GIFT OF 
 Agriculture education 
 
THE 
 
 
 FIRST YEAR OF SCIENCE 
 
 BY 
 
 JOHN C. HESSLER, Ph. D. 
 
 \ s 
 
 PROFESSOR Or CHEMISTRY, THE JAMES MILLIKIN UNIVERSITY. 
 
 LATE INSTRUCTOR IN THE UNIVERSITY OF CHICAGO AND 
 
 IN THE HYDE PARK HIGH SCHOOL, CHICAGO 
 
 nblX aUd 
 
 BENJ. H. SANBORN & CO. 
 1914 
 
1 
 
 144 
 
 COPYRIGHT, 1914 
 
 BY 
 JOHN C. HESSLER 
 
 HGRIC, DEPT, 
 
 Ur" 
 
 R. R. DONNELLEY & SONS COMPANY 
 CHICAGO 
 
PREFACE 
 
 The chief interest in Secondary School science, which 
 for a long time was concentrated upon the later years of 
 the course, has recently been shifted to the work of the 
 first year. The leading reason for this is the conviction, 
 which is rapidly becoming general, that the first science 
 of the High School should be fundamental to the entire 
 field of science and should not be any one of the special 
 sciences. It is hard to see how Physiography, Physiology, 
 and Biology, the usual subjects of the early High School 
 years, can be taught satisfactorily unless the pupil has 
 previously acquired the elementary physical and chemical 
 conceptions which underlie Physiography, Physiology, 
 and Biology. A proof that this need is felt is the fact 
 that many teachers of first-year science, no matter what 
 their subjects may be called, find themselves obliged, 
 even now, to give a large part of their class time to the 
 presentation of fundamental physical and chemical ideas. 
 
 The problem involved in the proper preparation of 
 pupils for the study of Physiography and the biological 
 sciences cannot be solved by the transfer of Physics and 
 Chemistry, as formal subjects, to the first year of the 
 High School curriculum. The cause lies both in the 
 difficulty of the subjects themselves and also in the high 
 development which these sciences have reached in 
 Secondary Schools. For Physics and Chemistry are 
 now taught in Secondary Schools in a way and with an 
 
 iii 
 
 >* O A 
 
iv PREFACE 
 
 equipment far in advance even of College instruction in 
 these subjects a generation ago. Work of this character 
 requires a certain maturity on the part of the pupil, as 
 well as some knowledge of other High School subjects, and 
 it cannot be maintained unless Physics and Chemistry 
 are kept in the later years of the course. 
 
 While Physics and Chemistry as such ought not to be 
 put into the early years of the High School, yet instruction 
 in the simpler principles of these sciences can be given 
 in a first-year General Science course. The most im- 
 portant part of this course will be introductory notions of 
 physical and chemical phenomena, but the course should 
 include much more than this. The problems of modern 
 conveniences and of their relation to scientific discovery, 
 the soil as the basis of agriculture, plants and animals and 
 their ascent from simpler forms to those that are more 
 complex, all can find a place in such a course. So can 
 sanitation, the application of science to community life. 
 
 When we assign to General Science the scope suggested 
 in the foregoing paragraph, the need of it in the first 
 year of the High School course is self-evident. This is 
 true even if we confine ourselves to the staple High School 
 curriculum of a decade ago. But when we remember 
 that this curriculum has been immeasurably enlarged by 
 the introduction of short courses, business courses, do- 
 mestic science courses, agricultural courses, and of voca- 
 tional guidance in all courses, the demand for adequate 
 first-year science instruction becomes imperative, and 
 the argument for its introduction overwhelming. The 
 question that remains is: "Can such a General Science 
 course be given to large, first-year High School classes, 
 
PREFACE V 
 
 with their varied needs, without special teachers par- 
 ticularly prepared for this subject and without expensive 
 equipment for laboratory work?" The answer is certainly 
 "Yes." To give the answer in expanded form is the 
 purpose of this book. 
 
 The "First Year of Science" is written to meet the 
 need of General Science instruction. It consists of three 
 parts: the text proper, the laboratory manual, and the 
 Teacher's Handbook. The text and laboratory manual 
 may be had either bound together or in separate volumes. 
 If the writer were asked to characterize the book in a 
 phrase or two, he would say that it is intended to stimu- 
 late uncommon thinking about common things, to produce 
 a scientific attitude toward everyday problems, to give 
 scientific knowledge to as large a body of our people as 
 possible in order that modern inventions may be the 
 tools and not merely the toys of the men and women into 
 whose hands they are placed. 
 
 The text proper consists of descriptive matter, of 
 exercises, and of chapter summaries. There are twenty 
 chapters. As the Table of Contents shows, about half 
 of these consist of elementary Physics and Chemistry. 
 The chapters on Physics contain no formulas and only a 
 few simple calculations; there are no symbols or equations 
 in the chapters on Chemistry. The author's plan is to 
 give only the primary notions of matter, force, and chem- 
 ical action. These are needed for all subsequent work 
 in pure or applied science, as well as for that general 
 knowledge of common things which every person ought 
 to carry away from a High School course. 
 
 In the latter half of the text are' chapters on "Water, 
 
vi PREFACE 
 
 Heat, Air, and Light in the House," "The Weather," 
 " Rocks and Soil," "Plants," and " Animals." Chapters 
 XVII to XX are given to elementary Physiology and 
 Sanitation. The book therefore contains the material 
 needed by schools that desire to give a short course in 
 Physiology at the end of the first year. Coming, as it 
 does, after the elementary Physics and Chemistry of the 
 earlier half of the book, and immediately after the 
 chapters on " Plants" and "Animate," the work in 
 Physiology ought to mean far more to the pupil than if 
 it were an isolated appendix to the first year's work. 
 
 The illustrations of the "First Year of Science" are 
 unusually numerous and especially adapted to the text. 
 They have been prepared with great care, for they are 
 intended, by their direct appeal to the eye, to enlarge 
 materially the teaching power of the text. To this end 
 descriptive matter has been added to them and they 
 have been made very simple. The parts of drawings 
 have usually been designated by names rather than by 
 letters. 
 
 Exercises are given at the end of each chapter and 
 also in the body of each chapter except the first. The 
 exercises are questions taken from the chapter; they en- 
 courage the pupil to apply to common phenomena what 
 he has learned in the text and the laboratory work. 
 
 Summaries are placed at the end of each chapter to 
 bring together in a bird's-eye view the leading topics of 
 the chapter. 
 
 An appendix contains useful tables and a reference 
 Glossary of terms used in the book. 
 
 The laboratory exercises are such as can be per- 
 
PREFACE VII 
 
 formed with simple apparatus, and the directions are 
 specific both as to the form of apparatus and as to the 
 quantity of materials to be used. A special feature is a 
 series of alternative experiments, in which the apparatus 
 used is so simple that it can be made at home. If desired, 
 most of these alternative experiments may be performed 
 by the pupil at home. If the laboratory facilities of the 
 school are limited, none but these simple experiments 
 need necessarily be used. We have become so accus- 
 tomed, in our well-equipped schools, to laboratory ap- 
 paratus which has certain definite forms and requires 
 certain set manipulations that we are likely to forget that 
 the setting up of home-made apparatus is usually far more 
 stimulating to the pupil than even the best of ready- 
 made equipment. Only by linking our science with 
 everyday things can we hope to convince the pupil that 
 science is only common sense applied to daily life. 
 
 The handbook on the " Teaching of First- Year Science " 
 forms the third part of the book. It contains material 
 intended chiefly for the teacher's use. Here are dis- 
 cussed the topics suitable for recitation and the methods of 
 presenting them, the amount and kind of work to be 
 expected of pupils, answers to exercises, and a list of 
 experiments, carefully planned, to be performed by the 
 teacher before, or, better, with the class. The handbook 
 is designed to assist the teacher in every possible way in 
 making the elementary science course profitable and 
 stimulating. 
 
 In the preparation of this book the writer has neces- 
 sarily consulted many textbooks of Science, and put 
 himself under deep obligation to their authors. To all of 
 
Vlll PREFACE 
 
 these he desires to express his thanks. He is especially 
 grateful to his friends, Dr. Eugene C. Woodruff, of Penn- 
 sylvania State College, and Miss Marion Sykes, of the 
 Chicago High Schools, for valuable criticisms and sug- 
 gestions. 
 
 The author desires likewise to thank the many in- 
 dividuals and firms who have so generously assisted him 
 in the procuring of illustrations. Among these are Drs. 
 O. C. Farrington and C. F. Millspaugh, of the Field 
 Museum of Natural History, Chicago; the International 
 Stereograph Co., Decatur 111.; Dr. S. W. Stratton, of the 
 Bureau of Standards, Washington; Dr. Orville Wright, 
 Dayton, Ohio; Mr. William D. Richardson, of Swift and 
 Company; Professor Frederick Starr, of the University 
 of Chicago; Professor Martha Van Rensselaer, of the 
 Department of Home Economics, Cornell University; and 
 many others whose names appear under the figures. 
 
 The drawings for the illustrations have been made by 
 Messrs. William F. Henderson, Macknet Van Deventer, 
 Otto Roth, Alex. Van Praag, Milford Davis, and Leland 
 Smith, and by Miss Hila Ayres. The drawings for Figs. 
 88, 206, and some others were made by Miss Ruth Fuller. 
 To all of these the author hereby expresses his apprecia- 
 tion and gratitude. J. C. H. 
 
 Decatur, Illinois. 
 
CONTENTS 
 
 CHAPTER I. 
 Matter and Its Measurement 1 
 
 The Earth and Science. Phenomena. The Scientific Way or 
 Method. Matter. Substances. How We Measure Space and 
 Matter. Common Units of Length. The Metric System. The 
 Standard Meter. Metric Tables of Length, Area, and Volume. 
 Larger Units of Length. Weight. Units of Weight. Metric 
 Units of Weight. Bureau of Standards. Summary. Exercises. 
 
 CHAPTER II. 
 Force and Energy 17 
 
 Gravity. Gravitation. Mass and Weight. Falling Bodies. 
 Exercises. Force. Force of Expanding Gases. Work and Energy. 
 Power. Inertia of Matter. Flying from the Center. Exer- 
 cises. Cohesion and Adhesion. The Surface of a Liquid. Capil- 
 lary Action. Density and Specific Gravity. Buoyant Force of 
 Liquids. Center of Mass or Gravity. Summary. Exercises. 
 
 CHAPTER III. 
 
 Air and Fire 38 
 
 The Atmosphere. Weight of Air. Atmospheric Pressure; Ba- 
 rometer Changes in Atmospheric Pressure. Pumps. Compressed 
 Air. Exercises. Collection of Gases. Discovery of Oxygen. 
 The Air a Mixture. Burning and Oxidation. Flames. Prepara- 
 tion of Oxygen. Properties of Oxygen. Oxygen and Life. Exer- 
 cises. How Nitrogen is Prepared, Properties of Nitrogen. Nitro- 
 gen and Life. Liquid Air. How the Atmosphere is Purified. 
 Summary. Exercises. 
 
 CHAPTER IV. 
 
 Heat 59 
 
 Heat and Matter. Thermometers. The Two Thermometer 
 Scales. Heat and Temperature. Ways of Distributing Heat. 
 Radiation. Convection. Exercises. Physical States of Matter; 
 Solids. Liquids. Gases. Kindling Temperature. The Measur- 
 ing of Heat. Heat and Life. Clothing. Sources of Heat. Sum- 
 mary. Exercises. 
 
 ix 
 
X CONTENTS 
 
 CHAPTER V. 
 
 Water . 76 
 
 How Water Occurs in Nature. Substances Dissolved in Natural 
 Water. Drinking Water. Hardness of Water. Purifying Water. 
 Filtering. Filtering City Water. Exercises. Why Ice Forms 
 j Only at the Surface. Artificial Ice. Steam. The Boiling Point 
 Changes with Pressure. Solutions. Properties of Solutions. 
 Freezing Mixtures. Solubility. Crystals. Summary. Exercises. 
 
 CHAPTER VI. 
 
 Elements and Compounds 94 
 
 Physical and Cheniical Changes. Composition of Water. 
 Electrolysis of Water. Elements and Compounds. Mixtures. 
 Preparation of Hydrogen. Properties of Hydrogen. Burning of 
 Hydrogen. Diffusion of Gases and Liquids. Exercises. Salt. 
 iSodium. Chlorine. Hydrochloric Acid. Ammonia. Sulphur. 
 <. Number of Elements and Compounds. Summary. Exercises. 
 
 CHAPTER VII. 
 Carbon and its Compounds . .110 
 
 Carbon as an Element. Coal. Uses of the Forms of Carbon. 
 Hydrocarbons. Petroleum. Flashing Point. Other Compounds 
 of Carbon. Dry Distillation of Coal and Wood. Exercises. 
 Carbon Dioxide. Carbon Dioxide in the Air. To Prepare Carbon 
 Dioxide. Carbon Dioxide in Fermentation. Baking Powders. 
 Carbon Dioxide as a Fire Extinguisher. Limestone. Summary. 
 Exercises. 
 
 CHAPTER VIII. 
 Magnets and Electricity . ( . . .125 
 
 Magnets. Poles of a Magnet. Magnetic Substances. The 
 Magnetic Field. The Earth a Magnet. Exercises. Electric 
 Charges from Friction. Conductors and Insulators. Attraction 
 and Repulsion. Induction of Charges. Electric Discharge. Stor- 
 ing a Charge; Leyden Jar. Electricity of the Atmosphere. Light- 
 ning Rods. Exercises. Electric Currents. Kinds of ' Cells. Sal 
 Ammoniac Cell. Currents and Magnetism. Electro-Magnets. 
 The Telegraph. Electric Bell. Changing the Current into Light. 
 Electric Furnaces. Electroplating. The Dynamo. Electric Mo- 
 tor. Electric Power. Summary. Exercises. 
 
CONTENTS XL 
 
 CHAPTER IX. 
 
 Light and Sound 150 
 
 Luminous Bodies. Transparent and Opaque Bodies. Light and 
 Its Properties. Images through Small Openings. Shadows. 
 Brightness or Intensity of Light. Candle Power. Exercises. 
 Division of Light Striking a Body. Reflection of Light. Mirrors. 
 Dispersed or Diffused Light. Refraction of Light. The Lens. 
 Composition of White Light. The Rainbow. Absorption of Light; 
 Color. The Sky and Its Colors. Change of Light into Heat. 
 Light and Life. Exercises. Simple Microscope. Compound Mi- 
 croscope. The Camera. How Sounds are Made and Carried. 
 Sound Waves. Echoes. Noise and Tone. The Telephone. 
 
 Summary. Exercises. 
 
 CHAPTER X. 
 
 Simple Machines 174 
 
 Need of Machines. Law of Machines. The Lever. Classes of 
 Levers. Exercises. Pulleys. Wheel and Axle. Inclined Plane. 
 
 The Wedge. The Screw. Friction. Sailboat. The Kite. 
 The Airship. The Windmill. Summary. Exercises. 
 
 CHAPTER XI. 
 
 Acids, Alkalies, and Cleaning 188 
 
 Acids. Classes of Acids. Acids and Coloring Matter. Action 
 of Acids with Metals. Action of Acids with Carbonates. Alkalies 
 or Bases. Caustic Soda and Caustic Potash. Neutralization; 
 Salts. Tests for Certain Salts. Exercises. The Washing of Cloth- 
 ing. Soap and Soap Making. Action of Soap. Soap and Hard 
 Water. Materials of Clothing. Dyes. Paints. Removal of 
 Stains. Summary. Exercises. 
 
 CHAPTER XII. 
 
 Water, Heat, Air, and Light in the House . 207 
 
 Modern Conveniences. Water Supply. Plumbing. Hydrants 
 and Traps. Kindling a Fire; Matches. The Fireplace. Stoves. 
 Gas Stoves. Gasoline Stoves. Electric Stoves and Heaters. 
 Stream and Hot Water Heating. Thermostat. Exercises. Need 
 of Ventilation. Methods of Ventilation. Ventilation without 
 Fans. Need of Moisture in Air. Light in the House. Glass. 
 Artificial Lighting. Gas for Lighting. Incandescent Mantles. 
 Gas Pipes and Fixtures. The Gas Meter. Acetylene for Lighting. 
 
 Electric Lighting. The Electric Meter. Summary. Exercises. 
 
Xll CONTENTS 
 
 CHAPTER XIII. 
 The Weather . . 232 
 
 Causes of Weather. Changes in Density and Pressure of Air. 
 Heating of the Air. Moisture of the Air. Humidity. Dew and 
 Frost. Fogs and Clouds. Forms of Clouds. Rain and Snow. 
 Hail. Rainfall. Exercises. The Winds. Regular Win ds. 
 Storms and Cyclones. Thunderstorms. Tornadoes. Cyclones of 
 the Tropics. Weather Service. Weather Maps. Summary. 
 Exercises. 
 
 CHAPTER XIV. 
 Rocks and Soil . 258 
 
 The Earth's Crust. Some Common Rocks. Classes of Rocks. 
 Origin of Stratified Rocks. Origin of Igneous and Metamorphic 
 Rocks. Weathering of Rocks. Causes of Weathering. Drift. 
 Erosion. Exercises. Soil. Structure of Soil. Tilling the Soil. 
 Irrigation. Fertility. Loss of Fertility. Preserving and Re- 
 storing Fertility. Rotation of Crops. Artificial Fertilizers. 
 Summary. Exercises. 
 
 CHAPTER XV. 
 
 Plants . . , . ... . . . . .;, ' ,-, - ..,.. ... . 282 
 
 Plants and the Soil. Functions of Plants. Germination of a 
 Bean. Other Seeds. Leaves. Work of Leaves. Modified 
 Leaves. Stems. Structure of Stems; Wood. Sap. Buds. 
 Roots. Underground Storage of Food. Flowers. Formation of 
 Seeds. Dispersal of Seeds. Exercises. Classes of Plants. 
 Algae. Fungi. Mosses. Ferns. Seed Plants. Economic 
 Plants. Distribution of Plants. Summary. Exercises. 
 
 CHAPTER XVI. 
 
 Animals . . . . . 312 
 
 What is an Animal? One-Celled Animals. Simple Many-Celled 
 Animals. Starfishes. Worms. Mollusks. Crustaceans. In- 
 sects. Exercises. Fishes. Amphibians. Reptiles. Birds. 
 Mammals. Importance of Animals to Man. Summary. Exer- 
 cises. 
 
CONTENTS Xlll 
 
 CHAPTER XVII. 
 
 The Human Body and Its Food 338 
 
 Chief Divisions of the Body. Cells and Tissues of the Body. 
 Structure of Bones. Joints. The Skeleton. Muscles and Tendons. 
 Injuries to Bones and Muscles. Kinds of Food. Organs of Di- 
 gestion; Glands. The Mouth. The Teeth. The Swallowing of 
 Food. Exercises. The Stomach. Gastric Juice. The Intestines. 
 
 The Liver. The Pancreas. Changes in Food by Digestion. 
 Absorption and Assimilation of Food. Storage of Food. Alcohol 
 and Its Effects. Summary. Exercises. 
 
 CHAPTER XVIII. 
 
 Circulation and Respiration 372 
 
 Circulation of the Blood. The Heart. Arteries and Veins. 
 Capillaries. Blood. Lymph. Excretion. Respiration. The 
 Lungs. Exchange of Gases in the Lungs. Inspiration. Expira- 
 tion. Exercises. The Nostrils and Pharynx. The Larynx and 
 Trachea. The Voice. Speech. Care of the Organs of Respiration. 
 
 The Skin. Perspiration. Hair and Nails. Functions of the 
 Skin. Summary. Exercises. 
 
 CHAPTER XIX. 
 
 The Nerves and the Sense Organs 395 
 
 The Nervous System. Nerve Cells and their Structure. The 
 Brain and its Parts. Spinal Cord. Sympathetic System. Nervous 
 System as a Whole. Voluntary and Involuntary Action. Reflex 
 Action. Habit. Effect of Alcohol and Tobacco on the Nerves. 
 Exercises. The Special Senses. Touch. Taste. Smell. Hear- 
 ing; Structure of the Ear. Sight. Eye Socket and Lids. Parts of 
 the Eye. Accommodaton. Near and Far Sight. Summary. 
 Exercises. 
 
 CHAPTER XX. 
 
 Sanitation 425 
 
 Bacteria and their Relation to Disease. How the Body Resists 
 Bacteria. Natural Destruction of Germs. Artificial Destruction 
 of Germs; Antiseptics. The Housefly and Mosquito in Relation to 
 Public Health. Exposed Food. Drinking Fountains. Typhoid 
 and Sewage. Exercises. Tuberculosis and its Cure. Spitting in 
 Public. Colds. Diphtheria. Antitoxins. Smallpox. Vaccina- 
 tion. Malaria and Yellow Fever. Quarantine. Disinfection. 
 Summary. Exercises. 
 
THE FIRST YEAR OF SCIENCE 
 
 CHAPTER I 
 
 MATTER AND ITS MEASUREMENT 
 
 1. The Earth and Science. In order that we may get 
 a knowledge of the earth we must study the separate 
 parts that make it up. We have already done this some- 
 what in Geography. Hence we know that the earth con- 
 sists of many different rocks and soils, trees and plants; 
 of bodies and streams of water; of the air; of a multitude 
 of animals that live on or in the soil, the vegetation, and 
 the water. We call any particular rock, tree, lake, or 
 animal an object, or body. The sum of all its objects, 
 large and small, is the earth itself. Nature, or the Uni- 
 verse, includes the earth together with the sun, moon, 
 stars, etc. 
 
 Science is the study of the truth about the objects of 
 nature. Since the number of objects is very large, one 
 method of studying nature is to find important resem- 
 blances and differences between objects. We can then 
 arrange objects in groups or classes. Thus, we can make 
 a division of all objects into (a) living objects and (6) 
 non-living objects. Living things may then be classified 
 as either animals or plants. Plants in their turn may be 
 
 i 
 
"/ 
 
 2 MATTER AND ITS MEASUREMENT 
 
 grouped as flowering or non-flowering plants, and each of 
 these will have many divisions. To take one illustration : 
 the daisy, the dandelion, and the sunflower belong in one 
 great group of flowering plants because the structure of 
 their flowers is similar, while the rose, the strawberry, 
 and the apple belong in an entirely different group. 
 
 But the classifying of objects, while very valuable, is 
 only a part of science. By far the greater part is taken up 
 with the study of the objects themselves. We want to 
 know their beginning, or origin, what they do, and what 
 becomes of them. For the objects of nature are always 
 changing. Living things grow, and then decay; rocks 
 are made, and then crumble. Even the "eternal hills" 
 are worn away, and the "fixed" stars appear to be fixed 
 only because, to the eye, they change their positions so 
 slowly. 
 
 2. Phenomena. By a "phenomenon" (plural, phe- 
 nomena) we mean simply a happening, a change, that takes 
 place in some object. It is not necessarily a strange 
 occurrence, like the appearing of a comet or an eclipse. 
 We observe a phenomenon when we see a marble roll over 
 the floor, when an apple falls to the ground, when a com- 
 pass needle takes a north and south position, when an 
 electric light is "turned on" or "goes out." Other phe- 
 nomena are such common changes as the burning of wood, 
 the souring of milk, the freezing of water, and the rusting 
 of iron. 
 
 * 3. The Scientific Way, or Method. Primitive man 
 probably reasoned in a very childish way about objects 
 
THE SCIENTIFIC WAY 
 
 and phenomena. We know that men were once satisfied 
 to explain an eclipse of the sun (cf. 169) by saying that 
 it was caused by a great dragon, or bird, or spirit, passing 
 across the sky. Even in comparatively recent times 
 people have had ideas only a little better, for when Colum- 
 bus asserted that the earth was a sphere the men of his 
 day ridiculed him. They were sure that if the earth were 
 round, the people on the other side of the earth must be 
 standing on their heads. 
 
 But men interested in finding out about nature have 
 kept on experimenting and reasoning, until they have 
 come to understand something of nature's ways. They 
 have made the most progress when they have used the 
 method of study which we now call the scientific method. 
 This method consists in 
 
 (a) getting together as many facts as possible regard- 
 ing the object or phenomenon studied; 
 
 (b) arranging these facts in the order of their impor- 
 tance; 
 
 (c) drawing some conclusion. 
 
 Men now use the scientific method to get at every sort 
 of knowledge, even the knowledge needed to conduct a 
 business or to "keep house." 
 
 We may, therefore, define science a second time and say that it is 
 organized knowledge. We call such knowledge "organized" because, 
 like a plant or animal, it is composed of parts called, in the plant or 
 animal, organs each of which has a particular place and a particular 
 duty. 
 
 General Science, which we are now to study, takes up many topics 
 also found in the special sciences, such as Physics, Chemistry, Botany, 
 Physiology, etc. A knowledge of these topics is necessary not only to 
 the students who are later to study the special sciences, but to every 
 
MATTER AND ITS MEASUREMENT 
 
 FIG. 1. 
 Flask with 
 a glass-stop- 
 pered tube. 
 
 one who wants to understand and to use scientific methods and 
 apparatus in the home, in the shop or store, on the farm in short, 
 anywhere in his daily life. 
 
 4. Matter. Suppose we examine a number of objects, 
 
 such as pieces of marble, sulphur, wood, lead, etc. They 
 are certainly unlike in color, size, and shape. 
 Are they alike in any particulars? In the first 
 place, they all take up room, or occupy space. 
 We cannot think of a body that does not. A 
 second way in which objects are alike is that all 
 of them have weight (cf. 20). We accept these 
 statements readily when we think of lead, of 
 marble, of water, of rock. These are solids or 
 liquids, and are readily seen and handled. But 
 even invisible gases, like the air, take up room 
 and have weight, just as solid and liquid objects 
 
 do. A vessel, such as a flask (Fig. 1), 
 
 from which the air may be removed, is 
 
 lighter when empty than when full of air. 
 
 Again, a vessel full of air cannot be filled 
 
 with water unless the air is allowed to 
 
 escape. We see this when we try to pour 
 
 water rapidly into a narrow-mouth bottle; 
 
 the water can enter only a little at a time, 
 
 as bubbles of air come out to make room 
 
 for it. Another illustration is seen in the 
 
 construction of a kerosene can (Fig. 2). The can has 
 
 an opening at the top not only to allow the can to be 
 
 filled with kerosene, but also to permit air to enter in 
 
 a steady stream as the kerosene is poured out of the 
 
 spout. 
 
 FIG. 2. 
 
 As kerosene comes out 
 air enters. 
 
SUBSTANCES 5 
 
 Now, why do all bodies occupy space? We answer by 
 saying that bodies are portions of matter, and that matter 
 occupies space. Matter not only occupies space, but it has 
 weight. When we give the weight of an object we give 
 the weight of the matter in it. 
 
