An introduction to science

Front matter

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Foreword

Thirty years ago the study of science was fighting for a position of academic respectability much as the various special sciences are fighting for the same position to-day. Science edged its way in through the popular fourteen weeks in physics or chemistry, which aflForded a very valuable scientific interpretation of the immediate environment of the pupils. But when the colleges agreed to accept science for entrance on the same basis as mathematics and the foreign languages, they prescribed the content of the science courses and totally changed their character. The new syllabi were determined by college professors who had in mind only the needs of the pupils destined to go to college.

For these reasons, without real blame being attributable to any one, the proper aim of the study of science in the high schools was defeated. Disturbers of the educational peace then pointed to the fact that approximately only five per cent of the high school pupils go to college. They questioned the dictum that the best education for the pupil preparing for college is the best education for the pupil going immediately into active life. It was pointed out that everybody who took science was being forced to study a great deal of pure theory that could not be connected with practical life without much subsequent study.

The first movement toward a reformation of this unfortunate condition was the organization of short courses in biology for the first year of the high school. When this science was studied for its human relations, an immediate change in the

8 FOREWORD

interest and success of the pupils was evident. However, this course did not furnish a basis for preparation acceptable to the colleges, and a long and acrimonious debate ensued. As the high school came to be more and more conscious of itself, schools here and there boldly insisted that they would settle their own problems, and many prepared courses which were of vital interest and importance to the pupils. One of the first books to lead the way in reconstructing the subjects of physics and chemistry was General Science, by Doctor Bertha M. Clark of the William Penn High School. Doctor Clark began this book after an exhaustive questionnaire had been sent to graduates of the William Penn High School, which proved that the traditional physics had been to the pupils an object of no real value and of almost universal dislike. The reformed general science, on the contrary, immediately proved to be a very popular course in the school. Pupils brought to the class their home problems for scientific analysis. Heating, lighting, and ventilating the home, the analysis of foods, the detection of adulterants, the composition of fabrics, the removal of stains, and a thousand practical, everyday questions showed the improved relation of the rejuvenated science to life.

General Science as a pioneer was a marked success. The present volume is an extension of the general science idea to cover a broader field. When the history of American education of the first two decades of the twentieth century shall be written, this movement to humanize science will prove one of its interesting chapters, and the present volume and its precursor will undoubtedly appear as landmarks along the road of real educational service.

W. D. LEWIS, Principal of William Penn High School.

Preface

Scientific knowledge and scientific management are at the root of all successful present-day projects and enterprises. The business man who would keep his place in the modern competitive struggle must have a thorough knowledge of the factors which enter into his business and must know how to utilize these factors in a constructive scientific way. Not only the lives of staid business men, but also the lives of youths and maidens are full of projects. The setting up of a homemade telephone is as important an enterprise to the youth as is the forging ahead in business to the mature man ; the planning of a trial menu for household \ise is as great a project to a high school girl as is the direction of a dietary kitchen to a skilled dietitian.

The aim of this book is to start young high school pupils on scientific projects which will influence for good their present lives, and which under different guise will equally influence for good their future lives. Among the scientific projects presented to the pupils are those of the selection of economic menus of dietary standards; the selection of suitable paints, oils, and varnishes for actual daily use ; the examination of different fuels, and their adaptability to furnace and kitchen range ; the investigation of home and school lighting and its influence on eyesight; the utilization of simple labor-saving devices to relieve physical exertion ; the employment of chemical agents to transform useless waste products, such as grease and sewage, into useful products, such as soaps and fertilizers; and the application of hygienic facts and theories to school, home, and community sanitation.

