solid
particles.
Cleansing metals involves the removal of oxide or sulfide films. Fluxing forms
a slag and cleans metals in a furnace.
Antiseptics are compounds that kill bacteria with little damage to their host.
Many antiseptics are produced by chemists.
Like the newly discovered sulfa drugs, some compounds are given to persons
for their specific effects; most medicines, however, produce a general, not a
specific, effect; that is, they aid the body in overcoming the invading bacteria.
Some are hormones, like insulin or adrenalin. Some are organic compounds, like
morphine or aspirin, which reduce pain.
Physiological chemistry is the study of the chemical reactions of body func-
tions.
Cosmetics are mixtures and compounds for aiding personal attractiveness.
Included among cosmetics are talcum powder, face creams, lipsticks, and nail
polish lacquers.
Dentifrices serve to clean and polish the teeth. Most dentifrices consist of a
mild abrasive, a little soap or soaplike material, and a pleasant flavoring.
QUESTIONS
32. What antiseptics are usually found in the household medicine cabinet?
33. Write a theme on the history of chemotherapy, mentioning Dr. Ehrlictis
Magic Bullet.
34. Are hormones drugs? What is insulin? Adrenalin?
36. Compile a list of safe household remedies for stocking a medicine cabinet.
36. What compounds are used as pigments in lipstick? Are lipstick pigments
ever a source of irritation to the user?
37. What are the usual ingredients of tooth powders? Face powders? Talcum
powders? Foot powders? Dusting powders?
38. In what way are fingernail lacquers and high explosives similar?
39. Why should one not remove stains from an acetate rayon garment with
fingernail-lacquer solvent?
UNIT EIGHT CHAPTER XXXVI
CHEMISTRY FOR SAFETY, PEACE,
AND WAR
The twentieth century has been marked by a steady increase in the
insurance business, especially in the United States. This business has a
peculiar interest in keeping people alive and well. Investigators for in-
Courtesy of The Travelers Insurance Company
FIG. 36-1. — In this gas-air explosion at Oakland, California, the newspapers estimated
damage of $50,000.
surance companies study the causes of accidents and deaths at home and
in industry. Facts are gathered about deaths from disease, also. For ex-
ample, when a disease, such as cancer or heart disease, is one of the leading
causes of death, public attention is drawn to it through advertising.
Equal enthusiasm is devoted to the study of the cause and prevention
of accidents. Safety engineers find out about safe and unsafe practices
and materials.
detonation
cordite
New Terms
allergy
vesicant
617
projectile
618 CHEMISTRY FOR OUR TIMES
Gas-air Mixtures. In a hospital, the tense atmosphere of a
certain busy operating room has relaxed. The operation has been con-
cluded successfully, and the instruments are being put away. The air is
still full of the gas used as an anesthetic. A nurse disconnects a light by
Courtesy of The Travelers Insurance Company
FIG. 36-2. — This lady is far safer with dynamite on her ironing board than with an
open pan and jug of gasoline and a flame at the stove.
••)
pulling out an electric plug at a convenience socket. A spark is caused,
and the entire room explodes.
C2H4 + 3O2 -* 2CO2 + 2H2O
People are hurt, possibly killed, and property destroyed.
A mechanic is working on a car. The guard has slipped off his port-
able electric light bulb with which he lights his work. The bulb swings
against the motor, breaks, and exposes the white-hot tungsten wire to
a mixture of air and gasoline vapor. A blinding flash of burning gasoline
sears the mechanic and destroys the car.
C7H16 -f 11O2 -> 7CO2 4- 8H,O
These are all too frequent happenings. Mixtures of flammable gas
CHEMISTRY FOR SAFETY, PEACE, AND WAR 619
and air (see page 527) have been known to flash back 600 ft and ignite
the source. (See Fig. 36-1.)
Household fuel gas explodes when mixed with air in an oven.
Gasoline, ether, some dry-cleaning fluids, turpentine, fingernail polish
and other paints, and many similar liquids give off heavy vapors that
mix with air and explode. It cannot be emphasized too often that the
surest way to prevent accidents from such volatile flammable liquids as
these is knowledge of their danger.
The carrying of gasoline into a hj)me is dangerous. (See Fig. 36-2.)
Most people do not understand that
the vapors formed when gasoline is
used constitute the chief hazard and
that it is only a matter of chance
whether or not these vapors will find
some source of ignition, such as a pilot
light in a kitchen stove or a glowing
ember in the fireplace from yester-
day's fire.
Sample
RWire
Holder
Colorless Bunsen
Flame
FIG. 36-3. — A sample of a stron-
tium compound heated in a Bunsen
flame colors the flame red.
Colored Flames. When a truck
stops by the roadside for repairs, a
kerosene-burning, bomb-shaped lamp
with an open flame is frequently
used to warn travelers of the danger.
This light will burn even in a rain-
storm and will not be blown out in
a high wind — hence its use around
excavations.
If the truck must be stopped on the highway itself, red flares are used.
The burning material contains fuel, a supporter of combustion, such as
potassium perchlorate (KC104) and some compound of strontium, for
example strontium nitrate [Sr(NOs)2]. These red flarru\s are used in cele-
brations as well as for danger signals on railroads and highways. The
red-colored flame from all vaporized strontium compounds is character-
istic and is a means of identifying them in the laboratory. The method of
performing the test is illustrated in the diagram. (See Fig. 36-3.)
Lithium flames are scarlet and those from sodium compounds yellow.
When held on a clean metal in a colorless flame, barium compounds
produce a green color. Copper chloride gives a blue-green flame.
Curiously, no one yet has made candles suitable for home decorative
lighting that burn with a colored flame. Many patents have been granted
on this subject, but no satisfactory candles have been produced thus
far. Colored smokes, however, are used successfully in warfare.
620 CHEMISTRY FOR OUR TIMES
Safe at Home. Many accidents at home, such as a fall from a step-
ladder, are purely mechanical, but chemical knowledge will help prevent
many other types. Chemistry cannot keep soap from being slippery,
but chemists have helped develop nonskid mats for the bathroom.
All fires should have a proper draft to prevent the deadly carbon
monoxide gas from entering the home. All furnaces and hot- water heaters
should be connected to a chimney with sheet-metal pipes to remove all
the carbon monoxide. This is especially true in the case of gas hot-water
heaters, for the gas flame striking against a water-cooled surface is chilled
^il^ikiiii^v1:^ $•
> v.i
v "^n^^^HBRj;'^/;1',,!1;;;1''"' ry ;
Courtesy of The Travelers Insurance Company
FIG. 36-4. — This is a safe method of pouring corrosive acid from a carboy.
below its ignition point, permitting some of the carbon monoxide to
escape.
Toilet articles, such as combs, brushes, and ornaments, made of
celluloid or other flammable plastic material should be kept from hot-air
driers. Photographic films, lacquers, and some toys are made of cellulose
nitrate, which is violently flammable; they should therefore be kept away
from open flames.
Modern technical chemistry applied to glass furnishes stronger,
clearer glass, more free from strains than the product of a generation
ago. The milk bottle of today makes five times as many trips as did the
now-broken milk bottle of twenty years ago. The gas, Freon (CF2C12),
used in a modern mechanical refrigerator is nontoxic, noncorrosive, and
nonflammable, thanks to chemistry. Freon, however, does form poisonous
hydrogen fluoride and hydrogen chloride in an open flame.
Other Safety Devices. The treads of stairways, especially in public
buildings, are nonskid even when wet by virtue of the presence of some
CHEMISTRY FOR SAFETY, PEACE, AND WAR 621
form of ground abrasive aluminum oxide (AUOa) in the wearing surface.
Today's steel is more uniform, stronger, and less subject to fatigue and
corrosion than the metal of our father's day.
Spring steel, which failed after 3 million flexings in a corrosive at-
mosphere, is now replaced by beryllium-copper alloy, good for at least
1 billion flexings. The part that this alloy plays in making airplanes safe
can be seen from the fact that more than 100 small but important parts
of a modern transport plane are made of it.
Courtesy of The Travelers Insurance Company
FIG. 36-5. — These boys are trying a dangerous experiment — they were not fore-
warned. The bottle contains Dry Ice. Dry Ice in a bottle with the top screwed on has
caused serious and painful wounds. What might happen?
Irritating Dust. A great deal of rock wool and similar substances
is used for home insulation purposes, and this is often installed by the
homeowner. The dust produced during installation, although not dan-
gerous, is irritating to the nostrils, and it is desirable that a filter type
of respirator be worn. The dust is needlelike in form and, being alkaline,
is likely to produce skin irritations, especially should a person perspire.
For this reason, it is recommended that sleeves be kept rolled down
and gloves be worn.
Allergies. Skin irritations, dermatitis, and allergies cause more losses
from an occupational-disease standpoint than all other occupational dis-
eases— silicosis, lead poisoning, benzol poisoning, and the like. Poison
ivy is the classic example. Protective clothing against known irritants is
helpful. Protective ointments, such as hand creams, are being prepared
622
CHEMISTRY FOR OUR TIMES
Courtesy of For (I and Cement Association
FIG. 36-6. — The crunching hard steel jaws of a gyratory crusher engulf a whole carload
of rock. Observe the safety chain on the worker's belt.
FIG. 36-7.— Ti
Courtesy of The Travelers Insurance Company
•orrert way to avoid carbon monoxide poisoning.
CHEMISTRY FOR SAFETY, PEACE, AND WAR 623
and used as a protection against irritants and solvents. Less irritating
soaps or detergents are being recommended, especially where dyes or
grease must be removed from the hands.
Courtesy of United Stales Metals Refining Company
FIG. 36-8. — This chemical engineer is obtaining a sample of air suspected of contain-
ing poisonous fumes.
Courtesy of The Travelers Insurance Company
FIG. 36-1). — A flour-dust explosion at Omaha, Nebraska, caused this disaster.
Thus we see that, as a result of applying the facts learned through
chemistry, living is made safer and more secure. The careful observer will
be able to extend this list almost indefinitely.
684 CHEMISTRY FOR OUR TIMES
QUESTIONS
1. What gas was in the operating room in which the explosion described on
page 618 occurred? Name two other anesthetics that produce explosive mixtures.
2. Name three possible sources of ignition of a gas-air mixture.
3. An electric light bulb smashed in gasoline vapor continues to glow dur-
ing the explosion and for a short time afterward. Then it "burns out" quickly.
Explain.
4. Suggest four safety rules for marking and handling cans of gasoline.
5. A painter, who has just finished mixing a quantity of paint, pauses to light
a cigarette. A cigar lighter is struck in the dust-laden air of an attic that has just
been "housecleaned." Explosions result in both cases. Explain. Give another
example of an explosion that might take place at home.
6. List four flame colors and the elements that cause them.
7. Write formula equations for the following reactions: (a) barium chloride
solution and sulfuric acid; (6) barium nitrate solution and sodium sulfate solution;
(c) barium peroxide and sulfuric acid; (d) strontium nitrate heated.
8. Statistics show that persons are far safer riding in a train than at home.
Explain how this is possible.
9. Why should all gas heaters be vented?
10. What danger exists in having no ventilation in a room containing a fire
burning in a coal or wood stove?
11. Some rooms are heated by gas-fired radiant-heating devices. What dan-
ger accompanies their use?
12. Is it possible for combs in a lady's hair to catch fire?
13. Why are "starred" or chipped beverage bottles dangerous?
14. In a school building what measures are taken for (a) fire protection;
(b) public safety? Do these involve chemistry directly?
16. How do workmen handling coal protect themselves from dust?
16. What dangerous condition develops when a tunnel is driven through
granite? Does the same condition exist if the rock tunneled is limestone? What
protective measures should be taken?
17. How can one avoid ivy poisoning while working near poison ivy vines?
What first-aid measures are advisable to relieve ivy poisoning?
18. What is a safe manner of keeping and handling the following poisonous
materials sometimes found at home: (a) arsenical flypapers; (6) arsenical ant
baits; (c) insect sirup containing lead arsenate; (d) barium-containing rat poi-
erons; (e) insect powder containing sodium fluoride; (/) bichloride of mercury
CHEMISTRY FOR SAFETY, PEACE, AND WAR 685
tablets for making strong antiseptic solutions; (g) poison jars containing cyanides
for killing insect specimens; (h) garden poisons containing calcium or lead
arsenate?
19. What type of paint should be used on children's toys and play-pens?
What type should not be used?
20. Give a new example of " better things for better living through chemistry/'
Chemistry in War
Smoke Screens. Smoke screens for hiding ships as well as land tar-
gets are well known in naval and military strategy. (See Fig. 36-10.) On
the water a destroyer cuts down the air supply to its oil-burning boilers
and provides more oil than can be completely burned. A dense black
smoke billows from its stacks, screening the convoyed merchantmen or
battleships.
On land, white phosphorus is an effective material for creating smoke.
When dry, the element ignites spontaneously and burns, forming a dense
white cloud.
4P + 5Q2 -» 2P2O5
Other smokes depend on the presence of moisture in the air. Tin
tetrachloride (SnCl4), titanium tetrachloride (TiCl4), or sulfur trioxide
(SO3) dissolved in concentrated sulfuric acjd when released into the air
forms dense clouds of acid smoke.
SnCU + 4HOH -+ 4HCI + Sn(OH)4|
SO, + H2O -> H2SO4
Peacetime uses of this practice are seen in skywriting and spraying
or dusting growing plants from an airplane. Colored smokes are available.
Odds for Death — Gas 1 to Steel 12. Almost everyone thinks that,
given the choice of being overcome by gas in warfare or stopping flying
fragments of lead or steel, the second is the better choice. Death or
wounds from being struck is more understandable to the average person.
Let us take a look at the facts as revealed by World War I. The
Surgeon General of the United States Army reported that 27.3 per cent
of all disablements then were due to gas. Of these, 98 per cent recovered.
Of those wounded by other means, 25 per cent failed to recover. A
permanent or fatal injury from steel had 12 to 1 odds over injury from
gas.
That is, gas 'from a military standpoint was more effective in that it
disabled the enemy and put his men in the hospital, but as a whole it was
more humane than steel or disease. There are relatively few aftereffects
of gas if the soldier is in good health. Also, gas drives defenders out of
dug-in positions more effectively and humanely than any other known
method— that is, if war can be considered humane in any respect.
626
CHEMISTRY FOR OUR TIMES
Courtesy of U.S. Army Signal Corps
FIG. 36-10. — A tank battalion in training maneuvers rolls through a smoke screen.
Courtesy of Chemical Warfare Service, U.S. Army
FIG. 36-11. — This explosion of a gasoline-filled incendiary bomb was carried out to test
the destructiveness of such a device.
CHEMISTRY FOR SAFETY, PEACE, AND WAR 627
Gas Warfare. The first use of gas warfare goes back to nature herself.
The effective use of stinking mercaptans as a weapon of offense and of
defense is distinctly remembered by those who have molested a skunk.
The smoke and stench of burning sulfur and pitch were used in the siege
of some cities in ancient times.
Modern gas warfare started in April, 1915, when the Germans used
chlorine gas at Ypres, France. The gas was dense and hence was carried
by wind and gravity. Its successful use depended on surprise. Although
the Allied intelligence had informed the authorities of the planned attack,
no serious effort was made to combat it.
Later phosgene (COC12) was used. This irritates the eyes and causes
vomiting, as well as being extremely poisonous. It was used in an attempt
to make soldiers remove their gas masks. This gas was successful from
a military standpoint because the effects are often delayed, giving the
victim a short period of false security when he should be taking treat-
ment to counteract the poison.
In 1917 the Germans used the famous mustard gas [(CH2C1-CH2)2S].
This is really a liquid that evaporates in the heat <pf the sun. It irritates
the lungs, burns the skin, and disables men for a long time. It is classed
as a vesicant, and it is one of the most persistent of the war gases.
Just at the close of World War I, lewisite (CHCl:CHAsCl2) was
developed. This deadly liquid irritates the eyes and has all the poisonous
qualities of the other gases combined. Fortunately, lewisite was never
used for military purposes, and all that had been manufactured was
dumped into the sea shortly after hostilities stopped. No general use of
poison gas was reported in World War II.
The term poison gases includes both poison fogs and smokes. Their
purpose is to render an area untenable. If a persistent type of gas or
liquid is used, an area is forbidden to any occupation, enemy or friendly,
for several days, possibly a week.
To be effective for military use, a substance must either be a gas
or become a gas at ordinary air temperatures. It must not act chemically
on the steel tanks that hold it or on their metal fittings. It must be cheap
and simple to prepare. Mild heating should not decompose it, and it
must withstand compression. Moreover, when diluted by a relatively
large amount of air, it must still be intolerable to the human body.
Only a few substances are known that meet all these requirements, even
after an intensive search has been made. No great fear for new disastrous
war gases need be felt although the nitrogen-mustard gases are reported
as being extremely deadly. Also, protection against all sorts of war gases
is keeping pace with their production and use.
Defensive Gas Warfare. Along with offensive gas warfare, the pro-
tection of soldiers and animals from the effects of gas is equally important.
628 CHEMISTRY FOR OUR TIMES
The canister type of gas mask is generally used for this purpose. (See
Figs. 36-12, 36-13.) The canister contains activated charcoal (see page
549), soda lime [(NaOH— CaO) mixture especially prepared], other
chemicals, and layers of absorbent cotton and other filtering substances.
The breathed air passes in through the canister, which effectively filters
out poisonous fogs and smokes and absorbs poisonous gases. After a
limited time the canister must be replaced. No effective protection against
mustard gas had been devised at the end of World War I. Today gas
Courtesy of Chemical Warfare Service, U.S. Army
FIG. 36-12. — Three soldiers show how standard service, diaphragm (for shouting
orders), and optical gas masks are worn.
masks and a complete suit of protective clothing are available to protect
soldiers against various gases.
Experience gained in gas warfare has helped in developing effective
gas masks for protection in case of fire, industrial, or mining hazards.
Firemen, repair men, and rescue squads can be properly equipped to
save life, stop the spread of disaster, or remove the cause of trouble.
Explosives — Gunpowder. Black gunpowder was invented by the
Chinese and used for firecrackers. Later, it was adapted to military uses
by the Europeans. It contains saltpeter (KN03), carbon, and sulfur.
The more effective sodium nitrate, although hydroscopic, may be sub-
stituted for potassium nitrate if the powder is kept in an airtight con-
CHEMISTRY FOR SAFETY, PEACE, AND WAR 629
tainer. When exploded, black gunpowder makes much smoke. It is too
weak for modern military demands, but it is extensively used for blasting.
Detonation. In order to start a large explosion, an electric spark or
the mechanical shock of a small explosion is used. Such a preliminary
explosion shock, or detonation, may be caused by igniting mercury
Air Deflected Against
Eyepieces Before
Inhalation
Deflector
Facepiece
Mechanical
Filter
Courtesy Chemical Warfare Service, U.S. Army
FIG. 36-13. — The passage of air through the canister and the gas mask (service type).
fulminate [Hg(ONC)2] or lead azide [Pb(N3)2]. The extensive use of
mercury fulminate as a detonator in military explosives boosts the war-
time price of mercury.
Preparation of High-power Explosives. A nitrating mixture of
nitric and concentrated sulfuric acids is used in the preparation of the
so-called "nitro" explosives. The concentrated sulfuric acid serves to
remove water.
cone HzSO*
C»H6(OH)a
glyoerol
3HNO8
nitric acid
glyceryl nitrate
+3H,O
Glyceryl nitrate is a colorless oily liquid. It is commonly called nitro-
glycerin and is known as "soup" among "yeggs" according to the detec-
tive stories. In medicine it is used as a heart stimulant, but it should
630
CHEMISTRY FOR OUR TIMES
not be handled by the fainthearted, for it is a very sensitive explosive
and resents all kinds of rough treatment. We have seen how Alfred
Bernhard Nobel tamed this explosive by absorbing it in wood flour to
make dynamite (see page 364).
Courtesy of E. I. du Pont de Nemours <fc Company, Incm
FIG. 36-14. — American history and chemical history are tied together in this
picture. Here we see E. I. du Pont de Nemours, Esq., discussing the location of the
first American powder mill with President Thomas Jefferson.
Nitrocellulose, or guncotton, is made in a similar manner, except that
cotton instead of glycerol is the raw material. After nitration, the gun-
cotton is dissolved in ether and alcohol to form a jelly like mixture. This
is extruded into "grains," or cylinder-shaped rods of the explosive, ready
for use. The propellant charge for a projectile used frequently is cordite,
a mixture of 65 per cent guncotton, 30 per cent nitroglycerin, and 5 per
cent petroleum jelly.
Nitro Compounds. When the same nitrating mixture of acids men-
tioned in the previous paragraph is put on phenol, a chemical change takes
place, resulting in tri-nitro-phenol, or picric acid, a beautiful yellow
crystalline substance that is an excellent dye for silk as well as an explo-
sive compound when detonated.
C6H6(OH) -f 3HNO3
phenol
cone HzSOi
CflH2(OH)(NO2)3
picric acid
3H2O
Starting with toluene, a similar compound, except that the methyl
CHEMISTRY FOR SAFETY, PEACE, AND WAR 631
(CH3) group is present in place of the hydroxyl (OH) radical, a similar
result is obtained upon nitration, fri-nitro-foluene.
3HNO3
out; H2SO4
toluene
C6H2(CH3)(NO2)3 +3H2O
TNT
The bursting charge in a projectile, the explosive that is to shatter
the steel into bits and send them flying on their destructive errands either
on impact or on firing by a previously set fuse arrangement, is frequently
(a) (W
Courtesy of E. I. du Pont de Nemours & Company, Inc.
FIG. 36-15. — (a) Shows cases of 60 per cent gelatin dynamite unloaded and (6)
put into tubes to blast a trench for the "Big Inch" oil pipe line in the bottom of the
Susquehanna River, (c) The charge of 16,000 pounds is ignited and (d) a powerful
blast follows in part of an eight-foot-deep trench, 2000 feet long. In all, 60,000 pounds
of dynamite were used.
632
CHEMISTRY FOR OUR TIMES
called amatol. (See Fig. 36-16.) This explosive is a mixture of TNT and
ammonium nitrate (NH4NOa).
Detonator
Bursting
Charge
Fuse
Propellent Booster
Charge
FIG. 36-16. — A military projectile, simplified, consists of several types of explosives.
Dyes and Explosives. Before the start of World War I, Germany was
the only country in the world that specialized in manufactured synthetic
dyes from coal tar. As we have just seen, the methods of making dyes and
the methods of making explosives are much alike; similar materials are
used, and the same sort of manufacturing experience is needed. In fact,
picric acid is one example of a compound that can be used for either pur-
pose (see page 630). Thus Germany had a military advantage over the
allied countries opposing her through her knowledge of chemistry.
When the war was in progress and Germany was shut off from trading
with the rest of the world, dyes became scarce, and explosives more so.
Forced by this situation to manufacture these products for her own use,
the United States developed a vigorous chemical industry. After a period
of learning, dyes were eventually produced that equaled and surpassed
those formerly obtained from Germany.
Chemistry in Peace
Causes of War. Some of the wars of the past have been fought over
principles or religion, but many others have been wars of conquest for
land. Among the fundamental causes of war and mass movements of
people seeking new land, we must include hunger or fear of hunger. Their
own land limited or unproductive, people have started out in search for
better land, sometimes taking it from its former owners by force.
As related in the ancient Hebrew story in the book of Genesis (3: 19,
4: 12) in the Bible, among the punishments laid upon Adam for eating
forbidden fruit and upon his son Cain for murdering his brother Abel
was that the earth would yield crops only after a hard struggle. The
apparent unwillingness of the earth to produce food in abundance is
evident. Once a garden is used, its productivity drops off sharply unless
it is fertilized. After a few years' use the earth becomes well worked and
in good condition for farming, but the crop is not worth the effort to
CHEMISRTY FOR SAFETY, PEACE, AND WAR 633
raise it. This discouraging situation is explained and given a moral
meaning in the Bible stories.
We know now that the productivity of the land can be renewed by
the use of fertilizers (see page 290), but such knowledge came slowly.
The rivers, such as the Nile, that overflowed their banks each year and
brought fertility to the soil were the centers of early civilizations. In
such regions, where people were free from the fear of lack of food and
of the necessity of working hard all day long for enough food merely to
live, the arts flourished and a measure of culture developed.
Today, also, the growing of food does not occupy all the time of the
human race. Thanks to chemical fertilizers we have some time to spare.
We see, then, that applied chemistry offers a solution to the everpresent
food problem. The answer in the past has been war in many cases. If
nations that are growing rapidly in population can be freed from the
fear of lack of food, then time need not be spent in military activity in
preparation for conquest.
The Trade Route to Chile. What has been said about lack of food
holds true in less measure of other raw materials.
In the country of Chile in southwest South America lies an extensive
deposit of nitrates. This mineral deposit is unique; in no other place are
there such resources. Nitrates are needed for two important purposes —
for making explosives and for fertilizers. These two uses are important
in peacetime and indispensable in war. A nation that was cut off from a
trade route to Chile would feel handicapped, especially if that nation
was ambitious, energetic, and highly industrial in its activities. Such was
the situation of Germany before World War I. Stores of nitrates had been
accumulated, but the supply melted away when wartime demands were
added to normal needs. We have seen that, when nitrates are added to
sulfuric acid and warmed, nitric acid is produced. Nitric acid is needed
for manufacturing explosives, such as glyceryl nitrate (nitroglycerin)
and smokeless powder, or guncotton. The connection between Chilean
nitrates and explosives is therefore direct. Without nitrates no large
amounts of explosives could be made. Also, without a trade route to
Chile there was danger of starvation.
Nitrates for AIL Chemical work by Fritz Haber in Germany, by
the United States Fixed Nitrogen Laboratory, and by others has shown
clearly that nitrogen from the air, together with hydrogen from water,
could in the presence of catalysts be made into ammonia (see page 386).
The ammonia can be oxidized to nitric acid by oxygen from the air by
the catalytic method of Ostwald (see page 362).
No nation is lacking in air and water. Hence all can produce nitrates,
and a supply of the most easily exhausted fertilizing material is now
assured, depending only on power resources.
634 CHEMISTRY FOR OUR TIMES
Stakes of War. Military objectives in World War II included
sources of raw materials, such as coal, iron ore, rubber, manganese,
tungsten, and other metals and especially petroleum. A steady supply of all
these materials is demanded industrially, especially in wartime. Without
them, industries must shut down or find a suitable substitute; and if
factories shut down, people face starvation. Nature has distributed these
raw materials on the earth without the slightest regard to national
boundary lines or man's convenience in obtaining them. What help has
chemistry to offer in supplying these needed raw materials?
Assume that we had to get along with a smaller supply of iron ore.
Could we use wood, aluminum alloys, or plastics as substitutes? The
results of such substitution have not always been satisfactory, but some-
times interesting and valuable progress has resulted. In fact, for years
the timing gears of automobiles have been made of layers of cloth impreg-
nated with plastic material (phenolic resin, for example) instead of steel.
Among the possibilities of alternate materials must be mentioned
the following: (1) aluminum — or copper; (2) gasoline — or alcohol or
similar liquid fuel obtained from an annual crop; (3) white lead — or
titanium oxide; (4) tin — aluminum or, for foil, waxed paper; (5) tungsten
— or molybdenum; (6) rubber — or synthetic chlorinated rubberlike
material.
Thus a knowledge of chemistry points out the possibility of a satis-
factory or even a superior substitute for many substances. Chemistry
points the way to an improved use of our power resources. Chemistry
offers a solution to the ever-present problem of food supply. In these
ways chemistry becomes a force for peace.
SUMMARY
A knowledge of chemistry promotes our safety in many respects.
Flammable gas-air mixtures are among the most common causes of explo-
sions. Carbon monoxide poisoning may result from household fuel gas, from any
fire not properly vented, and from the tail-pipe exhaust gases of gasoline engines.
Celluloid and other nitrocellulose products burn rapidly. Dusts may produce
irritation if sharpedged or silica-containing. Some plants, such as poison ivy,
irritate the skin.
Steps to avoid accidents include the use of safety motion-picture film at home,
the use of nontoxic refrigerants, stronger glass, and more reliable metals, and
careful handling of poisons.
Colored flames warn of danger. Luminous flames from kerosene contain glow-
ing unburned carbon. Green flames contain barium compounds, sometimes cop-
per. Red flames contain strontium compounds. The color imparted to a flame by
lithium is crimson; by sodium, yellow; by potassium, violet.
Chemistry plays its part in war and in maintaining peace.