 5. Substances. While it is important for us to get 
 the general idea of matter, yet we always observe and 
 study matter in separate portions, or bodies (cf. 1). 
 Each body may be made up of one kind of matter or of 
 several kinds. Thus, we might have chips of marble, 
 each consisting of one kind of matter (marble), or we 
 might have chips consisting of a mixture of marble and 
 clay. The kinds of matter are called substances. The 
 qualities, or characteristics, of a body depend upon the 
 qualities of the substance or substances of which it is 
 composed. The qualities of a substance are called its 
 properties. We learn the properties of any given sub- 
 stance by the use of our senses or by experiment. 
 
 Some illustrations will make clear the meaning of properties and the 
 difference between bodies and substances. A lake is a body of water; 
 water is not a body but a kind of matter, that is, a substance. A pencil 
 is a body consisting of the substances wood and "black lead," or 
 graphite (cf. 117). We can readily tell the wood from the graphite 
 by the properties of each. Thus, the wood is soft when cut; it is brittle, 
 light in color, and it floats upon water; it burns when heated in the air. 
 Graphite, on the other hand, has different properties. It too is brittle, 
 but its color is black, it sinks in water, burns with great difficulty, and 
 leaves a black mark when rubbed on paper. All these properties dis- 
 tinguish graphite from wood. 
 
 Sulphur, or "brimstone," is another common substance. It is dis- 
 tinguished from wood and from graphite by the following properties: 
 
6 MATTER AND ITS MEASUREMENT 
 
 it is yellow, crystalline (Fig. 3), brittle; it sinks in water, and does not 
 dissolve in water; it melts when heated, giving a clear, yellow liquid; 
 it burns readily in the air (cf. 51). Wood 
 tipped with sulphur, phosphorus, and some other 
 substances makes up another body, a match 
 (cf. 72). Now, the properties of the substances 
 FIQ 3 composing a match make the uses of the match 
 
 A Sulphur Crystal. quite different from the uses of a pencil. 
 
 General and Special Properties. We must remember 
 that the properties of a body, such as its filling space, hav- 
 ing weight, etc., are the general properties of all matter, 
 and do not belong to one substance more than to another. 
 The special, or specific, properties of a substance belong 
 to that substance alone. No two substances have exactly 
 the same special properties. 
 
 6. How We Measure Space and Matter. We know 
 from experience that all bodies have three dimensions; 
 namely, length, breadth, and thickness. We also think of 
 space as having these dimensions. When we say that a 
 body has a definite volume, we mean that it fills a definite 
 amount of space. We do not know what space is, but we 
 distinguish between space and matter, 
 calling that " space" which is not filled 
 with some object. On the earth, a por- 
 tion of space from which matter has 
 been removed is called a vacuum. As 
 already stated (cf. 4), air and other 
 gases are matter, not space. FlG 4 
 
 If a body is regular in shape, we can 
 readily calculate its volume. Thus, we obtain the vol- 
 ume of a cube (Fig. 4) from the formula, 
 
THE METRIC SYSTEM 
 
 Volume = length X breadth X thickness. 
 
 We can get the volume of an irregular solid by im- 
 mersing it in some liquid (Fig. 5). The body displaces 
 its own volume of liquid. 
 
 The boundaries of a body, by which the mat- 
 ter of the body is separated from other matter, 
 or from space, are called surfaces. A cube has 
 six plane surfaces. A sphere has a uniformly 
 curved surface. A surface has two dimensions, 
 length and breadth. The boundaries of a sur- 
 face are lines, with only the dimension of length. 
 
 50 
 40 
 
 ,, 
 
 FIG. 5. 
 
 7. Common Units of Length. The 
 
 unit of length used in Great Britain 
 and the United States is the yard. Originally the yard 
 was probably the length of the King's arm, but this 
 changeable standard has become fixed, and is now the 
 length of a standard metal bar kept in London, with a 
 copy at Washington. The foot was originally the length 
 of the human foot, but became fixed as ^ of a yard. 
 The inch was fixed as ^ of a foot. 
 
 8. The Metric System. The yard and its subdivisions 
 and multiples are still used for ordinary measurements 
 in this country and England, but on the continent of 
 Europe a different system prevails. This is called the 
 metric system, from its standard, the meter. It is a 
 decimal system, and has been adopted by scientific writers 
 the world over. The coinage of this country has long been 
 upon the decimal basis, and the names used for subdivi- 
 sions of the dollar are also used for subdivisions of the 
 
8 MATTER AND ITS MEASUREMENT 
 
 meter. The name of the smallest money unit, the mill, 
 is derived from the Latin millia, meaning 1000. Cent is 
 from centum, or 100, and dime is from decem, meaning 10. 
 A mill is iffio of a dollar; a cent is 150 ; a dime, A. In 
 the same way 1^5 of a meter is called a millimeter ; n^, 
 a centimeter; and ^, a decimeter. 
 
 9. The Standard Meter. Men intended that the meter 
 should be 40,000.000 of the earth's circumference, but 
 we now define it as the distance between two fine lines 
 
 ruled on a metal bar 
 (Fig. 6). The bar is 
 made of an alloy (mix- 
 united StatefproLype Meter. tui>e ) f tn ^ metals pldtl- 
 
 num and indium. While 
 
 the distance between the lines is being measured, the 
 bar is kept at the temperature of melting ice; that is, 
 at Centigrade (cf. 63 and 69). Thirty-one inter- 
 national standard meters were made at Paris and dis- 
 
 D 1 23456 
 
 1 1 ii 1 1 II 1 i M I In 1 1 1 1 II 1 1 1 ii I 1 1 1 1 M 1 1 1 1 M li 1 1 il in i II 1 1 1 1 
 
 7 8 C 
 
 1 1 1 1 1 II 1 1 1 II II 11 1 
 
 .M 
 
 1 i ' j ' i ' 1 ' | ' | ' i ' 1 ' i | ' i ' | ' i i i 
 
 D I 2 
 FIG. 7. 
 Inches and Centimeters. 
 
 1 | ' 1 < | ' 1 ' 
 
 3 IN. 
 
 tributed among the principal governments of the world. 
 Two of them were brought to the United States and are 
 kept at Washington. 
 
 The length of the meter is 39.37 inches, or 3.28 feet. The exact 
 measurement of the meter is very difficult, because the metal bar 
 changes its length slightly, but in recent years the meter has been made 
 
LARGER UNITS OF LENGTH 9 
 
 equal to the length of a certain number of light-waves (cf. 179), so 
 that if all the standard meters were destroyed, a new, perfect meter 
 could be obtained. 
 
 10. Metric Tables of Length, Area, and Volume. 
 
 The metric table of length (Fig. 7) is 
 
 10 millimeters (mm.) = 1 centimeter. 
 10 centimeters (cm.) = 1 decimeter. 
 10 decimeters (dm.) = 1 meter. 
 1000 meters (m.) = 1 kilometer. 
 
 1 kilometer (km.) =0.6214 mile. 
 
 For surface measure the table is 
 
 100 square millimeters = 1 square centimeter. 
 100 square centimeters = 1 square decimeter. 
 100 square decimeters = 1 square meter. 
 
 For cubic measure the table is - 
 
 1000 cubic millimeters (c. mm.) = 1 cubic centimeter. 
 
 1000 cubic centimeters (c.c. or c.cm.) = 1 cubic decimeter. 
 1000 cubic decimeters (c. dm.) = 1 cubic meter. 
 
 One cubic decimeter is called a liter (pronounced leter). 
 It is a little larger than a U. S. liquid quart. As the last 
 table shows, the cubic decimeter, and therefore the liter, 
 contains 1000 cubic centimeters. The relation between 
 metric units and other ordinary units is shown in the 
 Appendix, Table II. 
 
 11. Larger Units of Length. For distances on the earth the mile 
 (5,280 feet) and the kilometer (3,281 feet) are convenient units. But 
 when we express, in miles, the distance of the earth from the sun, the 
 
10 
 
 MATTER AND ITS MEASUREMENT 
 
 /* 
 
 FIG. 8. 
 
 The Big Dipper and the North Star 
 on September 22, 8 p. m. 
 
 number about 93,000,000 is so large that it means very little to 
 us. We can get a better idea of the distance by saying that it takes 
 over eight minutes (499 seconds) for the sun's light to reach us, al- 
 , though light travels at the rate of about 
 186,000 miles (300,000 kilometers) each 
 second. Or we may say that a train 
 traveling a mile a minute would need 
 about 178 years to get to the sun. Yet 
 the earth's distance from the sun is very 
 small as compared with its distance from 
 the stars. The light of the nearest fixed 
 star requires about 4 years to reach the 
 earth; while the light of Polaris, the 
 " North Star" (Fig. 8), that enters our 
 eyes to-night left the star about 47 years 
 ago. In order to avoid the use of the 
 many figures needed to express such 
 enormous distances in miles astronomers use a larger unit for star 
 distances. This unit is the light-year; that is, the distance which 
 light travels in a year. The light-year is about 63,000 times as great 
 as the distance of the earth from the 
 sun, or 63,000X93,000,000 miles. 
 
 12. Weight. Just as we might 
 estimate moderate distances by 
 means of our ' ' sense of distance/' 
 or " sense of space," so we might 
 get the weights of many objects 
 by using our " sense of weight." 
 In fact, the experienced cashier 
 and baggageman often develop 
 
 the sense of weight to a remarkable degree, owing to 
 years of training in the "hefting" of coins and trunks, 
 respectively. However, to get distances accurately we 
 
 FIG. 9. 
 
 The Chemical Balance. 
 
UNITS OF WEIGHT 
 
 11 
 
 FIG. 10. 
 Trip Scale. 
 
 use measuring rods, tapes, chains, etc., and to get 
 accurate weights we use balances and scales. 
 
 If the balance has two arms of equal length, as in 
 the chemical balance (Fig. 9) and 
 the "trip" balance of the labora- 
 tory (Fig. 10), the weights used as 
 the counterpoise must be exactly as 
 heavy as the object weighed. The 
 
 object to be weighed on 
 
 such balances is placed in 
 
 the left-hand pan, and the weights in the right. 
 
 In making the spring balance (Fig. 11) the manufac- 
 turers stretch the spring by means of weights placed on 
 the hook, and then mark the successive positions of the 
 pointer on the graduated scale. A body which stretches 
 FIG. 11. the spring to the same extent must be just as heavy as 
 the weights used. Scales for weighing heavy objects, 
 such as cars, or loads of hay or coal, are made by putting together a 
 system of levers (cf. 198), so that the whole apparatus can be kept 
 in a small space under the weighing platform. 
 
 13. Units of Weight. Man has used many units of 
 weight. The old English pound (from the Latin pondus, 
 a weight) was originally the weight of 7680 grains of wheat 
 "all taken from the middle of the ear, and well dried." 
 From this origin of the pound came the word "grain," 
 the small division of the pound. Henry VIII, King of 
 England from 1509 to 1547, made the "avoirdupois" 
 pound the unit of weight. It contains 16 ounces, or 7000 
 grains. In 1758 a piece of brass of suitable size was de- 
 clared by Parliament to be a pound. Later, a piece of 
 
12 
 
 MATTER AND ITS MEASUREMENT 
 
 platinum was substituted for the brass. The English 
 pound weight is still this platinum standard pound. 
 Copies of it, also of platinum, are kept in the United 
 States (Washington) and in other countries. 
 
 The abbreviation "lb.," for "pound," comes from the Latin libra, 
 or scales. The word "ounce" is probably from unus, "one," and was 
 originally applied to & of a pound, as it still is in "Troy " weight. In 
 the form "inch" it was also applied to 1*3 of a foot. The ton probably 
 
 received its name from the "tun," a 
 large cask that held about 2,000 pounds 
 of water. 
 
 14. Metric Units of Weight- 
 In the metric system the com- 
 mon weight units are the gram 
 and kilogram (1000 grams). A 
 liter of pure water at 4 C. (cf. 
 87) weighs one kilogram. This 
 is abbreviated to "kilo" or to 
 1 i kg. ' ' The international stand- 
 ard kilogram is a piece of plati- 
 num, as is the English standard 
 pound. Forty of these were constructed in Paris, and 
 two of them are in the Bureau of Standards, at Wash- 
 ington (Fig. 12). 
 
 FIG. 12. 
 The Standard Kilogram. 
 
 One cubic centimeter of water, that is, i^bo of a liter, 
 weighs one gram. 
 
 Subdivisions of the gram, like those of the meter, are formed from 
 the prefixes "milli," "centi," and "ded." 
 
BUREAU OF STANDARDS 13 
 
 10 milligrams (ing.) = 1 centigram. 
 10 centigrams (eg.) = 1 decigram. 
 10 decigrams (dg.) = 1 gram. 
 1000 grams (g.) = 1 kilogram. 
 
 1 kilogram (kg.) = 2.2046 Ibs. 
 1000 kilograms = 1 metric ton. 
 
 Two advantages which the metric system has over the English sys- 
 tem are: 
 
 (1) It is a decimal system. 
 
 (2) It is already in use in practically all of Europe, and in Latin 
 America. 
 
 Just as we can gather together "one dollar, four dimes, and three 
 cents" into the expression "$1.43," so we can write "two grams, 
 five decigrams, three centigrams, and one milligram" as "2.531 g." 
 A weight consisting of several English units, such as two pounds, six 
 ounces, and fifteen grains, cannot be expressed in pounds without 
 much calculation. 
 
 15. Bureau of Standards. Since it is important that 
 all apparatus used for measuring shall be correct, several 
 governments have established "Bureaus of Standards/' 
 to which such apparatus may be sent for the purpose of 
 comparing it with the standard apparatus of the govern- 
 ment. The United States Bureau of Standards (Fig. 13) 
 was established at Washington in 1901. 
 
 Originally the Bureau was only a place for keeping the pound, yard, 
 gallon, bushel, meter, kilogram, etc., up to standard, but it has grown 
 to be much more than this. The many new industries that have 
 arisen in recent years and the application of scientific methods to old 
 industries make new standards necessary. It is also important that 
 both the quantities of the materials that go into manufactured articles, 
 as well as their qualities, or properties (cf. 5), shall be definitely 
 known. Hence the Bureau furnishes standards of measurement for 
 electricity, the unit of light intensity (known as the "candle power"; 
 
14 MATTER AND ITS MEASUREMENT 
 
 cf. 171), standard thermometers for determining temperature (c/. 
 63), and standard pyrometers for determining higher temperatures 
 than the thermometer will measure. We can realize the value of this 
 work when we understand that the measurement of high temperatures, 
 for example, is necessary in such important industries as making glass, 
 
 FIG. 13. 
 The Bureau of Standards. 
 
 pottery, and illuminating gas, and in the preparation and working of 
 the metals. Besides, the Bureau determines the strength of materials 
 such as wood, steel, and cement, the fuel value of coal, petroleum, etc., 
 as well as many other properties which the modern manufacturer 
 needs to know. 
 
 16. Summary. Science is organized knowledge. It arranges ob- 
 jects into groups or classes and studies the changes that objects 
 undergo. 
 
SUMMARY 15 
 
 The scientific method is necessary in everyday life quite as much 
 as in study and investigation. 
 
 Phenomena are the changes in objects. 
 
 Objects are portions of matter. 
 
 Matter exists in the solid, the liquid, and the gaseous form. 
 
 Matter occupies space and has weight. 
 
 Substances are the kinds of matter. 
 
 Properties are the qualities by which we distinguish one substance 
 from another. 
 
 Space is that which contains no matter. 
 
 A space from which the matter has been removed is called a vacuum. 
 
 Matter has three dimensions: length, breadth, and thickness. 
 
 The meter is the unit of the metric system. It contains 39.37 inches.. 
 
 The kilometer is 0.6214 miles. 
 
 The liter is the unit of volume. It equals 1 cubic decimeter, or 
 1.0567 U. S. liquid quarts. 
 
 The standard pound weight contains 16 ounces, or 7000 grains. 
 
 The gram is the weight of 1 cubic centimeter of pure water at 4 C. 
 
 The kilogram is 1000 grams. It is the weight of one liter of pure 
 water, and equals 2.2046 pounds. 
 
 The Bureau of Standards keeps the standard weights and measures, 
 compares common weights and measures with the standard ones, makes 
 new standards as new industries demand them, and determines the 
 properties of materials. 
 
 17. Exercises. 
 
 1. Name the so-called "five senses." Are there any senses besides 
 these? Explain. 
 
 2. Name two substances that you can distinguish from each other 
 by each of the five senses. For ' ' hearing," think of the way we test the 
 genuineness of a coin. * 
 
 3. Make a list of ten objects, and write opposite each the substance 
 or substances of which it is made up. 
 
 4. Make a list of all the properties you can think of for each of the 
 following substances: iron, water, sugar, wood, and coal. 
 
16 MATTER AND ITS MEASUREMENT 
 
 5. Name five phenomena besides those of 2. 
 
 6. Compare the way in which water is poured out of an inverted, 
 small-mouth bottle with the way in which it is poured out of a pitcher. 
 Explain. 
 
 7. Find the number of cubic feet of air in a room 14 ft. by 14 ft. by 
 9 ft. high. Find the weight of the air in ounces, if one cubic foot of air 
 weighs 1% ounces. Reduce the weight to pounds. 
 
 8. Write down as grams and decimal parts of a gram 6 grams, 5 
 decigrams, 3 centigrams, and 9 milligrams. Subtract from this number 
 the sum of 2 grams and 8 centigrams. 
 
 9. Locate the North Star to-night or the next clear night, note the 
 hour, and draw a diagram to show the position of the "Big Dipper" 
 with reference to the star. What stars of the dipper are the ' ' Pointers' ' ? 
 
 10. Look up (in the Glossary at the back of this book) the difference 
 between planets and fixed stars. Name some of the planets. Name 
 some fixed stars besides Polaris. 
 
 11. Look up the distance of the moon from the earth. What is the 
 moon's diameter? The earth's? 
 
 12. Look in a dictionary for the origin of the words quart, gram, 
 meter, vacuum, and substance. 
 
 13. What are the proofs that the earth is sphere-like and not flat? 
 
 14. Name some scientific methods or apparatus that have recently 
 been brought into our homes. Into factories. Into stores. Name 
 some that are used on the farm. In navigation. 
 
CHAPTER II 
 
 FORCE AND ENERGY 
 
 18. Gravity. Many of our most common phenomena 
 are simply changes in the position of bodies. The falling 
 of an apple, the movement of water in waves and tides, 
 the flight of a stone or a bullet through the air, all illustrate 
 this. So do the turning of a magnetic needle toward the 
 poles and the vibrating of a violin string. Now, why 
 does a stone or an apple "fall"? Sir Isaac Newton gave 
 the reason when he said that the earth pulls the apple 
 and all other falling bodies. We do not find it easy to 
 picture to ourselves just how the earth's ' ' pull " is applied. 
 A horse pulling a wagon is attached to the wagon, and the 
 strength of his muscles overcomes the tendency of the 
 wagon to remain at rest. Similarly, an engine is attached 
 to the cars it pulls. But the earth's attraction acts 
 through space, without visible or invisible attachment. 
 
 We can illustrate the earth's attraction, on a small scale, by the 
 action of a magnet upon an iron nail. The magnet is a piece of steel 
 which has been "magnetized," so that it has the power of drawing to 
 itself bodies consisting of steel, iron, nickel, etc. There is no connection 
 between the magnet and the attracted object, yet we know that there 
 is action between them. 
 
 It is just as necessary for us to assume that the apple 
 attracts the earth as that the earth attracts the apple. 
 It is also just as reasonable to suppose that the earth falls 
 
 17 
 
18 
 
 FORCE AND ENERGY 
 
 toward the apple as that the apple falls toward the earth. 
 But the distance that the earth moves before they meet 
 must, of course, be very small, owing to the much greater 
 size of the earth. This earth-pull we call gravity. 
 
 19. Gravitation. The attraction which exists be- 
 tween the earth and bodies near its surface exists also 
 
 between all bodies of matter on the earth 
 and between the earth and the sun, moon, 
 and other heavenly bodies. It is called gravi- 
 tation. Gravity is merely a particular case 
 of gravitation. 
 
 The gravitation, or attraction, between two 
 bodies on the earth, as, for example, between 
 two suspended balls (Fig. 14), is not easily 
 observed, because the great attraction of the 
 earth for both of them holds them in a ver- 
 tical position. By means of a celebrated 
 experiment first carried out in the latter part 
 of the 18th century this attraction was made 
 visible. A large ball of lead and a small one 
 of copper were suspended side by side, with 
 
 the result that the copper ball was drawn aside from a 
 
 vertical position. 
 
 20. Mass and Weight. We need to distinguish be- 
 tween the mass of a body and the weight of a body. New- 
 ton saw that the earth's attraction for a body depends on 
 the quantity of matter in the body, and not upon its kind. 
 A pound of feathers is attracted with the same force as a 
 pound of lead. The quantity of matter in a body is called 
 
 FIG. 14. 
 
 The two balls 
 
 attract each 
 
 other. 
 
MASS AND WEIGHT 
 
 19 
 
 the mass of the body. The weight of the body is the re- 
 sult of the earth's pull upon the mass of the body. If, in 
 some way, the pull upon a given body is increased, the 
 weight will be in- 
 creased; but if the 
 pull is weakened, the 
 weight will be de- 
 creased. Now, how 
 can we change the 
 effect of gravity, that 
 is, the attraction of 
 the earth for a cer- 
 tain mass? We can 
 do it by changing the 
 distance between the 
 earth and the body. 
 In other words, the 
 attraction between 
 two bodies depends 
 not only on their 
 masses, but also on the distance they are apart. The 
 distance between two bodies is taken to be the distance 
 between their centers. 
 
 Suppose we have two balls weighing, say, 10 grams each, and 1 inch 
 apart. If we place them 2 inches apart, the force of the attraction be- 
 tween them will be only % as great as at 1 inch. If the distance be- 
 tween them is made ^ an inch, the attraction will be 4 times what it 
 was originally. Now, we have learned that the earth is not a perfect 
 sphere, but is flattened at the poles. An object at the poles is about 13 
 miles nearer the earth's center than if it were at the equator. As a 
 result of this difference a body weighing 589 pounds at the equator 
 would weigh 590 pounds at the poles. 
 
 Copyright International Stereograph Co., Decatur, 111. 
 
 FIG. 15. 
 Leaning Tower of Pisa. 
 
20 FORCE AND ENERGY 
 
 If we remove a body from the earth at any given place, that is, if we 
 take it ' 'up in the air," or on a mountain top, it will also lose in weight. 
 The mass of the body will, of course, remain the same everywhere. 
 
 21. Falling Bodies. We know that if we drop a stone 
 it falls "straight down." We have also seen bricklayers 
 using a string with a weight attached 
 a plumbline to be sure that they were 
 making a wall vertical. The position taken 
 by the plumbline, like the path of the 
 falling ball, shows that gravity pulls ver- 
 tically downward. 
 
 But objects that are very light, like 
 feathers, seem to fall more slowly than 
 heavy objects. Why is this? Galileo, 
 dropping balls of different sizes and differ- 
 ent materials from the "leaning tower" of 
 Pisa (Fig. 15), insisted that all objects, 
 FIG. 16. heavy and light, if let fall from the same 
 Bodie va^uum gina height, should reach the ground at the 
 same time. A feather and a bullet would 
 fall at the same rate were it not for the air, which resists 
 being pushed out of the way. In a tube free from air, that 
 is, in a vacuum (Fig. 16) they do fall at the same rate. 
 
 On a very windy day even a heavy body may not fall straight down. 
 Thus an apple blown off the tree by a sudden gust will go in the direc- 
 tion of the wind (horizontally) and also downward. It cannot go in 
 either of these directions alone, so it goes down in a curved path. But 
 it will reach the ground by the longer, curved path in the same time 
 as if it fell vertically to the ground. This fact may be illustrated by 
 two marbles (Fig. 17) one of which is given a horizontal blow, while 
 the other is permitted to fall vertically. 
 
FORCE 21 
 
 22. Exercises. 
 
 1. Name five phenomena, besides those of 18, that are "changes 
 in the position of bodies." 
 
 2. Suppose that the moon and the earth were of exactly the same 
 mass, and that a ball weighing a ton were placed half-way between 
 them. What would its weight be? 
 
 Why? 
 
 3. If you dropped wooden, iron, and 
 lead balls from an upper window, which 
 would reach the ground first? 
 
 4. Suppose the wind were blowing 
 hard down the street, and you dropped 
 a tennis ball from an upper window. 
 Where would it strike the ground? 
 Why? 
 
 5. Draw a diagram to show the kind The Marbleg ^ &t ^ 
 of a path a ball takes if you throw it Same instant. 
 horizontally. If you throw it upward 
 
 at an angle of 45 degrees (half a right angle). In which case would 
 the ball have the greater range? 
 
 6. Who was Sir Isaac Newton? When did he live, and where? 
 What did he add to our knowledge? 
 
 Answer the same questions regarding Galileo. 
 
 23. Force. Let us imagine we are at a baseball game. 
 The pitcher throws a "fair" ball, the batter strikes at it 
 but makes a "foul" hit, and the catcher catches the ball. 
 Three persons were concerned in the flight of that ball: 
 the pitcher, who set it in motion ; the batter, who changed 
 the direction of its motion; and the catcher, who stopped 
 its motion. We say that all three exerted force upon the 
 ball. 
 
 Besides the players, two other bodies exerted force upon 
 the pitched ball: (1) the air, which resisted being pushed 
 
22 
 
 FORCE AND ENERGY 
 
 out of the way and hence made the ball move more and 
 more slowly; (2) the earth, which by its downward pull 
 made the ball move in a path curving downward instead 
 of in a horizontal one. 
 
 This illustration shows us the ways in which one body 
 may exert force upon another: (1) it may set the other 
 body in motion; (2) it may change the direction of the 
 motion; (3) it may stop the motion. In addition, (4) one 
 body may change the velocity, or rate of motion, of another 
 and so exert force upon it. 
 
 Air exerts force, not simply by resisting other bodies 
 as they pass through it, but also as wind air in motion. 
 We use the force of the wind to sail a kite, to run a wind- 
 mill, or to drive a ship through the sea. 
 
 24. Force of Expanding Gases. What exerts the force 
 that sets a bullet in motion? The cartridge used in 
 modern firearms is partly filled with powder (Fig. 18), 
 and the open end of the cartridge is closed by the bullet. 
 
 Besides powder, the cartridge 
 contains a small amount of a 
 white solid called mercury ful- 
 minate, which, when given a 
 blow (percussion), sets the pow- 
 der on fire. The pulling of the 
 trigger releases the hammer of 
 
 the gun; the blow of the hammer causes the mercury 
 fulminate to ignite the powder, so that it "explodes." 
 By the explosion of the powder a gas is formed that will 
 take up, when released, perhaps 300 times as much space 
 as the original powder. In the cartridge the gas is under 
 
 FIG. 18. 
 
 Kinds of Powder: (1) Ordinary 
 Form; (2) Giant Powder. 
 
FORCE OF EXPANDING GASES 
 
 23 
 
 great pressure, because it is crowded into so small a 
 space. As it rushes out of the cartridge it expands, and 
 drives the bullet rapidly before it. 
 