I am indebted to many for the illustrations which are used in the text. Acknowledgment is made to Professor Alvin lO PREFACE

Davison for Figs. 23, 27, 37, 38, 44-46, 7i> 3^7; to G. W. Hunter for Figs. 30, 306, 308, 311 ; to Messrs. Blackwelder and Barrows for Figs. 5, 226, 228, 229, 234-237, 242, 244, 256, 257, 259, 260, 271, 276, 278, 284; to Messrs. Mayne and Hatch for Figs. 302, 307, 321, 325, 333, 334; to J. G. Coulter for Figs. 43, 295; to Dr. C. R. Dryer for Figs. 216, 231, 258, 262, 267, 272, 275 ; to E. F. Andrews for Figs. 290-292, 299, 300, 303, 304. Acknowledgment is also made to Miss Alma Waldie, Miss Helen Shriver, Mr. A. H. Rosewig, and Mr. Philip Lee.

Illustrations have been freely given by The American Radiator Co., General Electric Co., Hershey Chocolate Co., Scientific American, Aluminum Cooking Utensil Co., Goulds Manufacturing Co., Carnegie Institution, Illuminating Engineering Society, U. S. Bureau of Fisheries, U. S. Department of Agriculture, Canadian Pacific R.R., Northern Pacific R.R., Johns Hopkins Press, and many other firms and publishers.

Mr. W. D. Lewis, Principal of the William Penn High School, has given the stimulus of his interest and approval. Miss Helen Hill, Librarian of the school, has kept me supplied with the most recent publications of practical scientific interest and has been of invaluable service in numerous ways. Miss Mathilde Droege of the Brearley School, New York, has read the manuscript and made many helpful suggestions.

. Without the cooperation of the science teachers of the William Penn High School, the writing of the book would have been difficult. They have tested and retested projects, have criticized again and again, and have cooperated in every way to make successful the book and the course on which it is based. Among those who have given most freely of their time are Miss Jean Weber and Miss May Laramay. Thanks are also due to Miss Helen Price, Miss Ruth Flanagen, Miss Anna Biddle, and Miss Catherine Way.

BERTHA MAY CLARK.

Contents

CHAPTER PAGB

I. Heat 13

II. Temperature and Heat 33

II Contents

CHAPTER

XXVII.

XXVIII.

XXIX.

XXX.

XXXI.

XXXII.

XXXIII.

XXXIV.

XXXV.

XXXVI.

XXXVII.

XXXVIII.

XXXIX.

XL.

XLI.

XLII.

XLIII.

XLIV.

PAGB

Photography and the Chemical Action of Light 262

Color 271

Artificial Lighting 275

The Work of the Atmosphere 388

The Rocks and Building Stones of the Earth . . 417 Plants and Their Relation to Man . . -423

AN INTRODUCTION TO SCIENCE

Chapter I Heat

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 the forging of iron, as in the blacksmith's shop, and 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 the facts and theories relative to it are among the most important that can be studied.

General effect of heat. Expansion and contraction, — One of the . best-known effect* of heat is the change which it causes in the size of a body. Every housewife knows that when a kettle is filled with cold water and heated, there is an overflow as soon as the water becomes hot. 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. If loo pints of ice water, for example, are heated in a kettle, the loo pints steadily expand until, at the boiling point, they occupy as much space as 104 pints of ice water.

The expansion of water can be easily shown by heating a

H

HEAT 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.

Not only liquids are aflPected by heat and cold, but solids also are subject to similar changes. A Fig. I.— -As the metal ball which when cool just slips through a

water becomes , . ^ i^ o

warmer, it ex- ring is, when heated, too large to slip through the pandsand rises ^^^ Telegraph and telephone wires in winter

m the narrow o o r r

tube. are stretched taut from pole to pole. In summer,

when they are exposed to the fierce rays of the sun, they expand and sag until they are much too long. If the wires were stretched taut in the summer, there would not be sufficient leeway for the contraction which accompanies cold weather, and they would snap under the strain.

Air expands greatly when heated (Fig. 2), 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 glass tube, inserting the tube in the cork of a flask, and applying heat to the flask (Fig. 3).

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 ^^?; 2- -As the airing isheated,

'^ it expands and escapes in the

ink shows that the air in the flask form of bubbles.