Smoke screens may be formed from clouds of sooty smoke, phosphorus pent-
oxide from burning white phosphorus, or hydrogen chloride mist formed by
CHEMISTRY FOR SAFETY, PEACE, AND WAR 635
hydrolysis of certain chlorides. Gas warfare in World War I proved less disastrous
than other forms of destruction.
Chlorine was the first gas used in offensive gas warfare. Phosgene, used later,
caused extensive casualties. " Mustard gas," a volatile liquid, is a persistent
vesicant. Lewisite, an arsenic-containing vesicant, is available. Only a few sub-
stances have the properties needed for offensive gas warfare.
Gas masks are used in defensive gas warfare. In the canister type of gas mask,
the canister contains filters for smoke and fog and activated carbon, soda-lime,
and other chemicals to absorb poisonous gases. A complete suit of gas-resisting
clothing is needed to protect against vesicant gases. Improved masks are now
available to meet industrial hazards.
Gunpowder, a mixture of sulfur, saltpeter, and charcoal, was the first military
explosive. Detonators are explosives that set off other explosives. Mercury fulmi-
nate is used extensively as a detonator. High explosives are made by nitrating,
that is, by using a mixture of concentrated sulfuric and nitric acids.
Nitrating glycerin produces giyceryl nitrate. Nitrating cotton produces gun-
cotton. Nitrating phenol produces picric acid. Nitrating toluene produces TNT.
Military explosives are usually mixtures of the foregoing materials, including
ammonium nitrate in some cases.
In World War I the chemical industry of Germany gave that country an
advantage over the Allies. World War II found the United Nations with chem-
ical resources matching those of the Axis nations.
Chemistry has aided in removing the causes of war by providing chemical ferti-
lizers. The trade route to Chile saltpeter is now less coveted. Chemical resources,
especially petroleum, rubber, tin, manganese, iron ore, and tungsten, were impor-
tant factors in World War II. Applications of chemistry are sought more and more
by nations to provide many needed substances or suitable substitutes.
QUESTIONS
21. How are smoke screens made (a) at sea; (6) by land troops; (c) by air-
planes?
22. Is it possible to (a) sow seeds; (6) spread insecticides by airplane?
23. Write an essay supporting the use of poison gas in warfare.
24. Present the case against the use of poison gas in warfare.
25. When pitch and burning sulfur are mixed, what two ill-smelling gases are
formed?
26. Name a marine creature that uses a "smoke screen" for protection.
27. In event of a gas attack on a city we are told that civilians are reasonably
safe in a closed room on the second floor. Account for this.
28. Make a list of the specifications of a gas suitable for offensive warfare.
29. Outline the specifications for a gas mask and canister suitable for pro-
tection of soldiers.
636 CHEMISTRY FOR OUR TIMES
30. Will a military gas mask give protection (a) against carbon monoxide;
(6) against sulfur trioxide mist; (c) in a room where the oxygen content is low;
(d) indefinitely?
31. Point out the similarity in the manufacture of TNT, "nitroglycerin,"
picric acid, and guncotton.
32. A 100-pound lot of gunpowder contains 75 pounds of potassium nitrate.
What weight of sodium nitrate will supply an equivalent amount of oxygen?
33. For what purpose can wet gunpowder be used?
34. Under what conditions may sodium nitrate be substituted for potassium
nitrate in gunpowder?
36. What is the composition of (a) dynamite; (6) cordite; (c) amatel; (d)
guncotton; (e) gunpowder?
36. During World War II, government advertising displayed in grocery
stores and newspapers urged housewives to "Save Fat for Gunpowder." What
was the intended meaning?
37. A large projectile contains two detonators, two booster charges, a pro-
pellant, and a bursting charge. State the purpose of each explosive.
38. Point out three chemical advantages that Germany possessed at the
beginning of World War I.
39. World War I started soon after the development of the Haber process of
nitrogen fixation in Germany. World War II started soon after the development
of synthetic high-octane gasoline in Germany? How are these chemical facts
connected with the starting time of hostilities?
40. In what respects may World War I be called the Nitrogen War?
41. Point out ways in which chemical progress may act as a force for (a) war;
(6) peace.
42. What effect have the sulfa drugs made upon the death rate from wounds
in World War II?
UNIT
NINE
ADDITIONAL TOPICS
THE petroleum industry deserves considerable study. Petroleum
is our principal liquid fuel. From it are derived many products,
many of them pure compounds.
Explosives are used to explore for oil fields. Sound waves, set
up by a small dynamite explosion (1), are recorded by a seismograph
(vibration-indicating instrument), indicating the presence of struc-
tures favorable to petroleum discovery.
Picture (2) shows a worker who has climbed onto the "Christ-
mas tree," one of the many devices used to control the flow of oil
and gas and to prevent wasteful "gushers."
Drilling for oil is a rugged task. It calls for heavy equipment, a
trained crew, and technical skill. Picture (3) shows a rotary-drill
rig good for a 15,000-ft crunch into the rock below.
A refinery is a complicated maz;e of pipes and towers. While
some may look like the product of futuristic artists or crasy plumbers,
they are, on the contrary, carefully designed and engineered. In
these towers (4) oil absorbs gases to aid in yielding gasoline. Each
run of gasoline must be tested in the laboratory for performance.
The testing engine (5) has an adjustable compression ratio and
interchangeable carburetors. Volatile flammable petroleum products
are shipped by steamer (6), tank cars, or pipe lines, and stored in
spheroid tanks (7).
Photos courtesy of American Petroleum Industries and Free-Lance Photographers Guild
UNIT NINE CHAPTER XXXVII
RADIOACTIVITY
The sight of a beautiful wild mustang stirs something in the heart of
a stalwart cowboy. He wants to saddle and ride the spirited animal. The
same challenge of the untamed is felt in the element radium by scien-
tists. No one has tamed radium. It goes its own way unaltered by man's
most extreme efforts.
Where Radium Is Found. The element radium is widely distributed,
but it is by no means abundant. One of the most interesting sources of
this element is the ore from a region almost on the Arctic Circle, near
Great Bear Lake in northern Canada. Besides radium, silver and uranium
are present in the ore. From the northern mine the ore is transported
partly by airplane to extraction plants, where it is treated by a method
which resembles that first used by Mme Curie.
The Discovery of Radium. Marie Sklodowska, later Mme Mario
Curie (1867-1934), the leading woman scientist, the greatest woman
of her generation, and the first person to receive a Nobel prize twice,
started her career unimpressively. Driven by intolerable political op-
pression from her home town of Warsaw, Poland, she studied at Cracow
and later went to Paris. There she lived in very poor circumstances, but
happily, doing laboratory drudgery while studying at the Sorbonne. It
was here that she met Pierre Curie, a young physics professor. Romance
entered the laboratory. The two married and continued their careers
with scientific fervor. When in 1906 Pierre Curie was killed in a traffic
accident, Marie bravely carried on her researches alone, comforted by
her two children and encouraged by scientists all over the world. (See
Fig. 37-1.)
Antoine Henri Becquerel (1852-1908), a French physicist, had
previously made a study of a radiation resembling X rays that is
emitted from certain minerals. He found that uranium, an element of
New Terms
radium transmutation fractional crystallization
alpha particles uranium mother liquor
beta particles fission atomic bomb
gamma rays subatomic energy
639
640 CHEMISTRY FOR OUR TIMES
high atomic weight, has the ability to act on a piece of photographic
film although the film is covered and not exposed to light. This element,
he found, is apparently a source of X rays. It scatters rays that affect
photographic paper and makes the air
near it a conductor of electricity., These
rays are produced continuously, can pen-
etrate solid objects, and are easily de-
tected. This spontaneous production of
radiations he termed radioactivity.
Marie Curie investigated this new
property, radioactivity. She found it
FIG. 37-1. — This French com- exhibited by all compounds of uranium,
memorative postage stamp ftnd in intensity prOportional to the
honors the discoverers of radium. J ^ .
The premium above postage goes amount of uranium. Then she mvesti-
for cancer research. See stamp, gated all other known elements to find
If 75 for postage plus 50c for t whether an were radioactive. Tho-
cancer research. . J
rium proved to be the only other one.
Both uranium and thorium are elements of very high atomic weight.
Marie Curie wrote,
In my general examination of so many chemical products I had taken not
only the pure elements and their compounds, but also natural products, ores,
and minerals, and it is then that I came face to face with unexpected facts. I
expected, of course, that all minerals containing uranium and thorium — very
often the same minerals contain both elements — would be radioactive, but it
seemed also, from my point of view, that none of them ought to have as much
radioactivity as pure uranium or thorium oxide. But what I found was quite
different! I found several minerals that had stronger radioactivity than the
oxides of thorium and uranium, the ratio being as high as 4 in the case of
one sample of pitchblende. In order to explain this abnormal behavior of
minerals, I admitted that in those minerals was contained some new element
with an atomic radioactivity much stronger than that of uranium and thorium,
and which could be present in the minerals only in a very small proportion,
because they were not detected in the analysis of the mineral. This particular
hypothesis has been verified by the discovery of polonium and radium by Prof.
Curie and me.1
A ton of pitchblende ore residues was given to these courageous ex-
perimenters by the Austrian government. In this ton there was contained
only about }/*> g of radium. Finding a needle in a haystack would have
been a much simpler problem. The pitchblende had distributed in it
both radium and barium compounds. Radium is almost identical in its
behavior with barium. After chemical treatment of the pitchblende, the
rasulting solution was heated a certain time: barium bromide was thus
1 Chemical and Metallurgical Engineering, vol. 24, p. 1138, 1920.
RADIOACTIVITY 641
crystallized, and radium bromide crystallized with it. But when the two
compounds had partly crystallized, the Curies discovered that a little
more of one compound was in the crystals and a little more of the other
was in the mother liquor from which the crystals were forming. This was
the greatest difference between radium and barium compounds which
they were able to find and by which they could separate the two. With
this slight difference as their only key, they set about the laborious
task of isolating the radium compound from the bari-
um. The process involved fractional crystallization. A set
of radium bromide crystals was allowed to form; the
mother liquor was poured off and saved, and the crystals
were redissolved and recrystallized. The liquids of the
same radium concentration were combined, evaporated, FIG. 37-2.—
and recrystallized. After this process was repeated Tne nucleus of
hundreds of times, a liquid finally resulted that con- ? called1 an^a™
tained almost pure radium bromide, only Kog> but the pha particle
first in the world to be obtained. when it is
A small sample was enough to find out the atomic ejec e "
weight of the new element, 226, and to allow its spectrum picture to be
taken in a spectrograph (page 48).
Radium's Projectiles. The chemistry of radium, being similar to
that of barium, is not startling. Its atomic properties, however, are
amazing. We find that radium or its decomposition products, as well as
other naturally occurring radioactive elements, give off three sorts of
radiations, named for the first three letters of the Greek alphabet.
The alpha particles are positively charged helium atoms. They are
the nuclei of the helium atoms (see Fig. 37-2), consisting of two protons
and two neutrons. The outer shell pair of electrons is missing. Hence the
alpha particle has a net positive charge of two units. These alpha par-
ticles are shot out over 300,000 times faster than a car traveling at 100
miles per hour. They may drive through as much as 8 cm of air at ordi-
nary pressure, knocking a few million electrons off "air" molecules on
their way. When an alpha particle gathers in two electrons, it becomes
an ordinary helium atom. The tiny trace of helium found in the air has
its source in the minerals of the earth that contain traces of radioactive
compounds that are continually shooting out alpha particles.
The beta particles are electrons moving with almost the speed of
light. Just like electrons moving in a long glass tube, they can be deflected
from their path by a magnet or by an electric charge (see page 180).
They are attracted toward any positively charged object. Hence they
must carry negative electric charges. These particles or rays have more
penetrating power than alpha particles.
The gamma rays correspond to the splash created by the escape of
642
CHEMISTRY FOR OUR TIMES
the alpha or beta particles and are energy radiations. Gamma rays are
.shorter in wave length than visible, ultraviolet, or even X-ray light waves,
although of the same nature. They have high ability to penetrate solids.
The gamma rays from radium cause it to act on a photographic film.
Courtesy of Victor Division of Radio Corporation of America
FIG. 37-3. — The electron micro- FIG. 37-4. — Magnesium oxide
scope, shown above, has revealed to magnified 44,000 times by a stream
mankind a new realm of the ultra- of electrons in the electron micro-
small, scope reveals its crystalline nature.
They travel in a straight line at the speed of light and are not affected
by a magnet or an electric charge. They are shut off only by collision
with heavy atoms, for example, lead nuclei in sheets of lead about 4 in.
thick.
An Element Changes* In radium we have an entirely new sort
of property. Unlike elements of low atomic weight, this element changes
spontaneously into something else. In fact, radium is produced from
uranium and changes successively into nine other elements. Finally, after
RADIOACTIVITY 643
the loss of five alpha particles and four beta particles, in the process of
changing from one element to another, an isotope of lead with atomic
weight 206 is produced. Ordinary lead has atomic weight 207.2 and is
a mixture of several isotopes.
Even more interesting is the fact that radium itself came originally
from uranium, which has in the process of producing radium already lost
Courtesy of Radium Chemical Company, Inc.
FIG. 37-5. — The safe holds radium. Every day a supply of its decomposition
product, gaseous radon, can be pumped off and used for industrial or hospital uses.
three alpha and two beta particles. That is, radium is just one stopping
place in a long series of radioactive transmutations (the conversion of
one element into another).
We must think of an element, then, not as a simple substance that
cannot be changed into a different simple substance, but rather as a
simple substance that cannot be changed into a new substance by ordi-
nary chemical means.
The decomposition of radium is curious from another standpoint.
In 1690 years, half of any given sample of radium will have disappeared
by radioactive decomposition and started down the atomic-weight scale
toward lead. In another 1690 years half of the remainder will have dis-
appeared, and so on. By calculation toward the opposite direction, scien-
tists have estimated the age of the earth's crust. The number of years
estimated by this chemical means agrees well with the number estimated
by geologists from a study of rocks and the amount of salt in the sea. It
is about 2000 million years. The earth itself is much older.
The Uranium Nucleus. The atomic weight of the most common
isotope of uranium is 238. Its atomic number is 92, near the bottom of the
644 CHEMISTRY FOR OUR TIMES
list. By subtraction of the atomic number from the atomic weight
(page 186), we find that the nucleus of an uranium atom contains 146
neutrons as well as 92 protons. In the outer shells 92 electrons occupy
places in various orbits. The outer electrons of uranium that show no
special properties are not as important as the nucleus that is erupting.
This heavy nucleus apparently is unstable. Its group of neutrons and
protons can be pictured as quarreling among themselves. The quarrel
Courtesy of Radium Chemical Company, Inc.
FIG. 37-6. — Filling radium salt into platinum containers requires a special handling
technique.
is continual and violent. Neither the low temperature of liquid helium
nor the high temperature of an electric arc slows or hastens the turmoil
within the nucleus. Occasionally an atom of uranium disrupts. In the
fray a fragment of the nucleus is expelled, two neutrons and two protons
together, or an alpha particle. An atom of a new heavy element remains,
but this is also unstable. Following this disturbance a neutron within the
nucleus is broken up, and its electron, a beta particle, is thrown out.
The melee rages, continuing to discharge both alpha and beta particles
from the nucleus until a lead nucleus is formed. Then a peaceable arrange-
ment is reached, one that is stable and does not lose projectiles.
In each 4 billion years half of the quantity of uranium on the earth
RADIOACTIVITY 645
has disappeared and started down the path toward lead. Which atom
will be next to disrupt cannot be predicted, but the exact number of
atoms that will disrupt each year can be told. This is quite like the statis-
tics used in life-insurance companies. They cannot predict who will die,
but they can predict accurately how many policyholders will die within
a year.
New Energy. All the while this nuclear rearrangement is proceeding,
large amounts of energy are being given off. Any sample of radium is
warmer than its surroundings because of the energy constantly being
emitted. Measurements of the force that is required to shoot out alpha
and beta particles with such enormous speeds show that here mankind
has discovered another source of energy, subatomic energy. This new
source of energy fascinates us because of its possibilities, for what shall
we do when all the cheaply-reached coal, oil, and gas have been burned?
The Sun. Our earth receives only a tiny fraction of the energy given
out by the sun. Yet that small amount is enough to move the winds,
evaporate and lift all the water of the rains, keep the earth at a livable
temperature, and grow all green plants; and, through the course of past
eons, it has provided the earth with a supply of fossil fuels.
What is the source of the sun's tremendous amount of energy? It is
probable that, under the terrific conditions of temperature on the sun,
new elements are being formed from protons and electrons, releasing
energy at the same time.
The Transmutation of Elements. The scientific attack on the
nucleus of atoms, using the cyclotron and other high-powered tools,
gives a partial answer to the fundamental puzzle of science: What is
matter?
The changing of the atom of an element into the atom of another
element is accomplished by changing its nucleus. The number of outer
electrons seems to change rapidly whenever necessary, either going out to
or coming in from the neighborhood.
The actual changing of one element to another was first accomplished
in 1919 by a British physicist, Sir Ernest Rutherford (1871-1937). He
used alpha particles for bullets and shot these at nitrogen atoms, hoping
to hit their nuclei. He succeeded in knocking a proton out of a few
nitrogen atoms, changing them to oxygen atoms of atomic weight 17.
i<N + <He -4 }H + 1JO ft £ (symbol)
alpha proton
particle
His hits were only one out of half a million. Very much more energy
was spent shooting, therefore, than was released by the change in the
few atom nuclei. His experiment, however, was extremely important
646
CHEMISTRY FOR OUR TIMES
FIG. 37-7. — X-ray photographs us-
gmillionth-of-a-socond exposure catch
bullet penetrating a block of wood,
ote the burst when the bullet emerges.
Couritty of Wettinffkous* Electric Corporation
RADIOACTIVITY 647
in proving that one element could be changed into another and in pointing
the way to our present ideas of the structure of an atom.
Since these first experiments neutrons and positrons have been dis-
covered. Neutrons have no electric charge; thus they make a better
bullet than an alpha particle for entering through the electron shell and
approaching the positively charged nucleus. Once they are moving
rapidly, with the impetus of a cyclotron behind them, they accomplish
changes in atomic nuclei readily. Lead has been made into gold, the
dream of the alchemist. Lithium has been knocked apart to become two
atoms of helium, and other^ changes have been accomplished.
7,Li 4- !D -4 2jHe + Jn
lithium deuterium 2 helium neutron
atoms
But none of these changes is on a large scale, and all are expensive.
The trace of gold made by this method is so small that it cannot be
fouad by careful examination with the spectroscope, nor can it be seen
with the most powerful microscope. It can be detected only because
when so made it is radioactive. We know that gold can be made in this
way, but the way is obviously not practical at present.
Induced Radioactivity. Careful examination of the products of
transmutation shows that they are often radioactive; that is, they give
out particles and decompose into elements of different atomic numbers.
This discovery was first announced in 1934, by Fr£d6ric and Irene Curie
Joliot, son-in-law and daughter of the famous Mme Curie. Since then,
Prof. Enrico Fermi at the University of Rome and later at Columbia
University and Prof. E. 0. Lawrence at Berkeley, California, and many
others have focused attention on this field of physics by producing other
artificial radioactivity. Radio-isotopes of all the elements have been
synthesized, including those which have not been found occurring
naturally. Thus, it has been found possible to investigate the chemical
reactions of as yet undiscovered elements !
Uses of radioactive isotopes of common elements made by the cy-
clotron have been found. Radioactive sodium in salt is used in medicine.
Its effects last for a limited time before the compound becomes ordinary
salt. A trace of a radioactive element put into the sprayed finish on
cars or refrigerators serves as the basis for a method of determining how
thick a coating of finish has been applied. The intricate course of phos-
phorus from the time sodium phosphate is eaten until the phosphate is
incorporated in bones can be followed by adding a trace of radio-phos-
phorus to the sample. Using radio-iron, the digestion of iron salts by
normal and anemic animals can be studied. Radio-iodine has given
information about the functioning of diseased and healthy thyroid glands.
In addition to their use in medicine in attacking cancerous body tis-
648 CHEMISTRY FOR OUR TIMES
sues, radium compounds are used industrially for nondestructive testing.
A container of radioactive material (radium sulfate) is supported on
one side of a piece of metal, often a casting, under investigation. A
photographic plate is fastened on the other side. The gamma radiations
from the decomposing radium cause a shadowgraph on the film just as
X rays do. Faults and flaws, if present in the metal, are readily detected
by studying these shadow pictures.
The Atomic Bomb. In August, 1945, atomic bombs were exploded
over Nagasaki and Hiroshima. Both these Japanese cities were almost
completely destroyed. Although the explosions were small compared with
some volcanic eruptions that have taken place in past eras, each never-
theless was of an enormous size never before achieved in the controlled ex-
plosion of a single bomb. They were accomplished by changing a small
amount of matter into energy. The two explosions brought World
War II to an abrupt end and ushered in a new era of possibilities for
mankind — possibilities of harnessing subatomic power or possibilities
of self-destruction.
Isotopes of Uranium. The success of the atomic-bomb project was
due to many factors. Important among them was a painstaking study
of the properties of uranium. Natural uranium is found to consist of
three isotopes, 99.3 per cent of U-238 (92 protons, 146 neutrons), 0.7 per
cent of U-235 (92 protons, 143 neutrons), and a trace of U-234 (U-II).
Neutron Bombardment. The two important isotopes of uranium
show an astonishing difference in their products when bombarded by
neutrons. U-238 is converted into two new synthetic elements, not
known in nature, elements 93 and 94, named neptunium and plutonium,
respectively.
U-235, on the other hand, when bombarded with neutrons, undergoes
fission. In this process it splits into two parts, radioactive isotopes of
elements such as barium and krypton, and emits additional neutrons.
The products of fission weigh less than the original U-235 that underwent
the change, and the destruction of matter is accompanied by a release of a
tremendous quantity of energy. This change is the basis of the atomic
explosion of U-235.
A Chain Reaction. If the neutrons emitted by U-235 during fission
can be directed toward additional U-235 atoms and they in turn undergo
fission and emit more neutrons, and so on, a chain reaction will be
established. In a U-235 atomic bomb practically all the atoms undergo
fission simultaneously. The amount of energy from this action in a small
bomb of less than 200 Ib. in weight is equivalent to that released by 20,000
tons of TNT in exploding.
RADIOACTIVITY
649
Production of Plutonium. Plutonium is a synthetic element that
undergoes fission and hence is capable of producing an atomic explosion.
Neutrons acting on U-238 may produce this synthetic element.
Jn + 'JSU -> ('If U)
or, more simply,
n + U-238 -» (U-239)
+ _J
'RPu + J!«
Np-239 + <r -* Pu-239 + e~
The device for accomplishing this transformation is called a pile,
(See Fig. 37-8.) Slugs of uranium are sealed in aluminum cans and placed
Rods of Natural Uranium
Sealed in Aluminum Cans
are Inserted m Piles of
Carbon or other Material
that Slows Fast Neutrons
Heat Output
£ Radioactive Rays
Neutron Bullet
from U235 Joins
I U238 Nucleus
to Make
Shortlived
I U239
E)— -
ranium
Plut
Mixed with! 'ntermed«atel ^
onium 1 Step Omitted/"'
Which Loses 2
Nuclear Electrons
(see text) Convert-
ing 2 Neutrons
into Protons
Forming
Q>1 \
Dissolved in Acid and
Separated Chemically
Ak
Metal or Salt of Plutonium <
Metal or Salt of Uranium
p
)145/
Pu239
PLUTONIUM
FIG. 37-8. — Man-made plutonium — U-235 substitute.
within a block of highly purified graphite. Stray neutrons (from cosmic
rays) start the reaction. Some neutrons are absorbed by the surroundings;
others hit U-235 nuclei and keep the chain reaction going, evolving energy
and using up U-235; and the remainder hit U-238 nuclei, producing
neptunium and plutonium.
The slugs are removed (by remote control) from the pile and dis-
solved. The plutonium is separated chemically from the unchanged
uranium and from the fission products. While the production of plutonium
is very expensive, it is a cheaper way of producing an atomic bomb than
separating U-235 from U-238. Both these processes were developed for
war purposes by the Manhattan Project between the years 1942 and
1945 at a cost of approximately 2 billion dollars.
Synthesis of Elements 95 and 96, Bombardment of U-238 and
Pu-239 with very high energy helium ions in a cyclotron results in the
formation of radioactive isotopes of two new elements of atomic numbers
95 americium and 96 curium. Even though these are produced in very
small amounts only, their chemical properties have been studied, and it
has been shown that they belong in the third group of the periodic table.
650 CHEMISTRY FOR OUR TIMES
The Atomic Era. Uranium piles will have peacetime uses. They are
the cheapest source of neutrons, and they can be used to convert many
of the ordinary elements into radioactive isotopes that are useful in all
fields of science, particularly in medicine. Investigations concerning these
and other developments are under way.
Not the least important among the by-products of atomic bombs
is the fact that they have made people think about the futility of war
and about the place that chemical laboratories and scientists in general
occupy in a normal, healthy society.
Courtesy of General Electric Company.
FIG. 37-9. — Dr. Irving Langmuir, Associate Director, Research Laboratory, ( Jcn-
eral Electric Company, Schenectady, New York, the inventor of the gas-filled electric
lamp and pioneer in many branches of electrical engineering. Millions of persons
throughout the civilized world depend on artificial light, and almost all of it comes
from lamps made on the Langmuir principle. He has also made important contri-
butions to the study of atomic structure.
SUMMARY
Radioactivity is the spontaneous emission of radiations from certain chemical
elements found in a number of minerals. These radiations resemble X rays in
that they have great penetrating power and travel at enormous speeds. Radia-
tions were discovered by Becquerel from uranium. The Curies, investigating
radioactivity, discovered the radioactive element radium in pitchblende and
isolated radium bromide by the process of fractional crystallization. Fractional
crystallization is the process by which a solvent is partly evaporated and the
less soluble substance crystallized and removed by filtration, leaving the
soluble compound in solution.
RADIOACTIVITY 651
Radioactive elements are continually emitting alpha or beta rays and fre-
quently gamma rays. Alpha rays are positively charged helium. nuclei, He++;
they travel at approximately 30 million miles per hour, or about one-fifteenth
the speed of light, and have the least penetrating power of the three types. Beta
rays are negatively charged electrons, e~; they travel in a crooked path at ap-
proximately nine-tenths the speed of light and have greater penetrating power
than the alpha rays. Gamma rays are energy radiations; they are very short,
highly penetrating light rays similar to X rays. They travel in a straight line at
the speed of light. Radium forms compounds similar to those of barium. It is
produced spontaneously from uranium and disintegrates successively through
nine other elements in turn until finally lead is formed. The disintegration pro-
ceeds at a constant rate; half of any sample transmutes in 1690 years. Transmuta-
tion is the conversion of one element into another.
The nucleus of uranium disintegrates to form other elements, radium being
among this series. Subatomic energy in tremendous quantities is continually
liberated when unstable nuclei, such as those of uranium and radium, disinte-
grate. Uranium (U-235) has been split by neutron bombardment; atoms of light-
weight elements are produced. The amount of energy liberated in nuclear fission
is much greater than in any other known process, equal weights being considered.
It is believed that new elements are being formed on the sun from protons
and electrons, releasing energy at the same time.
The transmutation of atoms involves the changing of their nuclei. The first
artificial transmutation was accomplished by Rutherford, who bombarded
nitrogen gas atoms with alpha particles, producing protons and atoms of oxygen.
Other transmutations have been accomplished with the aid of cyclotrons and
similar devices. Often, the isotopes produced artificially are themselves radio-
active; radioactive isotopes of all the elements have now been synthesized.
Atomic energy has been used for military purposes. Using the action of
neutrons on either U-235 or plutonium, a chain reaction can be started that
consumes matter and releases enormous quantities of energy. This discovery
has profoundly influenced human thinking.
QUESTIONS
1. List the properties of the radiations from uranium ores.
2. Review the reasoning of Mme Curie that led to her discovery of radium.
3. Why was the Curies' task in isolating radium bromide not a simple one?
4. Describe each of the three radiations from radioactive substances.
5. How do modern transmutations (a) differ from and (6) resemble those
sought by the alchemists?
6. Define chemical element.
1. State two facts about the nucleus of the uranium atom.
8. A thermometer placed in a sample of radium registers a few degrees higher
than the temperature of the surroundings. From what source does the energy
come?
652 CHEMISTRY FOR OUR TIMES
9. What is the meaning of 'JO; }H; l\C; JfCl; ffNa?
10. List two uses for compounds made radioactive by a cyclotron.
MORE CHALLENGING QUESTIONS
Reference Questions
11. What is a spinthariscope? Tell how it operates.
12. Describe Millikan's oil-drop experiment.
13. What is the composition of the luminous paint used on watch dials?
Account for its giving light in darkness.