 The steam engine, like the gun and cannon, is a device for producing 
 motion by means of the expansion of a compressed gas. Steam is pro- 
 duced, under high pressure, in a boiler (Fig. 19), and is allowed to ex- 
 pand in a cylinder, first on one side and then on the other, of a 
 
 FIG. 19. 
 Principle of the Steam Engine. 
 
 piston. The piston is thus moved rapidly to and fro. This forward and 
 backward motion is then changed to motion in a circle by means of a 
 shaft. The eccentric turns with the shaft and moves the slide valve. 
 The cause of motion in a gasoline engine is also the force exerted by 
 expanding gases. A mixture of gasoline vapor and air, which is ex- 
 ploded by an electric spark or a hot wire, is used in place of steam. 
 The explosion produces a large volume of hot gases, and the expansion 
 of the gases sets a piston in motion. 
 
 The force exerted in the examples given may be put in 
 one of the following classes : 
 
24 FORCE AND ENERGY 
 
 (1) Muscular force, such as that exerted by draught 
 animals and man. 
 
 (2) Gravity. 
 
 (3) The force of the wind. 
 
 (4) Resistance, such as that of air, water, the ground, 
 or the parts of machinery. We commonly call this 
 friction (cf. 206). 
 
 (5) The force of expanding gases. 
 
 Of course one body may exert force upon another and 
 yet not move it, as when you try to lift a weight too 
 heavy for you. 
 
 25. Work and Energy. When we raise a hammer 
 into the air, we do work upon it, for we lift it against grav- 
 ity. We also do work when we throw a ball, or wind up 
 a watch. In the last case we produce motion against the 
 elastic force of the spring. Because we can do work, we 
 say we have energy. Energy is the capacity for doing 
 work. A body that can do work upon another body 
 possesses energy. 
 
 The lifted hammer has energy because we have done 
 work upon it, and it, in its turn, can do work upon some 
 other body. If we let it fall, it can break a nutshell or 
 drive a nail into wood. While poised in the air, the 
 hammer has energy because of its position; while it is de- 
 scending it has energy of motion. In the same way, the 
 water of a waterfall has energy of position at the top of 
 the fall, but energy of motion as it descends. 
 
 A bullet in a gun at the instant of discharge can be said to have 
 energy of position because of the compressed gas behind it. In its 
 flight it has energy of motion. When it strikes a rock or a tree or other 
 
INERTIA OF MATTER 
 
 25 
 
 obstruction, it does work: it breaks the rock, or splits the tree, or flat- 
 tens itself. 
 
 When a body does work by lifting another body against gravity, the 
 amount of work done is obtained by multiplying the weight lifted 
 by the vertical distance it is lifted: 
 
 Work = weight X distance. 
 
 Thus, a workman carrying 50 Ibs. up a ladder 20 ft. high does just 
 as much work as one raising 40 Ibs. 25 ft., or 10 Ibs. 100 ft. 
 
 26. Power. In calculating the amount of work done 
 by a force we have not taken account of the time required. 
 Yet if we were choosing a 
 horse or an engine to raise 
 a weight (Fig. 20), we would 
 take the horse or engine that 
 could do the work most rap- 
 idly. The rate of doing work 
 is power. 
 
 The common unit of power 
 is the horse-power (written 
 H.P.) . James Watt, who de- 
 vised the unit, thought that 
 
 an average horse could raise 33,000 Ibs. 1 ft. in 1 minute, 
 or 550 Ibs. 1 ft. in 1 second. As a matter of fact, the 
 average American horse can exert only about three- 
 fourths of a horse-power; that is, it can raise about 25,000 
 Ibs. 1 ft. in 1 minute. 
 
 FIG. 20. 
 Horse Raising Weight of a Pile-Driver. 
 
 27. Inertia of Matter. In Chapter I we learned that 
 matter occupies space and has weight. What we have 
 now learned about force shows us that matter has another 
 
26 FORCE AND ENERGY 
 
 striking property helplessness. This property is com- 
 monly called inertia. We define inertia when we say that 
 matter cannot move itself, cannot stop itself if moving, 
 and cannot change the direction or rate of its motion. 
 
 There are many illustrations of inertia : 
 
 When you played "tag," and your playmate came rushing toward 
 you at full speed, you took advantage of the inertia of his body when 
 you l ' dodged." You knew he could not stop himself at once. 
 
 When you run around a corner, you go in a wide curve, because the 
 inertia of your body will not let you turn the corner sharply. 
 
 When you shake a rug, you are able to jerk the rug away from the 
 dirt because of the inertia of the dirt. 
 
 If you hit a suspended newspaper, you burst a hole in it, because 
 only the part struck moves forward while the rest of the newspaper 
 remains behind. 
 
 The air also has inertia. If we try to push it away suddenly, as by 
 thrusting forward a paper fastened in a large hoop, the air remains 
 where it was and tears the paper, just as a tree or a rock would. We 
 
 work against the inertia of air in mo- 
 
 ;/' N \ against a strong wind, or to "haul in" 
 
 / \ a sail in a gale. 
 
 
 \ 
 
 \ 28. " Flying from the Cen- 
 / ter." If a stone attached to 
 / a string is whirled about the 
 hand, it moves in a circle (Fig. 
 ^^ x 21). The circular path is the 
 
 FIG. 21. result of two forces: (1) the 
 
 The Circular Path is the Result of inertia rvf tVm rnr^nncr c+rmo 
 
 inertia and the string. uiertia oi me moving stone, 
 
 which, acting alone, would cause 
 
 the stone to move off in a straight line; and (2) the re- 
 sistance of the string, which compels the stone to remain 
 
EXERCISES 27 
 
 always at the same distance from the hand. Because 
 of the inertia of the moving stone we feel a decided 
 pull upon the string. The pull becomes the stronger the 
 more rapidly the stone is whirled. Finally the pull may 
 break the string. If it does, the stone will fly off in a 
 straight line. 
 
 This tendency of the matter of a revolving body to 
 fly off in a straight line is called centrifugal force. ' ' Cen- 
 trifugal" comes from words meaning "to fly from the 
 center." Centrifugal force is really no new kind of force, 
 but merely a result of the inertia of matter. 
 
 The flying off of mud from a revolving carriage wheel, and of water 
 from a turning grindstone, and our difficulty in turning a sharp corner 
 when we are running, are familiar illustrations of centrifugal force. 
 The planets continue in their paths around the sun because of inertia 
 together with the attraction between them and the sun. The dairy 
 separator is an apparatus for separating cream from milk by rapid 
 whirling. In this apparatus centrifugal force causes the milk, which 
 is the heavier, to move out farther than the cream, and so divides them. 
 
 29. Exercises. 
 
 1. Why is it so hard to walk upon a polished floor? Why is it easier 
 to skate on ice than to walk upon it? 
 
 2. Why does not gravitation draw the sun and earth together? 
 
 3. On which will a marble roll farther, a carpet or a smooth floor? 
 Why? Suppose we could roll the marble on a perfectly smooth, 
 horizontal plane, what force would there be to stop the marble? 
 
 4. When you strike the lowest of a pile of blocks a sharp blow, it 
 flies out, leaving the rest of the blocks piled up. Why? 
 
 5. What happens to a child sitting on a sled if the sled is 
 suddenly started? If the moving sled is suddenly stopped? In what 
 direction is the child thrown off if the sled turns a sharp corner? 
 Explain. 
 
28 
 
 FORCE AND ENERGY 
 
 6. What work was done upon the water of a waterfall to give it 
 energy? 
 
 7. What device is used to prevent a railway train from leaving the 
 track when rounding a curve? Is any similar device used in a gym- 
 nasium? On an automobile or motorcycle race course? 
 
 30. Cohesion and Adhesion. If we hold a sheet of 
 glass face down against the surface of some water, and 
 then pull the glass away from the water, we must use 
 more force than is needed to lift the glass against gravity 
 alone. Another force is being exerted on the glass. The 
 under side of the glass will be wet. This shows that in 
 pulling the glass away we did' not separate glass from 
 water, but water from water. We therefore did work 
 
 (cf. 25) against the force that 
 holds the water together. The 
 force that is exerted between 
 the particles of matter is called 
 cohesion. 
 
 We can find the amount of cohesion, 
 in the case of water, by attaching a 
 piece of glass by means of strings to 
 one arm of a balance (Fig. 22), allowing 
 the glass to touch the water, and then 
 adding weights to the other side of the 
 balance until we tear the glass away. 
 
 Of course we must subtract the weight of the glass from the total 
 
 weight to get the ''breaking weight" of the water. 
 
 FIG. 22. 
 
 Measuring the Force Needed to 
 Tear Water from Water. 
 
 When cohesion is exerted between different substances, 
 we call it adhesion. Thus cohesion holds water together, 
 and cohesion holds glass together, but adhesion holds 
 
THE SURFACE OF A LIQUID 
 
 29 
 
 water to glass. Since we pull water away from water, 
 we see that the cohesion of water is not as strong as the 
 adhesion of water to glass. 
 
 Cohesion in solids causes them to be rigid; that is, to 
 resist being strained or broken. 
 
 31. The Surface of a Liquid. We know that large 
 liquid surfaces are flat (horizontal) ; this is because grav- 
 ity pulls down equally on all parts of the surface. But 
 when the body of liquid is very small (a drop), the effect 
 of gravity is also small, and cohesion is able to pull the 
 liquid into the shape of a sphere. This is exactly the 
 shape that would be produced if the liquid were enclosed 
 in a tightly stretched, elastic covering, say, of rubber. 
 
 The shape of a drop of liquid depends on cohesion 
 alone, but a quantity of liquid in a vessel is acted upon 
 by three kinds of force, and the shape of its surface will 
 depend on all three. These are: (1) gravity, (2) cohesion 
 of the liquid, (3) adhe- 
 sion between the liquid 
 and the material of the 
 vessel. 
 
 FIG. 23. 
 
 Surfaces of Water (A) and Mercury (B). 
 
 Let us take the case of mer- 
 cury in a glass vessel (Fig. 23, 
 B). Mercury does not wet 
 glass. This means that the 
 cohesion of mercury is greater 
 
 than the adhesion between mercury and glass. Hence the surface 
 of the mercury curves outwards, or is convex, like the surface of a drop. 
 
 The case of water in a glass vessel is different (Fig. 23, A): water 
 wets glass. This means that the adhesion between water and glass is 
 greater than the cohesion of water. In such cases the liquid is drawn 
 
30 
 
 FORCE AND ENGERY 
 
 
 FIG. 24. 
 
 A Needle Floating on 
 Water. 
 
 up at the edges, and the surface curves inwards, or is concave ("hol- 
 lowed out"). 
 
 In a greased vessel water has a convex upper surface, like that of 
 mercury in a glass vessel. The cohesion of water is evidently stronger 
 than the adhesion between water and grease. 
 
 The curved surface of a liquid is called a meniscus. In 
 reading the level of water in a graduated cylinder (Fig. 5) 
 we read at the bottom of the meniscus. 
 That the surface of a liquid acts as 
 though it were an elastic covering, and 
 that it can be stretched, is shown by an 
 experiment in which a needle is floated 
 upon water (Fig. 24). The needle must 
 be put down carefully, or it will break 
 the elastic surface of the water. The experiment suc- 
 ceeds better if the needle is 
 slightly greased, so that the water 
 is certain not to wet it. 
 
 32. Capillary Action. If you 
 leave one end of a towel in a 
 bowl of water, the water rises, 
 against gravity, into the towel. 
 If you let a wet string, or> bet- 
 ter, a wet strip of cloth, hang 
 over the side of a dish of water 
 (Fig. 25), the water will rise 
 
 through the string or cloth, and so flow out of the dish. 
 If you touch a drop of ink with a blotter, the whole drop 
 will flow into the blotter. What causes these phenomena? 
 We say that the force exerted in these cases is " capillary " 
 
 FIG. 25. 
 
 Water Flowing by Capillary Action 
 Over the Side of a Dish. 
 
DENSITY AND SPECIFIC GRAVITY 
 
 31 
 
 
 B 
 
 FIG. 26. 
 
 A, Capillary Rise of Water; B, Capillary 
 Depression of Mercury. 
 
 action. "Capillary" means "hairlike." The phenome- 
 non is so called because it is commonly studied in tubes 
 of small diameter (Fig. 26). 
 
 Capillary action in water is due to adhesion between the 
 water and the capillary tube, and to the cohesion of the 
 water, which produces an 
 elastic surface. If the tube 
 is a large one, the water is 
 raised, but only at its edges, 
 as in the case of water in a 
 dish. The elastic surface 
 cannot exert force enough 
 to lift all the water in the 
 tube. But if the tube is of 
 small diameter a " capillary " tube the weight of the 
 water in the tube is small, and the elastic liquid surface 
 lifts the whole column of water up the tube. 
 
 Water rises in a capillary tube until the weight of the water is just 
 equal to the force exerted by the elastic surface. The upper surface of 
 the water column in a capillary tube is still concave. 
 
 If a glass capillary tube is placed in mercury (Fig. 26, B), the effect 
 is the opposite of that in water, and we have a capillary depression 
 instead of elevation. 
 
 Water rises up between two glass plates held close together just as 
 it does in capillary tubes. In the case of the blotter, cloth, string, etc., 
 the fibers of the material are so near one another that the spaces be- 
 tween them act like a multitude of fine tubes. 
 
 33. Density and Specific Gravity. If you were 
 "hefting" a piece of wood and a piece of lead, you would 
 say that wood is a light substance and lead a heavy one. 
 In saying this you would not mean that a large board of 
 
32 FORCE AND ENERGY 
 
 wood is lighter than a small lump of lead, but you would 
 mean that, taken volume for volume, wood is lighter than 
 lead. This is the same as saying that the density of wood 
 is less than the density of lead (Fig. 27). 
 
 We have already learned that the mass of a body is 
 the quantity of matter in it (c/. 20). We may now de- 
 
 Gold. Lead. Copper. Aluminum. Coal. Wood. 
 
 FIG. 27. 
 Cubes of Different Volumes, but of Equal Weight 
 
 fine the density of a body as the quantity of matter 
 packed in a given volume of the body. To get the mass of 
 a body we weigh it. To get the density of a body we 
 divide its weight, in grams, by its volume, in cubic 
 centimeters. 
 
 mass (in g.) 
 
 Density = 
 
 volume (in c.c.) 
 
 Suppose that a piece of marble weighs 5 g. and has a volume of 2 
 c.c. ; it is plain that 1 c.c. of the marble would weigh 2.5 g. We say that 
 the marble has a density of 2.5 g. for each cubic centimeter. The den- 
 sity of water is 1 g. for each cubic centimeter (c/. 14). In the Eng- 
 lish system the density of water is about 62.5 Ibs. for each cubic foot. 
 
 We often find the expression specific gravity used in place of density. 
 We get the specific gravity of a body by dividing the weight of the 
 body by the weight of an equal volume of water. 
 
 Wt. of body 
 Specific gravity = 
 
 Wt. of equal vol. of water 
 
BUOYANT FORCE OF LIQUIDS 
 
 33 
 
 When the density of a body is given as so many grams for 1 c.c., 
 the number representing the density is the same as the number for the 
 specific gravity. 
 
 34. Buoyant Force of Liquids. If we attach a string 
 to a block of wood, and lift the wood by the string, we 
 need to put forth a muscular effort equal to the weight of 
 the wood. But if we let the block rest on water, we do 
 not put forth any effort; the water supports the block. 
 We say that the block floats on the water. 
 
 If we hold a piece of stone by a string, first in air, and 
 then in water, we find that the stone is lighter (weighs 
 less) in water than in the air. Here the water does not 
 support all of the weight, but it does support part of it. 
 It is well known that a stone can be lifted much more 
 easily when it is under water 
 than when it is out of the water. 
 
 Suppose that some lead is cut or cast 
 in the form of a cube having a volume of 
 exactly 1 c.c., and is attached to one arm 
 of a balance, as in Fig. 28. If we weigh 
 it in air and then in water we shall find 
 that it weighs 1 gram less in water than 
 in the air. One cubic centimeter of iron, 
 glass, or marble, or of any solid which is 
 more dense than water, would lose the 
 same amount 1 gram when weighed 
 
 in water. Since the 1 c.c. of water displaced by each of the cubes 
 weighs just what the cube seems to lose, we conclude that a body put 
 under water is pushed, or buoyed, up by just the amount of the 
 water it displaces. A mass of iron, stone, glass, etc., having a volume 
 of a cubic foot would weigh 62.5 pounds less in water than in the air, 
 since this is the weight of a cubic foot of water (cf. 33). 
 
 FIG. 28. 
 
 A Solid Immersed in a Liquid is 
 Buoyed up by the Liquid. 
 
34 FORCE AND ENERGY 
 
 Not only water, but all liquids and gases, have this 
 buoyant power. The more dense the liquid or gas, the 
 greater is its power of buoyancy. Hence we may state 
 the facts regarding buoyant force as a general rule : 
 
 A body immersed in a liquid or gas is buoyed up with a 
 force just equal to the weight of the liquid or gas it displaces. 
 
 A floating body sinks into the liquid supporting it until it has pushed 
 aside its own weight of liquid. Thus a piece of cork 34 as dense as 
 water sinks until % of its volume is below water. A piece of ice 0.92 
 as heavy as water has 0.92 of its volume below water. 
 
 A needle (cf. 31) has really a much greater density than water, 
 but it can be supported on water because its weight is very small. As 
 a result the elastic surface of the water does not break. If the needle 
 becomes wet, the water surface breaks, and the needle sinks. 
 
 35. Center of Mass. Why does a slender stick 
 which has been set upright fall over so easily? Why 
 cannot we stand an egg "on end"? The answer is 
 found in a study of the center of mass of a body. 
 We all know what is meant by the center of a sphere: 
 it is the point around which the volume of the 
 sphere is arranged in a regular way. Let us call this cen- 
 ter the center of volume of the sphere. Now, in a wooden 
 ball or a lead ball the matter , as well as the volume, is all 
 grouped around the center; so we can call the center of 
 volume the center of mass, or center of gravity, of the ball. 
 
 If we were to mix small fragments of lead and sawdust 
 uniformly together, and pack thejn into a ball, the center 
 of mass of the ball would still be the same as its center of 
 volume. But if we were to make half of the ball of wood 
 and the other half of lead, and were to fasten the two 
 
CENTER OF MASS 
 
 35 
 
 halves together, the center of mass of the ball would not 
 
 be the same as its center of volume. Lead is so much 
 
 denser than wood that the center of mass would be 
 
 somewhere in the 
 
 lead half of the / 
 
 ball (Fig. 29). In /Lead wood\ 
 
 an egg the center \ 
 
 of mass is nearer \ 
 
 the larger than 
 
 the smaller end. 
 
 A body IS in its The Ball Takeg Pogition (2) The Heavy Knife Handles (3) 
 most ' ' Stable " pOSi- Bring the Center of Mass Below the Tip of the Pencil. 
 
 tion, that is, is best 
 
 able to stand, when the center of its mass is lowest, or nearest the 
 earth's center. A ball of wood is at rest in any position, because its 
 center of mass is as low in one position as in another, but a ball 
 half wood and half lead will be in a stable position ' only when the 
 lead half is the lower. An egg lies on its side but not on end because 
 when it is on its side its center of mass is lower. To make it stand on 
 end we would need to keep its center of mass exactly above the point at 
 which it rests upon the table or other support. As we cannot do this, 
 the egg rolls over. We ourselves stand when we keep the center of 
 mass of our bodies above the space bounded by our feet, but we fall 
 when we lean over so far that our center of mass is no longer vertically 
 above this space. 
 
 When an irregular body, such as a log or tree, lies on the ground, it 
 cannot shift itself so that it can bring its center of mass to the lowest 
 position, but if we float the body upon water, it turns over until it 
 finds this position. 
 
 36. Summary. Gravitation is the pull, or attraction, existing be- 
 tween all bodies of matter. 
 
 Gravity is the earth's pull upon bodies at or near its surface. Grav- 
 ity pulls vertically downward, that is, toward the earth's center. 
 
36 FORCE AND ENERGY 
 
 The mass of a body is the amount of matter in it. 
 
 The amount of attraction between bodies depends on the masses of 
 the bodies and on the distance they are apart. 
 
 The weight of a body represents the earth's attraction, at any given 
 place, for the mass of the body. 
 
 A body weighs more at the earth's poles than at the equator, and 
 more at the earth's surface than "up in the air." The mass does not 
 change. 
 
 In a vacuum all bodies fall with the same speed. 
 
 If a falling body is acted upon by a horizontal force, its path is 
 curved; but the time taken is the same as if gravity acted alone. 
 
 Force is exerted on a body by the muscles of men and animals, by 
 the earth (gravity), by the wind, by other bodies (as resistance or fric- 
 tion), by expanding gases, etc. 
 
 A body on which work has been done has energy, or the capacity for 
 doing work on other bodies. 
 
 There is energy of position and energy of motion. 
 
 Work (against gravity) = weight X vertical distance. 
 
 Power is the rate of doing work. 
 
 Inertia is the helplessness of matter to alter its condition of rest or 
 motion. 
 
 "Centrifugal force" is the pull of matter, when revolving, against 
 whatever holds it to the center. 
 
 The force that is exerted between the particles of matter and holds 
 matter together is called cohesion, or adhesion. 
 
 The cohesion of liquids causes them to form drops, and to have elas- 
 tic surfaces. 
 
 The upper surface of a liquid that does not adhere to the vessel is 
 like a flattened drop; that is, convex. 
 
 If the liquid wets the vessel, the surface is concave. 
 
 The cohesion of liquids and their adhesion to solids (wetting) 
 causes the liquids to rise in narrow spaces or tubes. This is "capillary 
 action." 
 
 The density of a body or a substance is the quantity of matter in a 
 .given volume. Pure water at 4 C. has a density of 1. 
 
 Buoyant force is the supporting, or lifting, power of liquids and gases. 
 
EXERCISES 37 
 
 A floating body is entirely supported. An immersed body is sup r 
 ported with a force equal to the weight of the liquid (or gas) displaced 
 by the body. 
 
 The center of mass of a body is the point around which the matter 
 of the body is arranged. A body is in a stable position when its center 
 of mass is directly over some part of the base on which the body rests. 
 It is most stable when its center of mass is in the lowest possible posi- 
 tion. 
 
 37. Exercises. 
 
 1. What is the chief force to be overcome when we drive a nail into 
 wood? 
 
 2. Why does a drop of mercury on a table remain almost spherical, 
 while a drop of water does not? 
 
 3. Why is it so hard to dry the hands on a new, unlaundered towel? 
 Why is writing paper " filled" or " sized"? 
 
 4. Name the following substances in the order of their densities, 
 beginning with the lightest (see Appendix, Table III): iron, cork, 
 kerosene, lead, paraffin, aluminum, marble, zinc, gold, silver, copper, 
 water, alcohol, and milk. 
 
 5. If one cubic foot of water weighs 62.5 Ibs., how much does a cubic 
 foot of iron weigh? 
 
 6. How does the addition of a life preserver to a person's body alter 
 the weight of matter that must be supported by the water? How does 
 it alter the density? Why? 
 
 .7. Why does a steel ship float? 
 
 8. We can find the volume of a body, such as a stone, if we weigh 
 the body first in air and then in water. Explain how. 
 
 9. An iceberg may turn over after the part under water has melted 
 for a time. Why? 
 
 10. How do you lean your body when you carry a pail of water? 
 When you run forward? When you climb a hill? Why? 
 
CHAPTER III 
 
 AIR AND FIRE 
 
 38. The Atmosphere. As we already know, the earth 
 has a diameter of about 7,900 miles. By means of wells, 
 of cracks in the earth, and of deep mines the solid surface 
 has been studied to a depth of about 6,000 feet. This 
 
 outer layer is called the crust to 
 distinguish it from the unknown 
 interior, or core. Filling the great 
 hollows of the crust is a layer of 
 water, which, if it were spread 
 evenly over the crust, would 
 cover all the land to a depth of 
 about two miles. Finally, sur- 
 rounding both land and sea is 
 the ocean of gas the atmos- 
 phere (Fig. 30) . The atmosphere 
 extends outward from the crust 
 an unknown distance, but most of it is within 50 miles 
 of the earth's surface. Half of it is within four miles. 
 The substance that makes up the atmosphere is air. 
 
 Because air is a gas, and therefore difficult to handle, 
 men looked upon it for a long time as a mysterious, un- 
 knowable part of the earth. Only when men became used 
 to the idea that air and other kinds of gaseous matter are 
 not really different from solid and liquid matter was it 
 
 38 
 
 FIG. 30. 
 
 Ideal Section of the Earth. Thick- 
 ness of the outer layers greatly 
 exaggerated. 
 
ATMOSPHERIC PRESSURE 39 
 
 possible for them to get a thorough knowledge of many of 
 our common phenomena. We now know that the atmos- 
 phere contains gases and living forms of great activity, 
 and that these have very important effects upon the sub- 
 stances and the living things of the earth's surface. Thus, 
 the respiration, or breathing, of animals and plants, and 
 the decay of all substances of animal and vegetable origin, 
 are due to the air. So are the rusting, or tarnishing, of 
 metals, and the phenomenon of fire, or burning. 
 
 39. Weight of Air. The atmosphere is drawn toward 
 the earth's center as all other bodies are; hence air has 
 weight (cf. 4). One liter of air ordinarily weighs about 
 1.2 grams. It takes a little over 4 liters (about a gallon) 
 to weigh as much as a nickel five-cent piece; that is, 5 
 grams. 
 
 We can get an idea of the weight of air in another way: 
 A room 20 x 20 x 10 feet holds 4,000 cubic feet of air. One cubic 
 foot of air weighs about 1M ounces; hence the air of the room weighs 
 4,000X1 M, or 5,000 ounces. Dividing this by 16 we get 312.5, the 
 weight in pounds. 
 
 40. Atmospheric Pressure ; the Barometer. Because 
 air has weight, it exerts pressure on all bodies in it, and 
 on the earth, which supports it. That the atmosphere 
 has pressure was first proved by Torricelli (pronounced 
 Tor-ri-tchell-y), a pupil of Galileo, in 1643. Finding that 
 no pump could lift water higher than 32 feet above the 
 water of a well, he reasoned that this was probably the 
 greatest height to which the atmospheric pressure could 
 push a water column. If this were so, then a mercury 
 
40 
 
 AIR AND FIRE 
 
 FIG. 31. 
 
 Filling a Barometer 
 
 Tube and Inverting 
 
 It in Mercury. 
 
 column ought to be raised only about 1 / 13 as high, since 
 mercury is about 13 times as dense as water. 
 
 The apparatus Torricelli used to test his conclusion (Fig. 
 31) was a glass tube about a meter long and closed at one 
 end. He filled the tube entirely with 
 mercury, closed the open end with his 
 finger, and inverted the tube in a vessel 
 of mercury. When he removed his fin- 
 ger, some of the mercury in the tube ran 
 out, but it stopped when the level was 
 about 29 inches (that is, */ of 32 ft.) 
 above the mercury in the vessel. It did 
 not fall lower because the pressure of the 
 atmosphere held it up. 
 