EXPANSION AND CONTRACTION

IS occupies more space than formerly, and since the quantity of ait has not changed, each cubic inch of space must hold a less weight of 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 which are not confined expand when heated and contract as they cool. Heat, as a general rule, causes substances to expand or become less dense.

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 J mile on a snowy day gains 25 inches in length Fig. 3. — As the on a warm summer day, and an aluminum wire air m ^4 is heated,

. . . . It expands and

under the same conditions gains 50 inches in forces the drop of

length. ink up the tube.

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 building a railroad, spaces 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. 4). Cracking from this cause can frequently be avoided by cutting the soft cement into squares, the spaces between them giving opportunity for expansion just as do the spaces between the rails of railroads.

1 6 HEAT

In the construction of long wire fences provision must be made for tightening the wire in summer, otherwise they sag.

Heat plays aii 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,

wait broken by eipansion , , , ,

due to sun heat. 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 change from the intense heat of the day to the intense cold of night. The heat of 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 causing the rocks to crumble.

The surface of the rock is the most exposed part, and during the day the surface, heated by the sun's rays, expands, becomes too large for the in- ' terior, and crumbles and splits as a result of 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 splits and crumbles (Fig. s).

On bare mountains, the heating and cooling effects of the

GENERAL EFFECT OF HEAT 17

sun are very striking. 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 (Fig. 6) are frequently buried several feet under debris which has been formed in this way from higher peaks, and which has slowly accumulated at the lower levels. Under the action of heat and cold exposed rock "weathers"; that is, it cracks and crumbles into fragments which can be blown away by wind and washed away by water. Heat and cold are powerful agents of weathering.

General effect of heat. 'Change in Umperature.

■ — Perhaps the best- F.g. 6. — Debris formed from crumbling t^ct.

known effect of heat is

the warmth it imparts to substances which come under its influence. In summer the sun's rays heat the cement walks until they burn the feet; in winter, the coals glowing in furnace and stove heat the icy air, and make it warm. When an object feels hot to the touch, we say it has a high temperature ; when it feels cold to the touch, that it has a low temperature. Changes in temperature are caused by heat : when cold water, that is, water with a low temperature, is placed over glowing coal it becomes warm water, thdt is, water with a high temperalure. The change in the temperature of the water is due to the heat given out from the burning fuel. As the fire dies out, it

1 8 HEAT

imparts less and less warmth to the water, which slowly cools to a lower temperature.

Man is a poor judge of temperature. — Man is not an accurate judge of temperature. 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 decidedlycold to 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 seems 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! The necessity, as well as the convenience, of having some accurate means of determining the temperature of substances 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.

The thermometer. — The modern thermometer consists of a glass tube at the lower end of which is a bulb filled with mercury or colored alcohol (Fig. 7). After the bulb has been filled with the mercury, it is heated a little above the boiling point of water and the tube is then sealed at the top. As the mercury ^Making^ cools, it falls and leaves an unoccupied space or thennom- vacuum above it. The thermometer is then 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. 8). A

SOME USES OF A THERMOMETER one of the fixed points of a thermometer.

scratcli 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. 9). 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 space between these two points, which represent the temperatures of boiling water and of melting ice, is divided into 180 equal parts pj^, g. — Detenninhig called degrees. The thermometer in use in the United States is marked in this way and is called the Fahrenheit thermometer after its designer. 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 Glass thermometers of the above type are the ones most generally used, but there are many different types for special purposes (Fig. 10).

Some uses of a thermometer. — One of the

chief values of a thermometer is the service it has

y^ rendered to medicine. When a thermometer is

Fig. 9. — Deter- held for a few minutes under the tongue of a

foTd^^/^of^a ^^^^^^y healthy person, the mercury rises to about

thermometer. 98.4° F. When the temperature of the body

CLAKK DJTRO. TO SC. — 2

HEAT

FC registers several degrees above or below this point; a physician should be consulted immediately. The temperature of the body is a trustworthy indicator of general physical condition; hence in all hospitals the temperature of patients is carefully taken at stated intervals.