14. What is the missing product of transmutation in the nuclear reaction. (Do
not write in this book.)
106Be + jHe -4 Jn + - • •
15. Write a book report on Madame Curie, Eve Curie (translated by Vincent
Sheean), Doubleday, Doran & Company, Inc., Garden City, New York, 1938; The
Men Who Make the Future, Chap. X, Bruce Bliven, Dueii, Sloan & Pearce, Inc.,
New York, 1942; The Advance of Science (edited by Watson Davis), Doubleday,
Doran & Company, Inc., Garden City, New York; Atomic Energy for Military
Purposes, H. D. Smyth, Princeton University Press, Princeton, New Jersey, 1945.
16. Tell how a uraniun pile operates and what it produces. How might an
uranium pile be adapted to serve as a power plant?
UNIT NINE CHAPTER XXXVIH
CHEMISTRY AND RADIANT ENERGY
(LIGHT)
The conditions under which mankind exists are so delicately balanced
that, if only slight changes should occur, life as we know it would cease.
Should the properties of substances be slightly altered — for example, if
ice became denser than water — the effects over a long period of time
would make life utterly impossible. If the sunlight contained just a little
more or less ultraviolet light, our doom would be sealed. In this chapter
we shall see how some chemical actions of light affect our very existence.
Action of Sunlight on the Upper Atmosphere. The tempera-
ture of the sun is now thought to be maintained by the conversion of
hydrogen into helium, a process of transmutation. As a result, a great
amount of energy is released, and the temperature of the surface of the
sun is at least 6000°C. A tremendous amount of energy is radiated, as light
and heat, and our comfortable climate is maintained by the small frac-
tion that reaches the earth continuously. The light that reaches the outer
atmosphere is comprised of nearly all wave lengths from short ultra-
violet rays to long infrared. If light of all of these wave lengths penetrated
very far into the atmosphere, life at the earth's surface would be de-
stroyed. Fortunately, most of the ultraviolet light is absorbed by oxygen,
which is thus converted into ozone.
Ultraviolet light + 3O2 -> 2O3
This produces a blanket of ozone in the upper atmosphere and reduces
the amount of short ultraviolet light. Only the less deadly rays reach the
earth's surface, and these can cause a severe sunburn and even death
if care is not exercised. The skin reacts to ultraviolet light, generating
pigments to absorb it, and a coat of tan results. One beneficial effect is
the production of vitamin D in the body.
New Terms
photochemistry ultraviolet print
primuline photographic negative fixing
radiant energy
653
654 CHEMISTRY FOR OUR TIMES
We see easily how intimately our health depends on the chemical
action of light. If light of shorter wave lengths penetrated the atmosphere,
we should perish; if some ultraviolet light did not get through, again life
would be impossible. The presence of vitamin D in fish oils goes back to
its origin in the foods of fish, where it is produced also by the action of
-sunlight.
Photosynthesis. The most important chemical action of light is the
conversion of carbon dioxide and water into cellulose and similar products,
together with gaseous oxygen. For this process chlorophyll must be
present. No one has yet been able to carry out this process artificially,
but the action is being studied in laboratories all over the world.
The total reaction is known to be
chlorophyll
Red light + 6CO2 + 5H2O ^ (C6H10O6)x + 6O2
The accumulation of stored sun's energy on the earth has resulted
in enormous beds of coal (see page 546), vast deposits of petroleum (see
page 533), and tremendously large volumes of natural gas (see page 529).
How the Firefly Lights Its Lantern. Most chemical reactions occur
with the evolution of heat; some, called combustions, occur with the
evolution of both light and heat; a few are known in which little heat
and much light are emitted. The firefly and many other light-emitting
organisms have developed chemical reactions of this sort. Boyle showed
in 1667 that air was necessary for the glowing of luminous wood. One
of the most spectacular experiments is the oxidation of luminol by means
of hydrogen peroxide and potassium ferricyanide. The light evolved is
so bright that it is possible to take photographs with it.
In the body of the firefly a similar oxidation of luciferin occurs in
the presence of an enzyme catalyst, luciferase.
2LH2 + O2 *=± 2L + 2H,O + light
luciferin oxyluciferin
In this equation L represents a compound, oxyluciferin, not an element.
Use of Light in Studying Chemical Reactions. If a mixture of
chlorine and hydrogen is exposed to light, it explodes violently. It has
been shown conclusively that the explosion is the result of a chain reac-
tion, the product of one step of the reaction being the reactant for the
next. The effect of light is to decompose the chlorine.
Light + CI2 -* 2CI* (Cl atoms with excess energy)
The next step is the combination of the single chlorine atom with a
hydrogen molecule to produce a molecule of hydrogen chloride and a
free hydrogen atom containing excess energy.
Cl* + H2 -> HCI + H* (H atom with excess energy)
CHEMISTRY AND RADIANT ENERGY (LIGHT) 655
The hydrogen atom, in turn, can react with chlorine molecules.
H* + CI2 -» HCI +CI*
Now we have an atom of chlorine to begin the chain all over again.
The reaction goes with increasing rapidity, and an explosion results. By
studies of this type, much has been learned about explosive mixtures —
air and gasoline vapor, and the like. This is the branch of science called
photochemistry.
QUESTIONS
1. What is the source of the earth 's energy?
2. What might happen to us if the short ultraviolet rays from the sun should
reach the surface of the earth?
3. What photochemical reaction of oxygen makes life possible?
4. What is the origin of vitamin D in cod-liver oil?
5. How can workers on a night shift make up for their lack of vitamin D?
6. Does ordinary window glass transmit all wave lengths of light?
7. Do plants grow better in red or in ultraviolet light?
8. By what process does the chemist hope someday to trap part of the wasted
energy of the sun?
9. What is the probable source of most of the oxygen in the atmosphere
of the earth?
10. How does the firefly produce light?
11. Compile a list of plant and animal organisms that emit light. (Look in an
encyclopedia under luminescence.)
12. Is "cold light " ever emitted in chemical reactions?
13. Compile a list of chemical reactions that emit light. (Look in an encyclo-
pedia under chemi-luminescence.)
14. What has the photochemist decided about the way an explosion of a
mixture of hydrogen and chlorine in sunlight proceeds?
Photography. The candid-camera enthusiast can take pictures of the
acts in the circus, of dimly lighted, rapidly moving objects; by studying
a photographic plate the astronomer " disco vers" new stars, the light
from which has been traveling toward the earth for millions of years;
the physicist detects the presence of traces of an impurity in steel by
photographing its spectrum and reports his results back to the foundry
within a few minutes after molten metal was poured into a mold; an
X-ray motion picture shows a skeleton foot kicking a football; a camera
20 miles above New York takes a picture of Philadelphia, using infrared
656
CHEMISTRY FOR OUR TIMES
light, and incidentally revealing the curvature of the earth on the hori-
zon; motion pictures have extensive uses. Photography is one of the most
important tools of the laboratory worker and the source of continual
pleasure to hundreds of milllions of people through all the reaches of the
earth.
The basic chemical reaction of photography is quite simple. Let us precipitate
silver chloride by adding hydrochloric acid to silver nitrate and allow the precipi-
tate to settle. In the dark the silver chloride retains its pure white color, but in the
light of the room it begins to turn purple. If a piece of magnesium is burned near
Court f an , , /'... .'i.ntrican InxtitlUe
Fio. 38-1. — This amateur photographer is at work in his darkroom printing pictures.
The box has gelatin-coated, transparent, red glass.
it, the highly active blue-white light produced causes the silver chloride to darken
instantly. The silver chloride decomposes into its elements. This decomposition
was discovered by Scheele in 1777.
Light + 2AgCI -» 2Ag -f CI2 T
The early photographs were produced in just this way. The victim
was clamped rigidly in a chair on the roof of a building and the camera
aimed at him for a half hour or longer, while he remained motionless.
In 1837 Louis Jacques Maud6 Daguerre (1789-1851) discovered that
even with a short exposure, during which only a little of the silver chloride
CHEMISTRY AND RADIANT ENERGY (LIGHT) 657
decomposes, a permanent effect, or 4< latent image, " is produced which
can be intensified by various means. Daguerre used mercury to bring
the picture to visibility, in what is called a daguerreetype. William Henry
Fox Talbot (1800-1877) in 1839 found it was possible to " develop " the
latent image by chemical reagents, by completing the reduction of the
silver chloride, which has been exposed to light, to metallic silver.
One difficulty with early photographs was that they were not perma-
nent. The remaining silver halide (chloride, bromide, or iodide) continued
to decompose on further exposure to light. This problem was soon solved
by removing the silver halide left undecomposed. The reagent universally
used is sodium thiosulfate (Na2S2O3-H20), erroneously called "hypo."
This dissolves the unreacted silver halides by converting them into
soluble, complex compounds. (See Fig. 38-1.)
Courtesy of Journal of Chemical Education
FIG. 38-2. — Types of photographic emulsions showing different grain sizes. Left : fine
grain, low speed; center: coarse grain, high speed; right: silver bromide grains.
The steps in producing a picture are as follows :
1. Preparation of the film (done by the manufacturer)
2. Exposure in the camera ("taking the picture")
Operations that must be carried on in the dark or dim nonactive light*
3. Development by an alkaline mixture of reducing agents (always derivatives of
benzene, an aromatic hydrocarbon) (see Fig. 38-2)
4. Washing to remove excess developer
5. Removal of excess silver halides by sodium thiosulfate ("fixing")
Operations that should be carried out in a lighted room :
1. Washing thoroughly to remove the last traces of thiosulfate
2. Drying carefully to prevent distortion
This produces a "negative " in which the scene or object photographed
is in reverse; the light parts are opaque, and the dark parts are trans-
parent. (See Fig. 38-3.)
The "positive" is produced by "printing" on film or paper in exactly
the same way used in making the negative. A camera (for enlarging)
may be used, or a contact print may be made by clamping the negative
to the sensitized surface of the printing paper and exposing it to light
658 CHEMISTRY FOR OUR TIMES
through the negative. The paper is then developed, washed, fixed, washed,
and dried.
Recently, tremendous advances have been made in extending the light
range that can be photographed and in reducing the time required to pro-
duce a latent image that can be developed. But the essential chemistry is
FIG. 38-3. — This is the negative of Fig. 30-17, page 549.
still the simple fact discovered over 150 years ago by Scheele, that silver
halides are decomposed by exposure to light.
Modern Photography. Modern photography is a comparatively new
industry. From America's research laboratories has come much of its advance.
When George Eastman started laboratory experiments that made possible
the present ramifications of photography, an industry was born. Eastman
made his first practical nitrocellulose film in 1889. Since that time rapid
strides have been made in the development of delicate and complicated film
emulsions. Cameras and camera equipment likewise have been designed to gain
greater efficiency. The advance on the two fronts has widened the field of
photography in many directions.
The development of motion pictures, safety film, high-speed film, and
color film — these are but four of the many factors that have been responsible
for the gigantic strides of this nearly 2-billion-dollar industry.
No longer is photography considered as a development for the amateur
market. Even with 24 million amateurs using 26 million cameras and taking
approximately 600 million snapshots yearly, the amateur market represents
only about one-tenth of the bill for photography and its allied fields.
The professional motion-picture industry alone represents one-half of the
volume — a cold billion. Lithography, photo-engraving, home " movies," news-
papers (especially tabloids), magazines (especially those reporting the news in
CHEMISTRY AND RADIANT ENERGY (LIGHT) 659
pictures), medicinal and industrial X rays, studio, industrial, and office
photography make up the balance.
The growth of the photographic industry has been spectacular since 1935.
Between 1935 and 1937 the sales of cameras tripled. Film sales grew by leaps
and bounds. The manufacture and improvement of photographic emulsions or
films became a challenge to the chemical industry, for the making of films is a
chemical process from beginning to end. The purity of the chemicals and the
quality of dyestuffs used in the manufacturing of film emulsions have a direct
relationship to quality and speed. Moreover, any foreign matter in such a chem-
ical as potassium bromide, ammonium bromide, potassium iodide, or silver
nitrate will immediately be magnified when the film is projected. Manufacturers
of gelatin faced similar problems of exacting purity.
The chemical industry has played no little part in giving the pleasure and
thrill of making fine pictures. It has contributed widely and has kept pace with
the needs of better photography. The chemical industry is still looking ahead —
for photography is in its infancy. New discoveries and applications in all
phases of film speed and photography are constantly broadening the scope of
the industry, and research will have its rich reward.1
Photography without Silver. In the preparation of certain dyes
(diazo compounds) there is an intermediate stage in which the material
is easily affected both by light and by heat. At this stage the dye inter-
mediate must be kept cool and in a subdued light. Such dyes are often
called "ice dyes/' for ice is used to keep them cool. Advantage may be
taken of this light sensitivity to produce photographs without the use
of .silver. As early as 1887, the dyes tuff primuline was used. The cloth
is dyed with primuline and, while ice-cold, is immersed in an acidified
solution of sodium nitrite (NaN02). This produces the light-sensitive
diazonium intermediate. If the cloth is now surmounted by a stencil
and exposed to bright light, the diazonium compound is decomposed
where the light strikes it, but not the unexposed portions. The print is
"developed" by immersing the cloth in an alkaline solution of beta-
naphthol or some similar aromatic alcohol, whereupon the unexposed
parts turn to a brilliant color (red) and the exposed parts remain yellow.
Recently the process has been improved greatly and made com-
mercially feasible. A new film, designed particularly for sound tracks,
is made by incorporating a mixture of diazo compounds into a strip of
Cellophane (see page 568). The product is only faint yellow in color.
Wherever light strikes, the diazo compounds are bleached. Developing
and fixing are done by passing ammonia gas (NHs) over the film in
subdued daylight. The ammonia causes the " coupling" to occur to
produce a dye. The result is a positive print. For sound-track recordings,
1 WALDRICK, S. B. (editor), editorial comment in Chemist- Analyst of J. T. Baker
Chemical Company, vol. 29, No. 4, p. 75, November, 1940. Used by permission.
660 CHEMISTRY FOR OUR TIMES
the contrasts are very accurate and the film can be exposed, developed,
and finished in a continuous operation at 80 ft per min.1
Because of the sharpness, the film can carry three times as much
sound track per inch at one-tenth the cost of the usual film, in which
silver salts are used.
Blueprints. Commercial processes of duplicating drawings may use
silver salts — photostats — but, more commonly, " blueprints" are made.
For these, paper is impregnated with a mixture of iron salts in the ferric
condition. The action of light is to change part of the iron to the ferrous
condition, which results in the formation of insoluble Turnbull's blue.
In the unexposed portions the iron salts remain in the ferric condition
and soluble and are removed by washing with water. In producing blue-
prints, a latent image is not developed, but the light must remain turned
on until the reaction is complete. Hence brilliant arclights are used to
speed up the production. The " fixing" operation is merely one of washing
in clean water. The print is then dried.
The Mechanism of the Human Eye. One of the effects of light
with which we are greatly concerned is the chemical action that occurs
in the retina of the eye. A substance called " visual purple," present in
the retina cells, is altered by the light reaching it. An impulse is sent
along a nerve to the brain by this action. To regenerate the visual purple,
vitamin A is required. Lack of this vitamin A slows up the recovery of
the sensitivity of the eye, and night blindness results.
SUMMARY
Transmutation of elements in the sun produces an enormous amount of energy.
Light from the sun covers a wide range of wave lengths, from the far ultraviolet
to the far infrared. Harmful ultraviolet light is absorbed in the upper atmosphere.
The remaining ultraviolet light is essential for life processes; that is, it produces
vitamin D.
Photosynthesis is the conversion of carbon dioxide and water into plant
cellulose and oxygen. The reaction occurs in sunlight in the presence of chloro-
phyll. In an early era of the earth's history, the atmosphere contained little
oxygen; the 21 per cent now found in the air is the result of photosynthesis.
Light from a firefly is the result of oxidation of luciferin in the presence of the
enzyme catalyst, luciferase. Photochemistry deals with the chemical reactions
caused by light action.
Photography is an art based on photochemical reactions, especially the de-
composition of silver halides. A latent image is produced, which can be developed
by several reducing agents, in the presence of alkali. Residual silver salts are
removed by sodium thiosulfate (hypo) and thorough washing in water. In the
above operations a negative is produced; a positive print is made in a nearly
identical manner (chemically speaking).
1 Time Magazine, Aug. 24, 1942, p. 44.
CHEMISTRY AND RADIANT ENERGY (LIGHT) 661
In making blueprints, paper is treated with two ferric salts. One is reduced
to a ferrous salt by the action of light. In the presence of water Turnbull's blue
precipitates in the paper. Color photography without silver may be accomplished
by means of photochemical reactions and dye formation.
In the eye, light causes a chemical reaction in the retina cells, and a nerve
impulse is sent to the brain.
QUESTIONS
15. Write a series of three equations to show what happens when a photo-
graphic film is exposed and processed.
16. Consult a book on photography to find out about the process of "toning"
a photographic print. Write an equation illustrating the process.
17. How does eating a carrot aid in preventing night blindness? What are
the symptoms of night blindness?
18. Is sunlight necessary for the development of chlorophyll in a plant?
(Allow a potato to sprout in the dark.)
19. Do you think that photography without silver will supplant the methods
commonly used today? Why?
20. How does the Kodachrome film produce pictures? (Look up Kodachrome
film in a book on color photography.)
21. How could one recover silver from used "fixing bath"?
22. Do all plants need chlorophyll? (What about a mushroom?)
23. What causes the color of blue overalls to fade?
24. Give an example of a photochemical reaction not cited in this chapter.
26. The glass in the windows of houses on Beacon Hill, Boston, Massachusetts
is famous for its purple color. Explain its origin.
26. What are some of the newer methods of copying drawings, letters, and
manuscripts? (Look up this topic in reference books.)
27. Explain the change from black to brown that may be noticed on photo-
graphic prints stored near rubber.
UNIT NINE CHAPTER XXXIX
THE NOBLE METALS AND SOME
LESS FAMILIAR ELEMENTS
The noble metals were believed by the ancients to be more pure and
precious than the ordinary metals that were readily corroded. It was
the purpose of many alchemists to transmute "base" or more " cor-
ruptible" metals into gold.
The elements that are usually classified as noble are silver, mercury,
gold, and platinum; but the list may also include the much less familiar
elements ruthenium, rhodium, palladium, osmium, and iridium. These
elements are all low in the replacement series (see page 89) and do not
react with atmospheric oxygen — hence their seeming permanence and
value compared with iron and copper. Their high price reflects in part
their scarcity and lack of major industrial applications. Many of them
have use as catalysts, but their compounds are not discussed extensively
in elementary books.
Mercury
Mercury has been known since very early times. It is also called
quicksilver. It was named hydr argyrum ("water of silver") by the
Romans. Some is found free in nature, but it is obtained mostly from a
bright-red rock, cinnabar (HgS). The total amount mined is not large —
8000 tons in 1937 — mostly from Italy, Spain, and the United States.
For a number of years Spain and Italy had control of the market, but
now the United States has nearly enough for 'its own uses.
Metallurgy. Where mercury occurs in the free state, it is removed
from the rock by distillation. It boils at 357°C. To obtain it from cinnabar,
the ore is roasted, since mercury oxide is unstable (see page 41), and
mercury distilled out.
HgS + O2 -> Hg + SO2
Properties and Uses. Mercury is the only common metal that is a
liquid at room temperature. It is 13.6 times as dense as water. Above the
New Terms
quicksilver smelting Parkes process
amalgams placer mining
663
664
CHEMISTRY FOR OUR TIMES
boiling point, it exists as a colorless, nonmetallic, poisonous vapor with
only one atom in the molecule.
Mercury-vapor turbine engines have been developed, but from some
standpoints they are not as satisfactory as steam turbines. Their efficiency
is high, however. (See Figs. 39-1, 39-2.) Mercury-vapor pumps are used
Courtesy of General Electric Company
FIG. 39-1. — This is a general view of a central power plant that uses mercury vapor.
in laboratories to produce a high vacuum. Liquid mercury is used ex-
tensively in thermometers and barometers. A relatively new use for
mercury vapor is in fluorescent lights. The arc is struck by the argon
present, but most of the ultraviolet light emitted comes from the glowing
mercury vapor. This, in turn, is converted to visible light by the " phos-
phor powders " on the walls of the glass.
Amalgams. Amalgams are alloys that contain mercury; they may be
solid or liquid. If a small drop of mercury is added to silver nitrate solu-
tion, needles of silver amalgam slowly form. The mercury displaces the
silver and forms a solid amalgam in the shape of fantastic needles of
brilliant luster. For filling back teeth, dentists mix complicated mixtures
of metals with a carefully determined amount of mercury. When the
amalgam filling solidifies, it expands slightly and fills the cavity com-
THE NOBLE METALS
665
pletely. Because of the dark color of amalgams, other filling materials
are used to repair cavities in the front teeth.
Chemical Properties, Chemically, mercury is not an active metal,
but when warmed1 to 300°C it reacts slowly with oxygen in the air to
STEAM
SUPERHEATER
MERCURY VAPOR
-WTER FEED PUMP
Courtesy of General Electric Company
FIG. 39-2, — The diagrammatic plan of a mercury-vapor-steam-electric gener-
ating system shows two turbines: one run by mercury vapor, the other by steam
produced by condensing mercury.
produce the red oxide (HgO). When the temperature is raised still higher,
well above 300°C, this compound decomposes into the elements. Mercury
1 Mercury vapor is very poisonous. This experiment must be carried out in a well-
ventilated hood.
666 CHEMISTRY FOR OUR TIMES
reacts with sulfur when two elements are ground together in a mortar.
Hg + S -4 HgS
Metallic mercury reacts with warm dilute nitric acid and hot concentrated
sulfuric acid.
Mercury Compounds in Two States of Oxidation. Mercury forms
compounds in two states of oxidation.
. . . . Hg^NO,),
mercuric (II) mercurous (I)
Mercury (I) chloride, calomel, exhibits the peculiar formula, Hg2Cl2,
representing mercury as a radical (Hgjj)*4", which has valence 2. The two
atoms are held together by a covalent bond (Hg:Hg)++. Mercury (I)
chloride is formed as a white precipitate when mercury(II) chloride is
reduced with tin(II) chloride.
2HgCI2 4- SnCI2 -> Hg2CI2| + SnCU
Calomel is used in diseases of the secretory organs and is nowhere near
as poisonous as mercury(II) chloride, which is known as corrosive sub-
limate, a powerful antiseptic.
Mercury fulminate [Hg(ONC)2] is the most important detonator for
high explosives. It is made by treating mercury with strong nitric acid
and alcohol.
Silver
Silver occurs as the free element, but the sulfide ore, argentite (Ag2S),
found with copper and lead sulfides, is the most important source. Much
of the silver produced is recovered from very low grade ores, often mined
for these other metals (see page 468) .
Metallurgy. Argentite ore is smelted by roasting and reduction with
coke, after being mixed with lead ore. The alloy produced is then treated
by Parkes process, which involves melting it and adding 1 per cent zinc.
The zinc dissolves the silver, gold, and copper, but not the lead, and
floats upon the lead. The solidified zinc crust is skimmed off. The silver
is then recovered by distillation of the zinc and purifying the residue
electrochemically. Silver is also obtained by a cyanide method similar to
that for gold.
Properties. Silver is most familiar in alloys, sterling silver (92.5 per
cent Ag, 7.5 per cent Cu) and coin silver (90 per cent Ag, 10 per cent Cu).
It has a warm, sligKtly yellowish, metallic luster and is most popular for
tableware. It is the best conductor of heat and electricity. It is deposited
on glass for mirrors because of its high luster. Silver does not combine
directly with oxygen but does form an oxide ( Ag20) at room temperature,
with ozone. The oxide decomposes on gentle warming, at 260*C. The
THE NOBLE METALS
667
metal dissolves readily in dilute nitric acid, forming silver nitrate ( AgN03) ,
a fairly stable compound. Upon being heated to 444°C silver nitrate yields
silver, oxides of nitrogen, and oxygen; and on exposure to blue light it
turns dark, owing to a similar decomposition. It must be stored in brown
bottles.
Compounds. Silver usually has a valence of 1. The halides, AgCl,
AgBr, Agl, are all very insoluble, but AgF is a very soluble salt. This is
Courtesy of The Gorham Company
FIG. 39-3. — This expert craftsman in silver is chasing a sterling centerpiece.
because AgF is ionic in structure but the other salts are increasingly
covalent. This change in structure is accompanied by a deepening of
the color. Silver chloride is white, the bromide is cream-colored, and the
iodide pale yellow. These compounds are unstable in light and are the
basis of the photographic industry (see page 655).
When ammonia solution is added to silver nitrate solution, white
silver hydroxide is precipitated. This soon turns dark as it is converted
to black silver oxide.
Ag+ + OH-
2AgOH
AgOH |
Ag2O -f H2O
If excess ammonia solution is added, the precipitate redissolves owing
to the formation of a soluble complex silver salt.
AgOH 4- 2NH3 -4 [Ag(NH3)2]+ + OH"
668 CHEMISTRY FOR OUR TIMES
This mixture is called "Tollen's reagent." It is used to test for alde-
hydes and ketones.
Silver Mirrors. Tollen's solution is readily reduced with formalde-
hyde to produce a beautiful mirror, but the article to be coated must be
chemically clean. Glucose is also frequently used as the reducing agent.
Care must be taken to discard the solution immediately after use, since
silver fulminate (AgONC) or silver azide (AgN8) may form and explode
violently. As soon as the solution has been used, it is treated with hydro-
chloric acid to precipitate the silver as silver chloride (AgCl).
For astronomical mirrors, aluminum is evaporated on the glass surface.
While a silver mirror is easier to produce, it does not reflect blue or
ultraviolet light and rapidly garnishes. The aluminum mirror is relatively
permanent and much whiter. The reaction by which silver tarnishes is
2Ag + S -» Ag2S
Tarnishing can be prevented by coating the metal with a colorless lacquer
or by wrapping the article in Cellophane. Boxes designed to store table
silver and to prevent tarnishing are lined with cloth that has been im-
pregnated with silver or lead salts, which react with the hydrogen sulfide
and thus keep it from the metal.
Gold
Gold is one of the rarer elements, but because it is not readily cor-
roded it is found free in nature and was therefore one of the first metals
used by prehistoric man. It has a beautiful yellow color, being the only
metal besides copper that is not gray in tone. It is readily worked and
was first used in jewelry and for ornamentation.
Metallurgy* About a quarter of the gold is recovered as by-products
of the smelting industries, by the same processes used to recover zinc,
lead, and copper. Placer mining accounts for another quarter; in this
process the gold metal sinks in a flow of water that carries away the sand
and other less dense gangue. Another quarter is recovered by the amal-
gamation process in which the gold is alloyed with mercury, on copper
plates or cleats. The mercury is removed by distillation. The last quarter
of the yearly production is based on the cyanide process. Metallic gold is
oxidized by the atmospheric oxygen in the presence of sodium cyanide
and dissolves as a complex compound [NaAu(CN)2].
4Au + Ot + SNaCN + 2H2O -» 4NaAu(CN)2 + 4NaOH
The gold is recovered electrochemically or by replacement by means of
zinc or aluminum. Very low grade ore can be worked over by this process.
Properties. Gold is the most malleable and ductile of metals. It is
beaten between "goldbeater's skins" to extremely thin sheets, known as
THE NOBLE METALS
669
Courtesy of American Museum of Natural History
FIG. 39-4. — "Gold is where you find it." This chunk was located in Nevada County,
California.
Courtesy of South Dakota Hij/hway Commission
FIG. 39-5. — This view shows the Homestake mine at Lead, South Dakota, where gold
is mined by the cyanide leaching process.
670 CHEMISTRY FOR OUR TIMES
"gold leaf." This is used in making signs on plate-glass windows. It is
usually alloyed with copper (yellow gold), nickel (white gold), or silver
(green gold) to harden it. Fourteen-carat gold contains l%4 parts of
gold and ^%± parts of copper. t
Chemically, gold forms compounds with two states of oxidation, I and
III, the latter being met with most frequently. If gold is dissolved in
Courtesy of General Electric Lamp Department
FIG. 39-6. — The inspection of a tungsten filament wire used in an electric light is
accomplished by magnifying and projecting the image on the screen before the
inspector.
aqua regia (3 parts concentrated HC1 and 1 part concentrated HNO8), the
yellow soluble compound formed is a complex chloroauric acid (HAuCl4)
in which gold(III) is present. All gold compounds are unstable.