 We can also make a barometer out of 
 a tube open at both ends, if we put one 
 of the ends under mercury, and remove the air of the tube 
 by means of an air pump. The mercury will rise about 30 
 inches, but not higher. 
 
 The simple barometer is still made as Torricelli made it. The ver- 
 tical distance between the top of the mercury in the tube and the 
 mercury in the vessel is called the height of the barometer. The 
 barometer height changes as the atmospheric pressure changes. Its 
 average at sea level is about 760 mm. (30 inches) ; hence this is called 
 standard pressure, or a pressure of one atmosphere. The space above ' 
 the mercury is a vacuum. 
 
 We can readily calculate the atmospheric pressure from the barom- 
 eter height. If the column of mercury in the barometer is 1 square 
 inch in cross section, and 30 inches high, it has a volume of 30 cubic, 
 inches. Now, 30 cubic inches of mercury weigh about 15 Ibs. Hence 
 the atmosphere presses down upon every square inch of matter at the 
 earth's surface with a force of 15 Ibs. 
 
PUMPS 
 
 41 
 
 Height 
 
 n Miles 
 
 35 
 
 Baro- 
 meter 
 
 n&es 
 
 41. Changes in Atmospheric Pressure. If you were 
 at the bottom of a haystack, trying to work your way up 
 through it, you would have the hardest time at the bot- 
 tom, and the task would become easier as you approached 
 the top. The reason is that the hay is most compact, or 
 dense, in the lowest layers, since these layers have to bear 
 the weight of all the hay above them. So it is with the 
 atmosphere : its lower layers are crowded together by the 
 weight of the air they support. 
 
 That this is so is proved by the bwhavior of a barometer as we carry 
 it up a mountain or up in a balloon. The mercury column falls more 
 and more, showing that the density and the pressure of the air grow 
 smaller as we ascend (Fig. 32). At a height of less than 4 miles the 
 barometer height is about 
 380 millimeters, or 15 inches; 
 hence half of the atmosphere 
 is within four miles of the 
 earth's surface. In a famous 
 balloon ascent the barometer 
 fell to 7 inches. The balloon 
 was then about 7 miles above 
 sea level, and had left more 
 than three fourths of the air 
 behind. When a barometer is 
 carried down into a deep mine, 
 the mercury column rises, 
 because the density and the 
 pressure of the air are greater 
 there than at the surface. FlG - 32 - 
 
 The density of the atmosphere grows less as we 
 ascend. 
 
 42. Pumps. Pumps 
 
 were used by man at least 2,000 years before Torricelli 
 showed that their action is due to the pressure of the 
 atmosphere. 
 
 15 
 
 10 
 
42 
 
 AIR AND FIRE 
 
 If we put the open end of a pipe under the water of a 
 well or cistern, and remove the air of the pipe, the atmos- 
 pheric pressure will raise the water into the pipe about 34 
 feet (cf. 40). In other words, the pipe 
 and the well become a water barometer. 
 
 The simple lift pump (Fig. 33) not only 
 removes the air from the pipe, but lifts the 
 water to the spout. It consists of a cylin- 
 der in which a tightly fitting piston can be 
 moved up and down by means of a handle. 
 The cylinder is attached to a pipe, which 
 extends into the water. 
 
 The Lift Pump. I n the bottom of the cylinder there is a cylinder 
 
 valve, which opens upwards so as to admit water 
 from the pipe. There is also a valve in the piston. This, too, opens 
 upwards, admitting water above the piston. When the piston is 
 forced downwards, the water in the cylinder opens the piston valve 
 and closes the cylinder valve. Some of 
 the water of the cylinder then collects 
 above the piston. When, now, the piston 
 is raised, as in Fig. 33, the water above it 
 closes the piston valve, and the water 
 above the piston is discharged through 
 the spout. At the same time the cylin- 
 der valve is opened by the water below it, 
 and more water is forced into the cylin- 
 der. Thus the up and down strokes of 
 the piston cause a more or less regular 
 discharge of water from the spout. 
 
 Force Pumps and Rotary Pumps. In 
 the force pump (Fig. 34) the piston has 
 
 no valve. When the piston is raised, water rises into the pipe and 
 into the cylinder. When the piston descends, the water below it 
 closes the cylinder valve, and water is forced out through the discharge 
 
 FIG. 34. 
 
 A Force Pump with Its Air 
 Chamber. 
 
COMPRESSED AIR 
 
 43 
 
 Discharge 
 
 valve. The pressure of the water in the discharge pipe compresses 
 the air in the air chamber. When, now, the piston is raised once 
 more, the discharge valve is closed by the pressure of the water in 
 the discharge pipe; yet the stream of water does not stop flowing, 
 because of the pressure of the air in the air chamber. The steam 
 fire-engine is a good example of a force pump. 
 
 A rotary pump (Fig. 35) consists of a wheel with inclined blades. 
 The wheel is turned rapidly by an engine, and removes the air of a 
 pipe dipping into water. The 
 water is then raised by atmos- 
 pheric pressure into the case 
 in which the wheel revolves. 
 The blades of the wheel force 
 the water out through the dis- 
 charge pipe. 
 
 Since the rotary pump has 
 no valves, it can pump water 
 carrying grit and dirt, mate- 
 rials which would clog a pump 
 with valves. This fact makes 
 it especially valuable for the 
 draining of swamp lands, 
 marshes, etc., and for pumping into canals and ditches the water 
 that is to be used in irrigation, the artificial watering of land. 
 
 43. Compressed Air. -While an ordinary pump re- 
 moves air from a given space, a compression pump (cf. 
 71) packs as much air as possible into a given space. A 
 bicycle or automobile tire pump is such a pump. 
 
 When compressed air is released, it expands, and, like 
 other expanding gases, it can do work (cf. 24). Thus, 
 a sand blast is a current of air released from pressure, and 
 carrying sharp sand with great speed. If the sand strikes 
 glass, it chips its surface, forming ground glass. If part 
 of the glass is protected with wax, while the rest is exposed 
 
 take] 
 
 I 
 
 
 
 1 I 
 
 Pulley 
 
 
 
 FIG. 35. 
 
 This rotary, or centrifugal, pump is driven by a 
 belt placed over the pulley. 
 
44 
 
 AIR AND FIRE 
 
 to the blast, a design will be made on the glass. The 
 blast is used to clean castings, and will even drill holes into 
 steel. 
 
 The pneumatic hammer is a hammer kept in rapid motion by com- 
 pressed air. It is with this hammer that large pieces of steel, such as 
 those of bridges and of the framework of largeuil bdings, are riveted 
 
 together. 
 
 compressed ci.r The air brake, which 
 
 stops the motion of trains, 
 is worked by compressed 
 air stored in the locomo- 
 tive. 
 
 In making foundations 
 for bridges and buildings 
 men must often work under 
 water. They can do this 
 by going down in large 
 caissons, or diving bells 
 (Fig. 36). Compressed air 
 is forced into the bell at 
 sufficient pressure to keep 
 the water from rushing in, 
 and to give fresh air to the 
 workmen. The used air bubbles out around the edge of the bell. 
 
 A submarine boat is supplied with compartments which can be 
 filled with water when the boat is to go under water. The boat also 
 carries compressed air for forcing the water out when the boat is to rise 
 to the surface. 
 
 44. Exercises. 
 
 1. What is the volume of the air in a room 40 x 25 x 9 ft.? Its 
 weight in ounces? In pounds? 
 
 2. If the surface of a man's body is 2,600 square inches, what is the 
 pressure, in pounds, of the atmosphere upon it? Why does not this 
 weight crush the body? 
 
 
 Diving Bell. 
 
 FIG. 36. 
 How men can work under water. 
 
COLLECTION OF GASES 
 
 45 
 
 3. If an elastic balloon holding 1 cu. ft. of gas at the earth's surface 
 were to ascend until the barometer height is 15 in., would the volume 
 of the gas in the balloon grow smaller or larger? Why? 
 
 4. Pouring a little water upon the piston of a dry pump is called 
 "priming" the pump. Why does this help the action of the pump? 
 
 5. Explain why you can ''suck" lemonade through a straw or other 
 tube. If the lemonade had the density of water, and you had the 
 necessary strength, how high could you suck it? 
 
 45. Collection of Gases. When we wish to collect a 
 gas for study, we must remember that so-called " empty 7 ' 
 vessels are filled 
 with air, and that 
 to fill a vessel with 
 another gas we 
 must have some 
 way of removing 
 the air. One way 
 is to " sweep out" 
 the air by passing 
 the other gas 
 through the vessel for some time. Fig. 37 shows how 
 we might fill a bottle with illuminating gas by sweeping 
 out the air. We must use a large excess of the gas to 
 make sure no air remains. 
 
 FIG. 37. 
 
 Collecting Gas by Displacement of Air and Air by Dis- 
 placement of Water. 
 
 A better way to get the air out of the collecting vessel is to fill the 
 vessel with water. Then we close the mouth of the full bottle with the 
 hand, or with a piece of cardboard, and set it, upside down, in a pan of 
 water (Fig. 37). We must have the mouth of the bottle under water 
 before we uncover it, or, as we well know, the water will fall out, and 
 air will take its place. Now, if we wish to collect a bottle full of the 
 air from the lungs, we can "blow" through a tube the end of which is 
 
46 
 
 AIR AND FIRE 
 
 placed under the mouth of the bottle of water. The air, being lighter 
 than water, will displace the water of the bottle. We can fill a bottle 
 exactly full of illuminating gas by attaching a "delivery tube" to the 
 gas outlet, and allowing the gas to displace water in the same way. 
 
 46. Discovery of Oxygen. The phenomenon of fire, 
 or burning, has fascinated men for ages, but what the air 
 has to do with it no one understood until 1774. The 
 explanation was given by Lavoisier, a French scientist, and 
 was as important, in its way, as the explanation of gravity 
 by Newton (cf. 18) ; for it was the beginning of modern 
 Chemistry. Priestley, an English experimenter, had just 
 prepared oxygen (Aug. 1, 1774) by heating a red powder 
 which we now call mercuric oxide. 
 
 Sunlight 
 
 Mercury 
 Oxide 
 
 Oxygen 
 
 Priestley's apparatus (Fig. 38) was a bottle filled completely with 
 mercury, and inverted in a "bath" of the same liquid. He put the 
 
 mercuric oxide under the mouth of the 
 bottle; the oxide, being lighter, floated to 
 the top of the mercury. He then brought 
 sunlight to a focus (cf. 178) upon the 
 mercuric oxide by means of a burning 
 lens. The heat produced caused the red 
 powder to disappear; but a colorless gas 
 appeared in its place. When Priestley put 
 into the gas a splinter with a glowing tip, 
 the spark burst into flame. He also put 
 a live mouse into the gas, and, to his sur- 
 prise, it continued to live. Priestley called 
 the gas "good air." 
 
 FIG. 38. 
 
 Priestley's Way of Getting Oxy- 
 gen from Mercury Oxide. 
 
 47. The Air a Mixture. When Lavoisier heard of 
 Priestley's discovery, he reasoned that the gas obtained 
 by Priestley, which supported burning and life so much 
 
THE AIR A MIXTURE 
 
 47 
 
 Mercury 
 
 better than air, must be present in the air. So he planned 
 an experiment to prove that he was right. 
 
 Lavoisier set up the apparatus shown in Fig. 39, putting some 
 mercury in the glass retort. The drawn-out tube of the retort was 
 bent so that it dipped into the pan of mercury. Over the end of this 
 tube, and dipping below the mer- 
 cury, was the bell jar. The air of 
 the bell jar and of the retort was 
 thus cut off from the outer air, 
 and nothing but mercury could 
 get into the apparatus. Lavoisier 
 then heated the retort for 12 days. 
 Gradually a red powder collected 
 on the mercury in the retort. At 
 the same time the atmospheric 
 pressure pushed some mercury into 
 the bell jar. This showed that the 
 
 volume of air in the apparatus became smaller. When no further 
 change took place, Lavoisier let the apparatus become cool, and found 
 that only 4 / 5 of the air remained. The air that was left "put out" a 
 burning candle, and mice could not live in it. So Lavoisier reasoned 
 that the active part of the air was removed by the heated mercury, and 
 that it makes up about 1 / 5 of the air. 
 
 FIG. 39. 
 
 Lavoisier's Experiment. Heating Mercury 
 in a Confined Portion of Air. 
 
 When Lavoisier heated the red powder that had collected 
 in the retort, he obtained all the gas that had been lost 
 by the air. When he applied to this gas the tests which 
 Priestley had used for his "good air/' he obtained the 
 same results as Priestley. Lavoisier had thus proved that 
 the air consists of two substances, one of them active, 
 and able to support burning and life; the other, inactive. 
 The active gas is oxygen; the inactive one, nitrogen (cf. 
 also 54). 
 
48 
 
 AIR AND FIRE 
 
 48. Burning and Oxidation. Many metals besides 
 mercury unite with the oxygen of the air. Thus, iron 
 rusts at the ordinary temperature. Hot, melted lead, if 
 stirred so that a fresh surface of it is kept exposed to the 
 air, is gradually changed to lead oxide, a yellow powder. 
 Tin is changed in the same way to tin oxide, a white pow- 
 der. Zinc and magnesium burn with bright flames to give 
 their oxides. Powdered magnesium is burned to give the 
 light for "flash light " photographs. If we weigh a 
 quantity of any one of these metals, and then weigh the 
 
 oxide formed, we always notice a 
 gain in weight; this is due to the 
 oxygen that is taken up (Fig. 40) . 
 The uniting of a substance with 
 oxygen is called the oxidation of 
 the substance, and the substance 
 is said to be oxidized. Burning 
 is also called combustion, and a 
 substance that can burn in the 
 air is called a combustible sub- 
 stance. But burning is not differ- 
 ent from other oxidation : it is oxidation which is so rapid 
 that heat and light are given off. The phenomenon of 
 burning was mysterious for so long a time because the 
 matter of a burning body seems to be destroyed. This is 
 because most of our common combustibles, such as wax, 
 coal, wood, and paper, give invisible gases when they burn 
 (Fig. 41). Of course these escaped unnoticed (cf. 38). 
 
 FIG. 40. 
 
 A burning body takes up oxygen 
 from the air, and gains weight. 
 
 49. Flames. There is a difference in the way in 
 which substances burn: some have a large, bright flame; 
 
TO PREPARE OXYGEN 49 
 
 while others, like charcoal, merely glow. The explanation 
 is simple. A flame is a burning gas. Substances that do 
 not give off gases when burning do not 
 have flames. In fact, coke and charcoal 
 are the material that is left when the 
 gaseous part of coal and wood, respec- 
 tively, is driven off by heat (cf. 117 
 and 124). 
 
 When a candle burns (Fig. 42), a little of the 
 wick is consumed in melting the wax; then the FIG. 41. 
 
 melted wax is drawn, by capillary action (cf. 32), Burni s?ov e a al 
 up the wick into the flame. The heat of the burn- 
 ing wick changes the liquid wax into a gas, or vapor, and 
 this burns with a flame, producing heat and light. The 
 flame itself is merely the region in which oxidation is 
 taking place. The materials burning in the flame are 
 constantly changing, but they are constantly renewed; 
 hence the flame has a somewhat definite shape and size. 
 
 50. To Prepare Oxygen. Since oxygen is 
 the active element of the air, we cannot pre- 
 pare it by simply removing the nitrogen. We 
 can, however, capture the oxygen by means 
 of some such substance as hqated mercury (cf. 47). 
 By heating the mercury oxide that is formed to a higher 
 temperature we can get the oxygen by itself. 
 
 Mercury and oxygen (at about 350 C.) give mercury oxide. 
 Mercury oxide (at about 380 C.) gives mercury and oxygen. 
 
 This is what Lavoisier actually did. 
 In the laboratory, oxygen is generally made by heating 
 potassium chlorate. This is a white solid which melts 
 
50 
 
 AIR AND FIRE 
 
 FIG. 43. 
 The Common Way of Preparing Oxygen. 
 
 when heated, and foams, or "effervesces," as the oxygen 
 passes off. If a small amount of iron oxide (rust) is mixed 
 with the potassium chlorate when it is heated, it gives off 
 
 its oxygen more easily. 
 The substance manga- 
 nese dioxide, a black 
 solid, has the same effect. 
 
 The apparatus required for 
 making oxygen is shown in 
 Fig. 43. A test tube contains 
 the mixture of powdered po- 
 tassium chlorate and manga- 
 nese dioxide. The delivery tube is attached "gas tight" to the test 
 tube by means of a rubber stopper. The test tube is then heated 
 with a very small flame, and the oxygen given off is collected over 
 water in the bottle. When the bottle is full of oxygen, it is stoppered, 
 or covered with a glass plate, and set, right side up, on the table. 
 
 A still easier method of mak- 
 ing oxygen is to let a solution of 
 hydrogen peroxide drop into a 
 flask (Fig. 44) upon some crys- 
 tals of potassium permanganate 
 just covered with water. 
 
 51. Properties of Oxy- 
 gen. With the bottles of 
 oxygen made as directed 
 in 50 we can study the 
 properties of oxygen. 
 
 Potassium Permanganate 
 
 and 
 Dilute Sulphuric Acid 
 
 FIG. 44. 
 Another Way of Preparing Oxygen. 
 
 (1) In the first place, we can 
 
 test a bottle with a glowing splinter (the test used by Priestley). 
 (2) Iron does not burn readily in air, but it burns in oxygen. This 
 may be shown as follows (Fig. 45): 
 
OXYGEN AND LIFE 
 
 51 
 
 FIG. 45. 
 
 Burning Iron Wire in 
 Oxygen. 
 
 Sand is put into one of the bottles of oxygen, so that the bottom is 
 completely covered. Then a bundle of fine iron wires (picture cord) 
 is tipped with a little sulphur, or with a splinter of wood. The sulphur 
 (or wood) is lighted, and the wire is put into the 
 bottle of oxygen. The burning tip heats the iron 
 to its "kindling temperature," so that it burns 
 brilliantly in the oxygen. Iron oxide is formed, 
 as in rusting. The melted oxide collects as a drop 
 upon the end of the wire, or falls into the bottle. 
 The sand is used to protect the bottle from the 
 hot iron oxide. 
 
 (3) Sulphur, which burns with an almost invis- 
 ible, blue flame in the air, burns with a brilliant, 
 violet flame in oxygen. The sulphur is held in a 
 
 "combustion spoon" (Fig. 46), and is melted and 
 lighted in a burner before being put into the oxygen. 
 The product formed is sulphur dioxide, the same 
 choking gas that results when sulphur burns in air. 
 
 (4) Charcoal burns in air with a faint glow; but in 
 oxygen it burns vigorously, giving off a brilliant light. 
 The charcoal is held by means of a copper wire, or in a 
 combustion spoon, and is ignited in a flame before 
 being put into the oxygen. The product is the color- 
 less gas, carbon dioxide. If we put " lime water " 
 (cf. 127) into the bottle in which charcoal has been 
 burned, the lime water and carbon dioxide unite to form a white, 
 insoluble solid which makes the lime water look "milky." In a bottle 
 of pure oxygen or air, lime water is not changed. 
 
 Oxygen dissolves slightly in water. Like air, of which 
 it forms a part, oxygen has no color, odor, or taste. 
 
 52. Oxygen and Life. Oxygen forms a part of all 
 living things, and an abundant supply is needed to main- 
 tain life. The process of getting oxygen in contact with 
 the tissues of an animal or plant is called respiration. 
 
 FIG. 46. 
 
 Burning Sulphur 
 in Oxygen. 
 
52 AIR AND FIRE 
 
 Respiration consists both of breathing, which is performed 
 for the higher animals by lungs (cf. 343), and also of the 
 actual oxidation that takes place throughout the body. 
 A grown man takes in (" inspires") about 350 cubic feet 
 (10 cubic meters) of air in a day. 
 
 The purpose of respiration is to get the oxygen of the 
 air to combine with the materials of the body that are 
 constantly wearing out, and to oxidize them (cf. 48) to 
 substances that the body can get rid of. Since this worn- 
 out matter, like the body itself, is largely made up of 
 carbon and hydrogen, it is changed chiefly to carbon 
 dioxide and water when oxidized (cf. 51 and 105). The 
 oxidation within the body is not an actual burning; but 
 it produces heat. This heat keeps the bodies of animals 
 warm. In man the normal temperature is 98.6 Fahren- 
 heit, or 37 Centigrade (cf. 63). In certain diseases the 
 lungs are not able to get oxygen rapidly enough from the 
 air; so pure oxygen is used. 
 
 Water animals depend upon the oxygen dissolved in 
 natural water. Fishes, clams, etc., take in oxygen through 
 their gills (cf. 337 and 341). In the gills the same ex- 
 change of carbon dioxide for oxygen takes place as in the 
 lungs of higher animals. 
 
 53. Exercises. 
 
 1. How can you show that the expired breath contains water? 
 Carbon dioxide? 
 
 2. Give the dates of the birth and the death of Priestley and of 
 Lavoisier. What did each do for science? (See Glossary.) 
 
 3. What substance is used to polish stoves (cf. 119)? How does 
 it prevent rusting? What other materials are used to cover iron to 
 prevent rusting? 
 
HOW NITROGEN IS PREPARED 
 
 53 
 
 4. Why do we use, first, paper, then wood, and then coal in starting 
 a coal fire? 
 
 5. Why are oxides used as fire-proofing materials? 
 
 6. Compare the composition of the air that enters at the bottom of 
 a stove with that which passes out into the flue. 
 
 7. Why does a kerosene lamp need a wick? Why a chimney? 
 
 8. Why does a blanket or rug put out a fire? Why does water? 
 
 9. When a gas is collected over water, why does the gas force the 
 water out of the bottle? 
 
 54. How Nitrogen is Prepared. One method of pre- 
 paring nitrogen is to remove the oxygen from air. We 
 may remove the oxygen, as Lavoisier did, by means of 
 heated mercury; but an easier 
 way is to burn phosphorus in a 
 bottle or jar of air (Fig. 47). 
 
 A small heap of red phosphorus is 
 placed in the middle of a thin slice cut 
 from a cork about three fourths of an 
 inch in diameter. A wire pushed into 
 tfye cork supports it. To hold the wire 
 upright, we stick it into a rubber stop- 
 per, placed, large end downward, on the bottom of a pan of water. 
 The water is about two inches deep. The phosphorus is lighted, and 
 the jar of air (a fruit jar does very well) is immediately placed over 
 the burning phosphorus, and pressed tightly against the bottom of 
 the pan. After the phosphorus has burned for a moment, the hand 
 may be removed. Water rises into the jar to take the place of the 
 oxygen used up. 
 
 The white smoke is phosphorus oxide. The jar is left until the 
 smoke has entirely disappeared (it dissolves in the water) ; then a piece 
 of glass or cardboard is slipped under the jar, and the jar is set upright 
 on the table. A burning splinter "goes out" when put into the jar. 
 If too many bubbles did not escape when the jar was put over the 
 
 FIG. 47. 
 
 Burning Phosphorus in a Jar of Air 
 Over Water leaves Nitrogen. 
 
54 AIR AND FIRE 
 
 phosphorus, the volume of water that enters the jar, and, therefore, 
 the volume of the oxygen, will be about one fifth of the volume of air in 
 the jar at first. 
 
 Nitrogen made in this way contains argon, a gas even more inactive 
 than nitrogen itself. Argon makes up almost one per cent, by volume, 
 of air. 
 
 Perhaps the most convenient way to get a 250 c.c. bottle 
 of nitrogen is to heat carefully a solution of 5 g. of sodium 
 nitrite and 5 g. of ammonium chloride in 100 c.c. of water. 
 The nitrogen escapes, and is collected over water. 
 
 55. Properties of Nitrogen. Unlike oxygen, nitrogen 
 does not unite readily with other substances, and does 
 not support burning and life. It dilutes the active oxygen 
 of the air. Nitrogen is somewhat lighter than the air, 
 and is very slightly dissolved by water. Like oxygen, it is 
 colorless, tasteless, and odorless. 
 
 Nitrogen finds it hard not only to unite with other 
 substances, but also to hold its place in many substances 
 that contain it. As a result of this property it is made a 
 part of all our common explosives, such as gunpowder, 
 nitroglycerine, guncotton, etc. These are all substances 
 that hold nitrogen loosely. When the explosive is set on 
 fire, or is given a "shock" (cf. 24), the nitrogen is set 
 free as a gas under great pressure, and in expanding does 
 the work required of the explosive. 
 
 56. Nitrogen and Life. The properties and uses of 
 nitrogen described in preceding sections are due to the 
 fact that it has little activity, or little power of uniting 
 with other substances. But nitrogen is important also 
 because of certain positive qualities: it forms a necessary 
 
NITROGEN AND LIFE 
 
 55 
 
 part of proteids, or albumins, materials needed by all 
 living cells. Nitrogen is, therefore, a necessary part of 
 all animals and plants. The proteids make up a large 
 part of such food as meat, eggs, cheese, and milk. 
 
 Animals cannot make their own proteid; they must get 
 it by feeding upon plants. Plants make proteids out of the 
 carbon, hydrogen, oxygen, nitrogen, etc., which they ob- 
 tain from the soil and the air. Now, most plants can take 
 up nitrogen only when it is a part of certain compounds 
 dissolved in the water of the soil. Hence soils must con- 
 tain nitrogen compounds to be fertile. 
 
 While most plants can make proteids only out of nitrogen com- 
 pounds present in soil, some plants seem to take up nitrogen directly 
 from the air. Such are beans, peas, clover, and alfalfa. It has been 
 found that the plants named have this power because " colonies" of 
 bacteria very small plants (cf. 324) 
 find a home upon their roots. It is the 
 bacteria that take the nitrogen out of the 
 air, and build it into the complex albumins 
 upon which the beans, etc. feed. But the 
 bacteria produce not only enough proteid 
 for the beans, etc., but they produce an 
 excess of it, and leave it in the soil. Be- 
 cause they themselves contain so much 
 proteid, beans, peas, and clover are valu- 
 able as food for man and animals; but 
 they are even more important because 
 they, or, rather, the bacteria growing 
 upon them, are the means of bringing into 
 
 a soil the nitrogen it needs for other plants. As all farmers know, 
 clover is grown in a field, and " ploughed under," to enrich the soil 
 for crops of grain. Artificial fertilizers, containing nitrogen com- 
 pounds, are often added to the soil for the same purpose. 
 
 TUBCffCLE 
 
 FIG. 48. 
 
 A Clover Plant with its 
 Tubercles. 
 
56 
 
 AIR AND FIRE 
 
 FIG. 49. 
 
 A Dewar Bulb 
 for Holding 
 Liquid Air. 
 