Commercially, temperature readings are extremely important. In sugar refineries the temperature of the heated liquids is observed most carefully, since a difference in temperature, however slight, affects not only the general appearance of sugars and sirups, but the quality as well.

The many varieties of steel show the influence which heat may have on the nature of a substance. By experiment it has been found that if hardened steel is heated to about 450° F. and quickly cooled, it gives the fine cutting edge of razors; if it is heated to about 500° F. and then cooled, the nietal is much coarser and is suitable for shears and farm implements ; while if it is heated but 50° F. higher, that is, to 550° F., it gives the fine elastic steel of watch springs.

A thermometer can be put to good use in every kitchen ; the inexperienced housekeeper who cannot judge of the " heat " of the oven will be saved bad bread, if the thermometer is a part of her equipment. The thermometer can also be used in detecting adulterants. Butter should melt at 94° F. ; if it does not, you may be sure that it is adulterated with suet or other cheap fat. Olive oil should be well-made a clear liquid above 75° F. ; if, above this temperacommercial |.yrg Jt looks cloudy, you may be sure that it. too,

thermome- ' 1 • 1 "r

ter. is adulterated with fat.

i i.

METHODS OF HEATING BUILDINGS

Methods of heating buildings. Open fireplaces and stoves. — If heat did not cause expansion and change in temperature, it would be impossible to heat our houses and to protect ourselves against the biting blasts of winter. The burning coal warms and expands the air within the furnace, causing it to rise through the stovepipes and thus to carry heat to the different parts of the house. Open fireplaces, old-fashioned stoves, and newfashioned furnaces owe their existence to these two effects of heat. In olden times, man heated his modest dwelling by open Bres alone. The burning logs gave warmth to the cabin and served as a primitive cooking agent ; and the smoke which usually accompanies burning was carried away through the chimney. But in an open fireplace much heat escapes with the smoke and only a small portion streams into the room and gives warmth.

When fuel is placed in an open fireplace (Fig. ii) and lighted, the air immediately surrounding the fire becomes warmer and, because of expansion, becomes lighter than the cold air above. The cold air, being heavier, falls and forces the warmer air upward, and with the warm air goes the disagreeable smoke. The fall of the colder and heavier air, and the rise of the warmer and hence lighter air, is similar to the exchange which takes place when water is poured upon oil; water, being heavier than oil, sinks to the bottom and forces the oil to the surface.

Zz.tl-1

— The open fireplace a;

22 HEAT

As the air is heated by the fire, it expands and is pushed up the chimney by the cold air which is constantly entering through loose windows and doors. Open fireplaces are very healthful because the air which is driven out is impure, while the air which rushes in is fresh, and brings oxygen.

But open fireplaces, while pleasant to look at, are not efficient for heating, because most of the heat escapes through the chimney and only a small portion remains in the room where warmth is needed. Neither are open fireplaces practical for cooking, because there is no convenient arrangement for placing cooking utensils over the burning fuel. Owing to the loss of heat from open fireplaces, and their inconvenience in cooking, the invention of stoves was a great advance in efficiency, economy, and comfort. A stove is a receptacle for fire, provided with a definite inlet or draft for air and a definite outlet to the chimney for smoke, and able to radiate into the room most of the heat produced from the fire which burns within. The inlet, or draft, admits enough air to cause the fire to burn brightly or slowly, as the case may be. When we wish a hot fire, the draft should be opened wide and enough air secured to produce a strong glow. When we wish a low fire, the inlet should be partly closed, and just enough air admitted to keep the fuel smoldering.

When the fire is started, the outlet damper should be opened wide in order to allow the escape of smoke ; but after the fire is well started there is less smoke, and the damper may be partly closed. If the damper is kept open, coal is rapidly consumed, and the additional heat passes out through the chimney and is lost.

