General Science | Page 2

recitations and laboratory experiments.
Practical laboratory work in connection with the study of this book is
provided for in my Laboratory Manual in General Science, which
contains directions for a series of experiments designed to make the
pupil familiar with the facts and theories discussed in the textbook.
I have sought and have gained help from many of the standard
textbooks, new and old. The following firms have kindly placed cuts at
my disposal, and have thus materially aided in the preparation of the
illustrations: American Radiator Company; Commercial Museum,
Philadelphia; General Electric Company; Hershey Chocolate Company;
Scientific American; The Goulds Manufacturing Company; Victor
Talking Machine Company. Acknowledgment is also due to Professor
Alvin Davison for figures 19, 23, 29, 142, and 161.
Mr. W.D. Lewis, Principal of the William Penn High School, has read
the manuscript and has given me the benefit of his experience and
interest. Miss. Helen Hill, librarian of the same school, has been of
invaluable service as regards suggestions and proof reading. Miss.
Droege, of the Baldwin School, Bryn Mawr, has also been of very great
service. Practically all of my assistants have given of their time and
skill to the preparation of the work, but the list is too long for
individual mention.
BERTHA M. CLARK.
WILLIAM PENN HIGH SCHOOL.

CONTENTS


CHAPTER
I.
HEAT
II. TEMPERATURE AND HEAT
III. OTHER FACTS ABOUT HEAT
IV. BURNING OR OXIDATION
V. FOOD
VI. WATER
VII. AIR
VIII. GENERAL PROPERTIES OF GASES
IX. INVISIBLE OBJECTS
X. LIGHT
XI. REFRACTION
XII. PHOTOGRAPHY
XIII. COLOR
XIV. HEAT AND LIGHT AS COMPANIONS
XV. ARTIFICIAL LIGHTING

XVI. MAN'S WAY OF HELPING HIMSELF
XVII. THE POWER BEHIND THE ENGINE
XVIII. PUMPS AND THEIR VALUE TO MAN
XIX. THE WATER PROBLEM OF A LARGE CITY
XX. MAN'S CONQUEST OF SUBSTANCES
XXI. FERMENTATION
XXII. BLEACHING
XXIII. DYEING
XXIV. CHEMICALS AS DISINFECTANTS AND
PRESERVATIVES
XXV. DRUGS AND PATENT MEDICINES
XXVI. NITROGEN AND ITS RELATION TO PLANTS
XXVII. SOUND
XXVIII. MUSICAL INSTRUMENTS
XXIX. SPEAKING AND HEARING
XXX. ELECTRICITY
XXXI. SOME USES OF ELECTRICITY
XXXII. MODERN ELECTRICAL INVENTIONS
XXXIII. MAGNETS AND CURRENTS
XXXIV. HOW ELECTRICITY MAY BE MEASURED
XXXV. HOW ELECTRICITY IS OBTAINED ON A LARGE SCALE

INDEX
GENERAL SCIENCE


CHAPTER I
HEAT
I. Value of Fire. Every day, uncontrolled fire wipes out human lives
and destroys vast amounts of property; every day, fire, controlled and
regulated in stove and furnace, cooks our food and warms our houses.
Fire melts ore and allows of the forging of iron, as in the blacksmith's
shop, and of the fashioning of innumerable objects serviceable to man.
Heated boilers change water into the steam which drives our engines on
land and sea. Heat causes rain and wind, fog and cloud; heat enables
vegetation to grow and thus indirectly provides our food. Whether heat
comes directly from the sun or from artificial sources such as coal,
wood, oil, or electricity, it is vitally connected with our daily life, and
for this reason the facts and theories relative to it are among the most
important that can be studied. Heat, if properly regulated and controlled,
would never be injurious to man; hence in the following paragraphs
heat will be considered merely in its helpful capacity.
2. General Effect of Heat. Expansion and Contraction. One of the
best-known effects of heat is the change which it causes in the size of a
substance. Every housewife knows that if a kettle is filled with cold
water to begin with, there will be an overflow as soon as the water
becomes heated. Heat causes not only water, but all other liquids, to
occupy more space, or to expand, and in some cases the expansion, or
increase in size, is surprisingly large. For example, if 100 pints of ice
water is heated in a kettle, the 100 pints will steadily expand until, at
the boiling point, it will occupy as much space as 104 pints of ice
water.

The expansion of water can be easily shown by heating a flask (Fig. I)
filled with water and closed by a cork through which a narrow tube
passes. As the water is heated, it expands and forces its way up the
narrow tube. If the heat is removed, the liquid cools, contracts, and
slowly falls in the tube, resuming in time its original size or volume. A
similar observation can be made with alcohol, mercury, or any other
convenient liquid.
[Illustration: FIG. 1.--As the water becomes warmer it expands and rise
in the narrow tube.]
Not only liquids are affected by heat and cold, but solids also are
subject to similar changes. A metal ball which when cool will just slip
through a ring (Fig. 2) will, when heated, be too large to slip through
the ring. Telegraph and telephone wires which in winter are stretched
taut from pole to