 57. Liquid Air. In the liquid form air is colorless, 
 and has about the same density as water. It is composed 
 of liquid oxygen and nitrogen. Liquid air is constantly 
 evaporating; to prevent explosions we keep 
 it in open vessels called "Dewar bulbs," 
 from the inventor (Fig. 49). They have 
 double walls, and the air is removed from the 
 space between the walls, so that heat from 
 the outside cannot affect the liquid within. 
 The walls of the bulbs are silvered for the 
 same reason. "Thermos" and "Caloris" 
 bottles are made on the principle of Dewar 
 bulbs, to keep a cold liquid from getting warm and a hot 
 liquid from getting cool (cf. Ex. 12, 68). Air is made 
 liquid at a low temperature by great pressure. It boils 
 at about -190 C. (Fig. 50). 
 
 Alcohol held in liquid air becomes solid, like ice. Mercury is 
 changed to a hard metal, and may be used as a hammer head, to drive 
 nails. A rubber ball put into liquid air be- 
 comes brittle, and flies into fragments when 
 thrown on the floor. A piece of meat be- 
 haves in the same way. Liquid air that 
 actually wets the skin burns it like white- 
 hot iron; yet the hand may be put into the 
 liquid for a moment without injury, because 
 a layer of gaseous air covers the hand like a 
 glove. 
 
 FIG. 50. 
 
 Liquid Air Boiling 
 on Ice. 
 
 58. How the Atmosphere is Puri- 
 fied. Since the air receives impurities from the breathing 
 of animals and plants, from all burning, and from all 
 decay, why does it not become foul, and unfit to breathe? 
 
HOW THE ATMOSPHERE IS PURIFIED 57 
 
 The answer is that the impurities are constantly being 
 removed. The wind scatters foul air, and mixes it with 
 fresh air from the country, the mountains; and the sea. 
 The rain washes out impure gases, dust, smoke, and 
 bacteria, or germs. Sunlight destroys many bacteria that 
 produce disease. Other bacteria bring about the oxida- 
 tion of dead organic matter, and so destroy it. Plants 
 use up the carbon dioxide cast off by animals, and give 
 back oxygen in its place (cf. 309). 
 
 59. Summary. The atmosphere is the gaseous ocean that forms 
 the outer layer of the earth. Air is the substance that makes up the 
 atmosphere. 
 
 Air is matter, for it takes up space, and has weight, inertia, etc. 
 
 The pressure of the atmosphere is due to the weight of the air. It 
 is measured by the barometer, and is equal to about 15 Ibs. for each 
 square inch of surface at sea level. The pressure becomes less as we 
 go up a mountain, and greater as we go down into a mine. 
 
 The lift pump is a device for removing the air that is over a liquid, 
 so that atmospheric pressure will raise the liquid. Its limit is about 
 34 feet for water, and 30 inches for mercury. 
 
 Compressed air, like other compressed gases, can do work when it 
 expands. 
 
 Gases are " collected " by displacement of air or water. 
 
 Priestley discovered oxygen in 1774 by heating mercury oxide. 
 
 Lavoisier proved that air consists of two substances, oxygen and 
 nitrogen. 
 
 Oxygen makes up about one fifth, by volume, of air. 
 
 Burning in air is union with oxygen, or oxidation. Oxidation may 
 be slow, as in rusting and decay, or rapid, as in burning. 
 
 A flame is a burning gas. 
 
 Oxygen is prepared by heating mercury oxide or a mixture of 
 potassium chlorate and manganese dioxide, or by putting hydrogen 
 peroxide with potassium permanganate. 
 
 Oxygen is colorless, tasteless, odorless, and slightly soluble in water. 
 
58 AIR AND FIRE 
 
 Bodies that burn slowly in air burn vigorously in oxygen. Oxygen is 
 a part of all living things. 
 
 Respiration consists of breathing and of oxidation. The heat pro- 
 duced in the oxidation keeps the body warm. Water animals use the 
 oxygen that is dissolved in water. 
 
 Nitrogen is made from air by removing the oxygen. It is also made 
 by heating a solution containing ammonium chloride and sodium 
 nitrite. 
 
 Nitrogen is colorless, tasteless, odorless, lighter than oxygen, and 
 inactive. 
 
 Nitrogen is held loosely in many substances, and is set free from 
 most explosives. 
 
 Nitrogen is necessary to life, since it is a part of proteids. Proteids 
 are made by plants. 
 
 Clover, beans, etc., support colonies of bacteria that make proteids 
 out of nitrogen and other materials. 
 
 Liquid air is a mixture containing liquid nitrogen and liquid oxygen. 
 Most substances change their properties when exposed to it, owing 
 to its low temperature. 
 
 The atmosphere as a whole does not become unfit for breathing 
 because of the winds, ram, sunlight, oxidizing bacteria, and plants. 
 
 60. Exercises. 
 
 1. How can you tell a bottle of air from one of oxygen? One of air 
 from one of nitrogen? One of nitrogen from one of carbon dioxide? 
 
 2. What gases do plants take from the air? Animals? What gas 
 does each restore to the air? 
 
 3. If the cover of a fruit jar has an area of 5 square inches, and the 
 jar is empty (a vacuum), how great a weight must I lift to get the cover 
 off, not counting friction? 
 
 4. Why does the air seem so refreshing after a rain or a snowfall? 
 Why should sunlight and air be admitted into the rooms in which we 
 live? 
 

 
 Fio. 51. 
 
 Metal Ball and 
 
 Ring. 
 
 CHAPTER IV 
 
 HEAT 
 
 61. Heat and Matter. It is a familiar fact that most 
 bodies increase in volume as they grow hot, and shrink as 
 they grow cold. Thus, a brass or iron ball (Fig. 
 51) which just goes through a ring when cold 
 will not go through it when hot. If, however, 
 the ring, as well as the ball, is heated, then the 
 ball will go through it. A liquid, like water or 
 mercury, which just fills a flask at the tem- 
 perature of the room, 'overflows when heated, 
 but does not fill the flask when cooled. A gas 
 behaves in the same way. Thus, if a flask of 
 air is heated (Fig. 52), some of the air escapes; but the 
 volume of the air contracts when the flask is cooled. 
 
 How can we explain 
 these changes of volume? 
 It is hard to see how the 
 volume of a body can 
 change unless the matter 
 of the body is broken up 
 into particles, with spaces 
 between them. Then, 
 if the volume becomes 
 smaller, as is the case 
 when a body is cooled, we 
 
 Heating expands air" cooling makes it shrink. Can explain the shrinkage 
 
 FIG. 52. 
 
60 HEAT 
 
 by saying that the particles are crowded closer together. 
 Scientists believe that matter really consists of such 
 particles, and call them molecules, or " little masses." 
 The molecules are believed to be in motion. Each 
 molecule needs a portion of space in which to move 
 about; hence the volume of a body is the sum of the 
 spaces needed by all the molecules, in addition to the vol- 
 umes of the molecules themselves. 
 
 The motion of the molecules is heat. When we add heat to a body, 
 each molecule moves more rapidly, and pushes its neighbors farther 
 away. Because of this the distance between molecules becomes 
 greater, and the volume of the body increases. We assume that 
 when bodies expand and contract the volumes of the molecules remain 
 unchanged. 
 
 The molecules are very small. Scientists estimate the number of 
 molecules in 1 c.c. of a gas as about 27 million million millions (27,000,- 
 000,000,000,000,000). 
 
 62. Thermometers. We make use of the expansion 
 and contraction of matter in the thermometer, the instru- 
 ment with which we measure temperature. The common 
 thermometer consists of a glass tube having a bulb at one 
 end. The bulb and part of the tube contain mercury. 
 The inside of the tube is of a very small bore, so that if 
 the mercury expands only a very little in the bulb, it will 
 make a great difference in the length of the mercury 
 "thread" inside the tube. Glass expands when heated, 
 as well as mercury, but only y 7 as much; hence the ex- 
 pansion we see in a thermometer is the difference between 
 the expansion of mercury and that of glass. 
 
 When a thermometer is made, the end of the tube is open, and there 
 is enough mercury to fill the bulb and a little of the tube. The instru- 
 
THE TWO THERMOMETER SCALES 
 
 61 
 
 ment is then heated, so that bulb and tube are completely filled, and 
 the open end is sealed by melting the glass. 
 
 The thermometer is then graduated, that is, the "degree" marks are 
 put on it. First the bulb is put into melting ice 
 (Fig. 53), and the point at which the mercury comes 
 to rest is marked the freezing point. Then water 
 is made to boil under " standard pressure" (cf. 40), 
 and the bulb is put into the steam that comes off 
 
 (Fig. 54). The place at which 
 
 the mercury stops is called the 
 
 " boiling point" mark of the 
 
 thermometer. 
 
 FIG. 53. 
 
 Getting the Freezing 
 Point of a Ther- 
 mometer. 
 
 FIG. 54. 
 
 Getting the Boiling 
 Point of a Ther- 
 mometer. 
 
 63. The Two Thermom- 
 eter Scales. The differ- 
 ence between the two common thermom- 
 eters the Fahrenheit and Centigrade 
 thermometers is in the number of de- 
 grees that are put between the freezing 
 point mark and the boiling 
 The maker of the Centigrade 
 He divided the space 
 
 point mark, 
 instrument was Celsius. 
 
 between the two marks into 100 degrees (Fig. 
 55). "Centigrade" means just that: "100 
 degrees" or "steps." Celsius made the freez- 
 ing point of his thermometer 0, and the 
 boiling point 100. If the thermometer tube 
 is of the same bore throughout, and a new 
 mark is made as far above 100 as is below 
 it, the new mark will be 200. In this way 
 the other marks of the thermometer are fixed. 
 
 The Fahrenheit thermometer is named from The Fahrenheit 
 its maker, who took for his the temperature lcfi entigrade 
 
62 HEAT 
 
 produced by a certain "freezing mixture" (cf. 93). The 
 melting point of ice, on the Fahrenheit thermometer, is 
 32, and the boiling point of water 212. 
 
 The number of degrees between 32 and 212 is 180; consequently 
 100 Centigrade degrees equal 180 Fahrenheit degrees. Each Fahren- 
 heit degree is, therefore, 5 / 9 of a Centigrade degree, and each Centi- 
 grade degree is 9 / 5 of a Fahrenheit degree. If we multiply the number 
 of degrees shown by a Centigrade thermometer by 9 / 5 , and then add 
 32, we get the Fahrenheit reading. 
 Fahr. = (Cent.X 9 A)+32. 
 
 If we subtract 32 from the Fahrenheit reading, and then multiply 
 the remainder by 8 / 9 , we get the Centigrade reading. 
 Cent. = 5 / 9 (Fahr. 32) . 
 
 The Centigrade scale is used almost everywhere on the continent of 
 Europe, and practically everywhere, the world over, for scientific 
 work. For temperatures below 39.1 C., such as are found in the 
 Arctics, alcohol is used instead of mercury (cf. 57). 
 
 64. Temperature and Heat. We must know the 
 difference between quantity of heat and degree of heat. 
 We know whether a body is hot or cold, generally speak- 
 ing, by its degree of heat, that is, its temperature. The 
 temperature of a body depends upon the rapidity with 
 which its molecules are moving, and not upon whether 
 there are many molecules or few. But the heat which a 
 body possesses depends upon the speed of the molecules 
 and also upon the number of molecules, that is, upon both 
 the temperature of the body and its mass. We shall see 
 later ( 73) that it also depends upon the substance of 
 which the body is composed. 
 
 The unit of heat quantity is called a calorie, just as the unit of mass 
 is called a gram. A calorie is the amount of heat needed to warm 
 1 gram of water 1 C. It is also the amount given off by 1 g. of water 
 
CONVECTION 63 
 
 when its temperature falls 1 C. So 1 g. of water in cooling from 100 
 C. to C. gives off 100 calories of heat. The same amount is given 
 off when 2 g. of water are cooled from 50 C. to C., and when 10 g. 
 are cooled from 10 C. to C. 
 
 65. Ways of Distributing Heat; Conduction. If a 
 
 flat-iron is placed on a stove, the iron becomes warm, 
 because heat (motion of molecules) from the stove is 
 given to it. If you touch the flat-iron, it gives some of 
 its heat to the hand; hence the iron feels warm. The heat 
 has been conducted, first from the stove to the flat-iron, 
 then from the flat-iron to your skin. But if you hold a 
 piece of ice in your hand, the hand becomes cold, because 
 heat is conducted from your hand to the ice. So the 
 objects you handle are either hot or cold according as 
 they give heat to the hand, or take it from the hand. 
 
 The handle of a flat-iron can still be held comfortably after the 
 bottom is hot; but in a short time the handle, also, is heated by con- 
 duction from the part nearer the stove. To hold it then, we use a non- 
 conducting handle of cloth or of wood. It would take longer to heat 
 a brick from the bottom to the top, because it is a poorer carrier, or 
 conductor, of heat. Metals are the best heat conductors; air is 
 probably the poorest. Water, wood, and paper are poor conductors. 
 Conduction is only one of the ways in which heat is distributed; other 
 ways are by radiation and by convection. 
 
 66. Radiation. If you stand near a stove, you become 
 warm without touching the stove. Heat is radiated to 
 you from the stove. If you are near a block of ice, you 
 become chilled, because your body is radiating heat to the 
 ice. Heat reaches the earth from the sun by radiation 
 through space. 
 
 67. Convection. Convection is not really a new way 
 
64 
 
 HEAT 
 
 of distributing heat, but depends on the other two ways. 
 The air near a stove becomes heated by conduction and 
 radiation. As a result it expands, and becomes lighter. 
 While a cubic foot of air at 32 F. (0 C.) weighs about 1.2 
 oz., at 80 F. (27 C.) it weighs 1.1 oz. The lighter air 
 then rises to make room for the cooler 
 air, which flows in to take its place 
 (Fig. 222, 274) . Thus ' ' convection 
 currents " are set up, and the air 
 rises while it is warm and descends 
 again when it has become cooled. 
 
 ' ' Hot air " furnaces heat our houses 
 (Fig. 56) because the warmed air 
 flows upward through the "registers " 
 to make room for the cold air taken 
 in at the bottom of the furnace (' ' cold 
 air intake" ;c/. 248). 
 
 Fio. 56. 
 
 Convection Currents from 
 a Furnace. 
 
 When air is cooled, convection currents are also set in motion. 
 Because of its greater density the cold air falls, and warm air flows in 
 to take its place. Hence in ice-boxes (Fig. 57) the waste water is not 
 allowed to drop directly into the air, but is controlled by a "trap" 
 
 which permits only the waste water, and not 
 
 the cold air, to flow out at the bottom of the 
 refrigerator. 
 
 Convection currents can also be seen 
 when a liquid is heated and cooled, if bits 
 of paper or sawdust are put into the 
 liquid. Hot water heating of houses de- 
 pends upon such currents (cf. 243). 
 Convection currents, and the fact that water 
 is most dense at 4 C., prevent the freezing 
 of lakes and rivers except near the surface 
 (cf. 87). 
 
 FIG. 57. 
 
 Trap in an Ice-Box, to Pre- 
 vent Cold Air from 
 Falling Out. 
 
PHYSICAL STATES OF MATTER 65 
 
 68. Exercises. 
 
 1. When the glass stopper of a bottle "sticks," we can often loosen 
 it by heating the neck of the bottle. Why? 
 
 2. If you heat water in a thick glass bottle over a flame, the bottle 
 usually breaks, while a thin glass flask does not. Why? 
 
 3. Why do telephone wires sag in summer and become taut in winter? 
 
 4. Alcohol boils at 78 C.; what temperature is this on the Fahren- 
 heit scale? The room temperature is 70 F. ; what is this on the 
 Centigrade scale? 
 
 5. How could you make an air thermometer, that is, one using the 
 expansion of air instead of that of mercury? 
 
 6. Which feels colder in a room, oilcloth or carpet? Wood or 
 metal? Is there any real difference of temperature? Explain. 
 
 7. Why can ice cream be carried in a paper box through heated air, 
 and yet not melt? Would a tin box be better? 
 
 8. Which feels hotter, the handle of a silver spoon, or that of an 
 iron spoon, if the bowl of each is in boiling water? Why? 
 
 9. Why does air enter a stove at the bottom, and go out at the top? 
 
 10. Where should steam pipes be put to heat a room? Where 
 should pipes of cold water be placed in a cold storage room in order to 
 cool the room? 
 
 11. Why are houses built with double walls having air spaces be- 
 tween them? 
 
 12. How is a "fireless cooker" made? Why is the heat not given 
 off? How is it like a Thermos bottle (cf. 57)? 
 
 69. Physical States of Matter; Solids. If we believe 
 that matter is broken up into molecules ( 61), we can 
 understand the differences between solids, liquids, and 
 gases, the three physical states, or forms, of matter. The 
 two causes at work upon the molecules are cohesion and 
 heat. Cohesion represents the attraction of the molecules 
 for one another; heat is the motion of the molecules. 
 Cohesion draws the molecules together; heat causes them 
 to fly apart. 
 
66 HEAT 
 
 In a solid, like ice or sulphur, the cohesion between the 
 molecules greatly overbalances the motion of the mole- 
 cules; therefore a solid has a definite form. Usually a 
 solid forms crystals (cf. 95). 
 
 When solids are melted, their temperature does not 
 rise during the melting; but the heat added is used up in 
 overcoming cohesion. Thus, when ice at C. is brought 
 into a room at the ordinary temperature, the ice melts; 
 but its temperature remains C. until all of the ice is 
 melted. If the ice and the water formed by its melting 
 are stirred thoroughly, the temperature of the water also 
 remains C. until the ice disappears. The reason is that 
 the heat which the ice receives from the room is used up 
 in melting the ice instead of in raising the temperature of 
 the water or the ice. 
 
 To change a gram of ice at G. to water at G. requires as much 
 heat as to warm a gram of water from C. to 80 C., that is, 80 calories 
 of heat. 
 
 All the heat taken up by ice in melting is given off again when water 
 freezes. The heat that is given off by tubs of freezing water is used to 
 keep vegetables from freezing. The temperature in the vegetable 
 cellar cannot fall much below C. until all the water is frozen. The 
 vegetables themselves do not freeze at C. 
 
 70. Liquids. We know that liquids are different from 
 solids in one important way: they have no definite shape, 
 but take the shape of the vessel that holds them. We 
 explain this by saying that the heat, or motion, of the 
 molecules of a liquid is greater than in the case of a solid; 
 so that cohesion cannot keep the liquid molecules in any 
 particular order or arrangement. 
 
 Most liquids contract, or grow smaller in volume, when 
 
GASES 67 
 
 they freeze. Water is an exception: 100 c.c. of water at 
 C. become 109 c.c. of ice at C. On this account water 
 pipes often burst in winter, and water that freezes in the 
 cracks of rocks breaks the rocks in pieces (cf. 289). 
 
 Metals that have about the same volume when solid as 
 when liquid can be used to make castings; for the casting 
 will then fill the mold completely. Cast iron, type metal, 
 and brass are metals of this sort. But gold and silver, 
 which shrink when they become solid, cannot be cast; 
 they must be stamped, or " minted." 
 
 When a liquid becomes a gas, or vapor, an enormous increase in 
 volume takes place. Thus, 1 c.c. of water at 100 C. becomes about 
 1,200 c.c. of steam at 100 C. Engineers express this by saying, "A 
 cubic inch of water gives a cubic foot of steam." 
 
 The heat taken up in changing a gram of water at 100 C. to steam 
 at 100 C. is 536 calories (cf. 64). The same amount of heat is set 
 free when a gram of steam at 100 C. is condensed to water at 100 C. 
 Hence a scalding from steam is much more painful than one from hot 
 water. 
 
 When a liquid is evaporating rapidly, it is always a little colder than 
 the surrounding air. In tropical countries people take advantage of 
 this fact to cool their drinking water. The water is put into porous 
 jars. A little of the water goes through the jar, and by its evaporation 
 on the outside cools the jar and the water in it. 
 
 71. Gases. Gases do not have either a definite shape 
 or a definite volume. The volume of a gas depends upon 
 its temperature (cf. 61) and its pressure (cf. 41). 
 Cohesion between the molecules of a gas is slight, because 
 the molecules are so far apart. Because of the motion of 
 its molecules, a gas placed in a vacuum expands, until 
 it fills the vacuum. 
 
 If we force the molecules of a gas closer together, we 
 
68 
 
 HEAT 
 
 TO BICYCLE 
 FIG. 58. 
 Bicycle Pump. 
 When the 
 handle is 
 raised, air en- 
 ters around 
 the piston. 
 
 are working against the energy of the molecules. There- 
 fore the compression of a gas liberates heat. This is 
 illustrated in the compression pumps (Fig. 58) 
 used to fill the tires of bicycles and automo- 
 biles. They become hot. 
 
 Since compressing a gas heats it, expansion 
 cools it. The air rising from the earth in con- 
 vection currents ( 67) is cooled as it ascends. 
 This is because its volume increases as the 
 atmospheric pressure becomes smaller. The 
 heat needed to increase the volume of the 
 rising air is taken from the air itself. In the 
 balloon ascent described in 41 the temperature at 7 
 miles height was 60 F. 
 
 To change a gas into a liquid we can (1) force the molecules together 
 by increasing the pressure; or (2) make the motion of the molecules 
 smaller by lowering the temperature (Fig. 
 59); or (3) combine both methods. 
 
 The liquefying of air requires both a 
 very low temperature and a great pressure. 
 The method consists, first, in compressing 
 the air greatly in long tubes; then in re- 
 moving the heat produced by the com- 
 pression; and, finally, in allowing some of 
 the compressed air to expand. The heat 
 needed to produce the expansion comes 
 from the air that is still under pressure. The removal of this heat 
 cools the air until it condenses in drops of liquid. 
 
 S'ulphur Dioxide 
 
 VSulphur Dioxide 
 FIG. 59. 
 
 Liquefying Gaseous Sulphur 
 Dioxide by Cooling It. 
 
 72. Kindling Temperature. All of us know that 
 fires must be "started" by some hot or burning body. 
 The temperature at which a substance begins to burn is 
 called its kindling temperature. A piece of iron picture 
 
THE MEASURING OF HEAT 69 
 
 cord will burn in oxygen (cf. 51), if tipped with burning 
 sulphur to start the action. A match consists of several 
 substances, each of which is used to kindle another sub- 
 stance having a higher kindling temperature. Friction 
 ignites the phosphorus, the burning phosphorus ignites 
 the sulphur, and the burning sulphur sets the wood on 
 fire. A stick burns from one end to the other, each part 
 giving out enough heat to ignite the part next to it. 
 
 73. The Measuring of Heat. While the thermometer 
 is the instrument for finding the degree of heat of a body, 
 the calorimeter is the instrument by means of which we 
 get the amount of heat in a body (cf. 64). We measure 
 this amount by finding out how much heat 
 the body can give to a certain weight of 
 water. 
 
 The simple calorimeter is a metal vessel 
 (Fig. 60) with polished sides. A covering 
 of felt (a non-conductor) prevents the air 
 from taking heat away from the vessel, or FIQ 6Q 
 adding heat to it. Suppose that we wish to A simple 
 
 eter Surrounded 
 
 find out which holds more heat at the same by a Non-con- 
 
 ductor. 
 
 temperature, lead or iron. We put into the 
 calorimeter a known weight of water, at room temper- 
 ature, let us say. We then put into the water 10 g., say, 
 of lead having a temperature of 100 C. The hot lead 
 gives heat to the water, until the water and the lead have 
 the same temperature. A thermometer, kept in the 
 water, tells us how many degrees the temperature of the 
 water has been raised. We now put into the calorimeter 
 another portion of water of the same weight as before, 
 
70 
 
 HEAT 
 
 get its temperature, and add 10 g. of iron having a 
 temperature of 100 C. In this case the temperature of 
 the water rises more than 3 times as far as when lead 
 was used. This shows us that the iron has more than 3 
 times as great a heat capacity, or specific heat, as the 
 lead. (See Appendix, Table VII.) 
 
 The calorimeter has very important, practical uses. A factory 
 using a large amount of coal needs to test different kinds of the fuel 
 (cf. 15), in order to find which one gives the most heat for the least 
 money. The worker in Domestic Science wants to know how much 
 heat the different kinds of food, such as butter, potatoes, beef, and 
 fish, will give out in our bodies (cf. 74). In this way he can get an 
 idea of the values of these foods. The heat that can be obtained from 
 both the coal and the food is found by burning them in a calorimeter. 
 A calorimeter such as is needed to give the heating value, in calories, 
 of a fuel or a food (Fig. 61) is more complicated than 
 the simple calorimeter, but the principle according to 
 which it " works" is the same. Some of the fuel or 
 food is burned in an inclosed space containing com- 
 pressed oxygen, or some oxidizing substance (cf. 48), 
 and the heat given off is imparted to a known weight 
 of water. From the increase in the temperature 
 of the water the calories of heat given off can be 
 calculated. 
 
 FIG. 61. 
 
 74. Heat and Life. A healthy man has a 
 temperature of 98.6 F., or 37 C. This does 
 
 eter. By means , -, . , , . . 
 
 of it we find the not change, day or night, summer or winter, 
 
 amount of heat 1 1 .. . _ , 
 
 given off in burn- although the temperature oi the air may 
 vary 50 F. in a day, and 150 in a season. 
 The body is warmed by the changes (oxidations) of its 
 own cells and of digested food. We have seen (cf. 25) 
 that energy is the capacity for doing work. The body is 
 
CLOTHING 
 
 71 
 
 FIG. 62. 
 
 Distribution of Heat Obtained 
 from Food. 
 
 thus a complex engine, using its changes to produce heat, 
 and to enable it to do work. 
 
 It has been calculated that about 3 / 4 of all the heat produced in the 
 body is used to heat the body (Fig. 62). A day's work requires about 
 3 /ie, respiration about 1 / 6 o, and the heart 
 about 1 /ie. While the oxidation changes 
 are much greater in some organs than 
 in others, the heat is carried away by 
 the blood as fast as it is produced. 
 Hence the temperature does not vary 
 in any two parts as much as half a 
 degree Fahr. The skin is, of course, 
 cooler than the rest of the body, both 
 because it is exposed to the air, and 
 also because it is cooled by the constant 
 evaporation of the perspiration (cf. 
 70). The excess heat of the body acts 
 like the heat of a stove in turning 
 
 perspiration into steam. Ordinarily the perspiration is evaporated 
 as rapidly as it is formed, and we do not notice it. This is insensible 
 perspiration. Sensible perspiring, or sweating, takes place only when 
 water is given off by the perspiration glands more rapidly than it can 
 be evaporated by body heat. 
 
 75. Clothing. Man protects his body against sudden 
 loss of heat by clothing. The best clothing for this pur- 
 pose is that which is made of a non-conductor (cf. 65), 
 and permits little heat to escape. Of the common non- 
 conducting materials the best is wool. Wool prevents 
 heat from coming to the body as well as its escape from 
 the body. Hence firemen, who are obliged to work where 
 it is hot, use woolen clothing to keep cool. Linen and 
 cotton are better conductors of heat than wool is, and so 
 are better for summer clothing than for winter clothing. 
 