Furnaces. Hot air, — The labor involved in the care of numerous stoves is considerable, and the use of a central heating stove, or furnace, is a great saving in strength and fuel. A furnace is a stoye arranged as in Figure 12. The

HOT-WATER HEATING 23

stove S, like all other stoves, has an inlet for air and an outlet C for smoke; but in addition, it has built around it a chamber in which air circulates and is warmed. The air warmed by the stove is forced upward by cold air which enters from outside. For example, cold air constantly entering at F drives the air heated by S through pip>es and ducts to the rooms to be heated.

The metal pipes which convey theheated air from the furnace to the ducts are sometimes covered with felt, asbestos, or other non-conducting material in order that heat may not be lost duringtransmission. The ducts which f

receive the heated air Fto. n. — ACurnace. Pipes conduct hot air to

from the pipes are built ' looma.

in the non-conducting walls of the house, and hence lose practically no heat. The air which reaches halls and rooms is therefore warm, in spite of its long journey from the cellar.

Not only houses are warmed by a central heating stove, but whole communities sometimes depend upon a central heating plant. In the latter case, pipes closely wrapped with a non-conducting material carry steam long distances underground to remote buildings. Overbrook and Radnor, Pa., are towns in which such a system is used.

Hot-water heating. — Th^ heated air which rises from furnaces is seldom hot enough to warm large buildings well ; hence furnace heating is being largely supplanted by hot-water heating.

HEAT

The principle of hot-water heating is shown by the following simple experiment. Two flasks and two tubes are arranged as in Figure 13, the upper flask containing a colored liquid and the lower flask, clear water. If heat is applied to 5, one can see at the

end of a few seconds the downward movement of the colored liquid and the upward movement of the clear water. If we represent a boiler by By a radiator by the coiled tube, and a safety tank by C, we shall have a very fair illustration of the principle of a hot-water heating system. The hot water in the radiators cools and, in cooling, gives up its heat to the rooms and warms them.

In hot-water heating systems, fresh air is not brought to the rooms, for the radiators are closed pipes containing hot

Fig. 13. — The principle of hot-water heating.

water (Fig. 14). For this reason it is necessary to raise windows at intervals.

Some systems of hot-water heating secure ventilation by confining the radiators to the basement, to which cold air from outside is constantly admitted in such a way that it circulates over the radiators and becomes strongly heated. This warm fresh air then passes through ordinary flues to the rooms above. In Figure 15, a radiator is shown in a boxlike structure in

HOT-WATER HEATING

Fio. 14. — Hot-water heatinj

Fic. IS— Fresh

the cellar. Fresh air from outside enters a flue at the right, passes over the radiators, where it is warmed, and then makes its way to the room through a flue at the left. The warm air

FRESH AIR 27

which enters the room is thoroughly fresh. Figure 16 shows how a schoolroom is supplied with warm fresh air. The actual labor involved in furnace heating and in hot-water heating is practically the same, since coal must be fed to the fire, and ashes must be removed ; but the hot-water system has the advantage of economy and cleanliness.

Fresh air. — Fresh air is essential to normal healthy living, and 2000 cubic feet of air per hour is desirable for each individual. If a gentle breeze is blowing, a barely perceptible opening of a window gives the needed amount, even if there are no additional drafts of fresh air into the room through cracks. Most houses are so loosely constructed that fresh air enters imperceptibly in many ways, and whether we will or not, we receive some fresh air. The supply is, however, never sufficient in itself and should not be depended upon alone. At night, or at any other time when gaslights are required, the need for ventilation increases, because every gaslight in a room uses up the same amount of air as four people.

In the preceding section, we learned that many houses heated by hot water are supplied with fresh-air pipes which admit fresh air into the rooms. In some cases the amount which enters is so great that the air in a room is changed three or four times an hour. The constant inflow of cold air and exit of warm air necessitates larger radiators and more hot water and more coal to heat the larger quantity of water, but the additional expense is more than compensated by the gain in health.