Uses. Gold has few uses other than for coins and jewelry. If it were
less expensive, it would be used more widely for chemical apparatus and
to coat other metals to prevent corrosion, but gold-plated milk pails are
for the future. Gold-plated jewelry, available at very low prices, has a
very thin coat and, because of the softness of gold, very poor wearing
qualities.
THE NOBLE METALS 671^
Tungsten
Tungsten was discovered by Scheele in 1781. The symbol W comes
from its German name wolfram. The most common ores are scheelite,
composed of calcium tungstate (CaW04), and wolframite, iron and
manganese tungstate [(Fe,Mn)WO4]. These ores fluoresce in ultraviolet
light. Tungsten is a dark-gray, hard metal with the highest boiling point
of all the elements, 4727°C. It cannot be machined well and therefore
is formed as a powder into blocks and compressed to a bar. The bars can
Courtesy of General Electric Lamp Department
FIG. 39-7. — The steps in. the manufacture of an electric light bulb.
be heated in an electric arc, hammered, and drawn into fine wires for
lamp filaments. (See Figs. 39-6, 39-7.) High-speed tool steels contain
18 per cent tungsten, 4 per cent chromium, 1 per cent vanadium, and
iron and carbon. Tungsten carbide (WC) and tungsten titanium carbide
(WTiC2) are embedded in metallic cobalt and used for the cutting edge
of high-speed tools. These can be used at red heat without losing their
keen edges.
Platinum
Platinum occurs in nuggets containing the other metals of the plati-
num group — iridium, osmium, ruthenium, rhodium, and palladium.
Russia has been the best source, but now the largest amount of platinum
is obtained in the Canadian nickel ores, where it is an important im-
purity. Here it exists as sperrylite (PtAs2). Platinum is used for jewelry,
dental bridges, and laboratory apparatus. The chief industrial use is as
a catalyst in producing sulfuric acid by the contact process. Platinum
compounds, for the most part, are laboratory curiosities, but platinum
oxide (PtO) has possibilities as a catalyst. It is fairly stable, not being
decomposed until 550°C. When dissolved in aqua regia, platinum forms
672
CHEMISTRY FOR OUR TIMES
chloroplatinic acid (H2PtCl6). This is readily decomposed on asbestos fiber
to produce a finely divided metal that can serve to demonstrate the catalytic
properties of platinum.
H2PtCI6 -> Pt + 2HCI T 4- 2CI2 T
Courtesy of American Platinum \\'orka
FIG. 39-8. — This display of platinum and other precious metals emphasizes the useful-
ness of inactive metals for laboratory vessels.
SUMMARY
The noble metals are relatively inert elements. They do not react with atmos-
pheric oxygen and do not corrode readily. They are generally found free in nature,
though some are found in combination.
Mercury is found in ores free or in the compound cinnabar (HgS). It is a dense
liquid with a metallic luster. It is a good conductor of electricity. It is readily
vaporized. At 300°C mercury forms mercuric oxide in the air, but this decom-
poses at higher temperatures. Mercury reacts with warm dilute nitric acid.
Compounds of mercury in two states of oxidation are common. For example,
Hg(N(>3)2 (mercuric nitrate), Hg2(NOa)2 (mercurous nitrate). Mercury fulminate
Hg(ONC)2 is useful as a detonator for high explosives.
Much silver is recovered in the purification of copper and also of lead, since
the ores occur together. Silver has a beautiful, soft, yellowish- white luster, mak-
ing it valuable for tableware, jewelry, and mirrors. It does not oxidize readily but
dissolves in hot dilute nitric acid. It reacts with sulfur and sulfide compounds to
form the familiar black tarnish.
Silver salt% of the halogens (except AgF) are insoluble and used as tests for
halides. Halides are unstable in light and are used in photography. Silver com-
pounds form complex compounds with ammonia. They tarnish with sulfides to
form silver sulfide.
Silver mirrors are produced by chemical reduction of silver salts.
THE NOBLE METALS 673
Much gold is recovered from smelting industries. Free gold is mined by three
methods: (1) placer (hydraulic); (2) amalgamation; (3) cyanide. Gold has a
pleasant, yellow, metallic luster. It is a good conductor of electricity. Gold is also
extremely malleable; it can be made into very thin sheets, called gold leaf. Gold
is used primarily for jewelry and for coins.
Tungsten is important for tool steels, superhard carbides (WC and WTiC2).
It is used for electric light filaments in the form of fine wire produced by powder
metallurgy.
Platinum is found free, principally in Russia. In Canada it is recovered as a
by-product of nickel smelting. Platinum is a very inactive element. It dissolves
in aqua regia. Its chief industrial use is as a catalyst. It is also used in jewelry
and dental alloys and for laboratory apparatus.
QUESTIONS
1. In what part of the replacement series of metals are the noble metals?
2. What can be said about the stability of the oxides of the noble metals?
3. Which of the metallic elements do not possess a silvery color?
4. What states of oxidation (valence) are exhibited by compounds of mer-
cury, gold, silver, copper, platinum, tungsten, sodium, aluminum, iron, and zinc?
6. What properties of platinum or platinum alloys make this metal useful in
the form of ribbons or wires for heating units in electric-resistance furnaces?
Comment on the cost of building such a furnace.
6. In what reactions does platinum serve as a catalyst?
7. What function does mercury vapor serve in fluorescent lamps?
8. What happens to mercury oxide when it is heated in a test tube?
9. What happens to silver oxide when it is heated in a test tube?
10. Write equations for the chemical changes suggested by questions 8 and 9.
11. How can mercury be removed from a gold ring that has become amalga-
mated?
12. Tell how a dentist prepares an amalgam for filling tooth cavities.
13. Which is the more toxic, calomel or corrosive sublimate? Write the formula
of each, and give its chemical name; state a use for each.
14. What is the chief use of mercury fulminate?
15. Mercury di-iodide exists in two forms, one yellow and the other red. What
term is applied to such forms?
16. Write the formula equation for the reaction of mercury with dilute nitric
acid.
17. Write ionic equations for the reaction of hydrogen sulfide on solutions of
(a) silver acetate; (6) mercuric dichloride; (c) mercurous nitrate.
674 CHEMISTRY FOR OUR TIMES
18. Write ionic equations for the reaction between (a) hydrochloric acid and
silver nitrate solution; (6) hydrochloric acid and mercurous nitrate solution.
19. Outline the procedure for obtaining silver from silver sulfide ore.
20. How may one make a mirror of metallic silver on glass?
21. For astronomical purposes, what advantages has an aluminum mirror over
a silver mirror?
22. Write a formula equation for the decomposition of silver nitrate when it is
heated.
23. How can one prevent silver from tarnishing? How is this done in jewelry
stores?
24. Describe three methods by which gold is obtained from low-grade ores.
25. Can gold be deposited electrochemically? Why does it drop as a sludge
below the copper anode when impure copper is refined electrochemically?
26. Explain what is meant by IQ-carat gold; 14-carat gold; 1-carat diamond;
solid silver; sterling silver; coin silver; 1 pennyweight of gold. (Refer to a dictionary.)
27. How is gold applied to the edges of inexpensive drinking glasses?
28. Which countries have the greatest supply of tungsten?
29. Explain how the invention of the tungsten carbide cutting tool gave Ger-
many temporary advantage in the machine-tool industry.
30. What novel means is used in prospecting for tungsten ores?
31. Make a labeled diagram of an apparatus for electroplating gold onto a
vanity case.
32. Review the contact process for making sulfuric acid. Find out the approxi-
mate cost of the catalyst for a typical plant.
33. Which of the following materials could be chosen for the production of
elementary fluorine (F2): copper; glass; gold; platinum; Monel metal; stainless
steel; aluminum?
34. Write an equation for the effect produced when a photographic plate con-
taining silver is dipped into a gold cyanide solution [Au(CN)3].
UNIT TEN CHAPTER XL
WHAT LIES AHEAD
Preparation for Further Training in Chemistry
If a pupil has decided to take additional chemistry courses when he
reaches college,^and particularly if he intends to enter a branch of the
chemical profession, he is fortunate if he makes this decision while still
in high school. He has then the opportunity to seek advice in regard to
the best courses to select as a preparation for college work.
High-school Training. In addition to the course in chemistry a high-
school pupil should elect as much mathematics as possible, take a thor-
ough course in physics, and start his work in modern languages while
still in the secondary school. If he cannot do this, it is not too late to
start them in college.
Professional chemists emphasize the tremendous importance of
training in English. The value of the ability to express oneself in clear,
concise language, both written and oral, cannot be overemphasized. The
results of chemical research must be conveyed to employers or to the
public, and those who have been well trained in the use of the English
language have an advantage over those of equal chemical ability who
lack this power of expression.
Many colleges include in their requirements for the bachelor's degree
in chemistry a reading knowledge in two foreign languages. For an
American, German is still the most important second modern language
and French Is usually rated next. Russian is gaining in prominence,
however; we may predict that in the future many chemists will wish to
possess at least a reading knowledge of this language.
Students who plan to enter the medical and similar professions will
be required to study chemistry intensively in the early part of their
college training, and the same preparation for college is advised. Medical
schools are glad to accept well-trained and able undergraduate chemists
in their first-year classes. These students usually substitute biology
courses for the more specialized advanced chemistry courses, but through
the first two or three years of college the training of doctors and of
chemists may be identical.
The high-school course in chemistry is the best starting point for
those who wish to receive such professional training, and those who have
675
676 CHEMISTRY FOR OUR TIMES
done well in it may be encouraged 'to continue their work in this science
in college. Many colleges give placement tests to entering freshmen and
assign those who show ability to more advanced sections, where there is
little repetition of the work covered in this book. By selecting the founda-
tion courses in secondary school and working diligently, a student may
even receive advanced standing in many colleges. This gives such a stu-
dent a great advantage in that he may complete his elementary train-
ing at an earlier date; in the time gained he may elect cultural courses
that otherwise would be denied him or take advanced work in the field
of his profession.
College Training. The training of a professional chemist in college
will include much of the following:
General
1. Language:
a. English — clear logical otylo in writing and speaking
b. German — a reading knowledge of scientific German
c. Other foreign languages — one of the following: French, Russian (Latin or
Greek)
2. Cultural subjects:
a. History, psychology, sociology, philosophy, economics, and fine arts
3. Mathematics — all that the student can absorb:
a. High-school mathematics, including plane geometry, trigonometry, and solid
geometry
b. College mathematics, including differential and integral calculus
c. Advanced courses in mathematics for those who plan to go to graduate schools
Special courses
1. Chemistry — general, analytical, organic, physical, and industrial; advanced
courses in special fields of chemistry
2. Physics — general physics, mechanics, electricity and magnetism, electronics,
and other specialized courses
3. Other sciences — at least one of the following: biology, bacteriology, geology,
mineralogy, crystallography, metallurgy
4. Special fields of training — law (contracts, patent law, government regulations),
finance, management, or engineering
5. Special skills — glassworking, machine-shop practice, drafting, photography
Graduate Training. After high school and college, many an ambi-
tious young chemist will wish to complete the training for the degree
of doctor of philosophy and enter the research work for which this
advanced degree is frequently required. Usually he is^tble to receive some
financial support during this period of training, and frequently he is
asked to assist in the teaching of the undergraduate students at the
institution in which he is enrolled.
WHAT LIES AHEAD 677
College Chemistry Courses
General Chemistry. In colleges where there is a sufficient number of
students to warrant it, the entering students are distributed, on the basis
of ability and previous training, between two courses — elementary chem-
istry and general chemistry (the specific designation of these courses
varies). Those who have had good high-school courses are usually placed
in the more advanced general chemistry course. The classwork is more
theoretical here, and it emphasizes numerical calculations more than the
descriptive elementary course. Frequently the time required for this
course is only one term, and those who do well in it proceed with qualita-
tive analysis during the second term.
Qualitative Analysis. Much of the knowledge of inorganic chemis-
try expected of the undergraduate chemist is taught in the course in
qualitative analysis. The emphasis here is on laboratory work and on the
application of chemical principles learned in the first year of study.
The analysis of solutions and solids, alloys and ores for about 26 of the
common metallic elements is mastered. Frequently, analysis for a number
of negative ions is also included. In recent years the laboratory work has
been conducted with small amounts of material, on what is known as the
semi -micro scale. The amount of each ion present in a mixture may be
estimated but is not determined accurately.
Quantitative Analysis. In a course with this designation, the labora-
tory skill of the young chemist as an analyst is improved by emphasizing
precise technique and accuracy. Various methods of carrying out the
determination of the exact quantity of a substance present (in a mixture
or solution) are studied. After a student has completed this course, he
begins to feel that he is a chemist; no one can consider himself a chemist
unless he has developed the skills and techniques of quantitative analysis.
Organic Chemistry. In college, the course in organic chemistry is
a systematic examination of the various classes of organic compounds
and their interrelations. The various types of reactions are studied, and
in the laboratory the preparation of many typical carbon compounds is
undertaken. In advanced courses the student also encounters qualitative
and quantitative analysis of organic compounds and mixtures.
Physical or Theoretical Chemistry. The laws of physics and chem-
istry and their application to problems in chemistry are topics that are
discussed in physical chemistry. The theoretical interpretation of the
behavior of chemical substances is closely examined. The laboratory work
emphasizes the methods by which various properties of substances are
pleasured and by which information concerning the mechanism of
chemical reactions is derived.
678 CHEMISTRY FOR OUR TIMES
Industrial Chemistry. The methods of carrying out chemical reac-
tions on a large scale are taken up in industrial chemistry. The work is
usually divided into what are called unit processes, by which the com-
mercial manufacture and processing of materials are undertaken. In this
course the chemist gets away from the test tube and funnel and uses a
barrel and a filter press. He needs more skill in pipe fitting and plumbing
From the News Service, Afaaaachuaetta Institute of Technology
FIG. 40-1. — These advanced college students are using their knowledge of chemistry
in research work in a biology laboratory at the Massachusetts Institute of Technology,
Cambridge, Massachusetts, which had one of the first departments of biology in this
country.
than in glassworking, and a floor mop is inadequate to clean up his
floods. This is his introduction to the workaday world of chemistry,
in which he applies all that he has learned in his long course of
training.
/
Chemical Engineering. The work of the chemical engineer is the
building of chemical plants and the supervision of thoir operation. Mis
training includes much more engineering than that of the industrial
chemist. His training is quite rigidly specified as he has to meet profes-
sional requirements.
WHAT LIES AHEAD 679
Employment in the Chemical Industry
Following the college courses in chemistry and allied subjects, a small
percentage of the students, particularly those who stand near the top of
the class, may wish to continue their training in a graduate school. Those
who complete their training with the bachelor's degree receive ready
employment in various capacities in industry — in research laboratories,
production departments, and sales departments. Many work in control
laboratories where routine and special check analyses are carried out to
ensure that the company's product will be up to the standards set.
Details of the jobs that chemists, both men and women, carry on in
public and private laboratories are described in the following books:
The Chemist at Work, Roy I. Grady and John W. Chittum, editors,
published by the Journal of Chemical Education, Easton, Pennsylvania,
1940; a collection of papers describing the type of work done by profes-
sional chemists, written by chemists (men and women) actually engaged
in specialized fields of chemistry. Your Career in Chemistry, Norman V.
Carlisle, E. P. Button & Company, Inc., New York, 1943; Mr. Carlisle
was formerly the vocational-guidance editor of Scholastic, the national
high-school weekly. So You Want to Be a Chemist? — Herbert Coith,
McGraw-Hill Book Company, Inc., New York, 1943; this little book
describes the activities of chemists and chemical engineers, is packed
with incidents from practical experience, and is written in an entertaining
manner.
Happiness
And Science dawns though late upon the earth,
Peace cheers the mind, health renovates the frame;
Disease and pleasure cease to mingle here,
Reason and passion cease to combat there,
Whilst mind unfettered o'er the earth extends
Its all-subduing energies, and wields
The sceptre of a vast dominion there.
— SHELLEY
REVIEW EQUATIONS
(Do not write in this book.)
1. Sodium carbonate + hydrochloric acid — >
2. Potassium carbonate + sulfuric acid — *
3. Sodium hydroxide solution + carbonic acid ->
4. Barium hydroxide solution + carbon dioxide — >
5. Burning carbon monoxide — >
6. Common salt + sulfuric acid — >
680 CHEMISTRY FOR OUR TIMES
7. Common salt + sulfuric acid + manganese dioxide — *
8. Common salt solution + silver nitrate solution — >
9. Calcium chloride solution + silver nitrate solution — >
10. Copper + chlorine — >
11. Arsenic + chlorine — »
12. Hydrogen burned in chlorine — »
13. Zinc + hydrochloric acid — >
14. Hydrochloric acid + sodium hydroxide solution — >
16. Hydrochloric acid + calcium hydroxide solution — >
16. Manganese dioxide + hydrochloric acid — »
17. Zinc chloride solution + silver nitrate solution — >
18. Zinc hydroxide + hydrochloric acid — »
19. Sodium + water — »
20. Hydrogen chloride + sodium — >
21. Aluminum hydroxide + nitric acid — »
22. Ammonium nitrate heated — *
23. Aluminum sulfide + water — *
24. Lead acetate solution + zinc — »
25. Copper + dilute nitric acid — *
REVIEW QUESTIONS
1. Copy the following words in a vertical column: Haber, Dewar, Ostwald,
Moseley, Solvay. Opposite each write the word or phrase from the following
group that is most closely related: air conditioning; periodic law; nitric acid;
liquid air; spectrum analysis; baking soda; fixation of nitrogen.
2. Use the words acid, basic, or neutral to predict how water solutions of the
following salts would react toward litmus: copper chloride; sodium sulfate; lead
acetate; potassium carbonate. Name the process that causes a salt solution to
act as either an acid or a base.
3. Write the common name and one use of N20; Na2COs'10H20; CaO;
Na8P04; NaHCOa.
4. Write three equations to show respectively, (a) the fixation of nitrogen;
(b) replacement of one halogen by another; (c) a reversible reaction.
6. Name three substances that are put into a blast furnace and three that
come out.
(Continued on next page.)
REVIEW QUESTIONS
Bars of cast iron, wrought iron, and steel are supported at both ends and struck
sharply in the middle with a sledge hammer. What happens to each?
6. Name a steel alloy, and give its special use.
In the equation 2FeCls + Fe — > SFeCU, point out (a) oxidation; (b) reduction.
Make a labeled diagram of a furnace for the production of aluminum.
7. Write equations for all chemical actions which occur in the following
group, and indicate those in which no action takes place by the letters N R:
(a) zinc and dilute hydrochloric acid; (6) copper and dilute hydrochloric acid;
(c) aluminum and concentrated nitric acid; (d) lead and copper sulfate solution;
(e) iron and silver nitrate solution.
8. What weight of magnesium can be made by the electrolysis of jonn
pounds of magnesium chloride that is 95 per cent pure? MgCl2 — > Mg + CU
9. Answer briefly:
Name two ways in which the casein in milk can be coagulated.
When a sample of an anhydrous substance takes up a definite amount of
water and becomes crystallized, the product is then classed as what sort of
substance?
What is the common name of a material produced by passing chlorine over
moist calcium hydroxide suspension?
Tell how the famous Carlsbad (limestone) Caverns were formed.
What is Carborundum?
10. What two gases are present in the composition of water gas? Give one
use for water gas.
Write a formula for (a) cane sugar; (b) corn sugar (glucose).
How would you identify each of the following : silk, wool ; cotton ?
Explain the cleansing action of soap. %*
11. Le Chatelier's principle may be stated thus : when an equilibrium mixture
is put under stress of any sort (addition of any one of the reacting substances or
products, changes in temperature or pressure, or alteration of other conditions),
the amounts of all the different substances present will always change in such a
way as to reduce the strain produced.
In an equilibrium mixture in general, what is the effect of (a) adding more of
a reacting substance; (6) removing a product; (c) permitting a gaseous product
to escape; (d) forming an un-ionized product from ions; (d) increasing the pres-
sure, assuming at least one of the reacting substances is a gas; (/) increasing the
temperature if an endothermic reaction; (g) increasing the temperature if an
exothermic reaction; (h) adding a catalyst upon (1) the composition of equilib-
rium mixture and (2) the time required to attain equilibrium?
12. Does an equilibrium mixture ever go entirely to completion in either
direction?
13. Predict which way each of these reactions will proceed and tell why the
reaction goes in that direction:
682 CHEMISTRY FOR OUR TIMES
(a) CaCO, 4- 2HCI ^t CaCI, + H2O + CO*
(6) 2NaCI 4- CO* 4- H2O ** Na2CO, + 2HCI
(c) Fe8O4 4- 4H2 *± 4H2O -f 3Fe
(d) BaSO4 4- 2HCI ?=t BaCla 4- H2SO4
(e) CaS04 -I- 2HF i=t CaF2 -f H2SO4
(/) FeS + 2HCI & H2S 4- FeCI2
(^) CuS -f 2HCI (dilute) ?H CuCI2 4- H2S
(h) NaCI 4- H2O *± HCI 4- NaOH
14. What is the percentage of nitrogen in ammonium carbonate?
15. State three physical properties of chlorine.
Give three uses for sodium hydroxide.
Sodium hydroxide should be kept in tightly sealed containers. Why?
16. What weight of lime can be made from 10 tons of limestone, assumed to
be pure calcium carbonate?
17. Distinguish between liquid chlorine and chlorine water.
Explain why chlorine bleaches colored cloth better when the cloth is moist
than when it is dry.
State three uses for chlorine.
18. Complete and balance formula equations for the following reactions: (a)
electrolysis of salt and water ; (6) action of sodium hydroxide on an acid ; (c) action
of phosphorus on copper; (d) decomposition of hypochlorous acid; (e) action of
chlorine on cadmium.
19. Write four informative sentences, using in each, respectively, the fol-
lowing words or expressions: (a) impurities in common salt; (b) passive condition;
(c) corrosion; (d) alkali.
20. Assuming that cottonseed oil is pure olein [CsH^CisHaaC^s], determine
* f5
the weight of soap made in a laboratory experiment from •{ ~ grams of cottonseed
oil.
21. A compound contains 92.31 per cent carbon and 7.69 per cent hydrogen.
One liter of its vapor at STP weighs 3.48 grams. Find its molecular formula.
22. What should the weight of 1 ton of blue vitriol become after it is com-
pletely dehydrated?
23. What mathematical ratio should be used to show the percentage of
phosphorus in calcium phosphate?
24. Compute the cost per day of lighting a house with acetylene if •{ . 4ft liters
(STP) of gas is used per day and calcium carbide costs \ „ cents per kilogram.
26. A wax candle is 85 per cent by weight carbon and the rest hydrogen.
{60
40 grams of the candle burns.
REVIEW QUESTIONS 683
26. How many pounds of iron could be obtained from 1 ton of ore consisting
of 70 per cent magnetite?
27. A certain specimen of water contains 1.2 grams of calcium bicarbonate per
gallon. What weight of calcium hydroxide should be added to soften 1000 gallons
of this water?
28. Classify as physical of chemical changes: (a) heated iron expands; (b) iron
dissolves in dilute sulfuric acid; (c) a ray of light changes silver chloride to
metallic silver and chlorine; (d) water is heated from 14.5 to 15.5°C; (e) heated
iodine forms a purple vapor; (/) iodine rubbed with mercury forms a red powder.
29. Why can you not light a lump of coal with a match?
30. In tabular form give (1) name, (2) formula, and (3) one use of (a) a fat;
(6) a soap; (c) an acid found in vinegar; (d) an alcohol; (e) a sugar.
31. When \ - ^ grams of wine was treated with iodine and lye solution, 78.8
grams of iodoform was precipitated. What percentage of alcohol was present in
the wine?
32. How many liters of air are necesvsary for the complete combustion of j -~~
milliliters of acetylene gas?
33. Which is the richer source of carbon dioxide, sodium bicarbonate 90 per
cent pure or dolomite 95 per cent pure?
34. In tabular form give (1) common name, (2) formula, and (3) one use of
(a) calcium oxide; (6) calcium hydroxide; (c) zinc oxide; (d) aluminum oxide;
(e) copper sulfate crystals.
35. Write equations for the following reactions, using formulas throughout:
(a) burning methane; (b) action of soap on water containing calcium chloride;
(c) heating copper nitrate; (d) the chief reduction in a blast furnace; (e) formation
of slag from silica and limestone.
36. A compound colors a Bunsen flame green. When sodium sulfate solution
is added, its solution forms a white precipitate, insoluble in hydrochloric acid.
Also, when fresh ferrous sulfate solution and concentrated suifuric acid are added
carefully, a brown ring forms above the acid. Give the name and formula of this
compound.
37. Answer briefly: (a) What is the most important source of iron? (b) What
is the most important source of aluminum? (c) By what method is aluminum
prepared commercially? (d) Name a zinc alloy, tell the metals present, and give
a use for the alloy, (e) What is oxidation in terms of valence change?
38. (a) What property of aluminum is exhibited in the Thermit reaction?
(6) In the following list write the name(s) and formula(s) of substances that do
not have the formula CaCOs: marble; gypsum; limestone; chalk; calcite. (c)
MgS04'7H2O is sold under what name? (d) Name a copper alloy, tell the metals
684 CHEMISTRY FOR OUR TIMES
present, and give a use for the alloy, (e) Name three substances that are used to
make glass. Name another substance that may be added to color glass, and state
the color produced.
39. (a) After metallic potassium acts with water, what is the effect on litmus
of the resulting solution? (b) Write the equation for the action in (a), (c) What
ions are dissociated when caustic soda is melted? (d) Select the correct conclusions :
The formula of the most common natural compound of phosphorus is P2O6;
H3PO4; Na3P04; Ca3(PO4)2; P4S3. (e) Give the name of a commercial abrasive
made in an electric-resistance furnace.
40. Tell what conditions produce a dust explosion.
41. Examination of the stomach of a poison victim showed the presence of
12 25 Srams °f arsenic- How much white arsenic (As2O3) had been swallowed by
the victim?
42. A compound analyzes as follows: magnesium 9.8 per cent; sulfur 13 per
cent; oxygen 71.5 per cent; hydrogen 5.7 per cent. Find the simplest formula of
this compound.
/ OA
43. How many liters of air are needed to burn completely \ «Q liters of arsine
(AsH3)?
44. Describe a method for the complete purification of water, using a labeled
sketch. Tell what impurities are removed.
45. Give the reason for the following: (a) filtered salt water tastes salty; (b)
chemists use distilled water for making solutions; (c) soap is not made in alu-
minum vessels; (d) nylon is not a suitable material for making lampshades; (e)
nitrates are scarce in wartime.
46. Name and state three important laws of chemistry.
47. Define and illustrate by an example : catalyst; oxidation; reduction; replace-
ment,; electrolysis.
48. Write equations for making each of the following compounds in four
different ways: (a) sodium chloride; (6) potassium nitrate; (c) zinc sulfate; (d)
magnesium chloride.
49. Show by equations the ions dissociated from each of the following com-
pounds: (a) sodium chloride; (6) zinc nitrate; (c) calcium hydroxide; (d) sulfuric
acid: (e) aluminum chloride.
60. Write formula equations for the following reactions, and below each write
the equation in ionic form: (a) zinc + hydrochloric acid — >; (b) iron + copper
sulfate solution —>; (c) ammonium hydroxide + phosphoric acid — >; (d) sodium
sulfate and barium chloride solutions — »; (e) sodium carbonate solution -f calcium
hydroxide solution -».
51. Explain why a piece of wood burns with a flame at first and later without
a flame.
GLOSSARY
abrasive. A hard substance used for grinding or polishing another substance. Sand
and emery are much-used abrasives.
absolute temperature scale. A scale of temperatures, sometimes called the Kelvin
scale. On the absolute scale the complete absence of heat is considered as 0°A, a
point that corresponds to — 273°C. The freezing point of pure water (0°C) is
273°A or 273°K
absorption. The act of (1) swallowing up one substance by another; (2) taking in
radiant energy and changing it to other forms. Sponges absorb water. Green
leaves absorb sunlight, using the energy to carry on chemical changes.
acid. A compound that will neutralize an alkali. Water solutions of acids dissociate
hydrogen ions. The most extensively used acid is sulfuric acid (H2SO4).
acid anhydride. An oxide that, when combined with water, forms an acid. Sulfur
trioxide (SO8) is the anhydride of sulfuric acid (H2SO4).
activity. The relative degree of ease or difficulty with which an element reacts in a
chemical change. Potassium has the greatest activity of all common metals.
adsorption. The clinging of a gas, liquid, or solid to the surface of a solid. Activated
charcoal is used in gas-mask canisters because of its adsorption of poisonous gases.
alchemy. An art, chiefly of the Middle Ages, in which those who practised it tried
mainly to make gold from base metals. Alchemists are incorrectly called the
predecessors of chemists.
alcohol. An organic compound containing the hydroxyl radical (OH). The most
common alcohol is ethanol (O2H5OH).