72 HEAT 
 
 But whether a material will be a conductor or a non- 
 conductor depends largely upon whether it is woven loose- 
 ly or tightly. For it is the air in the meshes of the cloth 
 that acts as the best non-conductor. Fur and feathers 
 are warm chiefly because they imprison so much air. 
 For the same reason moderately loose winter clothing is 
 warmer than tightly fitting clothing. 
 
 76. Sources of Heat. The chief sources of heat are 
 the sun, body heat, the burning of fuels, friction and 
 collision, and electrical resistance. 
 
 a. The Sun. The earth gets some heat from the 
 moon and stars and its own interior, but the amount is 
 small. Practically all the warmth of the earth's surface 
 and of its atmosphere comes from the sun. The sun is so 
 far away, and our earth is so small, that we get only a 
 very little of the heat sent forth by the sun, perhaps 
 1 part out of 2,000,000,000, yet this is enough to make 
 the earth fit for living things instead of a frozen, unin- 
 habited sphere. The gain and loss of heat in the temperate 
 and frigid zones cause the seasons of these zones, and the 
 cutting off of the sun's rays from any place brings its 
 night. 
 
 b. Fuels. Man is the only animal that uses fire. Other 
 animals and the world of plants store up some of the energy 
 received from the sun, and man uses them for food and 
 fuel. In causing a fuel to unite with the oxygen of the 
 air, man is getting back some of the sun's energy. The 
 chief fuels are wood, coal, charcoal, coke, natural gas, 
 petroleum, and alcohol. Petroleum (cf. 121) is the 
 natural product out of which kerosene, gasoline, and par- 
 
SUMMARY 
 
 73 
 
 affin (white wax) are prepared. Coal is the chief source of 
 illuminating and fuel gas (cf. 124). 
 
 c. Collision and Friction as Sources of Heat. If you slap your 
 hands together briskly, they become warm. When a bullet is stopped 
 by a rock, it becomes hot. What is the source of the heat in these 
 cases? The answer is that the moving bodies (the hands and the 
 bullet) have their motion changed into heat, the motion of the mole- 
 cules. The heat is due to the collision. When you rub your hands 
 together, they become warm, because their motion is partly changed 
 into heat. The loss of motion 
 
 is due to the friction of one 
 hand against the other. 
 
 Early man learned to use 
 friction to kindle his fires (Fig. 
 63), and thus exchanged mus- 
 cular energy for heat. Later 
 he obtained sparks by striking 
 together flint and steel, or 
 flint and iron pyrites ("pi-rl'- 
 tes"; also caUed " fools' gold," 
 from its deceptive color). In 
 the modern match man is still 
 exchanging motion for heat; 
 for he uses friction to kindle 
 the match. 
 
 d. Electrical Resistance. 
 The energy of the electric 
 
 current is easily changed into heat, and gives us electric lights, 
 heaters, and furnaces. We can understand these better after we have 
 studied Chapter VIII. 
 
 FIG. 63. 
 
 Batua Fire-Drilling, Congo Free State. Copy- 
 right, 1912; Frederick Starr. 
 
 77. Summary. Bodies usually expand when heated, and con- 
 tract when cooled. This is explained by the theory that matter is 
 composed of molecules, and that heating separates them further, while 
 cooling causes them to come closer together. 
 
74 HEAT 
 
 Thermometers measure differences of expansion between mercury 
 and glass. 
 
 The "freezing point" of a thermometer is the temperature of 
 melting ice. The " boiling point " mark is the temperature of steam 
 given off by water that is boiling under standard pressure. 
 . = (Cent.X 9 A)+32. 
 = 5 /9(Fahr.-32). 
 
 Degree of heat is temperature. It depends upon the rapidity of 
 molecular motion. 
 
 Quantity of heat in a body depends upon the temperature and the 
 mass; also upon heat capacity (cf. 73). 
 
 The calorie is the unit of heat quantity. 
 
 Heat is distributed by conduction (or contact), by radiation, and by 
 convection. 
 
 Convection currents are set up in liquids or gases if they are heated 
 from the bottom or cooled from the top. 
 
 The three physical forms of matter are solids, liquids, and gases. 
 They depend on the cohesion and the energy of the molecules. 
 
 Heat of melting, or of fusion, is the number of calories of heat 
 needed to melt 1 g. of a solid. 
 
 Heat of freezing is the number of calories given off in the freezing 
 of 1 g. of a liquid. It is equal to the heat of melting. 
 
 Water expands when it freezes; most liquids contract. 
 
 Heat taken up in the change of liquid to vapor is given off in the 
 condensation of the vapor. 
 
 Compression of a gas liberates heat. Expanding gases take up 
 heat; that is, become cold. 
 
 Kindling temperature is the temperature at which a substance 
 begins to burn. 
 
 A calorimeter is an apparatus in which the heat given off in burn- 
 ing, or in some other change, can be given to some water, and so 
 measured. 
 
 The human body is a complex engine. It uses the changes in its 
 cells and in food to produce heat and the ability to do work. 
 
 Evaporation of perspiration keeps the body's temperature constant. 
 
 Wool makes the best clothing for those exposed to extremes of 
 temperature. 
 
EXERCISES 75 
 
 Sources of heat are the sun, fuels, collision, friction, and electrical 
 resistance. 
 
 78. Exercises. 
 
 1. If you mix 100 g. of water at 80 C. with 100 g. of water at C., 
 what temperature will the mixture have? 
 
 2. How many calories are needed to melt 100 g. of ice? If you mix 
 100 g. of water at 80 C. with 100 g. of ice at C., what will happen? 
 What will the temperature of the mixture be? 
 
 3. If a glass fruit jar is filled completely with water, then sealed, 
 and put outdoors in zero weather, what is likely to happen? Why? 
 
 4. If you open the valve of a full bicycle tire, the escaping air feels 
 cold; why? 
 
 5. If steam at 100 C. enters the steam coil of a room, and water at 
 100 C. leaves the coil, how is the roorn heated? 
 
 6. Why does sprinkling a lawn in hot weather cool the air? 
 
 7. If some liquid air is poured into an open beaker, its temperature 
 does not rise above 182.5 C., no matter how warm the room is. 
 Explain. 
 
 8. What do we mean by saying that the specific heat of water is 9 
 times that of iron? 
 
 9. Why does a nail struck repeatedly with a hammer become hot? 
 Why does a bit used to drill holes in a board become hot? What 
 causes a "hot box" on a railway car? Give other illustrations of the 
 same phenomenon. 
 
CHAPTER V 
 
 WATER 
 
 79. How Water Occurs in Nature. We commonly 
 think of water as a clear, easily poured liquid; we must 
 also think of it as a solid : snow, frost, and ice, and as a 
 gas or vapor : steam. Water is very abundant, not only 
 in rivers, lakes, and the ocean, but also in the earth's 
 solid crust. No matter where we dig, we find it even in 
 the desert. The atmosphere likewise contains a great 
 deal : as steam. Water makes up a large part of all plants 
 and animals. The following table shows how much of 
 our bodies and our food is water: 
 
 Human body. .... 70% Watermelon. .'. . . . 92% 
 
 Milk 87% White bread 35% 
 
 Potatoes 78% Beef 62% 
 
 Natural water is never pure. The rain gathers material 
 from the atmosphere (cf. 58) ; the water that flows over 
 or through the earth's crust dissolves substances from 
 the* soil and the rock; and both rain and running water 
 take up living creatures, such as bacteria (cf. 56 and 
 324). Rivers and lakes become impure because of the 
 sewage, or waste matter, of the cities, factories, and farms 
 upon their banks. 
 
 The purest natural water is probably obtained by melt- 
 ing some ice obtained from a pure source. 
 
 76 
 
DRINKING WATER 
 
 77 
 
 80. Substances Dissolved in Natural Water. Lakes 
 and rivers are usually fresh because the salty substances 
 brought into them are also carried away; but the ocean 
 becomes more and more loaded with dissolved material. 
 The same is true of such lakes as Great Salt Lake and the 
 Dead Sea. The reason is that while these bodies receive 
 both water and dissolved substances, only the water 
 evaporates. The solids are left behind. Nearly 2.7 per 
 cent of sea water is common salt. 
 
 Mineral waters contain so much solid material in solution that it is 
 usually perceptible to the taste. The most common substances in 
 mineral waters are salt, soda, potash, limestone, gypsum, and com- 
 pounds of iron and of sulphur. As many as 15 grams of solids are 
 sometimes present in one liter of mineral water. Salt springs and 
 wells furnish most of our table salt (cf. 108 and Fig. 84). 
 
 COMPOSITION OF SOME NATURAL WATERS 
 
 Source of Water 
 
 Grams of Solids in 
 10GO g. of Water 
 
 Cubic Centimeters of Gases 
 in 1 1. of Water 
 
 Nitrogen 
 
 Oxygen 
 
 Carbon 
 Dioxide 
 
 Rain 
 
 .029 
 .097 
 .282 
 .438 
 35.25 
 40.00 
 228.60 
 271.40 
 
 13.1 
 15.0 
 15.8 
 
 12.Q 
 
 6.4 
 
 7.4 
 8.5 
 
 6.'0 
 
 1.3 
 30.0 
 1.1 
 
 i7'6 
 
 Rivers and Lakes 
 Springs 
 
 Deep Wells 
 English Channel 
 Mediterranean Sea. . . . 
 Dead Sea 
 
 Lake Elton 
 
 
 81. Drinking Water. By "pure water" different 
 classes of people mean different things, for each is thinking 
 of some impurity that is especially objectionable to him. 
 If the water is to be used for drinking, the chief impurities 
 
78 
 
 WATER 
 
 we are troubled about are injurious bacteria, and the de- 
 caying matter upon which they live. Dissolved gases and 
 minerals are not usually considered impurities in a drink- 
 ing water; but if the bacteria of certain diseases, such as 
 typhoid fever, get into the water, we may " catch' 7 the 
 disease by taking the bacteria into the stomach. Hence 
 drinking water should be tested carefully. This is espe- 
 cially true if the source of the water is not well known, or 
 if it is suspicious. Whether a water is pure or impure 
 cannot be told by its appearance: a dirty looking water 
 may be safe to drink, while one clear as crystal may be 
 
 filled with deadly 
 germs. Shallow 
 wells are always sus- 
 picious ; for filth may 
 be washed in from 
 the surface by the 
 rain, and kitchen 
 drains, outbuildings, 
 or barns may be 
 sufficiently near to 
 pollute the well (Fig. 
 64). We must re- 
 member that ice 
 made from polluted 
 water is also dan- 
 gerous. The disease germs are not killed by freezing, but 
 live on in an inactive state. They become active again 
 when they find lodging in our bodies, or in favorable 
 food, such as milk. 
 
 FIG. 64. 
 
 A well may be polluted by a cesspool or by drainage 
 from a barn. 
 
PURIFYING WATER 79 
 
 82. Hardness of Water. To the manufacturer ' ' pure " 
 water usually means water that can be used in boilers, 
 to produce steam. The most objectionable impurity from 
 his point of view is the "hardness" of the water. Hard- 
 ness is also harmful in water to be used in the house- 
 hold for bathing and for the washing of clothes. Water 
 is said to be "hard" if it does not wet the skin readily, 
 and if soap put into the water forms, at first, an in- 
 soluble scum. Suds, or lather, is not formed in hard 
 water until the hardness is removed by the soap; hence 
 hardness is defined as the soap-consuming power of a 
 water. Distilled water, water from melting ice, and rain 
 water form a lather almost immediately; hence they are 
 called " soft " waters. Some of the impurities that cause 
 hardness become insoluble, and settle, when the water is 
 boiled. In this case the hardness is said to be temporary. 
 Hardness that cannot be removed by 
 
 boiling is called permanent hardness 
 (c/.226). 
 
 If a boiler is filled repeatedly with hard 
 water, it becomes clogged with a deposit 
 "boiler scale" just as a kettle does (Fig. 65). 
 Iron is a conductor of heat (cf. 65) ; hence the 
 
 walls of a new iron boiler cannot become much The kettle is lined with solids 
 hotter than the water in the boiler. But boiler deposited from boiling 
 scale is so poor a conductor that a boiler con- 
 taining much of it needs to be heated very hot, or the water will not 
 boil. As a result of this over-heating, the "scale" is often broken up 
 into substances that act upon the iron, and weaken it. Boiler scale 
 has caused very serious explosions and loss of life. 
 
 83. Purifying Water. Water may be purified 
 
 (1) by distilling it ; (2) by boiling it ; (3) by filtering it. 
 
80 
 
 WATER 
 
 Overflow 
 
 Distillation consists in heating a liquid until it bpils, 
 and then passing the vapor through a condensing appara- 
 tus to convert it back into the liquid state. The solid 
 
 substances, such 
 as salt, limestone, 
 gypsum, etc., do 
 not boil off, but 
 remain behind in 
 the boiler. The 
 form of distilling 
 apparatus much 
 used in laborato- 
 ries is shown in 
 Fig. 66. 
 
 Fia. 66. 
 Distillation of Water; Liebig's Condenser. The Condenser is 
 
 known as Liebig's 
 
 condenser, after the celebrated scientist of that name. It is of glass, 
 and consists of an inner tube for condensing the vapor, and an outer 
 jacket for the cooling liquid, which 
 is usually water. For distillation 
 on a larger scale a boiler and 
 a "worm" condenser are used 
 (Fig. 67). 
 
 Other liquids may be distilled 
 like water. Thus, while water 
 boils at 100 C., alcohol boils at 
 79 C. If a mixture of alcohol and 
 water is distilled, the alcohol boils FIG. 67. 
 
 Off first, and the tWO may thus be Large Still and Worm Condenser. 
 
 Boiling removes the temporary hardness of water, and kills the 
 germs. Since the taste of natural water is due to the dissolved gases 
 and solids it contains, distilled water tastes very "flat." Boiled 
 
FILTERING 
 
 81 
 
 placed in the funnel, 
 liquid is poured from a 
 beaker, down a glass rod, 
 upon the filter. The filtrate 
 runs through the filter. 
 
 water is more agreeable, because some dissolved solids are still present; 
 but both kinds of water are better if they are aerated; that is, if they 
 are made to dissolve air. We can add the air 
 to a water by filtering the water through 
 porous stone, or by pouring the water several 
 times from one vessel to another. 
 
 84. Filtering. A filter is a screen 
 or sieve with openings so small that 
 only liquids and the substances dis- 
 solved in them can get through. 
 Substances suspended in the Jiquid, 
 which make the liquid roily, or turbid, 
 can not get through. In the laboratory 
 we make a filter by folding a piece of 
 porous paper, as shown in Fig. 68, and 
 placing it in a funnel. If a milky mixture of water and 
 powdered chalk be poured upon the filter, the water 
 
 goes through, but the chalk does 
 not. 
 
 In household filters (Fig. 69) por- 
 ous stone and charcoal are used as 
 filtering materials. These strain 
 out the suspended impurities of 
 the water, including the bacteria. 
 However, unless a filter is cared 
 for, it may become so clogged with 
 organic matter that it will serve as 
 a breeding-place for bacteria, in- 
 stead of removing them. Water filters should be cleaned 
 frequently, and exposed to direct sunlight, to keep them 
 fresh and wholesome. This is especially true of filters 
 
 Charcoel 
 
 FlG. 69. 
 A Household Filter. 
 
82 
 
 WATER 
 
 attached to faucets, because of the large volume of water 
 that passes through them daily. 
 
 85. Filtering City Water. The best natural filter is 
 clean sand. It is loose, and contains much air; hence 
 oxidizing bacteria can penetrate far into it. If the sand 
 is not kept soaked too long at a time, impure water that 
 
 passes through it will be 
 made fit for drinking. 
 A soil containing much 
 clay does not make a 
 good filter, because clay 
 is too compact. 
 
 In filtering water for cities 
 (Fig. 70) men run the water 
 of rivers or lakes through 
 beds of sand. After soaking 
 through the sand the water 
 enters reservoirs, from which 
 it is distributed through the 
 water "mains" of the city. 
 But the large filters, like the 
 small ones, need to be emptied 
 
 often, and allowed to lie idle, so that the sand may be purified by 
 
 the direct action of sunlight and air. 
 
 Coagulation Filters. In some cases a coagulating, or clotting, 
 substance, such as alum, is added to the water before it enters the sand 
 filters. The alum causes the clay particles, which of themselves settle 
 only very slowly, to flock together and to come down rapidly, carrying 
 decaying matter and germs with them. Coke dust is often mixed 
 with the sand to improve the quality of the filter. 
 
 FIG. 70. 
 Filter Beds of a City System; Evanston, 111. 
 
WHY ICE FORMS ONLY AT THE SURFACE 83 
 
 86. Exercises. 
 
 1. Hard cookies placed in a box containing fresh bread become soft 
 and mellow; why? Why do crackers lose their crispness when taken 
 out of their box? 
 
 2. Tell why a potato loses weight when baked. 
 
 3. Why does candy become sticky, and why does salt "cake," in 
 damp weather? 
 
 4. The Jordan River flows into Lake Utah, and Lake Utah empties 
 into Great Salt Lake. Would you expect Lake Utah to have fresh 
 water or salty? Why? 
 
 5. Tell how the crew of a ship can prepare fresh water out of sea 
 water? How does nature do it? 
 
 6. Name some of the ways in which dirty water thrown into the 
 yard is purified by nature. Why should such water never be thrown 
 near a well or cistern? 
 
 7. Why does moisture condense on the windows of the house on a 
 cold wash day? 
 
 8. Why should bottles of alcohol, gasoline, and turpentine be stop- 
 pered? 
 
 87. Why Ice Forms Only at the Surface. Since ice 
 is lighter than water (cf. 70), it floats, and the ice cover- 
 ing usually prevents the water beneath from freezing. But 
 the chief reason why lakes and streams do not freeze to 
 a great depth is that water is most dense, or heavy (cf. 
 33), not at C., the freezing temperature, but at 4 C. 
 Let us see the results of this fact : 
 
 A lake or stream is cooled chiefly from the top, where it 
 touches the cold air. Now, when a lake having water at, 
 let us say, 10 C., is cooled by air at C., or below, the 
 surface layer becomes colder than 10 C., and heavier, 
 and so sinks to the bottom, while a warmer layer takes its 
 place. This movement of water goes on until all the 
 water is cooled to 4 C. But as the upper layer of water, 
 
84 
 
 WATER 
 
 which is now at 4 C., is cooled further, it becomes lighter 
 than the water at 4 C., and floats upon the warmer water. 
 When, finally, the surface of the water freezes, the ice 
 that is formed also floats. Hence the water below the 
 ice is rarely cooled below 4 C. Because of this fact water 
 animals and plants survive the winter, and live even in 
 Arctic waters. 
 
 88. Artificial Ice. The supply of natural ice is so un- 
 certain, especially in warm climates, that men have been 
 
 Hot Gas 130C 
 
 17C 
 
 -15C 
 
 Co.mpreseion Pump 
 
 Expansion Coils and Ice Molds 
 
 FIG. 71. 
 
 Cooling Brine for Ice Making by the Expansion of 
 Compressed Liquid Ammonia. 
 
 forced to make ice by artificial freezing. To freeze the 
 water some liquid is used that boils at a low temperature. 
 Usually the liquid is liquid ammonia. This is not "am- 
 monia water," but the gas, ammonia, which has been 
 liquefied by pressure. The liquid ammonia is made to 
 evaporate rapidly by the removal of the pressure. The 
 turning of the liquid into the gas requires heat, just as 
 
STEAM 85 
 
 the turning of water into steam does. In the ammonia ice 
 apparatus the heat comes from the water to be frozen. 
 
 The apparatus is shown in Fig. 71. In this apparatus the water 
 is not frozen directly by the evaporation of the liquid ammonia; but a 
 brine is cooled to 15 C. or 20 C., and this cold liquid is used to 
 freeze the water. The brine is a water solution of salt or of calcium 
 chloride, and freezes far below the freezing temperature of water. 
 The cold brine is also used in cold-storage warehouses, and in refriger- 
 ator cars, to produce a low temperature. In this way butter, eggs, 
 meat, fruit, etc., are kept cold, and prevented from spoiling (Fig. 72). 
 
 FIG. 72. . 
 
 Rooms for storage of meat are cooled by means of a cold brine 
 distributed through pipes. 
 
 "Iceless" refrigerators are now being made. They are really refriger- 
 ating machines, and are kept cold by the rapid evaporation of 
 liquid ammonia. 
 
 89. Steam. Steam is water in the vapor form. When 
 steam issues briskly from a vessel of boiling water, as 
 
86 WATER 
 
 from the spout of a tea-kettle, it is invisible until it con- 
 denses to fine drops, some distance away. The fine drops 
 are liquid water, not steam. Clouds are made of similar 
 droplets : ' ' fog," not of steam. 
 
 While water freezes at a definite temperature (0 C. or 
 32 F.), it is changed into steam at any temperature. 
 Even ice and snow pass directly into steam (evaporate) 
 on a cold winter's day, without melting. 
 
 Like air and other gases, steam has pressure. At the 
 ordinary temperature the pressure of the steam given off 
 by water is small (cf. Appendix, Table VIII) ; but as the 
 temperature of the water rises, its steam has a greater and 
 greater pressure, until at 100 C., or 212 F., the steam has 
 the same pressure as the air (760 mm.). The steam then 
 sweeps the air completely out of the vessel in which the 
 water is being heated. We say that the water is boiling, 
 and we call 100 C., or 212 F., the boiling point of water 
 (cf. 62). 
 
 90. The Boiling Point Changes with Pressure. If 
 
 water is boiled in a closed vessel, more and more steam is 
 packed into the space above the liquid water, and the 
 pressure of the steam increases accordingly. Under the 
 increased pressure of the steam, the water now boils 
 above 100 C. When the steam has twice the atmos- 
 pheric pressure (2X760 mm.), water boils at 121 C. In a 
 locomotive boiler producing steam at 13 " atmospheres " 
 pressure (191 pounds to the square inch) water boils at 
 192 C., or 378 F. When steam at high pressure is allowed 
 to escape, it expands greatly. This is the source of 
 motion in a steam engine (cf. 24). 
 
SOLUTIONS 
 
 87 
 
 Condenser 
 
 When the pressure under which water boils is less than 760 mm., 
 the boiling point is less than 100 C. (cf. Appendix, Table VIII). 
 Sugar refiners make use of this fact in boiling off the water from dilute 
 syrup. If the water were removed at the ordinary pressure, the syrup 
 would boil so high that the sugar would be spoiled. By the use of 
 evaporating vessels called "vacuum pans," which are covered with 
 tight hoods (Fig. 73), 
 this is avoided. If 
 the air is removed 
 from the pans until 
 its pressure is only 
 233 mm., the water 
 boils off at 70 C. 
 without injuring the 
 sugar. Salt is ob- 
 tained from salt brines 
 in the same way. 
 
 The boiling point 
 of water falls about 
 1C. for every 960 
 feet we ascend above 
 sea level. Thus, at 
 the city of Mexico, 
 
 7,500 ft. above the sea, water boils at 92.3 C., while at Denver, 5,000 
 ft. high, it boils at about 95 C. 
 
 91. Solutions. If we put salt or sugar into water, the 
 solids disappear. We say they dissolve in the water. They 
 have not really disappeared, however, for they give their 
 taste and other properties to the water. We call the 
 water the solvent, and the dissolved substance the solute. 
 The mixture of solute and solvent is called a solution. 
 Solutions in which alcohol is the solvent are called tinc- 
 tures. If the solute is of some other color than white, 
 its water solution will usually be colored. A minute 
 
 FIG. 73. 
 
 Vacuum Pan. Water is being distilled at 
 "reduced pressure." 
 
88 WATER . 
 
 amount of potassium permanganate, or of aniline violet, 
 shows a remarkable power of coloring water. But 
 whether colorless or colored, true solutions are clear, not 
 roily (cf. 84). 
 
 Milk is a mixture of water, sugar, etc., with suspended particles of 
 fat. The fat is very finely divided, and the casein of the milk (cf. 
 357) prevents the water and fat from separating at once into two 
 distinct layers. After a while, however, the fat (cream) rises to the 
 top. Such a mixture is called an emulsion. 
 
 92. Properties of Solutions. A solute not only im- 
 parts its taste and color to a solution, but it makes the 
 boiling point, freezing point, and density of the solution 
 differ from those of the solvent. A solution of a solid 
 boils at a higher temperature, and freezes at a lower 
 temperature, than the pure solvent. Thus, a solution of 
 40 g. of salt in 100 g. of water boils at about 108 C. A 
 saturated salt brine does not freeze until the temperature 
 is about 22 C. Because of its dissolved solids, ocean 
 water rarely freezes in temperate latitudes. 
 
 When a dilute salt brine freezes partly, but not wholly, 
 most of the salt remains in the solution, and the ice is 
 nearly fresh. 
 
 A solution of a solid has a greater density than the 
 solvent. Thus, while a liter of pure water weighs about 
 1000 g., the same volume of sea water weighs about 1026 
 g. (qf. 80). 
 
 93. Freezing Mixtures. When most solids dissolve 
 in water, they lower the temperature of the water. Thus, 
 if equal parts, by weight, of ammonium nitrate and water 
 are mixed at C., the temperature falls to 15 C. 
 
CRYSTALS 
 
 89 
 
 We have learned (c/. 69) that when ice is placed in water, the heat 
 needed to melt the ice (80 calories for each gram) comes from the 
 water; hence the water is cooled to its freezing point, C. Now, when 
 ice is mixed with salt, the salt dissolves in the water formed by the 
 melting of the ice. We thus get a salt brine. The heat needed to 
 melt the ice comes from the brine, and cools it to its freezing point, 
 22 C. If cream or ' ' ices " are placed in this brine, heat is taken out 
 of them until they are frozen. 
 
 94. Solubility. By the solubility of a solid we mean 
 the weight of it that will dissolve in a definite amount, 
 say, 100 grams, of the solvent. We know that if we add 
 too much sugar to our tea or coffee, some of it will not 
 dissolve, even though we stir the liquid vigorously. The 
 tea or coffee is then said to be " saturated " with sugar. 
 If a liquid is hot, it can usually dissolve more solid than 
 when cold. 
 
 A solid that is soluble in water may be insoluble in 
 another solvent. Thus, salt does not dissolve in alcohol. 
 Camphor and shellac dissolve in alcohol, but not in water. 
 
 The accompanying table shows that substances differ greatly in 
 solubility, and also that the solubility of solids generally increases as 
 the temperature rises. 
 
 Substance 
 
 Grams Soluble in 100 g. Water at 
 
 oc. 
 
 20 
 
 50 
 
 70 
 
 100 
 
 Potassium nitrate (saltpeter) 
 Sodium chloride (salt) 
 
 13 
 35 
 3 
 15 
 6 
 
 32 
 36 
 
 7 
 22 
 13 
 
 85 
 37 
 20 
 
 32 
 
 140 
 38 
 32 
 
 iis 
 
 246 
 39 
 59 
 73 
 
 Potassium chlorate 
 
 Copper sulphate (blue vitriol) 
 
 Alum 
 
 95. Crystals. The table of solubility shows us that 
 water at 100 C. can dissolve more of the substances 
 
90 
 
 WATER 
 
 FIG. 74. 
 
