General Science.

by Bertha M. Clark.

PREFACE

This book is not intended to prepare for college entrance examinations; it will not, in fact, prepare for any of the present-day stock examinations in physics, chemistry, or hygiene, but it should prepare the thoughtful reader to meet wisely and actively some of life's important problems, and should enable him to pa.s.s muster on the principles and theories underlying scientific, and therefore economic, management, whether in the shop or in the home.

We hear a great deal about the conservation of our natural resources, such as forests and waterways; it is hoped that this book will show the vital importance of the conservation of human strength and health, and the irreparable loss to society of energy uselessly dissipated, either in idle worry or in aimless activity. Most of us would reproach ourselves for lack of shrewdness if we spent for any article more than it was worth, yet few of us consider that we daily expend on domestic and business tasks an amount of energy far in excess of that actually required. The farmer who flails his grain instead of threshing it wastes time and energy; the housewife who washes with her hands alone and does not aid herself by the use of washing machine and proper bleaching agents dissipates energy sadly needed for other duties.

The Chapter on machines is intended not only as a stimulus to the invention of further labor-saving devices, but also as an eye opener to those who, in the future struggle for existence, must perforce go to the wall unless they understand how to make use of contrivances whereby man's limited physical strength is made effective for larger tasks.

The Chapter on musical instruments is more detailed than seems warranted at first sight; but interest in orchestral instruments is real and general, and there is a persistent desire for intelligent information relative to musical instruments. The child of the laborer as well as the child of the merchant finds it possible to attend some of the weekly orchestral concerts, with their tiers of cheap seats, and nothing adds more to the enjoyment and instruction of such hours than an intimate acquaintance with the leading instruments. Unless this is given in the public schools, a large percentage of mankind is deprived of it, and it is for this reason that so large a share of the treatment of sound has been devoted to musical instruments.

The treatment of electricity is more theoretical than that used in preceding Chapters, but the subject does not lend itself readily to popular presentation; and, moreover, it is a.s.sumed that the information and training acquired in the previous work will give the pupil power to understand the more advanced thought and method.

The real value of a book depends not so much upon the information given as upon the permanent interest stimulated and the initiative aroused. The youthful mind, and indeed the average adult mind as well, is singularly non-logical and incapable of continued concentration, and loses interest under too consecutive thought and sustained style. For this reason the author has sacrificed at times detail to general effect, logical development to present-day interest and facts, and has made use of a popular, light style of writing as well as of the more formal and logical style common to books of science.

No claim is made to originality in subject matter. The actual facts, theories, and principles used are such as have been presented in previous textbooks of science, but the manner and sequence of presentation are new and, so far as I know, untried elsewhere. These are such as in my experience have aroused the greatest interest and initiative, and such as have at the same time given the maximum benefit from the informational standpoint. In no case, however, is mental training sacrificed to information; but mental development is sought through the student's willing and interested partic.i.p.ation in the actual daily happenings of the home and the shop and the field, rather than through formal 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 ill.u.s.trations: 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, Princ.i.p.al of the William Penn High School, has read the ma.n.u.script 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 a.s.sistants 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.

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 s.p.a.ce, 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 s.p.a.ce 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 pa.s.ses. 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.

[Ill.u.s.tration: 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 pole, sag in hot weather and are much too long. In summer they are exposed to the fierce rays of the sun, become strongly heated, and expand sufficiently to sag. If the wires were stretched taut in the summer, there would not be sufficient leeway for the contraction which accompanies cold weather, and in winter they would snap.

[Ill.u.s.tration: FIG. 2--When the ball is heated, it become too large to slip through the ring.]

Air expands greatly when heated (Fig. 3), but since air is practically invisible, we are not ordinarily conscious of any change in it. The expansion of air can be readily shown by putting a drop of ink in a thin gla.s.s tube, inserting the tube in the cork of a flask, and applying heat to the flask (Fig. 4). The ink is forced up the tube by the expanding air. Even the warmth of the hand is generally sufficient to cause the drop to rise steadily in the tube. The rise of the drop of ink shows that the air in the flask occupies more s.p.a.ce than formerly, and since the quant.i.ty of air has not changed, each cubic inch of s.p.a.ce must hold less warm air than

it held of cold air; that is, one cubic inch of warm air weighs less than one cubic inch of cold air, or warm air is less dense than cold air. All gases, if not confined, expand when heated and contract as they cool. Heat, in general, causes substances to expand or become less dense.

[Ill.u.s.tration: FIG. 3--As the air in _A_ is heated, it expands and escapes in the form of bubbles.]

3. Amount of Expansion and Contraction. While most substances expand when heated and contract when cooled, they are not all affected equally by the same changes in temperature. Alcohol expands more than water, and water more than mercury. Steel wire which measures 1/4 mile on a snowy day will gain 25 inches in length on a warm summer day, and an aluminum wire under the same conditions would gain 50 inches in length.

[Ill.u.s.tration: FIG. 4.--As the air in _A_ is heated, it expands and forces the drop of ink up the tube.]