O
I!
aldehyde. An organic compound containing the — C — II group of atoms. Formalde-
hyde (HCHO), the most common aldehyde, is used to make plastics.
alkali. A very active base. Sodium hydroxide (NaOH) is a widely used alkali.
allotropic. Referring to the different forms of an element, due to differences in the
number and arrangement of atoms in a molecule. Sulfur has three common al-
lotropic forms.
alloy. A mixture made by cooling two or more metals that have been melted together.
Brass is a common alloy, containing zinc and copper.
alpha particle. The nucleus of a helium atom bearing a positive electric charge.
Some radioactive materials, such as radium, emit alpha particles.
alum. A complex compound formed by crystallizing together the sulfates of a va-
lence-1 (univalent) and a valence-3 (trivalent) metal. Common alum is hydrated
potassium aluminum sulfate (KA1SO4«12H2O).
amalgam. An alloy in which one of the metals is mercury. Dentists use amalgams
for filling cavities in teeth.
amorphous. Lacking definite shape. In chemistry, crystalline and amorphous are
opposite terms.
analysis. A process of decomposition. Also, the assay, or examination, of a substance.
Chemists carry out an analysis of a substance in order to find out its composition.
anesthetic. A substance used to deaden pain. General anesthetics produce uncon-
sciousness, while local anesthetics affect an area.
anhydrous. Without water. When gypsum (CaSO4-2H2O) is very strongly heated,
all the water combined in the crystalline material is removed; anhydrous calcium
sulfate (CaSO4) remains.
685
686 CHEMISTRY FOR OUR TIMES
anode. A positively charged electrical terminal or plate. Electrons are lacking at the
anode.
antiseptic. A substance used for killing bacteria or for slowing the rate of their growth.
The word antiseptic literally means " against poisoning." It refers to substances
that destroy micro-organisms.
aqua regia. A mixture containing three parts concentrated hydrochloric acid and
one part concentrated nitric acid by volume. Aqua regia will dissolve gold.
atmosphere. The gaseous layer surroundipg the earth's crust. The atmosphere at sea
level normally exerts a pressure that balances a column of mercury 760 mm high
in a closed tube.
atom. The smallest unit particle of an element. Atoms of the same element, due to
isotopes, may differ in respect to nuclei, but their outer electron arrangements
are the same.
atomic number. A number, assigned to an atom of an element, that designates the
number of positive charges, or protons, in excess of the neutrons in the nucleus.
The atomic number is a fundamental difference among atoms of different elements.
atomic weight. A number that compares the weight of a given atom with the weight
of an oxygen atom considered as 16. The atomic weight of magnesium is 24; thus
an atom of that metal weighs 1.5 times the weight of an oxygen atom.
barometer. An instrument for measuring pressure. Mercurial barometers are com-
monly used in laboratories.
base. Any compound that neutralizes an arid. Magnesium oxide and potassium hy-
droxide are bases; the latter is both a base and an alkali.
beta rays. Streams of electrons emitted by radioactive materials. Radium B (lead)
emits beta rays in the course of its decomposition to form radium C (bismuth).
binary. Referring to compounds that contain two elements. Sodium chloride is a
binary compound.
boiling point. The temperature at which the vapor pressure of a liquid just exceeds
the pressure of the atmosphere above it. The boiling point of water is 100°C at
760 mm pressure.
British thermal unit (Btu). The amount of heat needed to change 1 Ib of water
1°F. One Btu is equivalent to 252 cal.
burning (see combustion). The combining of elements accompanied by light and
heat. In ordinary burning, oxygen combines with a material. Chlorine and sul-
fur, however, may combine with the same elements as oxygen and have burning
take place.
calorie. The amount of heat needed to change the temperature of 1 g of water 1°C.
A large Calorie (capitalized) is 1000 times the (small) calorie.
calorimeter. An apparatus for measuring the quantity of heati In a calorimeter a
weighed amount of water is allowed to undergo an observed temperature change.
carbohydrate. A compound consisting of carbon, hydrogen, and oxygen, the latter
two elements usually in the proportion of 2 to 1. Common table sugar, sucrose
(Ci2H22On), is a carbohydrate.
catalyst. A substance that changes the speed of a chemical action but is not itself
permanently altered. Positive catalysts are sometimes called accelerators or
promoters; negative catalysts are called retarders or inhibitors.
cathode. An electric terminal with an excess of electrons, hence negatively charged.
In most electroplating the metal is plated out on the cathode.
ceramics. The art of producing useful articles from clay or similar materials. Ceramics
is an interesting hobby with many people. The ceramics industry is extensive.
GLOSSARY 687
chemical. A term loosely applied to a substance used in a chemical laboratory or to
a substance used to bring about a chemical change. Salt, soap, soda, and acids
might be called "chemicals."
chemi-luminescence. The production of light energy directly as a result of a
chemical change. Chemi-Iuminescence shows well in a darkened room.
chemistry. The science that deals with the composition of matter and the changes
it undergoes. Chemistry and physics are two useful sciences.
coagulation. Clotting or forming lumps. The coagulation of egg white is brought
about by heat.
colloidal condition (or colloid). A state of extremely small subdivision of particles.
Particles in the colloidal condition do not settle out when suspended in a liquid.
combining number. The number of atoms that combine with or replace an atom
of hydrogen. The combining number of oxygen is 2.
combining volume. The volume (liters, for example) of a gas that enters into a
chemical change. The combining volumes of hydrogen and nitrogen have a
ratio of 3 to 1 in forming ammonia.
combining weight. The weight of an element that combines with or displaces 1 g
of hydrogen. The atomic weight of an element divided by its combining number
is its combining weight.
combustion (see burning). The process of burning by which light and heat energy
are emitted. The combustion of coal is a great source of industrial power.
component (see constituent). One of the substances in a mixture. Quartz is a com-
ponent of granite. Zinc is a component of brass.
compound. A substance composed of two or more elements combined in definite
proportions by weight. Water is a compound.
concentrated. The opposite of dilute. Molasses^ is a highly concentrated (and im-
pure) sugar solution.
concentration. The amount of a substance in a given volume. The concentration of
potassium nitrate in a certain solution might be 25 g per 100 ml of solution; it
could also be expressed as the number of grams of the substance in 100 g of water.
condensation. The act of changing a gas or vapor to a liquid. The condensation of
water vapor produces rain.
constituent (see component). A part of a whole; in chemistry usually one of the
elements that make up a substance. Zinc is a constituent of zinc oxide (ZnO).
corrosion. The riisting or disintegrating of a material, sometimes caused by the
weather. Chemists study the cause and prevention of corrosion.
covalent linkage. One type of binding force between atoms. It consists of one or
more shared pairs of electrons. Hydrogen compounds are bonded by covalent
linkages.
cracking. The process of decomposing a hydrocarbon by heating. Much gasoline is
made by cracking heavier petroleum oils.
crucible. A thimble-shaped vessel made of clay, sand, graphite, alumina, or other
material. A crucible is used for holding a substance that is being intensely heated.
crystals. A solid of regular geometrical form, flat surfaces, and sharp edges, so formed
by nature. Common salt forms cubic-shaped crystals.
crystallization. The act of forming crystals. Crystallization takes place in freezing
liquids or in saturated solutions.
decomposition. The process of breaking down a substance into simpler parts.
The decomposition of mercury oxide takes place when the compound is heated.
dehydrated. That from which the water is removed. Dehydrated foods are usually
shipped when much food must be packed into a limited space.
688 CHEMISTRY FOR OUR TIMES
deliquescence. The property of a compound by which it takes moisture from the air
. and dissolves in the water so gained. Stick sodium hydroxide shows marked
deliquescence.
denatured. Deprived of its natural properties or qualities. Denatured alcohol is
violently poisonous for internal use.
density. A measure of the compactness of matter, expressed as weight per unit
volume. The density of a gas is commonly expressed in terms of grams per liter.
destructive distillation. The process of heating a substance out of contact with air
and condensing the volatile products different from the original material. Wood
alcohol may be produced by the destructive distillation of wood.
detergent. An agent used for cleansing. Soapy water is a good detergent.
detonator. A violently explosive substance that decomposes almost instantly. In.
mining, a detonator in a small copper cap is used to explode dynamite.
deuterium. Heavy hydrogen. Deuterium, atomic weight 2, is an isotope of hydrogen
developer. A chemical agent that makes a latent image visible. Developers are used in
photography.
dibasic. An acid that contains 2 g of replaceable hydrogen ions per formula weight.
Dilute sulfuric acid is dibasic.
diffusion. The act of intermingling. The diffusion of gases into the air takes place
readily.
dilute. The opposite of concentrated. A dilute solution contains a relatively large
amount of solvent and a little solute.
disinfectant. An agent that kills germs. Some coal-tar products, such as phenol, are
good disinfectants.
displacement (often replacement). A chemical change in which an element takes
the place of another element in a compound, setting the other element free. Setting
hydrogen free from an acid by replacing it by zinc is an example of this type of
reaction.
dissociation. Separation; the opposite of association. Ionic compounds dissolved in
water dissociate into ions readily.
distillate. The material, usually liquid, that is vaporized and condensed in the process
of distillation. The gasoline distillate is the most valuable petroleum product.
distillation. The process of heating a material and condensing the volatile products.
Water is purified by distillation.
double replacement. A chemical change between two compounds in which two
new compounds are formed. The action between solutions of sodium chloride and
silver nitrate by which sodium nitrate and silver chloride are formed is called
double replacement.
effervescence. The escape of a gas from a liquid, provided that the liquid and gas
are different substances. When zinc and an acid react, effervescence of hydrogen
takes place.
efflorescence. The process of losing water from a hydrated crystal. Sal soda crystals
undergo rapid efflorescence forming a dry powder.
electrode. A plate or rod from which electrons leave or enter a liquid or a gas. Elec-
tric cells have two electrodes.
electrolysis. The process of bringing about chemical changes by passing an electric
current through a liquid. Chlorine is produced by the electrolysis of common
salt solution.
electrolyte. A liquid that conducts electricity. In electrolysis the electrolyte is
decomposed.
GLOSSARY 689
electron. A unit of negative electricity. An electron is much lighter and smaller
than a hydrogen atom.
element. A simple substance of uniform chemical composition that cannot he decom-
posed by chemical means. Sulfur is an element.
emulsion. A suspension of droplets of a liquid in another. Immiscible (not capable
of being mixed or mingled) liquids, such as oil and water, form a temporary
emulsion when shaken together.
endothermic. A chemical change in which heat must be continually supplied; the
opposite of exothermic. The action of steam on hot coke is endothermic ; the
burning of coke, exothermic.
energy. Ability to do work. Heat, light, electricity, and chemical energy are some
forms of energy.
enzyme. An organic catalyst produced by living organisms. Yeast contains a number
of enzymes.
equation. A representation of a chemical change in symbol form. C -f- C>2 — > CC>2
is an equation that represents the burning of carbon.
equilibrium. A condition of balance between forces. In a chemical equilibrium two
opposite chemical actions are proceeding at the same rate so that the relative
proportion of the substances remains unchanged.
ester. An organic compound that may be formed by the action of an alcohol on an
acid. Ethyl acetate (CHaCOOCaHs) is a common ester.
ether. An organic oxide. Common ether is diethyl oxide [(C^H^O].
eudiometer. A stout graduated glass tube closed at one end and equipped with a
pair of platinum wires that project through the glass, forming a spark gap. When
chemical changes are carried out in a eudiometer, the volumes of gases used and
produced can be measured.
explosion. A violent chemical or physical action in which the greatly increased pres-
sure of an expanding gas (or liquid) causes it to erupt forcibly. The explosion of
dynamite loosens ore in a mine.
Fahrenheit. A thermometer scale in which the boiling point and the freezing point
of water at standard pressure are 212° and 32°, respectively. The Fahrenheit
scale is used extensively in the United States.
fermentation. Chemical changes of organic matter brought about by living or-
ganisms. Changing cider (alcohol) into vinegar (acetic acid) is an example of
fermentation.
fertilizer. Material added to the soil to promote growth of plants. Lack of fertilizer
will produce meager crops if the soil does not possess the needed food material
for the particular plants being grown.
nitration. The act of separating a solid from a liquid by passing the liquid through
cloth, paper, porcelain, or similar porous material. Filtration removes suspended
particles.
flame. Glowing burning gas. Wood burns at first with a flame.
flux. (1) A substance that aids the melting of other materials. (2) A cleaning agent
used in soldering. Silica is used as a flux in metallurgy; zinc chloride is used as a
flux in soldering.
formula. A group of symbols and figures representing an element or a compound
and showing its composition. The formula for water is H20.
fractional distillation. A variation in the process of distillation in which portions
of the distillate are collected between different boiling-point ranges. Water and
alcohol cannot be completely separated by fractional distillation.
690 CHEMISTRY FOR OUR TIMES
free. Native, uncombined, or alone. Gold is found free in nature.
freezing point* The temperature at which the solid and the liquid states of the same
substance can exist in equilibrium when mixed without an apparent change in
either. A cooling liquid remains at its freezing point until it has entirely solidified.
fusion. Melting. Brass is made by the fusion of copper and zinc together.
galvanize. To coat iron or steel with zinc. A steel nail can be galvanized by dipping
it into molten zinc.
gamma rays. Short X rays emitted from some radioactive substances. Radioactive
elements that emit beta rays also emit gamma rays.
gas. A state of matter having neither shape nor volume and consisting of independent
molecules. When coal is heated, a gas escapes.
glass. A fused hard mixture, usually of silicates, and often transparent. Glassmaking
is an ancient art.
gram. A unit of weight in the metric system. One gram is equal to Mooo kg, or the
weight of 1 ml of pure water at 4°C, or 0.0022 Ib, avoirdupois.
gram-atomic weight. Atomic weight of an element expressed in terms of grains.
The gram-atomic weight of oxygen is 16 g.
gram-molecular volume. The volume that holds one gram-molecular weight of a
gas at STP. The gram-molecular volume of any gas is 22.4 liters.
gram- molecular weight (or mole). The molecular weight of a compound or ele-
ment expressed in grams. The grain-molecular weight of water is 18 g.
gravimetric. Measured by weight. The result of the gravimetric analysis of sulfur
dioxide indicates 50 per cent of each element.
I la her process. A method of making ammonia by direct union of nitrogen and
hydrogen under proper conditions. The Haber process is of great economic
importance.
halide. A fluoride, chloride, bromide, or iodide. The halides of a given element have
similar properties.
halogen. A family of elements containing fluorine, chlorine, bromine, and iodine.
The halogens are active nonmetals; they combine with metals to form salts.
heat. A form of energy that may cause a rise in temperature of substances. Heat is
evolved by chemical action and by friction.
heavy water. Water in which the atoms of hydrogen are replaced by atoms of
deuterium. The density of heavy water is slightly above that for normal water.
homogeneous. Alike in all its parts. Elements and compounds are homogeneous.
Solutions are also homogeneous.
hormone. A chemical regulator of a function of the body. Hormones are put into
the blood stream by secretions from glands. Adrenalin is a hormone that prepares
the body for action in sudden emergencies.
hydrate. A crystal in which is incorporated a definite proportion of water. Blue
vitriol (CuSO4'5H2O) is a well-known hydrate.
hydrocarbon. A compound containing only hydrogen and carbon. Petroleum is a
mixture of hydrocarbons.
hydrogenation. The process of adding hydrogen to a compound, usually with the
aid of a catalyst. The hydrogenation of vegetable oils produces fats.
hydrolysis. The process by which the ions of a dissolved salt act on water.
The hydrolysis of sodium phosphate in water produces a strongly alkaline
solution.
hydroxide. A compound containing the radical OH. Soluble metallic hydroxides are
bases.
GLOSSARY 691
hydroxyl. The hydroxide group of elements. The hydroxyl radical, represented by
the symbol OH, is found in alcohols and in some alkalies.
identification. Definite recognition. Certain chemical tests are used in the identifica-
tion of a substance.
indicator. A substance that shows the nature of a solution. Some indicators, such
as litmus, show by their color change whether a solution is acid or alkaline.
inert. Inactive or slow in combining with another element. Helium is an inert gas,
as it forms no chemical compounds.
ingredient. A constituent of a substance or material. Carbonated? water is an ingre-
dient of soda pop.
inorganic. Not organic. Refers to compounds that do not contain carbon, except
carbonates and cyanides. Common salt is an inorganic compound.
insecticide. An agent for killing insects. Many insecticides contain arsenic.
ion. An atom or a radical carrying an electric charge as a result of the gain or loss of
one or more electrons. The sulfate ion (SOj ~~) is derived from the sulfate radical
(SO4) by the gain of two electrons.
ionization. The process of transferring electrons to an element or radical so that it
becomes an ion. Common salt is formed from its elements by the process of
ionization.
i Homers. Compounds with tho same composition, but differing in arrangement of
atoms within the molecule. Dimethyl ether and ethyl alcohol are isomers.
isotopes. Forms of the same element having identical outer-electron arrangement
but different weight nuclei. Isotopes differ in respect to atomic weight.
Kelvin scale. See absolute temperature scale.
ketone. An organic compound containing the characteristic group =C— O. Acetone
[(CHi)jCO] is the best-known ketone.
kilogram. One thousand grams. A kilogram weighs 2.2 Ib avoirdupois.
kindling temperature. The lowest temperature at which a material catches fire
and burns. The kindling temperature is not a definite temperature but depends
upon the rate of heat conduction of a material and other factors.
kinetic molecular theory. The present accepted theory that gases are composed of
tiny moving particles. The truth of the kinetic molecular theory is well established.
lake. An insoluble coloring agent or pigment formed by a precipitated metallic hy-
droxide adsorbing a dye. Some lakes are used as pigments by artists.
law. The statement of an observed generalization in the behavior of nature, based
upon many related experiments. Scientific laws seldom change.
liquid. A state of matter in which a substance flows freely; a state that is intermediate
between the solid and gaseous states. Liquids are formless and fluid, taking the
shape of the container. Liquid air is made by cooling and compressing gaseous air.
liter. The space occupied by 1000 g of water at 4°C. A liter is 1000.027 cc or 1000 ml.
litmus. A dye extracted from certain plants called lichens. Litmus is used as an
indicator.
lye. Sodium (or potassium) hydroxide. Lye is a strong alkali.
malleability. Ability to be rolled or hammered into a thin sheet. Gold has high
malleability. .
matter. Anything that has weight and occupies space. Matter is a fundamental idea
(concept) in chemistry.
melting point. Same as freezing point. The melting point is reached when the tem-
perature of a substance is increasing and a solid is changing into a liquid.
692 _ CHEMISTRY FOR OUR TIMES _
metal. Any one of a group of elements that is characterized by the formation of
positive ions and other general properties. Metals are good conductors of heat
and electricity. Most of them have a silvery luster.
metallurgy. The process of extracting metals from ores; the detailed study of the
properties of metals. Metallurgy is an important branch of applied chemistry.
mineral. An inorganic substance of definite composition found in the earth's crust.
Sulfur is a mineral obtained in the United States, Sicily, and elsewhere.
mixture. A material consisting of two or more intermingled substances without
regular composition. Brass is a mixture.
molal solution. A solution that contains a gram-molecular weight (mole) of a
compound in 1000 grams of water. Molal solutions are used in molecular- weight
calculations.
molar solution. A solution that contains a gram-molecular weight (mole) of a com-
pound with enough water to make a liter of solution. A one-tenth molar solution
of common table sugar contains 34.2 g of sugar in 1 liter of solution.
mole. See gram-molecular weight.
molecular weight. A number that represents the relative weight of a molecule of a
substance compared with the weight of an oxygen molecule. The latter is taken
as 32.
molecule. The smallest unit quantity of matter that can exist by itself in the gaseous
state. The hydrogen molecule is composed of two atoms.
monobasic. An acid that contains 1 g of replaceable hydrogen per formula weight.
Hydrochloric acid is a monobasic acid.
mordant. A sticky metallic hydroxide used for bonding dyes to cloth fibers. Aluminum
hydroxide is widely used as a mordant.
multiple proportions. A law in chemistry. The law of multiple proportions was
first stated by John Daltoii.
nascent. Freshly formed. Nascent hydrogen seems more active than hydrogen formed
some time before.
natural. Pertaining to nature. Natural chlorine is a mixture of several isotopes.
natural gas. A gas that comes out of a cave, volcano, or hole drilled into the earth.
Some natural gases are good fuels.
neutralization. A complete action between an acid and a base so that the products
have the characteristics of neither. Neutralization reactions are examples of
proton transfer reactions.
neutron. A unit of matter consisting of a closely connected electron-proton pair.
A neutron has no electric charge.
nonmetal. Opposite of a metal. Sulfur is a nonmetal.
normal solution. (1) Of an acid — contains 1 g of replaceable hydrogen per liter.
(2) Of a soluble metallic hydroxide — contains 17 g of hydroxide radical per liter.
Equal volumes of normal solutions of acids and soluble hydroxides entirely neu-
tralize each other.
nucleus. Central portion of an atom. Practically the entire weight of an atom is con-
centrated in the nucleus.
octane. A hydrocarbon containing eight carbon atoms. The formula for octane is
octane number. A number that gives the relative knocking rating of a motor fuel.
Aviation gasoline may be 100 or more in its octane rating number.
ore. A mineral from which a metal may be extracted profitably. Bauxite is an ore of
aluminum.
GLOSSARY 693
organic. An adjective that means pertaining to organisms or life. Organic chemistry
is a study of the compounds of carbon except carbonates or cyanides.
organism. A living creature, plant, or animal. Yeast is an organism.
oxidation. A chemical change involving (1) the combination of oxygen with a sub-
stance and (2) the loss of electron (s) by the substance oxidized. Simple burning is
an example of oxidation. (Memory aid: LEO, Joss of electrons is oxidation.)
oxide. A compound containing oxygen and another element chemically combined.
Copper has two common oxides, red cuprous (Cu2O) and black cupric (CuO).
ozone. An allotropic form of oxygen that can be made by passing oxygen through a
region of an electric discharge. Ozone (O3) is more vigorous in its chemical actions
ordinary oxygen (02).
paraffin. (1) A compound with small attractive force between itself and elements or
other compounds. (2) A waxlike fraction from the refining of petroleum. Methane
is the simplest member of the paraffin series of hydrocarbons. Paraffin is used to
cover the tops of jelly glasses.
pasteurization. A process of heating milk or other liquids to destroy bacteria.
Pasteurization improves milk from a health standpoint.
percentage. A part based upon the whole taken as 100 parts. The percentage com-
position tells the per cent of each element present in the substance.
petroleum. Natural oil. Petroleum is a mixture of hydrocarbons.
photosynthesis. A process that takes place in the green cells of plants whereby
water and carbon dioxide are changed into starch in the presence of sunlight by
the aid of chlorophyll. Photosynthesis is the most important chemical reaction in
that much of the food thus formed is consumed by humans and animals.
physics. The science that deals with energy and its'changes. In physical changes no
new products are formed.
pickling. The process of removing scale or rust from the surface of a metal. Sulfuric
acid is used in the pickling of steel.
pigment. An insoluble, finely divided, colored substance used as a coloring agent in
paints, cosmetics, or pottery. Chrome yellow (PbCrOO is a bright-yellow pigment.
plastics. Materials that take a useful shape under one set of conditions and harden
or "set," under another. The plastics industry is advancing rapidly.
polymer. A group or cluster of molecules, often a multiple of a definite structural
group. Many synthetic plastics are polymers; some are copolymers.
precipitate. An insoluble compound formed in a solution. A white precipitate forming
in limewater is a positive test for the presence of carbon dioxide.
properties. Characteristics, qualities. Color, odor, solubility, and density are de-
scribed in listing the physical properties of a substance.
protein. A complex nitrogen-containing organic compound. All proteins turn yellow
when concentrated nitric acid is added to them.
proton. The nucleus of the light hydrogen atom. The number of excess protons in
the nucleus of a neutral atom balances the number of electrons in its shells or
orbits.
qualitative* Dealing with the kind of material. A qualitative analysis discovers what
elements or compounds are present in a material or substance.
quantitative. Dealing with the amount of material. A quantitative analysis discovers
how much of each element is present in a compound.
quicksilver. An old name for the element mercury. Quicksilver is used in thermome-
ters.
694 CHEMISTRY FOR OUR TIMES
radical. A group of elements that act as a unit through several chemical changes. A
common radical is the sulfate group (S04).
radioactivity. The property of elements of decomposing spontaneously. During this
process they emit particles and rays of great penetrating power. Radium shows
the property of radioactivity.
rare. Uncommon. The rare earths are elements found in relatively small amounts.
rayon. A synthetic fiber made of reprecipitated cellulose. Rayon cloth has a pleasing
luster.
reaction. A chemical change. Some reactions are promoted by catalysts.
reagent. A reacting substance in a chemical change. Iodine is used as a reagent in
the chemical test for identifying starch.
reducing agent. An element or a compound that causes reduction, the opposite of
oxidation. Coke is a commercial reducing agent.
reduction. The gaining of electrons. Metals are obtained from their oxides by the
process of reduction.
replacement (sometimes displacement). A type of chemical change in which one
element or radical takes the place of another. Chlorine will replace bromine from
sodium bromide solution.
reversible. Interchangeable. A reversible reaction can take place in cither direction,
depending on conditions.
rust. Red-brown corrosion on iron. Iron changes to rust in the presence of moist air.
salt. A crystalline compound consisting of a positive ion (other than hydrogen) and
a negative ion. Salts are conductors of electricity when fused. Common salt is
sodium chloride (Na+Cl~).
saturated. Holding all that is possible under given conditions. A saturated solution
holds all solute possible at a given temperature in equilibrium with excess solute.
science. A systematic study of nature. Chemistry is a physical science.
slag. A glassy material formed by the combination of flux and gangue in a furnace.
Blast-furnace slag is an almost useless by-product of smelting iron.
smoke. Finely divided solid particles suspended in a gas. Smoke is a result of incom-
plete burning.
smelting. The process of treating an ore to obtain a metal. The smelting of tin ore
is a relatively simple process.
solder. An alloy used to join metal surfaces. Soft solder, an alloy of tin and lead, melts
at a low temperature.
solid. A state of matter that does not flow. Solids have definite crystalline forms. Dry
Ice is solid carbon dioxide.
solubility. The amount of solute that will dissolve in a given amount of solvent at a
given temperature usually expressed as the number of grams in 100 g of solvent.
The solubility of common salt increases only slightly when the temperature is
raised.
solute. A substance dissolved in a solvent. Sugar is the solute in ''simple sirup."
solution. A homogeneous mixture of solvent and solute. Water and salt shaken to-
gether form a solution.
solvent. A liquid that dissolves a substance. Water is the most commonly used solvent.
spectroscope. An instrument used for analyzing light by means of a prism. The
spectroscope is used in chemical analysis.
spontaneous. Of its own accord. In spontaneous ignition a substance catches fire by
the heat from its own slow oxidation.
stable. Not easily decomposed by raising the temperature. Water is a stable com-
pound.
GLOSSARY 695
standard. An accepted model. The standard conditions for measuring a* gas (STP)
are 0°C temperature and 760 mm of mercury pressure (1 atm).
strength. Of an acid or base — the ease of dissociating ions. A strong acid, such as
hydrochloric acid (HC1), has completely dissociated into ions in dilute solution
in water.
structure. Construction. A structural formula shows the probable arrangement of
atoms within a molecule of an organic compound, sometimes for inorganic com-
pounds also.
sublimation. The process of changing a solid to a gas, omitting (or almost entirely
omitting) the liquid condition. Dry Ice (solid carbon dioxide) sublimes.
substance. A material of uniform composition. Limestone is a substance. Hay is
called a material, not a substance.
supersaturated. Above saturation. Crystals form when seed crystals are dropped
into a supersaturated solution.
suspension. A finely divided state of matter distributed through a less dense state
of matter. Rivers hold clay particles in suspension.
symbol. The letter or letters that represent the atom of an element. Zn is the symbol
for zinc.
synthesis. The process of joining simple substances to form more complex ones.