 Crystals of Salt (A), Alum (B), and Blue 
 Vitriol (C7). 
 
 named than water at 20 C. (the ordinary temperature). 
 Suppose we were to saturate some water at 100 C. with 
 common salt, and were then to let the solution cool to 
 20; what might we expect to happen? We might expect 
 part of the salt to be deposited as a solid. If we examined 
 
 the deposited salt, 
 we would find 
 that it consisted 
 of small cubes 
 (Fig. 74, A). We 
 would also get 
 cubes of salt if 
 we were to let some salt solution evaporate slowly at the 
 ordinary temperature. The cubes are crystals of salt. 
 
 If we make a hot, saturated solution of alum, and let 
 it cool slowly, we shall get crystals like Fig. 74, B; while 
 crystals of blue vitriol are like I ig. 74, C. All of these 
 crystals have flat (plane) faces and straight edges arranged 
 in a definite way. 
 
 Each substance has its own crystalline form, but the crystals may be 
 imperfect if they are deposited on the sides of the vessel. The more 
 slowly the crystals separate 
 from solution, the larger they 
 will be. Sugar crystallized 
 upon a string which is sus- 
 pended in the sugar solution 
 is called "rock candy" (Fig. 
 
 FIG. 75. 
 
 Crystals of Sugar (A), Quartz (B), and 
 
 75, A). Sulphur crystallizes 
 
 (Fig. 3) from a liquid called Diamond (co 
 
 carbon disulphide. 
 
 Crystals may be formed notonly from solution, but also by the 
 freezing of a liquid; as ice is made by the freezing of water. Ice is 
 
SUMMARY 91 
 
 composed of small crystals packed closely together. The separate 
 crystals can be seen when freezing begins, and in the form of snow and 
 
 Fio. 76. 
 Crystals of Snow. 
 
 frost. Snowflakes take on many forms (Fig. 76), but all are six-sided 
 or six-pointed. 
 
 Substances that do not crystallize are said to be amorphous, that 
 is, "without form." Glass and many gums are examples. 
 
 96. Summary. Water exists as solid, liquid, and vapor. It is 
 very abundant in nature, but natural water is rarely pure. 
 
 Mineral waters contain so much material that it can be tasted. 
 The sea contains even more dissolved material than mineral waters. 
 
 Drinking water is considered pure if it does not contain too much 
 mineral matter, and if it is free from injurious "germs." 
 
 Hardness of water is its soap-consuming power. It may be tem- 
 porary or permanent. 
 
 Boiler scale is a deposit left in steam boilers and kettles that use 
 hard water. 
 
 Water is purified by distillation, boiling, filtration, and ' 'softening/' 
 
 Distillation is changing a liquid into its vapor, and then condensing 
 the vapor. The impurities are left behind. 
 
 The "flat" taste of distilled and boiled water is due to the absence 
 of dissolved substances, including air. 
 
 Filters "strain out" the suspended impurities of water and give a 
 large surface for the oxidizing bacteria of the air. 
 
 Water freezes at C. (32 F.). It expands as it freezes; hence ice 
 floats. 
 
 Artificial ice is made by the use of the principle that evaporation 
 requires heat. The heat needed to vaporize liquid ammonia is taken 
 from the water to be frozen. 
 
92 WATER 
 
 Steam is the gaseous form of water. Water and ice change to steam 
 at all temperatures. At 100 C. the steam from boiling water has a 
 pressure equal to the pressure of the atmosphere. 
 
 A solution consists of solvent and solute. An emulsion is a mixture 
 in which the suspended substance is so finely divided that it separates 
 itself from the solvent very slowly. 
 
 Solubility of a solid is the weight of it that will dissolve in a definite 
 weight, usually 100 g., of water or other solvent. 
 
 Crystals are solid bodies that take regular shapes when they sep- 
 arate from solution or from the liquid state. Non-crystalline sub- 
 stances are amorphous. 
 
 97. Exercises. 
 
 1. If water were most dense at C., what effect would this fact 
 have upon the depth of ice in winter? 
 
 2. If a test tube of water is placed in a cup of ether, and a rapid 
 current of air is forced through the ether, the water may be frozen. 
 Why? 
 
 3. Which should be kept in the colder room of a storage warehouse, 
 eggs or meat? 
 
 4. The sharp edges of a piece fo ice become rounded off even in 
 very cold weather; why? 
 
 5. In making " fudges," or the filling of French candies, why is the 
 candy first cooled without being disturbed, and afterwards stirred 
 rapidly? 
 
 6. Can you dissolve salt in water, and then recover the salt un- 
 changed by boiling off the water? Can you do the same with sugar? 
 Why? 
 
 7. At Quito, in Ecuador, water boils at 90 C., too low for the cook- 
 ing of potatoes; why? Can you suggest how you could make water 
 boil at 100 C. in Quito? 
 
 8. How is salt commonly obtained from salt water? In Northern 
 Russia the salt makers remove much of the water by partly freezing 
 the salt solution, and so save fuel. How is this possible? 
 
EXERCISES 93 
 
 9. Why is it easier to swim in the ocean than in fresh water? 
 
 10. If sugar is dissolved in a cup of tea, does its dissolving affect the 
 temperature of the tea in any way? Explain. 
 
 11. If you had some powdered alum, how would you make good- 
 sized alum crystals out of it? 
 
CHAPTER VI 
 
 ELEMENTS AND COMPOUNDS 
 
 98. Physical and Chemical Changes. If we heat a 
 flat-iron on a stove, it becomes hot. It may even become 
 red hot, so that it gives off heat and light. But if it is 
 taken from the stove, it becomes cold again, and looks 
 just as it did before the heating. A lump of coal thrown 
 into the air comes down again, still a lump of coal. The 
 water of the ocean is changed into steam, then carried 
 away by air currents, and finally falls again as rain or 
 snow. The iron is changed in temperature, the coal and 
 water are changed in position, and the water is changed in 
 physical state (cf. 69); but the changes do not really 
 alter the iron, coal, and water. We call such changes 
 physical changes. 
 
 But if a piece of iron is left in moist air, it rusts (cf. 
 48) . If water is added to quicklime , it combines with the 
 lime, forming "slaked" lime; it is no longer water. If 
 coal is burned, it disappears, as carbon dioxide and steam 
 (cf. 52). Such changes do alter the nature of substances. 
 They are called chemical changes, because they are stud- 
 ied in the science of Chemistry. Chemical changes are 
 also called reactions. 
 
 Digestion consists of the physical and chemical changes 
 that take place in food, in order that it may be taken up 
 by the blood for the use of the body. 
 
 94 
 
ELECTROLYSIS OF WATER 
 
 95 
 
 99. Composition of Water. By the " composition/ ' 
 or " make-up," of water we do not mean a list of the 
 materials present in a particular sample of water, such as 
 the carbon dioxide, limestone, salt, etc., that are dissolved 
 in a natural water (cf. 80). What we mean is that pure 
 water, which we obtain by purifying natural water, is 
 still made up of two different substances : hydrogen and 
 oxygen. We say that water is "composed of," or "is a 
 compound of," hydrogen and oxygen. 
 
 Water is formed when hydrogen is burned (cf. 52 
 and 105). Can we reverse the action that takes place in 
 burning, and break up water into hydrogen and oxygen, 
 just as we "decomposed" mercury oxide into mercury 
 and oxygen (cf. 50)? Water, like mercury oxide, can be 
 broken up by heat; but the temperature required is very 
 high, and the method is hard to carry out. The decom- 
 position of water is easy, if we use the electric current. 
 The operation is called the electro- 
 lysis of water. Electrolysis means 
 "loosing," or "breaking apart," by 
 the use of electricity. 
 
 100. Electrolysis of Water. The 
 
 "breaking apart" of water by the 
 electric current may be carried out 
 as follows (Fig. 77) : 
 
 FIG. 77. 
 
 Electrolysis of Water. The 
 electric current breaks up 
 water, containing a little 
 of an acid, into hydrogen 
 and oxygen. 
 
 Two wires from a battery or other source 
 of the current (cf. 150 and 160) pass into a 
 vessel. The vessel contains water and a very 
 
 little sulphuric acid. The liquid to be changed by the electric current 
 is thus a very dilute sulphuric acid. The wires inside the vessel are 
 
96 ELEMENTS AND COMPOUNDS 
 
 of the metal platinum (c/. 9), and they have tips of platinum foil. 
 We call the ends of the wires the poles of the battery. If we were to 
 put the two platinum poles together, the current would have a com- 
 plete passageway, or circuit, without going through the dilute acid. 
 But if we keep the poles apart, the current is compelled to pass 
 through the dilute acid. In the language of the electrician, the dilute 
 acid makes, or doses, the circuit. 
 
 While it is carrying the current from one pole to the other, the 
 dilute acid is changed chemically (cf. 98). What we see is that 
 bubbles of gas arise from the poles. We can collect the gas by placing 
 over each pole a test tube filled with some of the dilute acid. We then 
 see that one test tube collects gas about twice as rapidly as the other. 
 If we put a burning splinter into the gas that is collected the more 
 slowly, the splinter burns more brightly than in air, and if the splinter 
 is merely glowing, it will burst into flame. The gas collected in this 
 tube is oxygen. If we bring a flame near the other gas, the gas takes 
 fire with a slight "pop," or explosion, and then burns with an almost 
 invisible blue flame. This gas is hydrogen. It is so called because 
 it is -a part of water. The Greek word for water ' ' hydor " appears 
 in many other English words, such as hydra, hydrant, hydraulic, etc. 
 
 101. Elements and Compounds. Water is so hard 
 to decompose by heat that men were unable to learn its 
 real nature until 1781. In that year Cavendish, who had 
 prepared hydrogen in 1766, burned hydrogen, and ob- 
 tained water. The decomposition of water by the electric 
 current was first carried out in 1800. The question now 
 arises : ' ' Can the hydrogen and the oxygen obtained from 
 water be divided up into other substances?' 7 The answer 
 is that they have never been divided by any method used 
 for the purpose. A substance like water, which is not a 
 single kind of matter, but has at least two kinds of matter 
 in it, is called a compound. A kind of matter which we 
 have never been able to break up is called a simple 
 
MIXTURES 
 
 97 
 
 substance, or element. Hydrogen, oxygen, nitrogen, 
 carbon, iron, tin, mercury, etc., are elements (see Appen- 
 dix, Table IX). 
 
 How complete the change is, when substances unite chemically, is 
 seen when we compare water, the compound, with the two elements 
 that make it up. The formation of carbon dioxide by the burning of 
 carbon is another common illustration of the same thing. No one 
 would suspect that this colorless gas (cj. 51), which puts out fire, 
 which is exhaled from our lungs, and is taken up by plants (cf. 58), 
 is really the black carbon of coal and charcoal, and of the "black lead" 
 of our pencils, combined with the active gas oxygen. Yet this is 
 the case. 
 
 102. Mixtures. If, in the electrolysis of water, we 
 were to collect two test tubes of hydrogen and one of 
 oxygen, and were to mix them in a bottle over mercury 
 (Fig. 78), would they unite at once to produce water? 
 They would not. They would 
 remain in each other's presence 
 for a long time without any 
 noticeable change. It is neces- 
 sary for the temperature to be 
 raised to about 620 C. before 
 the two gases unite rapidly. 
 When they are mixed at the 
 ordinary temperature, they form 
 only a physical, or mechanical, 
 mixture. No heat is set free; 
 no new substance is formed. If we shake the mixture with 
 water, the hydrogen dissolves as if no oxygen were present, 
 and the oxygen dissolves as if no hydrogen were present. 
 
 FIG. 78. 
 
 A gas can be transferred from one 
 vessel to another under a liquid. 
 
98 
 
 ELEMENTS AND COMPOUNDS 
 
 The air is a physical mixture of nitrogen, oxygen, steam, 
 carbon dioxide, and small amounts of other gases. 
 
 Of course we have mixtures of compounds, as well as of 
 elements. Natural water is always a mixture (cf. 80). 
 All soils, and most rocks, are mixtures (cf. 285 and 294). 
 The forms in which the solid elements and compounds 
 are found in nature are called minerals. 
 
 103. Preparation of Hydrogen. The most common 
 way to prepare hydrogen is to bring certain metals and 
 certain acids together. All acids are compounds con- 
 taining hydrogen (cf. 214) ; but all do not give it off with 
 the same ease. The best acids to use are dilute sulphuric 
 acid and dilute hydrochloric acid; the best metals are 
 zinc and iron. 
 
 The apparatus needed (Fig. 79) is a bottle provided with a stopper 
 having two holes, a " thistle tube," and a delivery tube reaching to a 
 
 O 
 
 FIG. 79. 
 (A) Making Hydrogen and Collecting It over Water. 
 
 (B) Collecting It over Air. 
 
 water-pan. The thistle tube is the opening through which fresh 
 supplies of acid are put into the bottle; it also allows the hydrogen to 
 escape if the delivery tube becomes stopped up. Hydrogen is not very 
 
BURNING OF HYDROGEN 
 
 99 
 
 FIG. 80. 
 
 Soap Bubbles Filled with 
 Hydrogen. 
 
 soluble in water (cf. 100), and is collected "over water," just as 
 oxygen and nitrogen are. 
 
 104. Properties of Hydrogen. Like oxygen and nitro- 
 gen, hydrogen has no odor, taste, or color. It is the light- 
 est substance known. Oxygen is 16 times as heavy as 
 hydrogen, and nitrogen is 14 
 
 times as heavy. At the ordinary 
 temperature and pressure 1 gram 
 of hydrogen has a volume of 
 about 12 liters, i. e., about 3 gal- 
 lons (cf. Appendix, Table IV). 
 Because of its lightness, hydrogen 
 may be collected ' ' over air " (Fig. 
 79, B), and may be used to fill 
 balloons. Soap bubbles filled with the gas rise in air 
 (Fig. 80). 
 
 105. Burning of Hydrogen. If we wish to burn hydro* 
 gen in a jet (Fig. 81), we must light it with great care. 
 
 When we begin the prep- 
 aration of hydrogen, the 
 bottle is full of air; hence 
 the first portions of gas 
 that come off are a mix- 
 ture of hydrogen and air. 
 If we light this mixture, 
 there will be a violent ex- 
 plosion, which may break 
 the bottle, and blow the 
 
 FIG. 81. . 
 
 Hydrogen burns in air to form water. glaSS into OUr laCCS. 
 
100 ELEMENTS AND COMPOUNDS 
 
 Before we bring a flame near a jet of hydrogen, we hold a test tube 
 -over the outlet tube (Fig. 79, B) for a minute, and then carry the test 
 tube, with its mouth downward, to a flame at least 3 feet away. The 
 gas in the test tu*be burns rapidly, if it still contains air; but if it con- 
 sists of fairly pure hydrogen, it burns slowly. When we have lighted 
 the gas in the test tube, we carry the tube, with its mouth downward, 
 back to the jet of hydrogen. We do this until the test tube of burn- 
 ing hydrogen sets the jet of hydrogen on fire. 
 
 Hydrogen burns with a colorless flame when pure. 
 The flame is very hot. When 1 gram of hydrogen is burned 
 in oxygen, the heat given off is sufficient to heat 342 grams 
 of water from C. to 100 C. 
 
 Water is formed not only when hydrogen itself burns, 
 but also when compounds of hydrogen burn (cf. 52). 
 Thus it happens that when a kettle of cold water is placed 
 over a gas flame, water drops are deposited on the outside 
 of the kettle. When the kettle becomes hot 
 enough, the steam formed in the burning 
 escapes without being condensed. 
 
 106. Diffusion of. Gases and of Liquids. 
 
 If we attach a porous cup (Fig. 82) tightly 
 to a tube ending under water, and place a 
 jar of hydrogen over the cup, an interesting 
 Hydrogen 2 'pas- phenomenon takes place : bubbles of gas escape 
 P e o r l n us cup from the bottom of the tube. The bottom of the 
 S.a r n S^wS jar containing hydrogen is open; so the only 
 reason why gas escapes through the water 
 must be that hydrogen enters the porous cup. It can be 
 proved that air passes outward through the porous materi- 
 al; but it does this so much more slowly than the hydrogen 
 goes inward that there is a sudden increase in the volume 
 
EXERCISES 
 
 roi 
 
 Hydrogen 
 
 of gas inside the cup and tube. Hence some of it es- 
 capes through the tube. 
 
 This experiment shows that gases have the ability to 
 mix when placed together. We call this mixing diffusion, 
 and we explain it by saying that the energy of the molecules 
 (cf. 61) causes the molecules of the one gas to move 
 rapidly into the spaces between the molecules of the 
 other gas, until the mixing is complete. 
 
 If we place a bottle of hydrogen, with its mouth downward (Fig. 
 83), over a bottle of air, the hydrogen diffuses downward, and the air 
 upward, in spite of the fact that air is 14.4 times as dense 
 as hydrogen. When the gases are separated by a wall 
 through which they can pass, as in the porous cup ex- 
 periment, they still diffuse into each other; but we can 
 see that they move at different rates: the lighter gas 
 diffuses more rapidly than the heavier one. 
 
 Liquids and solutions diffuse, in spite of gravity, just 
 as gases do. Thus, if some blue vitriol (cf. 95) is put 
 into the bottom of a tall jar, under a deep layer of water, 
 the blue vitriol solution that is formed at the bottom 
 rises gradually to the top, coloring all the water. Also, 
 if some alcohol is put upon water, it descends into the 
 water, even though the water is the heavier; and water 
 ascends into the alcohol, until the mixture is complete. 
 
 The diffusion of oxygen inward, through the walls of 
 the blood-vessels, into the blood, and of carbon dioxide 
 outward causes the exchange of gases necessary for the 
 life of the higher animals (cf. 52). 
 
 107. Exercises. 
 
 1. Are the following changes physical or chemical? Souring of 
 milk, freezing of water, decomposition of mercury oxide by heat, dis- 
 solving of sugar in water, incandescence (" getting white hot") of an 
 electric light, burning of candy on a stove, heating a penny by striking 
 
 FIG. 83. 
 Hydrogen 
 passes down- 
 ward into 
 the air, and 
 air upward 
 into the hy- 
 drogen,. 
 
102 ELEMENTS AND COMPOUNDS 
 
 it with a hammer, changing of the starch of a cracker to sugar by means 
 of the saliva in the mouth. 
 
 2. Compare the properties of hydrogen with those of oxygen. 
 Compare hydrogen with water. 
 
 3. What properties of hydrogen and of oxygen can you show only 
 by changing these elements chemically? 
 
 4. In what proportions by volume would you expect hydrogen and 
 oxygen to unite in forming water? 
 
 5. Coal, wood, and kerosene contain carbon and hydrogen. What 
 products are formed when they burn? 
 
 6. How would you prove that wood ashes are a mixture of soluble 
 and insoluble substances? 
 
 7. If you were making the hydrogen for filling a balloon, which 
 would be the cheaper to use as the metal, zinc or iron ( 103)? For 
 what reason would illuminating gas be better than hydrogen? In 
 what way would hydrogen be better? 
 
 8. How many calories of heat are given off when 1 g. of hydrogen 
 burns ( 105)? 
 
 9. Carbon dioxide is 1.5 times as dense as air. If, in the porous cup 
 experiment (106), you were to surround the cup with a jar of carbon 
 dioxide, which would pass through the porous wall more rapidly, the 
 air or the carbon dioxide? Would air be forced out of the tube, or 
 would water be forced in? 
 
 108. Salt. Salt is found in large amount in sea 
 water; it is also mined as rock salt. To purify rock salt 
 
 we add water to it, so that the 
 salt dissolves, while the impuri- 
 ties do not. The water is then 
 boiled off, either at ordinary 
 FIG. 84. pressure or in "vacuum pans" 
 
 Hopper-shapjd t Massof Salt fa QQ). ^dlt Wells form an- 
 
 other source of salt. 
 
 Salt crystallizes in cubes (95); masses of the crystals 
 are "hopper shaped" (Fig. 84). Because the crystals do 
 
SODIUM 103 
 
 not fit exactly together, some of the brine is caught be- 
 tween them. When the salt crystals are heated, some of 
 the water is changed to steam, and bursts the crystal mass. 
 Hence small salt crystals " crackle " when heated; while 
 large ones "snap" vigorously, and fly out of the dish. 
 
 Salt is not changed, even when heated to fed heat. At 
 white heat it melts. Like water, it can be broken up by 
 the electric current. When the current is passed through 
 melted salt, its elements, sodium and chlorine, are formed, 
 one at each pole. The chemical name of salt is sodium 
 chloride. 
 
 109. Sodium. Sodium is a metal, like silver, gold, 
 copper, etc.; but it is so soft that it can be cut with a 
 knife. When it is freshly cut, its surface is white as 
 silver ; but it is soon tarnished by the moisture, the oxygen, 
 and the carbon dioxide of the air. Sodium is kept under 
 gasoline, or some other liquid containing no oxygen. 
 When heated in air or oxygen, sodium burns, forming 
 sodium oxide (cf. 48 and 51). 
 
 Sodium acts vigorously with water (Fig. 
 85) . The action produces so much heat that 
 the sodium melts, forming a round ball 
 which floats upon the water. A gas escapes 
 with a hissing noise, and the sodium finally 
 
 disappears. The gas produced is hydrogen. FlQ . 85 . 
 When the water is rubbed between the fin- ^p^wlte^ 
 gers, it feels soapy, or slimy. It contains 
 sodium hydroxide, also called caustic (i. e., burning) 
 soda (cf. 218). 
 
 Sodium + water give sodium hydroxide + hydrogen. 
 
104 ELEMENTS AND COMPOUNDS 
 
 Owing to the danger that sodium may be spattered into our eyes, we 
 never put more than a very small piece at a time upon water, and 
 we add it at arm's length, holding a piece of glass between our eyes and 
 the dish. An excellent way is to use a small wide-mouth bottle 3 / 4 
 full of water (Fig. 85). The bottle is provided with a glass cover, 
 which is drawn aside when the sodium is added, and replaced during 
 the action. Several pieces of sodium may be added, one at a time. 
 The hands and tongs used must be dry. If, after each piece of sodium 
 has disappeared, we apply a match to the mouth of the bottle, the hy- 
 drogen will burn. All sodium compounds make a colorless flame yellow. 
 
 110. Chlorine. While the element sodium is a solid 
 at the ordinary temperature, chlorine, the other element 
 present in salt, is a gas. The gases we have studied up 
 to this time are colorless, odorless, and tasteless; but 
 chlorine has a green color, a suffocating odor, and a dis- 
 agreeable action on the lining of the nose and throat. It 
 produces the effects of a bad cold. Its name comes from 
 chloros, the Greek word for " green." We have the same 
 word in "chlorophyll," the green coloring matter of 
 plants (cf. 309). 
 
 Chlorine has the power of bleaching; that is, of removing 
 the color of grass, straw, and other plant products. It also 
 bleaches cloth or paper dyed with indigo, litmus, cochineal, 
 
 etc. Large quantities of 
 chlorine are used in mak- 
 ing bleaching powder 
 FIG. so. ("chloride of lime")' an( l 
 
 The Bleaching of Cotton Goods. ,, ,. , .. -m 
 
 bleaching solutions. These 
 
 are used for the whitening of cotton goods (Fig. 86) 
 and, as "disinfectants," for destroying disease germs. 
 Bleaching solutions are also used to remove ink and 
 other stains from fabrics (cf. 230). 
 
AMMONIA 
 
 105 
 
 When a burning splinter is put into chlorine, it does not continue 
 to burn. Many metals, however, burn vigorously in chlorine. Thus, 
 warm copper foil takes fire, and burns to form copper chloride. If thin 
 shavings of sodium are put into chlorine, the sodium becomes covered 
 with a white deposit of common salt, and is soon used up. We thus 
 prove, both by breaking up salt, and by forming it again, that it is 
 a compound of sodium and chlorine. 
 
 111. Hydrochloric Acid. When a jet of burning hydro- 
 gen (cf. 105) is put into a bottle of chlorine (Fig. 87), the 
 hydrogen continues to burn, and the 
 chlorine disappears. Instead of chlorine, 
 the bottle now contains hydrogen chlo- 
 ride. This is a colorless gas. It fumes, 
 or "smokes," when exposed to moist 
 air, and forms a dense fog when you 
 blow your breath over it. Hydrogen 
 chloride is very soluble in water; the 
 solution is hydrochloric acid (c/. 214). Hydrogen bums in 
 
 i ~i f . . . j chlorine to give hy- 
 
 An old name for it is muriatic acid. drogen chloride. 
 
 112. Ammonia. The two elements nitrogen and hy- 
 drogen form a compound called ammonia. This is a 
 colorless gas, which dissolves readily in water, forming 
 "ammonia water" or "aqua ammonice." Ammonia 
 water has the sharp odor of ammonia itself. 
 
 Ammonia water is one of the bases (cf. 218). When 
 a bottle of "strong" ammonia water and one of "strong" 
 hydrochloric acid are brought together, the gases that 
 arise from the solutions unite to form a white cloud of 
 ammonium chloride, or "sal ammoniac" (Fig. 88). 
 This is the white solid used in making the solutions 
 
106 
 
 ELEMENTS AND COMPOUNDS 
 
 for the batteries that ring electric door-bells, etc. (cf. 
 
 152). The same substance is formed in solution, when 
 
 ammonia water and hy- 
 drochloric acid are put 
 together. Here we have 
 an illustration* of the 
 uniting of two com- 
 pounds to form a more 
 complex compound. 
 
 FIG. 88. 
 
 Gaseous ammonia and hydrogen chloride give 
 white fumes of sal ammoniac. After Mellor's 
 Chemistry. Courtesy of the publishers, 
 Messrs. Longmans, Green & Co. 
 
 113. Sulphur. Sul- 
 phur, or "brimstone/' 
 is another element. It 
 does not dissolve in water ; but it dissolves in carbon di- 
 sulphide (cf. 95). When the solution is allowed to 
 evaporate slowly, crystals of sulphur are obtained (Fig. 
 3). Carbon disulphide must be evaporated away from 
 a fire, as it is very inflammable. 
 
 Sulphur is found chiefly in volcanic regions such as in 
 Sicily, Mexico, and Japan. Louisiana now produces 
 more than any other state, and as much as Sicily. 
 
 Sulphur burns in air or oxygen to give the colorless, 
 suffocating gas, sulphur dioxide (cf. 51). This is used 
 to bleach straw, silk, lace, wool, etc., which would be in- 
 jured by chlorine (cf. 110). It is also used to destroy 
 the germs of disease, and vermin, such as fleas. We make 
 the gas for this purpose by burning sulphur "candles," or 
 by pouring liquid sulphur dioxide (cf. 71) into saucers, 
 and allowing it to evaporate. 
 