4. Advantages and Disadvantages of Expansion and Contraction. We owe the snug fit of metal tires and bands to the expansion and contraction resulting from heating and cooling. The tire of a wagon wheel is made slightly smaller than the wheel which it is to protect; it is then put into a very hot fire and heated until it has expanded sufficiently to slip on the wheel. As the tire cools it contracts and fits the wheel closely.

In a railroad, s.p.a.ces are usually left between consecutive rails in order to allow for expansion during the summer.

The unsightly cracks and humps in cement floors are sometimes due to the expansion resulting from heat (Fig. 5). Cracking from this cause can frequently be avoided by cutting the soft cement into squares, the s.p.a.ces between them giving opportunity for expansion just as do the s.p.a.ces between the rails of railroads.

[Ill.u.s.tration: FIG. 5: A cement walk broken by expansion due to sun heat.]

In the construction of long wire fences provision must be made for tightening the wire in summer, otherwise great sagging would occur.

Heat plays an important part in the splitting of rocks and in the formation of debris. Rocks in exposed places are greatly affected by changes in temperature, and in regions where the changes in temperature are sudden, severe, and frequent, the rocks are not able to withstand the strain of expansion and contraction, and as a result crack and split. In the Sahara Desert much crumbling of the rock into sand has been caused by the intense heat of the day followed by the sharp frost of night. The heat of the day causes the rocks to expand, and the cold of night causes them to contract, and these two forces constantly at work loosen the grains of the rock and force them out of place, thus producing crumbling.

[Ill.u.s.tration: FIG. 6.--Splitting and crumbling of rock caused by alternating heat and cold.]

The surface of the rock is the most exposed part, and during the day the surface, heated by the sun's rays, expands and becomes too large for the interior, and crumbling and splitting result from the strain.

With the sudden fall of temperature in the late afternoon and night, the surface of the rock becomes greatly chilled and colder than the rock beneath; the surface rock therefore contracts and shrinks more than the underlying rock, and again crumbling results (Fig. 6).

[Ill.u.s.tration: FIG. 7.--Debris formed from crumbled rock.]

On bare mountains, the heating and cooling effects of the sun are very striking(Fig. 7); the surface of many a mountain peak is covered with cracked rock so insecure that a touch or step will dislodge the fragments and start them down the mountain slope. The lower levels of mountains are frequently buried several feet under debris which has been formed in this way from higher peaks, and which has slowly acc.u.mulated at the lower levels.

5. Temperature. When an object feels hot to the touch, we say that it has a high temperature; when it feels cold to the touch, that it has a low temperature; but we are not accurate judges of heat. Ice water seems comparatively warm after eating ice cream, and yet we know that ice water is by no means warm. A room may seem warm to a person who has been walking in the cold air, while it may feel decidedly cold to some one who has come from a warmer room. If the hand is cold, lukewarm water feels hot, but if the hand has been in very hot water and is then transferred to lukewarm water, the latter will seem cold.

We see that the sensation or feeling of warmth is not an accurate guide to the temperature of a substance; and yet until 1592, one hundred years after the discovery of America, people relied solely upon their sensations for the measurement of temperature. Very hot substances cannot be touched without injury, and hence inconvenience as well as the necessity for accuracy led to the invention of the thermometer, an instrument whose operation depends upon the fact that most substances expand when heated and contract when cooled.

[Ill.u.s.tration: FIG. 8.--Making a thermometer.]

6. The Thermometer. The modern thermometer consists of a gla.s.s tube at the lower end of which is a bulb filled with mercury or colored alcohol (Fig. 8). After the bulb has been filled with the mercury, it is placed in a beaker of water and the water is heated by a Bunsen burner. As the water becomes warmer and warmer the level of the mercury in the tube steadily rises until the water boils, when the level remains stationary (Fig. 9). A scratch is made on the tube to indicate the point to which the mercury rises when the bulb is placed in boiling water, and this point is marked 212. The tube is then removed from the boiling water, and after cooling for a few minutes, it is placed in a vessel containing finely chopped ice (Fig. 10). The mercury column falls rapidly, but finally remains stationary, and at this level another scratch is made on the tube and the point is marked 32. The s.p.a.ce between these two points, which represent the temperatures of boiling water and of melting ice, is divided into 180 equal parts called degrees. The thermometer in use in the United States is marked in this way and is called the Fahrenheit thermometer after its designer. Before the degrees are etched on the thermometer the open end of the tube is sealed.

[Ill.u.s.tration: FIG. 9.--Determining one of the fixed points of a thermometer.]

The Centigrade thermometer, in use in foreign countries and in all scientific work, is similar to the Fahrenheit except that the fixed points are marked 100 and 0, and the interval between the points is divided into 100 equal parts instead of into 180.

_The boiling point of water is 212 F. or 100 C_.

_The melting point of ice is 32 F. or 0 C_.

Gla.s.s thermometers of the above type are the ones most generally used, but there are many different types for special purposes.

[Ill.u.s.tration: FIG. 10.--Determining the lower fixed point of a thermometer.]