The synthesis of water can be accomplished by burning hydrogen in air or in
oxygen.
technique. The way of conducting a laboratory experiment. The technique of a be-
ginner improves rapidly.
temper. The state of hardness and toughness of steel. The temper of steel is lost by
heating strongly and cooling slowly. •»
temperature. Degree of heat. Temperature may be measured by means of a ther-
mometer.
ternary. Referring to compounds that contain three elements. Nitric acid (HNOa) is
a ternary compound.
tincture. A solution in which alcohol is the solvent. Tincture of iodine is used as an
antiseptic.
tribasic. An acid that contains 3 g of replaceable hydrogen ions per formula weight.
Phosphoric acid (HaPCh) is a tribasic acid.
ultraviolet. Short light waves. Ultraviolet light is not visible to the unaided eye. It is
active in causing certain chemical changes.
valence (or combining number). (1) Electrovalence — the charge on an ion. (2)
Covalence — the number of shared pairs of electrons associated with an element.
The valence of oxygen is 2 in water (H^O).
vitamin. Organic compounds found in foods and needed in small amounts in the
body to maintain health. Vitamin BI is often lacking in sufficient amounts.
volatile. Evaporating readily at low temperatures. Camphor is a volatile solid. Ether
is a volatile liquid.
vulcanize. The curing of rubber by heating it with sulfur. A patch is vulcanized onto
a rubber inner tube.
water glass. Soluble silicates. A solution of water glass is used in fireproofing fabrics.
water of hydra tioii (see hydrate). Water combined in a crystal.
weak (see strength). Opposite of strong. Acetic acid is a weak acid because it is weakly
dissociated into ions in dilute solution.
696 CHEMISTRY FOR OUR TIMES
welding. The process of joining metals by melting them together. Good welding re-
quires skillful use of fluxes and torches.
X rays. Short-wave-length energy radiations that penetrate matter. X rays penetrate
flesh.
INDEX TO APPENDIX
PAGE
Metric system 697
Temperature measurement 700
Gas-volume corrections for changes in temperature and pressure 701
Vapor pressure of water 709
Normal solutions 709
pH value for Q.IN solutions 712
Flame tests 712
Borax-bead colors (after cooling) 712
Recipe for cold cream or cleansing cream 713
Facts about fuel gases 713
Properties of the gases in the air 713
Baking powder chart 714
The common gases 715
Composition of foods 716
Facts about common substances 719
The more common elements 722
International atomic weights 723
APPENDIX
The Metric System
The Meter. At the close of the French Revolution, the government
of France appointed a commission to establish a more satisfactory sys-
tem of weights and measures. This group decided that one ten-millionth
of a quadrant (quarter circumference) of the earth measured on the
meridian of Paris would be the unit of length. This distance, 39.37 in.,
they called the meter.
,, , quadrant , circumference v, ,~ .
Meter - 10,000,000 °r meter 4 X 10"
The length of the meter was determined with extreme care; in fact,
the distance was marked on a standard meter bar of noncorroding plati-
num-iridium alloy by two parallel scratches. This bar is preserved in
France, and copies have been made for the use of all governments and
laboratories requiring standards of extreme accuracy.
If all meter bars were destroyed, we should still be able to repro-
duce the distance accurately, for it is 1,553,164.13 times the wave length of
the red line of the spectrum of cadmium in air at 760 mm pressure at
15°C.
Prefixes. The meter and all other units in the metric system are di-
vided into 10 parts, something as the United States dollar is divided into
dimes, cents, and mills. Here is one of the advantages of metric system,
for units are interchangeable by merely changing the position of the
decimal point.
or 0.1 meter = decimeter or dm
or 0.01 meter = centimeter or cm
Jf ooo or 0.001 meter = mittimeter or mm
1000 X the meter = ftflometer or km
The same prefixes are used throughout the system with the same
meanings: deci-, one-tenth; centi-, one-hundredth; miWf-, one-thous-
andth; kilo-, one thousand times.
The Liter. A cube 1 decimeter (dm) on an edge contains a volume of
1 cubic decimeter (dm8), or about 1.06 quarts. This cube, if hollow, holds
about 1 liter. Accurately, the volume occupied by 1 kilogram (kg), or
2.2 pounds, of pure water at 4°C is called a liter.
Since 1 decimeter equals 10 centimeters, it follows that 1 cubic
decimeter equals 1000 cubic centimeters (cc or cm8). One thousand cubic
centimeters or, more accurately, 1000 milliliters (ml) is the same as 1
697
698
CHEMISTRY FOR OUR TIMES
liter. A liter of water, however, is not exactly 1000 cc, but 1000.027 cc,
a difference of 27 parts in 1 million. For most practical purposes, the
cubic centimeter and the milliliter may be used interchangeably.
The Gram. The weight of a liter of water at 4°C is 1 kilogram (kg).
By dividing each by 1000, we find that 1 milliliter of water at 4°C weighs
1 gram (g). The gram is the unit of weight in the metric system. A United
States nickel weighs about 5 g. Another advantage of the metric system
will now become evident. If we measure out some water in a gradu-
ated glass cylinder and find that we have, for example, 42 ml volume,
>^ Volume /
^ 1 UTER /
t
E
Weight of Water
0
0
1 Kilogram or
1000 Grams
t
y
/ Volume 1 QUART /
sr or 57.75 Cu. In//
m
5
Weight of Water
*
CO
2.08199 Pounds
x:
^
K
Metric Volume Units English
FIG. A-l. — The relative size of the liter and the quart.
then the water weighs just about 42 g. If the liquid were mercury with
specific gravity 13.6, then the weight of the same volume would be
42 X 13.6 = 571 2 g, about 1?£ Ib.
Unit
1000 fold
0.1
0.01
0.001
Length
Meter
km
dm
cm
mm
Volume
Liter
kl
dl
cl
ml or cc
Weight . .
Gram
kg
dg
eg
mg
Except for trading in the United States and England, the metric
system is used extensively throughout the world. It is the official United
States system and is coming more and more into use. It is used particularly
in scientific work, although many engineers still use the English system.
Relationships between the English and the Metric Systems.
Four simple relationships between the English and the metric systems
are sufficient for most purposes.
1 meter (m) = 39.37 inches
1 inch = 2.54 centimeters (cm)
1 liter (1) = 1.06 quarts
1 kilogram (kg) =2.2 pounds
APPENDIX 699
The following relationships may be used for reference.
1 mile = 1.6 kilometers (km)
1 kilometer (km) = 0.62 mile
1 ounce (avoirdupois) = 28.3 grams (g)
1 pound = 453.6 grams (g)
1 gallon (U.S.) = 3.8 liters (1)
1 ounce (fluid, U.S.) = 29.57 milliliters (ml)
QUESTIONS
1. How many milligrams are in a gram? In a centigram? In a kilogram? In
/63.4 9T J7.45
|525 grams? In |432 grams?
(1 42
' ~ meters tall. Helen is
5 feet 2 inches tall. Which of the girls is taller?
[75
3. A swimming pool is feet long. Find its length in yards and also in
meters.
4. Harry weighs j *c*r\ pounds. What is his weight in kilograms?
5. Butter is sold for j _~ cents per pound. What should be its price per kilo-
gram?
(6.5 by 11 centimeters . .
6. A camera film measures loa/ h 4*/ ' h * ™hat 1S ™*e 81ze
N ( in inches?
dimensions) -j . . 0
I in centimeters r
7. If you were driving a car in South Africa and wished to buy | ~ gallons of
gasoline, how many liters would you buy?
Q Light) . xx, , , . .. (300,000 kilometers
S d I ^rave*s a^ ^ne sPeed °f approximately 1 1 1 QQ r t P^r sec.
What is the speed in miles per second? In meters per second?
9. An automobile tire is \ ^ inches in diameter, and it weighs i . . Ibs.
Change the diameter to centimeters and the weight to kilograms.
{12 i 50 f 2 0
.. centimeters long, ( ,~ millimeters wide, and •(/. inches
deep. Find its volume in milliliters. How many kilograms of water will it hold? Of
mercury?
700
CHEMISTRY FOR OUR TIMES
Temperature Measurement
A common way to find the temperature of a liquid, solid, or gas is to
bring a thermometer into intimate contact with the substance and, after
waiting a sufficient time for both the thermometer and the substance to
M.P.ofNaCI 1,474
B.P of H20 212
F.P. of H20 32
o.
801
1,074
100
373
0
273
F.P.ofHg4-38.9*C)-40
B.P. Liquid N2 -321
B.P. Liquid H2 -423v
B.P Liquid He -452<
-40
233
-196
77
-253
20
Absolute >*-459*F
Zero
-273*C
0*A
Lowest Temperature
Yet Reached
FIG. A-2. — Fahrenheit, centigrade, and Kelvin temperature scales.
come to the same temperature, to "read the thermometer." The volume
of the mercury in the thermometer changes with the temperature. The
glass stem of the thermometer has scale markings, or graduations, etched
on it, showing the volume of the mercury at those temperatures. Among
these markings the boiling and freezing points of water are called the
fixed points. They are 100° and 0° on the centigrade scale and 212° and
32° on the Fahrenheit scale, respectively, at 760 mm pressure. (See
Fig. A-2.)
Since the number of degrees between the fixed points centigrade is
APPENDIX 701
100 and between them Fahrenheit is 180, on the same thermometer, the
ratio of the number of degrees centigrade to the number of degrees
Fahrenheit is 100 to 180 or 5 to 9.
!C = 100 = 5
°F 180 9'
But since the Fahrenheit scale does not start at zero, we must subtract
32° in order to get an accurate relationship.
°C 5
°F - 32° 9
or 1.8°C - °F - 32
A comfortable room is 70°F. What is the temperature on the centigrade
scale? We use the value 70 for F, substitute it in the equation, and solve
for C. as follows :
C __ 5 C _ 5 38X5 _
70-32-9 38 ~ 9 °~ ~9~~ " 2L1 ° AnS'
When the thermometer reads — 10°C, what is the corresponding
Fahrenheit reading?
— 10 ^
F _ g2 = ^ 5F - 160 = 9 X -10 5F = [9 X (-10)] + 160
F = 14°F Ans.
Absolute temperatures, or temperatures on the Kelvin scale, are
found by adding 273 to the centigrade reading. Absolute temperatures
are always used in gas- volume change problems.
Gas-volume Corrections for Changes in Temperature
and Pressure
The Effect of Pressure Changes. Experiments show that if the
temperature of a given quantity of gas is kept constant (unchanged)
and the pressure on it is doubled, its volume becomes one-half. If the
pressure is halved, the volume becomes doubled. In general, when the
temperature is constant, the volume of a given amount of gas is inversely
proportional to the pressure (Boyle's law) (page 118).
Let us assume that we have collected 400 ml of oxygen. We observe
that the temperature is 20°C by a thermometer reading and that the pres-
sure is 750 mm by a barometer reading. What volume will the oxygen
occupy if the pressure is changed to standard pressure, 760 mm, the
temperature remaining unchanged?
We reason that since the pressure is changed from 750 to 760 mm,
an increase, the volume is decreased. Hence we should multiply the origi-
nal volume, 400 ml, by a fraction composed of 750 mm and 760 mm in
702 CHEMISTRY FOR OUR TIMES
such a manner that the answer will be less than 400. Such a fraction has
a value less than 1; that is, it is a proper fraction composed of 750 over
760, namely, 750 mm/760 mm.
The new volume, therefore, is
X 400 ml = 394.7 ml. Ans.
Notice that the units are included in the problem and canceled where
possible. This shows the unit(s) in the answer.
Again, let us assume that we have collected 600 cu in. of hydrogen
at a pressure of 35 in. of mercury and at a temperature of 18°C. We wish
to find out what volume the hydrogen will occupy when the pressure
changes to standard, 30 in.1 of mercury, and the temperature is unchanged.
We reason that the change in pressure from 35 to 30 in. is a decrease.
Hence the volume of the gas should increase. We should, therefore,
multiply 600 by a fraction made up of 35 in. and 30 in. in such a manner
that the value of 600 is increased. Such a fraction is an improper fraction,
or 35 in. over 30 in.
The new volume, thus, is
35 fr.
30>ff.
X 600 cu in. = 700 cu in. of hydrogen. Ans.
In case we wish to find the pressure change needed to expand 1 .0 liter
of carbon dioxide at 735 mm of mercury pressure and 0°C to 1.25 liters
at the same temperature, we use similar reasoning. Since the volume is
to increase, the pressure must decrease. Hence 735 mm must be multi-
plied by a fraction made up of 1.0 1 and 1.25 1 in such a fashion that the
value of 735 mm will decrease. Such a fraction is the proper fraction,
1.0 1 over 1.25 1.
The new pressure, therefore, is
735 mm = 588 mm. Ans.
QUESTIONS
1. When 200 milliliters of chlorine is collected at 30°C and 740 millimeters
of mercury pressure, what does the volume become when the pressure is changed
to { nnn millimeters while the temperature remains at 30°C?
I you
f 720
2. Five liters of air is collected at 1 -.^ millimeters. What is the volume of
this sample of air at standard pressure, 760 millimeters, if the temperature is
unchanged?
1 Standard pressure is more accurately 29.92 in. of mercury.
APPENDIX 703
3. When the pressure on 44 liters of sulfur dioxide at 40°C is changed from
{390
.g- millimeters, what is the new volume if the temperature
is unchanged?
4. If a liter of hydrogen at atmospheric pressure is subjected to a pressure
w times that of the atmosphere, what is the new volume if the temperature is
unchanged?
6. When the pressure on 7 liters of oxygen at 77.0 centimeters pressure is
f66
changed from 77 centimeters to j - ^ centimeters what is the new volume if the
temperature is constant?
MORE CHALLENGING QUESTIONS
6. What is the volume of 14.3 cubic feet of oxygen at JIQ r pounds per
square inch if the pressure becomes standard (14.7 pounds per square inch) and
the temperature is unchanged?
7. What new pressure will change 1.25 liters of nitrogen collected at 760 milli-
meters into 1.75 liters without changing the temperature?
f 800
8. What volume of oxygen at lyon millimeters and 0°C will be generated
by the decomposition of 490 grams of potassium chlorate?
9. What is the new volume occupied by 100 liters of air when the pressure
changes from 14.7 pounds per square inch to 294 pounds per square inch?
10. A tank of air holds j -^ cubic feet, and the gauge reads 75 pounds per
square inch. Gauge pressure is the additional pressure above the atmospheric
pressure of 14.7 pounds per square inch. What volume of air escapes when the
valve is opened?
The Effect of Temperature Changes. Experiments show that, when
the pressure is unchanged, the volume of a given quantity of any dry
gas is directly proportional to its Kelvin, or absolute, temperature. The
absolute temperature is the centigrade reading plus 273. Thus, when the
temperature of a given volume of gas changes from 20°C to 313°C,
the volume is doubled, provided that the pressure does not change. The
absolute temperature in this case has doubled, 293 (20 + 273) to 586
(313 + 273). This behavior of gases is summarized in Gay-Lussac's
(Charles's) law.
In applying the principle we understand that when a gas is heated it
expands and, conversely, that when a gas is. cooled it contracts. Let us
find the new volume occupied by 60 liters of carbon dioxide when the
704 _ CHEMISTRY FOR OUR TIMES _
temperature changes from 27 to 57°C and the pressure remains constant.
We must remember to use absolute temperatures; 300° K and 330° K
[or absolute] are the temperatures to be used. In this case the gas is
being warmed from 27 to 57°C, and therefore the volume will increase.
We must thus multiply 60 liters by a fraction made up of 300° K and
330° K in a manner to make the value greater than 60. Such a fraction
is an improper fraction with its value more than 1, or 330° K over
300° K. Thus we multiply 60 liters by 330° K/3000 K, obtaining 66
liters. Ans.
Again, what is the volume occupied by 586 ml of hydrogen collected
at 20°C, at standard temperature (0°C), assuming no change in pressure?
First we change the temperatures to absolute, or 293° K and 273° K,
respectively. Here the gas has cooled, and therefore the volume has
decreased. We thus multiply 586 ml by a fraction made up of 273° K
and 293° K in a manner to decrease the value of 586 ml. The fraction
to be used is a proper fraction in which the numerator is smaller than the
denominator, or 273° K/2930 K.
Hence,
586 ml X o = 546 ml. Ans.
To what temperature must 1.2 liters of oxygen at 37°C be heated in
order that it may become 1.5 liters? We reason that, if the volume is to
increase, the absolute temperature must be increased in proportion. First
we convert 37°C to 310° K and multiply it by 1.5 liters/1.2 liters.
310° KX= 387.5* K
387.5° K - 273° = 114.5°C Ans.
QUESTIONS
{60
QQ liters of nitrogen collected at 17°C changes
to standard, 0°C, assuming no change in pressure, what new volume does it
occupy?
(44
12. What is the effect of heating |66 milliliters of oxygen from 27 to 47°C
without changing the pressure?
13. The volume of a captive balloon containing illuminating gas is 10,000
cubic feet when the sun is shining on it, and the average temperature of the gas is
52°C. When the balloon goes into a cloud and the average temperature becomes
{n/\
je°C, what new volume does the gas in the balloon occupy? Assume that the
pressure is unchanged. Does the balloon tend to rise or fall as it cools?
APPENDIX 705
{nr\
IQ°C-
What is the volume of the gas at standard temperature, 0°C, assuming no change
in pressure?
»7Q
;- o°C to 0°C, what does the
volume of a liter of oxygen become if the pressure does not change?
MORE CHALLENGING QUESTIONS
16. What new temperature is required if 1.2 liters of air at 0°C is to occupy
fl.4
| * liters without a change in pressure?
17. If the volume of a certain gas is represented by F, its centigrade temper-
ature by T, and its absolute temperature by T -f 273, what is the new centigrade
..... /doubled /2F
temperature when the volume islui j or 1 v/2
18. What is the volume occupied at 323°C by the carbon dioxide formed by
f2
the burning of | - liters of methane, measured at 23° C? Assume that the pressure
is unchanged.
19. What volume of acetylene, at 0°C, should be burned in order to form
|-. liters of carbon dioxide measured at IOKQ C?
{20
OQ°C, occupy
when the centigrade temperature is doubled? When the absolute temperature is
doubled?
The Combined Effect of Pressure and Temperature Changes.
When both pressure and temperature change, corrections for both changes
are applied together, one after the other, in the same manner as that for
the changes separately.
For example, what is the volume at standard conditions (STP, 760 mm
and 0°C) of 1172 ml of sulfur dioxide collected at 700 mm and 20°C?
The change in pressure from 700 to 760 mm tends to decrease the volume;
therefore we use 700 mm/760 mm. The change in temperature, 293 to
273°K, tends to decrease the volume; therefore we use 273° K/2930 K.
Hence,
" Ans-
Again, what volume of hydrogen, measured at 780 mm and 77°C, is
released when 1300 g of zinc acts with an excess of dilute sulfuric acid?
1300 g x liters
Zn + H,SO4 -» ZnS04 -f H,
65 g 22.4 liters
706 CHEMISTRY FOR OUR TIMES
Volume of hydrogen, x = X 22.4 liters = 448 liters at STP
^or* v, 760j»mr 350°.!? _„...
448 llters X X - 56° llters'
Gas-law-equation Method of Gas-volume Corrections. The
foregoing relationships of temperature, pressure, and volume changes are
summarized by the gas-law equation,
PV P'V
T T'
where P, V, and T are the original pressure, volume, and absolute tem-
perature and P', V, and T' are the new pressure, volume, and absolute
temperature. This equation is sometimes called the law of ideal gases.
What volume will 138 ml of hydrogen collected at 25°C and 790 mm
occupy at standard conditions (0°C and 760 mm)?
Here
P = 790 mm Pf = 7GO mm
V = 138 ml V = unknown
T = (25 + 273) 298° K T' = 273° K
We substitute these values in the gas-law equation and solve for the one
unknown value V.
790 mm X 138 ml 760nnO<
T7,
V =
298° K ~ 273° K
X 138ml
If the temperature is constant, the value of T equals that of T' in
the formula and cancels. This leaves PV = P'V1 ', a formula for Boyle's
law. The value for V = PV/P'.
If the pressure does not change, the value of P equals that of P' in
the formula and cancels, leaving V /T = V'/T' or VTr — V'T, formulas
for Charles's (Gay-Lussac's) law. The value for V = VT'/T. Here, as
before, T and T1 refer to absolute, or Kelvin, temperature.
The use of the gas-law-equation method depends on remembering
a formula; the use of the reasoning method involves less rote memory
and depends on an understanding of the principles involved.
QUESTIONS
21. | p. ,, liters of oxygen is collected at 27°C and 780 millimeters pressure.
What is the volume at standard conditions?
APPENDIX 707
22. What is the volume of 75 milliliters of argon at 700 millimeters pressure
(2100
and — 53°C when put under a pressure of ]2800 Im^imeters an^ warmed to
" 1 3 f 27
23. A neon tube holds 300 milliliters at j - millimeters pressure and ]47°C.
A sealed flask of neon holds 1 liter at 780 millimeters and 17°C. How many tubes
can be filled from the neon in the flask? HINT: Change the volume of one to the
conditions of the other.
24. A balloon on the surface of the earth holds 3 million cubic feet of helium-
hydrogen mixture at pressure 14.7 pounds per square inch and temperature 15°C.
What does the volume become when the balloon rises to a place where the pressure
(2 i / _ ^3
/2 pounds per square inch and the temperature is i o °C?
{'2Q T758
io°C and |7po m^~
meters pressure. What volume does this hydrogen occupy at standard conditions?
MOKE CHALLENGING QUESTIONS
26. What volume (liters) of hydrogen at 780 millimeters and 27°C is liberated
[2.4
when •!- £ grams of magnesium reacts with an excess of hydrochloric acid?
27. What volume of oxygen is liberated at 740 millimeters and 47°C when
IOKO grams of sodium chlorate is strongly heated?
loOZ
28. Steam from a certain boiler is supplied at 150°C and 150 pounds per
square inch pressure above that of the atmosphere. It is exhausted from a tur-
bine at 100°C and 4.7 pounds per square inch pressure above that of the atmos-
phere. How many times its original volume has the steam expanded? HINT:
Consider the original volume as 1 cubic foot. Atmosphere pressure is 14.7 pounds
per square inch.
29. A bubble of carbon dioxide is generated in an oil well where the pressure
is 10,000 pounds per square inch and the temperature is 97°C. How many times
its original volume is the bubble when it has risen to the surface of the earth?
f 500
30. When 1 OAA grams of pure calcium carbonate is dissolved in an excess of
lOUU
hydrochloric acid, how many liters of carbon dioxide are liberated, measured at
27°C and 765 millimeters pressure?
Collecting Gases over Water. When a gas is collected over mercury,
the pressure of the gas is that exerted by the bombardment of the mole-
cules of the gas against the surface of the mercury that encloses it. We
708 _ CHEMISTRY FOR OUR TIMES _
assume that mercury has only a very slight tendency to evaporate and
that very few mercury molecules are mixed with the gas molecules.
When a gas is collected over water, on the other hand, the water does
evaporate, and the gas contains considerable quantities of water-vapor
molecules. These water-vapor molecules exert a pressure, and thus the
pressure exerted by the gas is composed of two parts, the force exerted
by the molecules of the gas itself and that exerted by the water-vapor
molecules mixed with the gas on each unit of area (Dalton's law of partial
pressures).
The amount of pressure exerted by the water-vapor molecules de-
pends on the temperature only and may be found by consulting the table
on page 709.
For example, an experimenter collects 250 ml of oxygen by displace-
ment of water and reads a barometer at the same level. It is 762.0 mm.
The level of the water inside and outside the bottle are the same. The
temperature of both the gas and the water is observed to be 22° C, both
being at room temperature. From the table on page 709, the vapor pres-
sure of water at 22°C is 19.8 mm. The pressure due to oxygen alone is
762.0 mm - 19.8 mm or 742.2 mm.
The corrections for the vapor pressure of water should be applied
in making measurements in the laboratory, but the correction should be
used in problems only when specific directions are given, as, for example,
when a definite statement is made to the effect that the gas under con-
sideration was collected by displacing water.
QUESTIONS
31. What is the partial pressure of a gas when the barometer reads 758.8 milli-
meters and the gas is collected over water at (a) {i0°C; (b) | i/C; (c)
32. Fifty liters of oxygen is collected over water at a temperature of
{Q77 f»
-- ' millimeters. What is the volume of the dry gas at
STP?
33. What is the pressure due to hydrogen alone at 23°C if the gas is collected
over water and the barometer reads 765.9 millimeters?
34. With the temperature at 50°C, a bottle contains |™Q miililiters of
{792 5
OQ2 K millimeters pressure. What is the volume of the gas at
STP?
35. What volume of hydrogen will be collected from the action of 195 grams of
APPENDIX 709
{22 f 750
oQ°C and \ 7-~
millimeters pressure?
VAPOR PRESSURE OF WATER
(Aqueous vapor over water)
Temperature,
°C
Pressure,
mm of Hg
Temperature,
°C
Pressure,
mm of Hg
' 0
4.6
28
28.3
5
6.5
30
31.8
10
9.2
40
55.3
12
10.5
50
92.5
14
12.0
60
149.4
16
13.6
70
233.7
18
15.5
78.6
335.6
20
17.5
80
355.1
22
19.8
90
525.8
24
22.4
100
760.0
26
25.2
Normal Solutions
Let us assume that we have a solution that contains just one formula
weight of sodium hydroxide, 40 g, dissolved in enough water to make one
liter of solution. One formula weight, or 36.5 g, of hydrogen chloride in
solution is just enough to react with the sodium hydroxide solution to
produce complete neutralization.
NaOH + HCI -> NaCI + H2O
40 36.5 58.5 18
When sulfuric acid is used to neutralize a liter of the same sodium
hydroxide solution, one-half a formula weight, or 49 g, of hydrogen sul-
fate is required.
2NaOH + H2SO4 -*> Na2SO4 + 2H2O
80 98 142 36
A solution of sodium hydroxide that contains 40 grams dissolved in
enough water to make a liter is called a normal solution of sodium hy^
droxide. Such a solution contains 17 g of replaceable OH"* ion.
A solution of hydrogen chloride that contains 36.5 g of hydrogen
chloride in a liter of solution is called a normal solution of hydrochloric
acid, and one that contains 49 g per liter, one-half the formula weight,
is called a normal solution of sulfuric acid. Such normal acid solutions
contain 1 g of replaceable hydrogen per liter. A normal solution of phos-
phoric acid contains 98 g (formula weight) -5- 3, or 32.67 g of hydrogen
phosphate (H8PO4) with enough water to make a liter.
Fundamentally, a normal solution thus contains enough solute, dis-
solved to make 1 liter of solution, to be connected directly or indirectly
710 _ CHEMISTRY FOR OUR TIMES _
to 8 g of oxygen or 1 (accurately 1.008) g of hydrogen in a chemical
reaction.
Normal solutions of acids contain 1 g of replaceable hydrogen ions
per liter, and normal solutions of metallic hydroxides contain 17g of OH"
ions per liter in these basic solutions.
Solutions that are more or less concentrated than a normal solution
are used frequently. Such concentrations are expressed as follows, for
example: 6N HC1 means a solution containing six times the formula
weight of hydrogen chloride per liter. O.lN, KoN, or N/10 NaOH means
a solution having one-tenth the formula weight of sodium hydroxide, or
4 g, dissolved per liter of solution.
A Q.5N solution of calcium chloride contains one-fourth the formula
weight (formula weight divided by combining number of calcium) of
calcium chloride (27.8 g of CaCl2) per liter.
One liter of N solution of Na2CO3 contains 106 -r- 2 = 53 g.
One liter of N solution of A1C13 contains 133.5 -f- 3 = 44.5 g.
QUESTIONS
1. How many grams of the following compounds are required to make a liter
of a normal solution: (a) KOH; (6) Ca(OH)2; (c) H2SO3; (d) HNO3; (e) CH8COOH?
2. How many grams of solid are present in a liter of j -N NaOH solution?
i 300
3. A pupil needs onn niilliliters of 0.1 Ar NaOH. What supplies are required?
{g
JV
4. How many grams of hydrogen sulfate are present in 700 milliliters of
sulfuric acid?
5. What volume of water must be added to a liter of N NaOH solution so
that the final solution will be 0.2A7
Careful study of the previous discussion will show clearly that equal
volumes of basic and acid solutions of the same normality neutralize
each other.
If a one-tenth normal solution should be substituted for a normal solu-
tion, it is obvious that ten times the volume of the weaker solution is
required for the same effect as the stronger. Likewise, one-fifth the volume
of a 5N solution will be required for the same job that a certain volume
of normal solution does. That is, the more concentrated the solution, the
less volume is required for a given reaction. This may be expressed in
general as
Vl X Ni = F2 X #2
where Vi is the volume of the solution with normality Ni and Vi is the
volume of the solution with normality AT2.
APPENDIX 711
Examples : How many milliliters of 0.47V KOH solution will neutralize
100 ml of 0.05AT phosphoric acid?
100 ml X 0.05N = F2 X 0.4 N
T, 100 ml X 0.05 )f 10K . A
F2 = - 0 y - — = 12.5 ml Ans.
What weight of hydrogen nitrate is present in 3 liters of nitric acid
that just neutralize 234 ml of 4JV sodium hydroxide solution?
3 liters X Ni = 0.234 liter X 4AT
Ar 0.234 Piters' X 4JV nQ10Ar A
Ni = - 0 r.^» - = 0.312JV Ans.
sjtteflr
A normal solution of nitric acid contains (1 + 14 + 48) 63 g of hydrogen
nitrate per liter. Three liters of 0.312JV HN03 contains
63 X 0.312 X 3 = 58.97 g. Ans.
QUESTIONS
6. What volume of 0.1 JV hydrochloric acid will be needed to neutralize
1400 mi^*^ers °f 0.0 IN calcium hydroxide solution?
7. What is the normality of a sulfuric ticid solution if 42 milliliters of it
ralizes j^ milliiiters of 6N sodium hydroxide solution?
/4
8. How many grams of sodium sulfate are needed to make •{ . liters of
4
-Ar solution?
{35
O'r milliliters of it neu-
zo
tralizes \ _n milliliters of 0.2.V sodium carbonate solution?
150
10. How many grams of anhydrous sodium carbonate (Na2COa) are needed to
prepare the \ -~ milliliters of 0.2W solution mentioned in the previous question?
MORE CHALLENGING QUESTIONS
11. How many grams of hydrated sodium carbonate (Na2CO3-10H2O) are
needed to make j -~ milliliters of 0.2 AT solution?
12. What volume of 6N HC1 is needed to precipitate all the silver ions in
( 300
|45Q milliliters of 0.75AT silver nitrate solution? What weight of silver chloride
will form?
712
CHEMISTRY FOR OUR TIMES
13. What volume of 6N HC1 will be needed to react completely with
grams of zinc? What volume of hydrogen gas at STP is liberated? What volume of
f 760 f 20
gas at "{^A millimeters and \ 1Q°C is liberated?
I * i U I lo
14. At 18°C, 0.0023 grams of barium sulfate dissolves in a liter of water. Find
the normality of this saturated solution.
15. When hydrogen sulfide gas is passed into \Af\r\ milliliters of \~N silver
nitrate solution until no more precipitate forms, how many grams does the precipi-
tate weigh?
pH VALUE FOR O.IN SOLUTIONS*
pH
Hydrochloric acid (HC1) 1.0
Sulfuric acid (H2SO4) 1.2
Phosphoric acid (H3PO4) 1.8
Tartaric acid (H2-C2H4O6) 2.2
Citric acid (H.-CJIjOi) 2.3
Lactic acid (H-C8H*Os) 2.4
Boric acid (HsBOa) 5.1
Sodium bicarbonate (NaHCO3) 8.4
Disodium hydrogen phosphate (Na2HPO4) 9.0
Borax (Na2B4O7) 9.2
Ammonia water (NH4OH) 11.1
Sodium carbonate (Na2CO3) 11.3
Trisodium phosphate (Na»PO4) 12.0
Sodium hydroxide (NaOH) 13.0
FLAMK TESTS
Sodium compounds Yellow
Lithium compounds Crimson
Strontium compounds Red-scarlet
Calcium compounds Orange-yellow
Barium compounds Yellow-green
Copper chloride Blue-green
Potassium compounds Violet
BORAX-BEAD COLORS (AFTER COOLING)
Cobalt
Copper
Iron
Manganese .
Uranium . . .
Oxidizing
flame
Blue
Blue
Yellow
Violet
Yellow
Reducing
flame
Blue
Red
Green
Colorless
Green
* READ, ALLEN B., LaMotte Chemical Products Company, Towson, Baltimore, Maryland. Used by
permission.
APPENDIX
713
Recipe for Cold Cream or Cleansing Cream
Creams are essentially an emulsion of water and oil, the water evapor-
ating when the cream is applied.
In pan No. 1 place 1 qt mineral oil, light grade, specific gravity
0.845 to 0.865; 2 oz absorption base (a concentrate of cholesterol): 1 oz
lanolin, anhydrous; 7 oz beeswax, best grade, sun-bleached.
In pan No. 2 place 1 pt water; % oz borax.
Heat both mixtures gently up to 150°F. Pour slowly contents of pan
No. 2 (water) into pan No. 1 (oils), stirring slowly until well mixed.
When mixture is cooled to about 120°F, add 2 drams of a perfume oil.
Stir, and then pour into jars.
FACTS ABOUT FUEL GASES
(Per cent by volume)
Rela-
Type of gas
Methane
(CH4)
Hydro-
gen
(H->)
Carbon
mon-
oxide
Other
combus-
tible
Inert
gases
tive
heat
value,
(CO)
gases
Btu/cu
ft
Coke oven gas
30.3
49.2
5.5
3.2
11.8
555
Water gas
0 6
47 9
42.3
9 2
299
Enriched water gas. . . .
12 4
35.4
31.6
10.3
10.3
574
Producer gas
1 8
14.4
26.3
1.0
56.5
155.6
Natural gas ....
90.0
8.8
1.2
1110
Blast-furnace gas
1.0
26.0
73.0
87
Bottled fuel gas ("Pyro-
fax")
100
2509
PROPERTIES OF THE GASES IN THE AIR*
Name
%
by volume
Boiling
point, °C
Freezing point,
°C
Atomic
weight
Helium ....
0.0004
-268.9
-268.9 (140 atm)
4
Nitrogen
78.0
-195
-214
14
Oxygen
Neon
21.0
0.0012
-182.5
-245.9
-227
-248.7
16
20.2
Argon
0.94
-185.7
-189.2
39.91
Krypton
0.0005
-151.8
-169
82.9
Xenon
0 000006
-109.1
-140
130 2
Radon
- 61.8
- 71
222
* IDDLBS, H. A., J. A. FUNKHOUSER, and A. H. TAYLOR, Report, New England Association of Chem-
istry Teachers, vol. 35, Part 1, p. 21.
714
CHEMISTRY FOR OUR TIMES
I
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a
W)
J*
03
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IS "^
a» c
it
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APPENDIX
715
THE COMMON GASES*
Name
For-
mula
Com-
mercial,
purity
%
Melting
point,
°C
Boil-
ing
point,
°C
Density,
g /liter,
STP
Solubil-
ity in
cold
water
1 Ammonia . . .
NH3
99
- 77 7
- 33 4
0 77
vs
2. Argon
A
99
-189.2
-185.7
1.78
88
3. Butane (normal) . .
4. Carbon dioxide ....
5. Carbon monoxide . .
6 Chlorine
C4HlO
C02
CO
C12
99
99
99 5
-135
- 56.5
-207
-101.6
- 0.5
- 78.2
-192
- 34 6
2.60
1.97
1.25
3 22
88
ms
88
ms
7. Ethane
C2H6
95
-171.4
- 89 5
1 35
88
8 Ethyl chloride ....
C2H6C1
99 5
-141.6
14 0
{Liquid
0 92
88
9. Ethylene
10 Freon
C2H4
CCl2F->
98
-169
-102.7
- 29 2
g/ml
1.26
1 49
SS
ss
1 1 Helium
He
98
-272 2
— 268 9
0 18
SS
12. Hydrogen
H2
99.8
-258.9
-252.7
0.09
ss
13. Hydrogen chloride.
14. Hydrogen sulfide. .
15. Isobutane
HC1
H2S
^ 4 Jtl 1 0
97.5
99.9
98
-112
- 83
-145
- 83.7
- 60.2
- 10.2
1.64
1.54
2.61
vs
ms
ss
16. Methane
CH4
92 or 99
-184
-161.5
0 72
ss
17. Nitrogen
N2
99 8
-309.9
-195.8
1.25
ss
18. Nitrous oxide .
No()
98
-102.4
-89.4
1.98
ms
19. Oxygen ....
O,
99.5
-218.4
-183.0
1.43
ss
20. Phosgene
con 2
99.5
-104
8.3
{Liquid
1.39
Decom-
21. Propane
C%H8
99.9
-189 9
-44.5
g/ml
2.01
poses
88
22. Sulfur dioxide
S02
99.5
- 72.7
- 10.1
2.93
VS
* Data supplied chiefly by The Matheson Company, East Rutherford, New Jersey. Used by permis-
sion.
vs — very soluble, ms « moderately soluble, ss = slightly soluble.
716
CHEMISTRY FOR OUR TIMES
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Vegetables :
Bamboo shoo
Beans, dried.
Beans, green.
Beets
Carrots
Celery
Corn (green).
Cucumbers . .
Lettuce
Mushrooms. .
Onions
Peas (green).
Peppers, greei
Potatoes, swe
Potatoes, whi
Sauerkraut. . .
Spinach
Tomatoes . . .
Turnips
Turnip greens
APPENDIX
717
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Fruits:
Apples
Bananas
Dates, dried.
Figs, dried . .
Grapefruit . .
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nuts .
t
uts:
Almon
Brazil
Cocon
718
CHEMISTRY FOR OUR TIMES
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APPENDIX
719
FACTS ABOUT COMMON SUBSTANCES
Solubility
"
Formula
Common name
Melting point,
°C
Boiling point,
°C
in 100 g.
water,
Use
20°C
g
AlClg
190at371b/in.2
Sublimes at
46
Catalyst
177.8
Ai2(SO4)s-18H2O
Decomposes at
36
For clearing
86.5
water
(NH4)2CC>3-H2O
Decomposes at
100
In smelling
58
salts
NHiCl
Sal ammoniac
Decomposes at
Sublimes at 520
37
In dry cells
350
NHiOH
Ammonia water
-77
Unstable
Kitchen cleaner
NH4NO3
169.6
Decomposes at
192
In explosives
210
(NH4)2SO4
Decomposes at
76
Fertilizer
100
SbCh
73.4
223
999
As2O»
Sublimes at 193
Highly
Making insecti-
insoluble
cides
BaCla»2H?O
-2H2O at 113
36
Laboratory test
for SO 4~ ~
BaSO4
Bante
1580
Highly
In paints
insoluble
BiONO
Bismuth oxvni-
Decomposes at
Highly
In medicine
tratc or bis-
260
insoluble
muth subivi-
trate
HsBOs
Boric acid
Decomposes at
6
Antiseptic
185
CaCOa
Precipitated
Decomposes at
Highly
.Mild abrasive
chalk
825
insoluble
CaCla
772
Above 1600
73
Dehydrating
agent
CuCl (Ou2Cla)
422
1366
1
CuClt
498
Decomposes to
75
CuaCh at 993
CuSOi
200
Decomposes to
21
CuO at 650
CuSO4'5H2O
Blue vitriol
-4H2O at 110
-5H2O at 150
21
Electrolyte for
copperplating
It
114
183
Highly
Antiseptic
insoluble
FeCU
670
66
FeClt
282
315
92
Etching in met-
allurgy, wa-
ter purifica-
tion
FeSOr7HaO
Green vitriol or
-6H2O at 100
-71I2O at 300
27
Kills weeds
copperas
Pb(CaHiO2)a-3H2O
Sugar of lead
75
280
46
PbCla
501
950
1
— HaO — loses water.
780
CHEMISTRY FOR OUR TIMES
FACTS ABOUT COMMON SUBSTANCES.— (Continued)
Formula
Common name
Melting point,
°C
Boiling point,
°C
Solubility
in 100 g.
water,
20°C
g
Use
PbCK>4
•
844
Decom poses
Highly
Chrome yellow
PbO
Litharge
888
insoluble
Highly
pigment
Pigment, yel-
Pb»O4
Minium
Decomposes at
insoluble
Highly
low
Pigment, red
PbOi
Lead dioxide
500
Decomposes at
insoluble
Highly
Oxidizing
LiCl
290
613
1353
insoluble
79
agent: posi-
tive plate in
battery
In air-condi-
MgS04-7HiO
HgtCh
HgCU
HgO
Epsom salts
Calomel
Corrosive sub-
limate
-6H2Oat 150
302
276
Decomposes at
-7H*0 at 200
383.7
302
34
Highly
insoluble
7
Highly
tioning equip-
ment
Purgative
Medicine
Antiseptic
Historic com-
HgS
Cinnabar ver-
100
Sublimes at
insoluble
Highly
pound
Ore of Hg* pig-
milion
583.5
-SO a at 840
-6HaO at 103
insoluble
38
ment
For nickel-plat-
563
Sublimes at 347
Decom-
ing
Dehydrating
KBr
730
1380
poses
65
agent
In photography
KiCOa
KClOa
KC1
K»CrO4
Potash
Chlorate of pot-
ash
Sylvite
Chromate of
891
368.4
776
968.3
Decomposes
Decom poses at
400
Sublimes at
1500
111
7
34
62
Fertilizer
Preparation of
oxygen
Fertilizer
IAnticorrosion
KjCnO?
KCN
potash
Dichromate of
potash
Cyanide of pot-
398
634.5
Decomposes at
500
agents in ra-
diators of
automobiles
For casehard-
KF
KOH
KI
KMnO<
ash
Caustic potash
880
360.4
678
Decomposes at
1500
1320
1420
92
112
144
g
ening
To make soft
soap
In iodized salt
Strong oxidiz-
KNOB
KsS04
Saltpeter
240
334
1076
Decomposes
400
32
11
ing agent
In corned-beef
brine
KH804
210
Decomposes
51
- HsO •* loses water.
APPENDIX
721
FACTS ABOUT COMMON SUBSTANCES.— (Continued)
Formula
Common name
Melting point,
°C
Boiling point,
°C
Solubility
in 100 g.
water,
20°C
g
Use
SiC
Carborundum,
Above 2700
Sublimes 2000,
Highly
Abrasive
Crystalon
decomposes at
insoluble
2210
SiOs
Quartz
1710
2230
Highly
Making glass
insoluble
AgCl
455
1550
Highly
Test com-
insoluble
pound; in
photography;
photosensitive
AgNO.
Lunar caustic
212
Decomposes at
222
Antiseptic
444
NasBiOT'lOHjO
Borax
-8HzO at 60
- lOHjO at 200
2.8
Water softener;
making glass
NaBr
742
1390
90
Sedative in
medicine
Na«COi
Soda ash
851
Decomposes
22
In scouring pow-
ders; water
softener
NaaCOi-lOHtO
Washing soda
32.5
-H2O at 33.5
22
Water softener
NaHCO«
Baking soda
-COj at 270
10
Leavening
agent in dough
NaCl
Common salt
801
1413
36
Preservative
NaF
980
1700
4
Insecticide
NaOH
Caustic soda,
318.4
1390
109
Making soap
lye
Nal
651
1300
179
NatSOrlOHiO
Glauber's salt
Decomposes at
19
Horse medicine
32.4
SrCli
873
53
Gives red flame
SnClt
' ' ' , ' ' '
Decomposes at
231
ide
50
SnCh
Stannic chloride
37.7
Decomposes
Mordant in
dyeing
ZnCh
262
732
368
Wood preserva-
tive
ZnSO4-7HiO
White vitriol
-7HsO at 280
54
— HaO — loses water.
722
CHEMISTRY FOR OUR TIMES
THE MORE COMMON ELEMENTS
Name
Symbol
Atomic
number
Approximate
atomic weight
Electron ,
arrangement
Combin-
ing num-
ber(s)
(valence)
Aluminum . . .
Al
13
27
•2)8)3
3
Calcium
Ca
20
40
•2)8)8)2
2
Carbon
c
6
12
•2)4
4 (2)
Chlorine
Cl
17
35.5
/
•2)8)7
1 (3, 5, 7)
CoDoer ....
Cu
29
63.6
**/"/ •
•2)8)18^1
1,2
**/ *-*/ i
Hydrogen. . . .
H
1
1
•1
1
Iron
Fe
26
56
•2)8)l4)2
2,3
Magnesium. .
Mg
12
24
•2)8)2
2
Mercury
Hg
80
200
•2)8)18^32)18 \2
1, 2
o
I** f ^J • v«« m a.v .«.
Nitrogen. . . .
N
7
14
•2)5 /
3,5
Oxygen
0
8
16
•2)6
2
Phosphorus. .
P
15
31
** f \f
•2)8)5
3,5
Potassium . . .
K
19
39
•2)8)8)1
1
Silver
Ag
47
108
•2)8)l8^18 |1
1
o
**/ '•'/ I j
Sodium
Na
11
23 -
•2)s)l
1
Sulfur
S
16
32
•2)8)6
2, 4, 6
Zinc
Zn
30
65
*'/*-'/ ^
•2)8)18)2
2
APPENDIX
783
The following elements are not included in the table of interna-
tional atomic weights, for if these exist in nature they have never been
found in amounts sufficient for an experimental determination of their
atomic weights: 43 (masurium); 61 (illinium); 84 (polonium); 85, 87, 89
(actinium), 93, 94, 95, 96.
INTERNATIONAL ATOMIC WEIGHTS— 1943*
Name
Symbol
Atomic
number
Atomic
weight
Name
Symbol
Atomic
number
Atomic
weight
Aluminum
Al
13
26.97
Molybdenum
Mo
42
95 95
Antimony .
Sb
51
121.76
Neodymium
Nd
60
144 27
Argon
A
18
39 944
Neon
Ne
10
20 183
Arsenic
As
33
74 91
Nickel
Ni
28
58 69
Barium
Ba
56
137.36
Nitrogen
N
7
14 008
Beryllium
Be
4
9 02
Osmium
Os
76
190 2
Bismuth . .
Bi
83
209 . 00
Oxygen
o
8
16 0000
Boron
H
5
10 82
Palladium
Pd
46
106 7
Bromine
Br
35
79 916
Phosphorus
P
15
30 98
Cadmium
Cd
48
112 41
Platinum
Pt
78
195 23
Calcium
Ca
20
40 08
Potassium
K
19
39 096
Carbon
c
6
12.010
Praseodymium
Pr
59
140 92
Cerium
Ce
58
140. 13
Protactinium
Pa
91
231
Cesium
Chlorine
CH
Cl
55
17
132.91
35 457
Radium
Radon
Ra
Rn
88
86
226.05
222
Chromium
Cr
24
52 01
Rhenium
Re
75
186 31
Cobalt
Co
27
58 94
Rhodium . ....
Rh
45
102 91
Columbium
Cb
41
92 91
Rubiditfm
Rb
37
85 48
Copper
Cu
29
63 57
Ruthenium
Ru
44
101 7
Dysprosium.
Dy
66
162.46
Samarium
Sm
62
150 43
Erbium
Er
68
167.2
Scandium
Sc
21
45.10
Europium
Fluorine ... ....
Eu
F
63
9
152.0
19.00
Selenium. ...
Silicon
Se
Si •
34
14
78.96
28 06
Gadolinium
Gd
64
156 9
Silver
Ag
47
107 880
Gallium . . .
Ga
31
69.72
Sodium. . .
Na
11
22 997
Germanium
Ge
32
72.60
Strontium. .
Sr
38
87 63
Gold
Au
79
197 2
Sulfur
s
16
32 06
Hafnium
Helium
Holmium
Hf
He
Ho
72
2
67
178.6
4.003
164 94
Tantalum
Tellurium. .
Terbium
Ta
Te
Tb
73
52
65
180 88
127.61
159 2
Hydrogen
H
1
1 0080
Thallium . .
Tl
81
204 39
Indium
Iodine
Iridium
Iron
In
I
Ir
Fe
49
53
77
26
114 76
126.92
193.1
55 85
Thorium. . .
Thulium. . . .
Tin
Titanium
Th
Tm
Sn
Ti
90
69
50
22
232.12
169.4
118.70
47 90
Krypton
Lanthanum
Kr
La
36
57
83.7
138 92
Tungsten
Uranium. . . .
W
u
74
92
183.92
238 07
Lead . .
Pb
82
207 21
V an adiu m
V
23
50 95
Lithium
Li
3
6 940
Xenon
Xe
54
131 3
Lutecium
Magnesium
Manganese . .
Lu
Mg
Mn
71
12
25
174.99
24.32
54 93
Ytterbium.. .
Yttrium
Zinc
Yb
Y
Zn
70
39
30
173.04
88.92
65 38
Mercury
Hg
80
200 61
Zirconium
Zr
40
91 22
* From the Journal of the American Chemical Society.
INDEX
A
Abel, John J., 613
Abrasives* 251
aluminum oxide, 314
diamond, -317-319
emery, 314
silicon carbide, 251
Absolute temperature scale, 118,
701-703
Abundance of elements, 20
Acetate rayon, 601
Acetic acid, 554-555
Acetone, 557
Acetylene, 252, 530
Acids, 167, 216-219, 222-226
anhydrides, 216
dibasic, 218
monobasic, 218
naming of, 164, 167-168
organic, 553-555
Adrenalin, 563, 613
Adsorption, 263
Age of alloys, 436
Air, 35-51
composition of, 38
density of, 37
liquid, 38, 41, 44
supporter of combustion, 53-79
Alchemy, 16
Alcohol, 514-524
butyl, 521
denatured, 209, 520
ethyl, 209, 517-520
as gasoline substitute, 541
grain, 517
methyl, 516
propyl, 521
rubbing, 520
wood, 516
Aldehydes, 556
Alkali metals, 245-246, 323
group la, 329
Alkalies, 215
Alkaline earth metals, 246, 459-466
group Ha, 329
Allergies, 621
Allotropic forms, 334
Alloys, 25
aluminum, 449, 456
antimony, 338
beryllium, 465
bismuth, 338
copper, 476, 478, 482
in electrochemical series, 493
135, gold, 482, 670
lead, 470
magnesium, 461
mercury, (amalgams), 664
nickel, 485-486
silver, 666
steel, 443
tin, 473
zinc, 476
Aliiico magnets, 486
Alpha particles, 184, 641
Aluminum, 450-459
Alummum alloys, 449, 456
Aluminum ores, 452
Alums, 315
Aluiiitc, 452
Amalgams, 664
Amatol, 632
Amethyst, 396
Ammonia, 386-392
complex ions with, 391
nitric acid from, 362
nitridirig with, 445
oxidation of, 362
test for, 390
Ammonia fountain, 389
Ammonium compounds, 392
Ammonium hydrogen carbonate, 376
Ammonium ions, test for, 390
Ammonium nitrite, 44
Ammonium sulfate, 290, 354, 527
Amorphous materials, 132
Analysis, 23
Analytical chemistry, 677
Anderson, C. D., 183
Anesthetic, 367, 513, 559
Anhydrous powder, 114, 204
Aniline, 584
Anode, 240
725
726
CHEMISTRY FOR OUR TIMES
Anodic oxidation, 248
Anodizing, 248
Anthracene, 583, 585
Anthracite coal, 546, 547
Antifreeze mixtures, 209, 519-520
Antiknock compounds, 539-540
Antimony, 337
Antiseptics, 611
Aquafortis, 361
Aqua regia, 363, 670
Arc process, nitrogen fixation, 362
Argon, 47
Aristotle, 15
Aromatic hydrocarbons, 584-580
Arrhenius, Svante August , 236
Arsenic, 336
Arsenic sulfide, colloid, 261
Asbestos, 459
Ascorbic acid, 594
Asphalt-base oils, 534
Aston, F. W., 147, 186
Atmosphere, 35-39
Atom, 97
Atomic bomb, 648
Atomic disintegration, 639-650
Atomic energy, 645, 648
Atomic structure, J 7&-1 97, 641-648
Atomic theory, 139, 141
Atomic weights, 146, 328, 723
Atoms, 97, 141
nuclei of, 181
Attractive force, 122
Avogadro, Amadco, 139
Avogadro's hypothesis, 139-141
Avogadro's number, 96
Azunte, 479
B
Bacon, Francis, 18
Baekeland, Leo Hendrik, 571
Bagasse, 596
Bainbridge, K. T , 147
Bakelite, 571
Baking soda, 378
Bases, 215
dissociation of, 221
strong, 221
weak, 221
Basic oxides, 226
Basic salts, 233
Batteries, dry cell, 241
storage, 12, 241
Bauxite, 452
Bearing metal, 470
Bechcr, 53
Becquerel, Antoine Henri, 639
Beehive coke oven, 526
Beeswax, 562
Benedict's solution, 563
Benzaldehyde, 557
Benzene, 583
Benzine, 537, 584
Beryl, 465
Beryllium, 465
Berzelius, Jons Jakob, 111, 146, 153
Bessemer steel, 435, 437-438
Beta particles, 641
Bicarbonate of soda, 378
Biot, 137
Bismuth, 337
Bismuth subnitrate, 338
Bitter almonds, oil of, 557
Bituminous coal, 546, 547
Black, Joseph, 54, 71
Blast furnace, 430-433
Bleaching agent, 348
Bleaching powder, 304
Blister copper, 479
Blooming mill, 441
Blueprints, 660
Bohr theory, 187-189
Boiler scale, 110, 607
Boiling, process of, 126
Boiling point of liquids, 127
of solutions, 208
Bond, covalont, 190
ionic or electrovalont, 190
Bonds, double, 513, 577, 584
single, 513
triple, 513
Bone black, 597
Borax, 314
Borax-bead test, 403, 712
Boric acid, 315
Bosch, Karl, 387
Boyle, Robert, 6, 17
Boyle's law, 118, 701
Brass, 476
Breathing, 53-70
Bredig, 262
Brick, common, 400
British thermal unit, 527
INDEX
Bromine, 272, 306, 307
Bronze, 473
Bronze age, 478
Brown coal, 546
Bunsen, Robert Wilhelm, 531
Bunsen burner, 531
Burette, 223
Burning, 53-70
Butadiene, 578
Butter, 560
Butyric acid, 555
By-product coke oven, 526-527, 548
C
Calcite, 379
Calcium carbide, 252
Calcium carbonate, 72, 379-385, 607
Calcium chloride, 377-378
Calcium cyanamide, 388
Calcium hydrogen carbonate, 381
Calcium hydroxide, 384
Calcium hypochlorite, 304
Calcium oxide, 382
Calcium phosphate, 200, 252, 291-292,
333, 368
Calcium silicate, 407, 409, 432
(/ale illations, based on gas laws, 701-709
English units, 424
formulas, 156-161
metric system, 697-699,
molecular weights, 156-161
normal solutions, 709-712
percentage composition, 159
temperature conversions, 700-701
weights and volumes, 418-425
Calgon, 608
Caliche, 290
Calorie, 129, 592
Calx, 53
Cane sugar, 518, 596
Canned heat, 269
CannizzarOj Stanislao, 146
Carbohydrates, 592
Carbon, forms of, carbon black, 577
charcoal, 548
coke, 527
diamonds, 313, 317-319
graphite, 251
as reducing agent, 252, 280, 430-
432, 468, 474
Carbon compounds, organic, 509-521
Carbon dioxide, 35, 37, 57, 70, 71-78, $78
solid, 72-73
test for, 76
Carbon dioxide recorder, 76
Carbon disulfide, 252
Carbon monoxide, 77, 544
Carbon monoxide detector, 545
Carbon tetrachloride, 57, 252
Carborundum, 251
Carboxyl group, 514
Carnallite, 459
Carnauba wax, 561
Carotene, 593
Cassiterite, 471
Cast iron, 434
Castner, Hamilton F., 451
Catalyst, 42, 67, 229, 286, 349, 517-518,
562-563, 654, 672
Cathode, 240
Cavendish, Henry, 46, 82
Cell, electrical, 241
storage battery, 12, 241
Cellophane, 568
Cells, dry, 241
Celluloid, 571
Cellulose, 547, 565
Cellulose acetate, 572
Cellulose xanthate, 567
Colotcx, 596
Cement, 405-408
Ceramic industries, 400-404
Cevitamic acid, 594
Clwdurick, J., 182
Chalcocite, 479
Chalcopyrite, 479
Chalk, 382
precipitated, 382
Chamber process, 350-352
Charcoal, 548-549
Chemical actions, 227-236
extent of, 229
starting, 234
Chemical calculations, 156-161, 417-424,
697-712
Chemical change, 27, 171
energy changes in, 233
kinds of, 227
combination, 227
decomposition, 227
displacement, 228
double replacement, 228
replacement, 228
728
CHEMISTRY FOR OUR TIMES
Chemical change, kinds of, reversible,
231-233
rate of, 64-69, 234
Chemical engineering, 678
Chemical equilibrium, 228-235
Chemical industry, employment in, 679
Chemical properties, 58
Chemistry, animal, 553
in peace, 632-634
physiological, 612
plant, 553
science of, 11
training in, 675-679
in war, 625
Chile saltpeter, 290, 361, 633
Chloride ions, 358
test for, 359
Chlorides, insoluble, 359
Chlorinated lime, 304
Chlorine, 302-305, 627
Chloroform, 252
Chlorophyll, 71, 654
Chrome alum, 316
Cinnabar, 276, 663
Cinnamic aldehyde, 557
Cinnamon, oil of, 557
Citric acid, 555
Clay, 400, 452
Clothing, 600-601
Coagulation, 265
Coal, anthracite, 546, 547
bituminous, 546, 547
destructive distillation of, 525
Coal gas, 525-527
Coal tar, 527, 581-586
Cohesion, 122
Coke, 252, 280, 430-432, 468 474, 526,
548,583
Coke ovens, beehive, 583
by-product, 526, 583
Cold cream, recipe, 713
Collagen, 200
Colloidal dispersions, 200, 262
Colloids, 259-269
electrostatic precipitation of, 265
ferric hydroxide, 261
protective, 268
surface of, 263
Combining number, 163
Combustion, 53-63
danger from, 618
from incomplete, 544-546, 622
Combustion, rate of, 64-67
spontaneous, 68-69
Common substances, facts about, 719-
721
Compounds, 21-23
saturated, 513
unsaturated, 514
Condensation, 123
Conductors, 239
Confucius, 9
Constant composition, law of, 21
Copper, 478-483
alloys of, 482
metallurgy of, 479
ores of, 478-479
test for, 483
Cordite, 630
Corrosion, 491-503
Corundum, 314, 452
Cosmetics, 613-615
Cottrell, F. G., 265
Co valence, 191
coordinate, 192
Cracking of petroleum, 537
Cream of tartar, 555
Crucible steel, 439
Cryolite, 452
Crystalline, 132
Crystals, 313-319
Crystolon, 251
Cupric oxide, 481
Cuprite, 479
Cuprous oxide, 481
Curie, Irene, 647
Curie, Marie Sklodowska, 1, 639
Curie, Pierre, 1, 639
Cycle, carbon dioxide-oxygon, 70
nitrogen, 287
Cyclopropane, 513
D
Dakin's solution, 304
Dalton, John, 141, 153-154
Davy, Sir Humphry, 245, 459
Degree of ionization, 218
Deliquescence, 104
Denatured alcohol, 209, 520
Density, review of, 197
Dentrif rices, 615
Detonation, 629
Deuterium, 97, 185
INDEX
729
Deuteron, 195
Dextrin, 598
Dewar, James, 47
Diamonds, 317-318
Diastase, 517, 562
Diffusion, 39, 96
Dilute, 205
Displacement, 228
Dissociation in solutions, 218
Distillation, 107
destructive, 526
fractional, 207, 537, 582
Dobereiner, Johann Wolfgang, 322
Dolomite, 380
Dolomitic limestone, 459
Double bond, 513
Double decomposition, 228
Double exchange, 228
Double replacement, 228
Dowmetal, 461
Dry cell, 243
Dry cleaning, 610
Dry Ice, 73
Dry-Ice generators, 73
Dumas , Jean Baptiste A mh6, 1 1 1
Duralumin, 449, 456
Dust, irritating, 621
Dust explosions, 66, 623
Dynamite, 364, 630
E
Earth, diatomaceous, 398
infusorial, 398
whole, composition of, 20
Earth's crust, 273
composition of, 20
humus, 285
soil horizons, 285
Effervescence, 72, 203
Efflorescence, 114
Elastomer, 579
Electric furnace, 249, 253, 440
arc furnace, 250
induction type, 254
Electrochemical cells, 242-249
Electrochemical series, 89, 228, 493
negative iojis, 308
Electrochemistry, 23^-254
Electrodeposition of metals, 245
Electroforming, 247
Electrolysis, 199, 239-249
of water, 83
Electrolyte, 240
Electron, 179-181
Electron microscope, 260, 642
Electron shells, completed, 188
Electrons, arrangement of, 183-187
transfer of, 194, 503
Electroplating, 245
Electrorefining, 247
Electrotyping, 483
Electro valence, 190
Elements, 19-21
common, list of, 722
definition of, 17, 643
synthesis of 93, 94, 95, 96, 647-650
transmutation of, 645-648
Emeralds, 313
Emory, 314
Emulsion, 260
Enamelware, 404
Endothormic process, 203, 234
Energy, 11-13
changes in form, 128-134
conversion of matter to, 645, 648
omlothermic reactions, 234
exothermic reactions, 234
from fuels, 538
Enzymes, 517, 562-563
Equations, 171-175
balancing of, 174
calculations based upon, 418-424
complete meaning of, 417
limitations of chemical, 172
volume relationships of, 423
weight relationships of, 418
English units, 424
weight-volume relationships of, 420
writing of, 173
Equilibrium, chemical, 228-233
effect of catalyst on, 229
of concentration on, 230
of pressure on, 229
of temperature on, 229
dynamic, 210-211
Ergosterol, irradiated, 595
Esterification, 515
Esters, 559
Ethanol, 209, 518
Ethers, 514, 558
Ethyl acetate, 559
Ethyl alcohol, 209, 517-520
730
CHEMISTRY FOR OUR TIMES
Ethyl butyrate, 560
Ethyl ether, 558
Eudiometer, 110
Evaporation, 124
cooling by, 125
Exothermic process, 203, 234
Experiment, reproducible, 7
Explosive mixtures, 618-619
Explosives, 628-632
amatol, 629
atomic bomb, 648
cordite, 630
dynamite, 630
gunpowder, 628
high power, 629
liquid oxygen, 43
nitrogen in, 45
nitroglycerin, 629
Extinguisher, fire, 75 .
F
Face creams, 614
Faraday, Michael, 584
Fats, 560-561, 592
Feldspar, 400
Fermi, Enrico, 647
Ferric hydroxide, colloid, 261
Fertilizers, 285-295
Filtration, 106
Fire, 55, 57
Fire extinguisher, 74
Firefly, 654
Fireproof substances, 69
Fischer, Emil, 592
Fission, atomic, 648
Fixation of nitrogen, 45, 290-291, 362,
633
Flame tests, 712
Flames, colored, 619
Flotation of ores, 278
Fluorine, 300
Flip, 279, 432
Foam, 260
Foods, 591-598
composition of, table, 716-718
energy measurement of, 592
fuel value of, table, 716-718
for plants, 286-294
requirements, 593
Formaldehyde, 556
formalin, 557
Formic acid, 544, 553, 555
Formulas, writing and naming, 153-161
how to write, 164
percentage composition and, 159
true molecular, 159
Fractional distillation, 207, 537, 582
Frasch, Herman, 341
Frasch process, 341-344
Freezing point, definition of, 208
lowering of, 208-210
Freon, 331
Fuel gases, 713
Fuels, 525-551
fossil, 546
motor, 532
smokeless, 548
Furnace, blast, 430-433
electric, 440
glass, 409
open hearth, 438-439
reverberatory, 479
Fusible alloy, 337
G
Galena, 467
Galilei, Galileo, 117
Galvanized iron, 475, 496
Gamma rays, 641
Gangue, 277
Gas, coal, 526-529
natural, 529
producer, 529
Gas warfare, 625-628
Gases, in air, 35-52
properties of, 713
common, properties of, 715
kinetic molecular theory of, 96
state of matter, 26
Gasoline, 532-542
antiknock, 539
burning of, 541
dangers of, 542
octane number of, 538
polymer, 538
substitutes for, 541
Gas- volume corrections, 701-709
laws of, 117-120
Gay-Lussac, 137
Gels, 269
Gentian-violet dye, 612
INDEX
731
Glass, 408-414
borosilicate, 412
colored, 412
optical, 412
plate, 410
safety, 413
window, 409
Glass blocks, 414
Glass bottles, 410
Glass cloth, 413
Glass furnace, 409
Glauber's salt, 317
Glucose, 597
Glycerin nitrate, 364
Glyceryl butyrate, 560
Glyceryl oleate, 560
Glyceryl palmitate, 561
Glyceryl stearate, 560
Gold, 668-671
Goldschmidt, Hans, 456
Goldschmidt process, 455
Goodyear, Charles, 576
Graham, Thomas, 259
Grain alcohol, 517
Gram -molecular volume, 148
weight, 149
Graphite, 251
colloidal, 268
Gravimetric synthesis, 112
Guayule, 577
Gunpowder, 628-632
Gypsum, 315
H
Haber, Fritz, 387
Haber process, 387
Holes, 39
flail, Charles Martin, 450
Halogens, 300
comparisons of, 309
group VI Ib, 300, 329
tests for, 308
Hard water, 110, 605-609
permanent, 607-609
softening of, 606-609
temporary, 606-607
Hardness scale, 317
Health, 611-613
Heat, of formation, 235
of fusion, 131
measurement of, 129
Heat, of vaporization, 131
Heavy chemicals, acid, 343-372
basic, 373-394
Heavy hydrogen, 98
Heavy metals, 330, 467-487
Heavy water, 185
Helium, 48-50
alpha particles, 184, 641
structure of atom of, 183
Hematite, 430
fltroultj Paul Louis Toussaint, 450
Hormones, 563
Household bleach, 304
Hydration, 1 13, 204
Hydrocarbons, 510, 534-539
saturated, 513-514
unsaturated, 513-514
Hydrochloric acid, 72, 358-360
Hydrogen, 81-98, 528-530
Hydrogen chloride;, 357-359
Hydrogen ion, 182
Hydrogen peroxide, 248
Hydrogen sulfide, 355-357
Hydrogenation, of fats, 95
of petroleum products, 95, 533, 541
Hydrolysis, 232-233, 609-610
Hydroniurn ion, 218
(See also Hydrogen ion)
Hydroponics, 294
Hydroxides, 112, 167, 219
Hypochlorous acid, 304
I
Ice, 26, 102-104, 130, 132
Dry, 73
Ignition, spontaneous, 68
Impurities, 24
Incendiary bomb, 463
Indicators, 219
Indigo, 22
Industrial chemistry, 678
Inert gases, 46-51
zero group of, 329
Ingots, steel, 441
Insoluble substance, 202
Insulin, 563, 612
Invar, 485
Invertase, 562
Iodine, 307
sublimation of, 308
tincture of, 611
732
CHEMISTRY FOR OUR TIMES
lonization phenomena, 215-236
electricity and chemistry, 179-183,
239-249
Ion-exchange resins, 608
Ionic lattices, 189, 195
Ions, 179-183, 215-236, 239-249
hydrogen, 182 '
hydronium, 218
replacement of negative, 308
Iron, ores of, 430
passive, 497
pig, 434
rusting of, 491
wrought, 436
Iron castings, 434-435
Iron and steel, 429-446
Iso-amyl acetate, 560
Isomers, 535
Isoprene, 577
Isotopes, 185-186
Janssen, 48
Jewett, Frank F., 450
Joliot, Fredei'ic, 647
Joliot, Irene Curie, 647
K
Kaolin, 400
Kekutt, Friedrich August, 584
Kelvin degrees, 118
Kerosene, 537
Ketones, 557-558
Kiln, for lime manufacturing, 380
for Portland cement, 407
Kilocalorie, 129
Kindling temperature, 55
Kinetic molecular theory, 95-97, 117-134
Krypton, 60
Lacquers, nitrocellulose, 566
Lactose, 597
Lake, 316
Langmuir, Irving, 650
Lanital, 601
Latex, 577
Laughing gas, 366-367
Lavoisier, Antoine Laurent, 29, 54
Law, Avogadro's, 139-141
Boyle's, 6, 118, 701
of combining volumes, 140
of conservation of matter, 27-29, 174
of constant composition, 21
Gay-Lussac's, 140 *
Gay-Lussac's (Charles), 118, 703-704
of mass action, 231
of multiple proportions, 143
of octaves, 322-323
periodic, 328
scientific, 6
Lawrence, E. 0., 647
Lead, 467-470
tetraethyl, 469
Lead acetate, 555
Lead azide, 629
Lead dioxide, 409
Lead poisoning, 468
Leather, tanning hides, 267
Legumes, nodules on, 288
Leonardo da Vinci, 39
Lewisite, 627
Liebig's apparatus, 107
Light, 653
(See also Radiations)
Light alloys, 461
Light metals, 449-466
Lignin, 573
Lignite, 546
Lime, 379-385
kiln for manufacturing, 380
quicklime, 382
slaked, 382
Limestone, 274, 379-385, 409, 430, 432
Limestone caves, 380
Lime water, 77, 384
Limonite, 430
Linoleic acid, 555
Lipstick, 614
Liquefaction of gases, 38, 47-48, 138
Liquid air, 38, 47
Liquids, 26, 1 17
boiling point of, 127
freezing point of, 208
Litharge, 469
Litmus, 216
Lubricating oil, 542
Lucite, 574
Lye, 373
INDEX
733
M
Magnesite, 459
Magnesium, 246, 459-464, 501
Magnesium carbonate, 275, 437, 459, 501
Magnesium chloride, 218, 298, 460, 502
Magnesium citrate, 555
Magnesium hydroxide, 463, 501
Magnesium ores, 459
Magnesium oxide, 194, 460, 462
Magnesium sulfate, 298, 344, 459, 501
Magnetite, 430
Malachite, 479
Manganese, in steel, 437, 442, 443
Manganese dioxide, 42, 248, 302, 306, 307
Marble, 72
Mass action, principle of, 231
Matches, 335
Matte, 479
Matter, 11-17, 29
law of conservation of, 27-29
states of, 26, 117-135
Mauve, 581
MayoWj 39
Medicines, 612
Melting point, 130
Mendeleyev, Dmitri Ivanovich, 321
Mercury, 663-666
Mercury fulminate, 629
Mercury oxide, 41
Metallurgy, 281-283
powder, 486
Metals, corrosion of, 491-503
heavy, 330, 467-487
less familiar, 663-673
light, 449-466
noble, 663*673
replacement series of, 89, 228, 493
transitional, 329-330
Methane, 50, 510, 515, 527, 529
Methanol, 209, 516
Method, scientific, 4
Methyl acetate, 555
Methyl alcohol, 209, 515, 516, 556
Methyl salicylate, 560
Methyl-methacrylate, 574
Metric system, 697-699
Meyer, Julius Lothar, 323
Midgley, Thomas, Jr., 7, 330
Mill, colloidal, 261
Minerals, 273-275
Minium, 469
Mirrors, by evaporation of metals, 253
silver, 668
200-in. telescope, 254
Mixtures, 24
Moissan, Henri, 250
Molal solutions, 208
Molar solutions, 206, 224
Molecular formula, 160, 172
Molecular motion, 120-123
Molecular weights, 147, 156
Molecules, 96
Monel metal, 484
Mordant, 316
Mortar, lime, 384
Moseley, H. J., 184, 326
Motor knock, 539
Multiple proportions, law of, 143
Muriatic acid, 358
Muscle Shoals plant, 388
Mustard gas, 627
N
Nail polish, 614
Naming compounds, 167
Naphthalene, 583, 585
Nascent gases, 304
Natural gas, 529
analysis of, 50
Neon, 50
Neoprene, 578
Neutrality, electrical, 181
Neutralization, 215, 222
Neutrons, 182, 644-649
bombardment with, 648
Neivlands, John, 322
Niacin, 594
Nichrome, 250
Nickel, 484-485
alloys of, 485
ores of, 484
in steel, 442-444
Nickel carbonyl, 485
Nickel-silver, 486
Nicotinic acid, 594
Nitrate ion, test for, 364
Nitrates, from lightning, 289
Nitric acid, 361-365
action of, on cellulose, 566-
on copper, 363, 481
on glycerin, 364
Nitric oxide, 365
734
CHEMISTRY FOR OUR TIMES
Nitriding, 445
Nitrocellulose, 572
Nitrogen, 44-45, 332
compounds of, 290, 361-367, 629
family of elements, 332
group Vb, 329
fixation of, 45, 290-291, 362, 633
Nitrogen dioxide, 365
Nitrogen tetroxide, 366
Nitrogen-fixing bacteria, 288
Nitroglycerin, 364, 629
Nitrous oxide, 367
Nobel, Alfred Bernhard, 364, 630
Noble metals, 663-671
Nomenclature, chemical, 167
Nonmetals, 19, 330
Normal solutions, 709
Noyes, W. A., Ill
Nucleus, atomic, 181-186, 641-648
Number, atomic, 184, 328
Nutrition, 591-598
Nylon, 574-575
O
Ocean (see Sea)
Octane, iso, 513
normal, 513
Octane number, 538
Octaves, law of, 322-323
Octyl acetate, 560
Oersted, Hans Christian, 450
Oil, lubricating, 542
Oil of vitriol, 349
Oil-well drilling, 533
mud in, 268
Oleic acid, 555
Oleum, 350
Open-hearth furnace, diagram of, 439
Orbits, electronic, 182, 187-189
Ores, 273-276
of aluminum, 452
of antimony, 337
of arsenic, 336
of beryllium, 465
of bismuth, 337
of copper, 478-479
of gold, 668-671
of iron, 430
of lead, 467
of magnesium, 459
of mercury, 276, 663
Ores, methods of treating, 276-281
of nickel, 484
of platinum, 671
of silver, 666
of tin, 471
of tungsten, 671
of zinc, 474
)rganic chemistry, 677
)rganic compounds, 509-521, 553-563
Oxalic acid, 553, 555
Oxidation, 95
burning, breathing, rusting, 53-80
Oxidation-reduction, 502-503
electron transfer, 194-195
Oxides, 60
Oxidizing agent, 95
Oxygen, 39-43
Palmitic acid, 555
Paper making, 507-508, 566
Paraffin-base oils, 534
Paraform candles, 557
Parker's process of silver production, 666
Particles, subatomic, 179-197
Passive iron, 497
Peat, 547
Penicillin, 612
Percentage composition, 159
Periodic classification of elements, 321-
332
Periodic law, 326
Periodic table, modern, 328
Perkin, William Henry, 581
Permalloy, 485
Pcrmutit, 607 *
Petroleum, 532-543, 637-638
Pewter, 473
pH, 224-225
acid-base measuring stick, 224
changes in, due to hydrolysis, 232-233,
609-610
scale, 225
values, for natural and manufactured
products, 225
for 0.1 N solutions, 712
Phenol, 583, 585, 61 1
Phenolphthalein, 219
Phlogiston theory, 53
Phosgene, 545, 627
INDEX
735
Phosphates, 200, 252, 291-292, 333,
368-369
hydrolysis of, 609
Phosphoric acid, 368
Phosphorus, 252, 333
allotropic forms, red and yellow, 334
Photochemistry, 655
Photography, 655-660
Photomicrograph, 283
Photosynthesis, 71, 286, 654
Physical change, 171
Physical chemistry, 677
Physical properties, 58
Piccard, 37
Pickling of metals, 354
Picric acid, 364, 630
Pig iron, 434
Placer mining, 668
Planetary electrons, 183
Plant food, 286-294
Plastics, 571-580
Platinum, 671
Plexiglas, 574
Plutonium, 649
Pneumatic trough, 42
Poison gases, 627
Polonium, 640
Polymer, 366
Polymerization, 366, 538
Porcelain, 402-403
Portland cement, 405-408
Positive ions, 181
Positron, 183
Potassium chlorate, 42
in matches, 335
Potassium hydroxide, 375
Pottery, 401
Powder metallurgy, 486
Precipitate, 76, 222, 231
Precipitation, 231
Cottrell, 26,5-266
Pressure change, effect of, 120
Priestley, Joseph, 40-41, 53, 54, 576
Primuline, 659
Producer gas, 529
Propanoic acid, 555
Properties, chemical, 25-29
physical, 25-29
Propionic acid, 555
Proteins, 592
Proton, 181, 186, 218, 237
in hydronium ion, 218
IJroton, from nitrogen nucleus, 645
Pulp, wood, 566
Pyridine, 586
Pyrite, 430
Pyroxylin, 572
Ptyalin, 563
Q
Quartz, 398
Quicklime, 382
Quicksilver, 663
Radiation, gamma, 642
radiant energy, effects of, 653-661
X-ray, 327, 639
Radicals, 162
organic, 511
Radioactivity, 48, 639-650
induced, 647
Radium, 50, 639
Radon, 50
Ramsay, William, 47
Rayleigh, Lord, 5, 47
Rayon, 567-569
aoetate, 572-573, 601
viscose, 567-569, 601
Red lead, 469
Reduction, 94, 194, 503
Refrigeration, 132-134
Replacement series, 89, 228, 493
negative ions, 308
Resin, 571
Respiration (see Breathing)
Reverberatory furnace, 479
Reversible actions, 88, 231-233
Ribofiavin, 594
Richards, Theodore William, 1, 147
Rocks, 274
Rosin, 572
Rozier, Pilatre de, 82
Rubber, 576-578
synthetic, 577
Rubies, 313
synthetic, 314
Rusting, 53-70
Rutherford, Ern&st, 44, 645
S
Saccharin, 585
Safety, 617-623
736
CHEMISTRY FOR OUR TIMES
Safety film, 572
Sal soda, 378
Salt, common (sodium chloride), from
dried sea beds, 274
from ocean water, 298-300
solution of, 208
use of, in food preservation, 598
in glazing earthenware, 400
in production of, chlorine, 302
hydrogen chloride, 302, 357-358
soap, 603
sodium hydrogen carbonate, 376-
378
sodium hydroxide, 373-374
Salt cake, 316
Salts, 189
formation of, 190, 192, 194-195, 222
naming, 164, 168
solutions of, 204-209, 226-233 .
structure of, 189
Salvarsan, 612
Saponification, 603
Sapphires, 313
synthetic, 314
Saturated compounds, 513
Saturated solutions, 206, 210-211
Scheele, Karl Wilhelm, 39, 44, 54
Sea water, 297-300
bromine from, 271-272, 306
magnesium from, 459, 464, 501
Siderite, 430
Silica, 396
Silica gel, 269
Silicate industries, 395-416
Silicon, 251
abundance of, 20
in pig iron, 434
in steel, 442
Silicon carbide, 251
Silicon dioxide, 396
Silicon tetrafluoride, 399
Silk, 601
Silver, 666-668
German, 486
Silver mirrors, 668
Single bond, 513
Slag, 432
Smeatorij John, 405
Smelting, 668
Smoke, 542
Smoke screens, 625
Soaking pit, 441
Soap, 603-606
Soda, 375-379
mild, 378
strong, 378
Soda ash, 375
Sodium, 451
action of, on water, 85-87
Sodium acetate, 555
Sodium benzoatc, 584, 598
Sodium carbonate, 375-379
Sodium chloride (see Salt)
Sodium hydrogen carbonate* (sodium
bicarbonate), 375-379
Sodium hydroxide, 373-375
Sodium hypochlorite, 304
Sodium metaphosphate, 608
Sodium metasilicatc, 399
Sodium sjearate, 603
Softening of water, 605-609
Soil, 285-295
Solder, 470
Solid fuels, 546-549
Solid solution, 25
Solids, 26, 117, 208
Solubility, 202
of common salts, 227
of common substances, table, 719-721
Solute, 201
Solutions, 201-212
acid and alkaline, 215-233
neutral, 225
saturated, 206, 210-211
supersaturated, 207
Solvay, Ernest, 375
Solvay process, 376-378
Solvent, 201
Soya, 573
Spectrum, 48
Spirits, 202
Stable compound, 83
StaM, 53
Stalactite, 381
Stalagmite, 381
Standard conditions, 118
Starch, 261, 597
Stas, Jean Servais, 147
Statue of Liberty, 482
Steafic acid, 555
Steel, 429-447
alloy, 441-445
Bessemer, 435, 437-438
crucible, 439
INDEX
737
Steel, electric furnace, 440
open hearth, 437-438
stainless, 443, 496-498
Stevens, Captain, 37
Storage battery, 12, 240-241
Stratosphere, 37
Structural formulas, 511, 535
Styron, 574
Subatomic energy, 645, 648
Sublimation, 73, 308
Substances, 21
common facts about, table, 719-721
Sucrose, 596
Sugar, cane, 518, 596
invert, 597
milk, 597
Sulfa compounds, 612
Sulfate ions, test for, 352
Sulfides, insoluble, 356
soluble, 357
Sulfur, 341-346
Frasch method, 341-343
monoclinic, 345
plastic, 345
rhombic, 345
Sulfur dioxide, 347-348
Sulfur trioxide, 349
Sulfuric acid, contact process, 349-352
lead-chamber process, 350
mixing with water, 204
uses of, 352-355, 357-358, 361, 364,
368
Sulfurous acid, 347
Sun, temperature of, 653
Supersaturation, 207
Symbols, alchemical, 153
atomic (Dalton), 154
chemical, 154-155
Synthesis, 23
T
Table, atomic-weight, 146, 723
periodic, 329
Talc, 459
Talcum powder, 614
Tartaric acid, 555
Temperature, absolute scale, 118, 135,
701-703
centigrade scale, 118, 135, 701-703
Fahrenheit scale, 135, 701-703
kindling, 55
Tetraethyl lead, 469
Theory, 6
atomic, 141
kinetic-molecular, 95
Thermit, 455-456
Thermoplastic, 571
Thermosetting plastics, 571
Thiamine, 594
Thomson, Sir J. J., 180, 182
Thyroxine, 563
Tin, 471-473
Tincture, 202
Titration, end point, 223
Tollen's solution, 668
Toluene, 583-584
Transmutation, 643, 645-648
TNT (trinitrotoluene), 585
Triple bond, 513
Triple point of water, 130
Triptane, 539
Tungsten, 671
Tyndall effect, 260
Type metal, 470
U
Unsstturated compounds, 513
Uranium, isotopes of, 648
radioactivity of, 639
use of, in piles for atomic energy, 650
Urea-formaldehyde, 574
Urey, Harold C., 185
Valence, 163
coordinate covalence, 192
covalence, 191
electrovalence, 190
formulas for remembering, 164
Vapor pressure, 125
of water, table, 709
Vinegar, 554
Vinylite, 574
Viriyon textiles, 574
Viosterol, 595
Viscose rayon, 601
Visual purple, 660
Vitamin content of various foods, table,
716-718
Vitamins, 593-596
Volumetric, 111
Vulcanization, 577
738
CHEMISTRY FOR OUR TIMES
w
War, causes of, 632
stakes in, 634
Watches, jewels, 314
Water, 101-116
of crystallization, 113
decomposition of, 85
distilled, 107
hard, 109, 605-609
impurities in, 105
maximum density of, 102
relation of, to hydrolysis, 232-233,
609-610
supplies of, city, 108
Water gas, 527
Water glass, 399
Waxes, 561-562
Welding, with Thermit, 455
Wells, Horace, 367
White lead, Dutch process, 499
Whitewash, 385
Wintergreen, oil of, 560
Wood, 547
Wood alcohol, 516
Wood pulp, 566
Wood's metal, 337
Wool, 601
Wrought iron, 436
X-ray spectra, 327, 639
Xenon, 60
Zein, 573
Zeolite clay, 607
Zeppelin, Count, 449
Zinc, 474-476
Zinc stearate, 606
Zymase, 562
THE MORE COMMON ELEMENTS
Name
Symbol
Atomic
number
Approximate
atomic weight
Electron
arrangement
Combin-
ing num-
ber (s)
(valence)
Aluminum . . .
Al
13
27
•2)8)?
3
Calcium
Ca
20
40
•2)8)8)2
2
Carbon
C
6
12
•2)4
4 (2)
Chlorine
Cl
17
35.5
1 (3, 5, 7)
CoDDer
Cu
29
63.6
•2)8/18) 1
1,2
Hydrogen. . . .
H
1
1 <"
•1 - ^
1
Iron
Fe
26
56
*2lc)l4ifi
2,3
Magnesium. .
Mg
12
24
•2)8)2 1
2
Mercury
He;
80 '
200
•2ffe)'l£^32Vl8^2
1 2
Nitrogen ....
•*•*&
N
7
14 i
,•2)5 k
7
3,5
Oxygen
o
8
16
•2)6
2
Phosphorus. .
P
15
31
•* j \j
•2)8)5
3,5
Potassium . . .
K
19
39
•2)8)s)l
1
Silver
Ag
47
108
•2)8) 18) is) 1
1
Sodium
Na
11
23
•2)8) 1
1
Sulfur
S
16
32
•2)8)6
2,4,6
Zinc
Zn
30
65
/ v^/
•2)8)18)2
i i
2
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