 Hydrogen and sulphur form the compound hydrogen sulphide. 
 This is a gas having the disgusting odor of rotten eggs. When eggs 
 
NUMBER OF ELEMENTS AND COMPOUNDS 
 
 107 
 
 decay, part of the hydrogen and sulphur they contain is given off as 
 hydrogen sulphide. The gas burns in air, giving water and sulphur 
 dioxide (cf. 105). It is present in the mineral waters known as 
 "sulphur" waters. 
 
 114. Number of Elements and Compounds. The 
 
 total number of compounds known is very large : probably 
 several hundred thousand. All of these are made out of 
 80 or 90 elements. Most com- 
 pounds contain only 2, 3, or 4 
 of these elements, and only 
 about 30 elements are at all 
 common (Fig. 89). We may 
 compare the formation of com- 
 pounds out of elements with the 
 making of the many words of 
 our language out of its 26 let- 
 ters. In the following table Abundance of Eements in the 
 we have the names of some 
 
 compounds formed out of the elements we have been 
 studying. 
 
 Combined 
 with 
 
 Oxygen 
 
 Nitrogen 
 
 Carbon 
 
 Chlorine 
 
 Sulphur 
 
 Hydrogen 
 
 Water 
 
 Ammonia 
 
 Marsh 
 gas 
 
 Hydrogen 
 chloride 
 
 Hydrogen 
 sulphide 
 
 Oxygen 
 
 
 Nitrogen 
 oxide 
 
 Carbon 
 dioxide 
 
 Chlorine 
 oxide 
 
 Sulphur 
 oxide 
 
 Nitrogen 
 
 Nitrogen 
 oxide 
 
 
 Cyanogen 
 
 Nitrogen 
 chloride 
 
 
 Carbon 
 
 Carbon 
 dioxide 
 
 Cyanogen 
 
 
 Carbon 
 chloride 
 
 Carbon 
 disulphide 
 
 Chlorine 
 
 Chlorine 
 oxide 
 
 Nitrogen 
 chloride 
 
 Carbon 
 chloride 
 
 
 Sulphur 
 chloride 
 
 Sodium 
 
 Sodium 
 oxide 
 
 Sodium 
 nitride 
 
 Sodium 
 carbide 
 
 Sodium 
 chloride 
 
 Sodium 
 sulphide 
 
108 ELEMENTS AND COMPOUNDS 
 
 115. Summary. Physical changes do not alter the nature of a 
 substance; chemical changes do. 
 
 Water is composed of hydrogen and oxygen. 
 
 The electrolysis of water gives two volumes of hydrogen for one of 
 oxygen. 
 
 Elements are substances that have never been divided. 
 
 Compounds are made up of elements that are united as the result of 
 a chemical change. 
 
 Mixtures are made up of elements or compounds not united chemi- 
 cally. 
 
 Hydrogen is prepared by the action of certain metals upon certain 
 acids. It is the lightest substance known. 
 
 Hydrogen burns with a very hot flame, forming water. Water is 
 also formed in the burning of compounds of hydrogen, such as wood 
 and coal. 
 
 Diffusion is the mixing of substances because of molecular motion. 
 
 Salt is sodium chloride. It is broken up by electrolysis into sodium 
 and chlorine. 
 
 Sodium is a metal, which burns, and which acts upon water. It 
 reunites with chlorine, giving salt. 
 
 Chlorine is a green gas, which has the power of bleaching and dis- 
 infecting. Ordinary combustibles do not burn in it. 
 
 Hydrogen burns in chlorine, giving hydrogen chloride. In solution 
 this is hydrochloric acid. 
 
 Ammonia is a compound of nitrogen and hydrogen. It unites with 
 hydrogen chloride to give ammonium chloride, or "sal ammoniac." 
 
 Sulphur burns to give sulphur dioxide. Hydrogen sulphide is 
 formed by the decay of organic materials containing sulphur, such 
 as eggs. 
 
 The number of compounds is very large ; but most of them are made 
 out of only 2, 3, or 4 elements. 
 
 116. Exercises. 
 
 1. What are the melting points of the following metals : sodium, tin, 
 lead, copper, silver, gold, cast iron, steel? (See Appendix, Table V.) 
 
EXERCISES 109 
 
 2. Look up the densities of the following metals: sodium, alu- 
 minum, iron, lead, gold. Is sodium heavier than water? 
 
 3. Bromine is an element similar to chlorine. Give the name of the 
 compound it forms with sodium, with hydrogen, with carbon, and 
 with sulphur. 
 
 4. When a jet of hydrogen issuing from a glass tube is first lighted, 
 its flame is colorless and invisible; but when the glass becomes hot, the 
 flame is yellow. What element forms a part of glass? 
 
 5. When common salt is treated with concentrated sulphuric acid, 
 hydrogen chloride is formed. Where does its hydrogen come from? 
 Its chlorine? 
 
 6. What compounds are formed when carbon disulphide burns? 
 
 7. When a ton of soft coal is heated, it gives off about 6 Ibs. of 
 ammonia. What elements must coal contain? 
 
CHAPTER VII 
 
 CARBON AND ITS COMPOUNDS 
 
 117. Carbon as an Element. We all know carbon as 
 it exists in soot, coal, charcoal, and in the " black lead" 
 of our pencils. It is a black solid; it does not dissolve in 
 water; and even powerful chemicals, such as acids and 
 bases (cf. 214), do not change it to any great extent. 
 When it is heated to the right temperature, it burns, 
 forming carbon dioxide (cf. 51). It is hard to believe 
 that the bright, hard, and lustrous diamond (Fig. 75, 95) 
 is a form of the same element as the black graphite (' ' black 
 lead") and charcoal, yet it is true. If a pure sample of 
 each of these substances is completely burned in oxygen, 
 it gives nothing but carbon dioxide. If a diamond is heated 
 in a tube containing no oxygen, it is changed to graphite. 
 
 Carbon is of great importance for all life upon the earth. 
 Living things are made up of wonderfully constructed 
 compounds containing carbon. Proteids, sugar, starch, 
 and fats are such compounds. When compounds of car- 
 bon are heated, and can get plenty of oxygen, they usually 
 burn. But when they are heated without sufficient air, 
 or too rapidly, nearly all of them char, or "turn to car- 
 bon." We have all seen this happen when sugar or milk 
 have been spilled upon a hot stove, and when toast or 
 meat have been "burned" by overheating. 
 
 118. Coal. All of the many different kinds of coal 
 
 110 
 
USES OF THE FORMS OF CARBON 
 
 111 
 
 (Fig. 90) were probably formed from vegetable matter, 
 such as leaves, boughs, trunks, and roots, that collected 
 
 FIG. 90. 
 
 Parallel Seams of Coal Outcropping on a Hillside. Clay beds lie under the coal. Here the 
 other rock is sandstone; often it is limestone as well. After Hopkins. 
 
 under water in past ages. This material was prevented 
 from decaying by deposits of sand and mud, which kept 
 out the air (cf. 38) while the change to coal was going 
 on. In some imperfect coals the markings of the original 
 wood can still be seen. In "soft," or bituminous, coals 
 the change is usually more complete, but many carbon 
 compounds still remain; while in anthracite, or "hard," 
 coal the change of 
 vegetable matter to 
 coal is so complete 
 that very little is 
 present besides car- 
 bon. See Fig. 91. ' 
 
 119. Uses of the 
 Forms of Carbon. 
 The element carbon 
 is put to a multitude 
 
 YEAR 
 
 SHORT TONS 
 
 
 TOO, 000, 000 200,000,000 300,000,000 400,000,000 
 
 1814-1820 
 
 424 
 
 
 
 
 
 1821-18*0 
 
 140,331 
 
 
 
 
 
 1891-18*0 
 
 1.031.642 
 
 
 
 
 
 1841-1850 
 
 14,534 58<j 
 
 
 
 
 
 1851-1860 
 1861-1870 
 
 12, 513. ( 
 
 26,122, 
 
 06 
 Oil, 
 
 
 
 
 1871-1880 
 
 S^am 57 
 
 219.992 
 
 
 
 
 1881-1890 
 
 ncanoBCBi 
 
 1122. 844 
 
 ,.666 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FIG. 91. 
 
 Coal Produced Yearly in the United States. Average 
 
 by 10-year periods. Courtesy of Dr. 
 
 F. W. De Wolf. 
 
112 
 
 CARBON AND ITS COMPOUNDS 
 
 of uses by man. Charcoal made from wood and bones is 
 very porous, and the air in its pores is able to destroy 
 (oxidize) many natural coloring materials, as well as gases 
 
 and bacteria. Charcoal 
 (Fig. 92) is, therefore, 
 used to take the color out 
 of sugar solution and 
 vinegar, as a disinfectant 
 (cf. 110), and as a ma- 
 terial for filters (cf. 84). 
 Soot, or lampblack, is 
 FlG - 92 - j used to make printer's 
 
 Making Charcoal from Wood. Burning part . 
 
 of the wood gives off the heat necessary ink, black Daint, etc. 
 
 to char the remainder. * ; 
 
 Gas carbon (cf. 124) is 
 
 used for the carbon "pencils" of electric arc lamps and 
 for the plates of electric batteries (cf. 150). The 
 diamond is used not only as a jewel, but also as a 
 cutting and polishing material. It is the hardest substance 
 known. Graphite is used for lead pencils, as stove polish, 
 and to destroy "boiler scale" (cf. 82). 
 
 Charcoal, coal, and coke are used as fuels, and to reduce the ores 
 of iron and other metals (Fig. 93). Most of the metals are found as 
 oxides (cf. 48), or as compounds that can be changed easily into 
 oxides. When the oxide of the metal is heated with carbon, the carbon 
 unites with the oxygen, releasing the metal. We say that the ore is 
 reduced by the carbon. Copper, tin, lead, zinc, etc., are obtained in 
 this way. The commercial apparatus for reducing the ores of iron is 
 called a " blast furnace" (Fig. 94). 
 
 120. Hydrocarbons. There are thousands of sub- 
 stances consisting of carbon combined with other ele- 
 ments. Carbon compounds are also called organic com- 
 
HYDROCARBONS 
 
 11$ 
 
 FIG. 93. 
 
 Charcoal burns with a very hot flame in a rapid current of air. A Blacksmith's Forge. 
 
 On the right is an old bellows forge; on the left is an electric-power blower 
 
 forge. Field Museum of Natural History, Chicago. 
 
 FIG. 94. 
 
 Model of a Blast Furnace. The one in cross section shows coarse iron ore, limestone,. 
 
 and coke (or coal) at the top; below this, the slag; at the bottom, molten iron. 
 
 The blast of hot air enters through pipes near the bottom. 
 
 Field Museum of Natural History. 
 
114 
 
 CARBON AND ITS COMPOUNDS 
 
 pounds (cf. 3). The compounds that contain only car- 
 bon and hydrogen are called hydrocarbons. Among them 
 
 are marsh gas and acetylene (cf. 
 158 and 257), which are a part 
 of illuminating gas (cf. 124). 
 Another important hydrocarbon 
 is benzene, a colorless liquid ob- 
 tained from coal tar. 
 
 FIG. 95. 
 Collecting Marsh Gas. 
 
 Marsh gas gets its name from the 
 fact that it is found in marshes and 
 pools. It is formed by the decay of 
 leaves and twigs under water. If the bottom of a pool is stirred 
 with a stick, bubbles of this gas usually arise, and 
 may be collected over water (Fig. 95). 
 
 Marsh gas can be burned; in mines it is called fire 
 damp. When there is much of it mixed with the air 
 of a mine, and a flame is brought into the mixture a 
 violent explosion takes place. To avoid these explo- 
 sions, Sir Humphry Davy, who was himself a miner 
 when a boy, invented a safety lamp (Fig. 96), which 
 could be taken into the mixture of fire damp and air 
 without setting the mixture on fire. The safety lamp 
 
 is a lamp with its flame entirely surrounded 
 by wire gauze. 
 
 Natural gas is a mixture of hydrocarbons. 
 It is chiefly marsh gas. 
 
 FIG. 96. 
 
 Modern Form 
 
 of the Miner's 
 
 Safety Lamp. 
 
 Drill Hole 
 
 121. Petroleum. Petroleum is a 
 dark liquid obtained from oil wells 
 (Fig. 97). It is a mixture of hydro- 
 carbons, some gaseous, some liquid, 
 and some solid. If we were to distill some of it, we would 
 obtain, first, gases we could not condense, then liquids 
 
 FIG. 97. 
 
 How Petroleum is Found 
 in the Earth. 
 
FLASHING POINT 
 
 115 
 
 BARRELS 
 joo.ooo.ooo 
 
 with a low boiling point, then liquids with a higher boil- 
 ing point, and so on. Finally there would remain a black, 
 tarry material. 
 
 The distillation, or refining, of petroleum is carried out on 
 an enormous scale (Fig. 98). 
 The portions ("fractions") 
 having different boiling 
 points are collected sepa- 
 rately, and are known by 
 different commercial names. 
 Some of them are gasoline, 
 naphtha, petroleum ether, 
 kerosene, etc. Some of the 
 hydrocarbons of petroleum 
 have so high a boiling point 
 that they char before they distil, 
 low pressure, " vacuum " 
 
 
 
 
 
 
 
 
 
 
 I/ 
 
 
 
 
 
 
 A 
 
 & 
 
 $ 
 
 
 il 
 
 1 
 
 
 
 <{ 
 
 
 3 
 
 | 
 
 \\ 
 
 [ 
 
 I 
 
 1 
 
 
 
 
 1 
 
 ^- 
 
 ^ 
 
 1 L 
 
 If 
 
 
 
 
 
 1 I 
 
 1 I I 
 
 FIG. 98. 
 
 Amount of Petroleum Produced in the 
 United States. 
 
 These are distilled in 
 apparatus (c/. 90), just as the 
 water is distilled off commercially from sugar or salt solu- 
 tion. Vaseline is a high-boiling material obtained from 
 petroleum; paraffin, or "white wax," is another. A 
 residue of coke remains when petroleum is distilled. More 
 than 200 different commercial products are obtained from 
 petroleum. 
 
 122. Flashing Point. Kerosene, which is used in lamps, is composed 
 of hydrocarbons that boil at a moderately high temperature (150 C. to 
 250 C.). If kerosene contains hydrocarbons having too low a boiling 
 point, as is the case with gasoline, its vapor and the air will form an 
 explosive mixture. To prevent kerosene explosions governments 
 insist that a mixture of kerosene vapor and air shall not take fire below 
 a certain temperature; in other words, that the kerosene shall have a 
 certain " flashing point." We find the flashing point (Fig. 99) by put- 
 
116 
 
 CARBON AND ITS COMPOUNDS 
 
 ting a tube of kerosene into a vessel of water, and gradually heating the 
 water. At the same time we force air bubbles through the kerosene, 
 with the result that a froth rises to the mouth of 
 !==*- the tube. When the froth can be lighted with 
 a match, the temperature shown by the ther- 
 mometer is the flashing point of the kerosene. 
 In most states the flashing point is 150 F., or 
 65 C. 
 
 Air and 
 Kerosene 
 Vapor V 
 
 FIG. 99. 
 
 123. Other Compounds of Carbon. 
 Carbon, hydrogen, and oxygen form a 
 large number of compounds. Among 
 them are the fats and sugars, starch, cellulose (the 
 material of wood, cotton, and paper), acetic acid (the 
 acid of vinegar), lactic acid (the acid of sour milk), 
 ordinary alcohol, wood alcohol, ether, etc. 
 
 Carbon, hydrogen, and nitrogen form aniline, and the 
 poisonous prussic acid ; while carbon, hydrogen, nitrogen, 
 and oxygen make up the principal part of all living tissue. 
 These compounds of carbon are studied in Organic Chem- 
 istry. 
 
 124. Dry Distillation of Coal and Wood. By "dry 
 distillation 7 ' we mean the heating of solids, and the col- 
 lecting of the materials that distill off. It is not a physical 
 change, like the distillation of water 
 (cf. 83) ; because the solids we ' ' dry 
 distill 77 are decomposed in the pro- 
 cess. When coal is "distilled," gases, 
 liquids, and solids are given off, and 
 coke and ' ' gas carbon " remain behind 
 (cf. 119). The gases are known as illuminating gas; 
 they are chiefly hydrocarbons and hydrogen. Soft coal 
 
 FIG. 100. 
 Dry Distillation of Wood. 
 
CARBON DIOXIDE 117 
 
 contains nitrogen compounds, hence ammonia is also 
 formed (cf. 112). 
 
 The liquid that distils off from coal is called "coal tar." This is of 
 great commercial importance, for it contains benzene, aniline, etc., out 
 of which the wonderful coal tar dyes, as well as many other valuable 
 substances, are made (cf. 228). 
 
 The liquid obtained by the dry distillation of wood (Fig. 100) 
 contains wood alcohol, or "wood spirit," which is used to dissolve 
 certain gums, such as shellac, and as a fuel. Acetic acid is also formed 
 (cf. 123). 
 
 125. Exercises. 
 
 1. Do you think that the diamond would burn with a flame? 
 Why? 
 
 2. What fuel does the blacksmith use for his fire? Why does he use 
 bellows? 
 
 3. Does wood charcoal leave ash when burned? Does coke? Are 
 these pure carbon? Would sugar charcoal leave ash? 
 
 4. Is it possible that coal is being formed now? Where? What 
 is "peat"? 
 
 5. In what sense does coal contain the stored-up energy of the 
 sun? 
 
 6. Turpentine burns with a smoky flame, while the flame of alcohol 
 is smokeless. What element is probably present in turpentine? How 
 can we prove that the same element is present in alcohol? 
 
 7. Why does the wire gauze of the safety lamp prevent the flame 
 inside from setting the fire damp of the mine on fire? 
 
 8. Why cannot gasoline be burned safely in a lamp? Why cannot 
 kerosene be used in place of gasoline in the engine of an automobile? 
 
 126. Carbon Dioxide. Carbon dioxide, or "carbonic 
 acid gas/' is formed when carbon and carbon compounds 
 (tf- 51 and 101) burn in air or oxygen. It is a colorless 
 gas that dissolves slightly in water, giving the water a 
 mildly acid taste. The solution is called carbonic acid. 
 
118 
 
 CARBON AND ITS COMPOUNDS 
 
 If the carbon dioxide and water are brought together 
 under a pressure greater than that of the atmosphere (cf. 
 41), more of the gas dissolves than at ordinary pressure. 
 Water thus "charged" with carbon dioxide is called 
 "soda water." When soda water is exposed to the air, 
 it froths, or foams, because the excess of dissolved carbon 
 dioxide escapes. This escape of carbon dioxide causes the 
 effervescing, or frothing, of drinks containing it. Water 
 is often charged with carbon dioxide naturally, below the 
 earth's surface. ' When such water rises to the surface, 
 the carbon dioxide escapes. 
 
 Carbon dioxide does not burn; neither do burning bodies, such as a 
 candle or match, continue to burn when put into it. The higher 
 animals do not continue to live in carbon dioxide, because they cannot 
 live without free oxygen; they cannot get the oxygen of carbon dioxide 
 away from the carbon. 
 
 127. Carbon Dioxide in the Air. Carbon dioxide gets 
 into the air from all ordinary burning, from the breathing 
 of animals and plants, and from the de- 
 cay of animal and vegetable matter. 
 We can test the air for carbon dioxide 
 by exposing to the air a shallow dish of 
 lime water, which is a solution of slaked 
 lime (cf. 132). Or we can draw air 
 through lime water (Fig. 101). There 
 will be formed a scum, or a precipitate, 
 of calcium carbonate, the substance that 
 makes up marble and limestone. 
 
 We can prove that there is carbon dioxide in the breath 
 by blowing the breath through lime water. The same 
 white precipitate is formed. 
 
 Suction 
 
 FIG. 101. 
 
 Drawing Air through 
 Lime Water. 
 
CARBON DIOXIDE IN FERMENTATION 
 
 119 
 
 128. To Prepare Carbon Dioxide. When marble and 
 soda are treated with a dilute acid, carbon dioxide is formed. 
 Since the gas is only slightly soluble, it escapes. It 
 may be collected over water, just as oxygen and hydrogen 
 are (cf. 50 and 103), or, since it is 1% times as heavy as 
 air, it may be allowed to pour out of the delivery tube 
 (Fig. 102) into a bottle of air. In a 
 short time all the air will be replaced by 
 carbon dioxide. We can prove this by 
 putting a burning match into the bottle; 
 the match will "go out." 
 
 Carbon dioxide may be poured, like 
 water, from one bottle into another. 
 
 129. Carbon Dioxide in 
 tion. When fruit juices, 
 
 Fermenta- 
 like apple 
 
 FIG. 102. 
 
 The carbon dioxide falls 
 . . . into the bottom of the 
 
 juice and grape juice, stand exposed to bottle, and pushes the 
 the air, they "work," or ferment. If 
 we examine the fermenting juice, we find that it is 
 warmer than the surrounding air, that a gas comes off 
 from it, and that the sweet taste of the juice is changed 
 to the taste of dilute alcohol. The cause of the fermenta- 
 tion is the yeast plant. The spores, that is, seedlike bodies 
 
 (cf. 323), of wild yeast fall into 
 the fruit juice, and sprout, and 
 in their growth change the sugar 
 of the juice into alcohol and 
 carbon dioxide (Fig. 103). 
 
 If we put prepared yeast ("com- 
 pressed" yeast or "dry" yeast) into a 
 dilute solution of molasses, the fer- 
 
 FIG. 103. 
 Yeast Cells Budding. 
 
120 CARBON AND ITS COMPOUNDS 
 
 mentation is rapid. In three or four days the liquid can be distilled, 
 and alcohol can be obtained in the first droppings from the condenser. 
 The alcohol comes over before the water does (cf. 83). 
 
 When bread is made, carbon dioxide is produced by the action of 
 yeast upon sugar and flour, and causes the dough to rise. The 
 alcohol vapor also assists; but both alcohol and carbon dioxide are 
 largely expelled in the baking. 
 
 130. Baking Powders. Artificial sources of carbon 
 dioxide are used to "raise" biscuits and cake; these are 
 called " baking powders." Common baking powder 
 contains baking soda, cream of tartar, and starch. The 
 correct proportion is two parts of cream of tartar to one 
 of baking soda. The soda is the source of the carbon 
 dioxide, just as the marble is when we prepare the gas in 
 the laboratory. The cream of tartar is the acid. The 
 carbon dioxide passes off as it raises the dough, while the 
 other product of the action, sodium potassium tartrate, 
 is left in the baked article. It is important that the 
 
 solid substances formed by baking powder, which are 
 left in the food, shall not be harmful to the persons eat- 
 ing them. Acid phosphate baking powders contain acid 
 calcium phosphate instead of cream of tartar. 
 
 131. Carbon Dioxide as a Fire Extinguisher. Since 
 carbon dioxide does not permit burning to continue, it 
 can be used like water to put out fires. There is a great 
 advantage in using it if the fire is small, for the carbon 
 dioxide does not damage the things that do not burn, 
 while water does. It cannot be used for large fires, 
 because it cannot be put into the burning material in 
 large enough amounts. A chemical engine consists of a 
 strong vessel in which carbon dioxide is generated from 
 
LIMESTONE 
 
 121 
 
 soda and a dilute acid. When the stream of carbon dioxide 
 is turned upon the burning object, it expels the air, and 
 as there is then no free oxygen, the fire is put out. Fire 
 extinguishers (Fig. 104) of various sorts con- 
 tain about the same materials as chemical 
 engines. 
 
 132. Limestone. Limestone is found in 
 large deposits, usually as a gray solid. It is 
 composed of carbon, oxygen, and the metal 
 calcium. Its chemical name is calcium car- 
 bonate. Limestone is insoluble in water; but 
 if the water contains carbon dioxide (cf. 
 126), the limestone dissolves to some extent. 
 When thus dissolved, it causes the temporary hardness of 
 water (cf. 82). Water containing limestone is "broken" 
 
 bottle, sulphuric 
 acid. When 
 these substances 
 react, carbon di- 
 oxide is formed. 
 
 Fio. 105. 
 
 Marengo Cave, Ind. The masses hanging from the ceiling and those rising from 
 the floor are both deposited by water that drips from the ceiling. 
 
122 
 
 CARBON AND ITS COMPOUNDS 
 
 by boiling it. This drives off the carbon dioxide, and the 
 calcium carbonate then settles out. 
 
 Underground water charged with carbon dioxide wears away 
 limestone, forming caves. Sometimes these are very large. When, 
 later, water containing carbon dioxide and 
 limestone enters a cave, the carbon dioxide 
 usually escapes, and the dissolved limestone 
 is deposited. If the water drips from the 
 ceiling of the cave, each drop leaves its bit of 
 limestone behind. In this way hanging masses, 
 called stalactites, are formed. The limestone 
 deposited on the floor forms a rising column, 
 called a stalagmite. Often the two join to 
 form a pillar (cf. Fig. 105). 
 
 Marble is a finely crystallized form 
 of limestone. Limestone makes up not 
 only large rock deposits, but also the 
 shells and hard parts (bones, etc.) of 
 
 animals (Fig. 106). Enormous deposits of limestone (Fig. 
 
 107) are formed out of coral, the stony framework of the 
 
 coral animal (cf. Fig. 257, 334). 
 
 FIG. 106. 
 
 Chalk, as magnified by a 
 microscope. _ Note the 
 tiny shells it contains. 
 Chalk is not ordinary 
 blackboard crayon. 
 
 FIG. 107. 
 Eagle Cliff, Peninsula Park, Wisconsin. Note the layer formation of the limestone. 
 
SUMMARY 
 
 123 
 
 Carbon Dioxide 
 
 ~ t ~ 
 
 Lime- 
 stone 
 
 Lime 
 
 When limestone is heated to a high temperature, it is 
 decomposed, giving lime and carbon dioxide. The appara- 
 tus is called a lime kiln (Fig. 108). Lime 
 is used to make mortar and plaster. It 
 is first "slaked" with water, and the 
 "milk of lime" that is formed is mixed 
 with sand. When the mortar "sets," it 
 takes up carbon dioxide from the air, 
 forming limestone once more. This 
 fastens bricks and stones firmly together, 
 and we call it mortar. When it forms a 
 stony covering for our walls we call it 
 plaster. 
 
 133. Summary. Carbon exists as diamond, graphite, coal, coke,, 
 charcoal, soot, etc.; also as one of the elements of sugars, starches, 
 fats, proteids, and of living creatures. When heated, most substances 
 containing carbon are charred. 
 
 Coal was probably formed out of vegetation. 
 
 Uses of carbon are: for filters, black paints, printer's ink, pencils, 
 fuel, etc. Diamonds are used as jewels and as cutting materials. 
 Carbon is the element used to reduce the ores of the metals. 
 
 Hydrocarbons are compounds of carbon and hydrogen. 
 
 Petroleum is a mixture of hydrocarbons found in the earth. Dis- 
 tillation of petroleum gives gasoline, kerosene, vaseline, paraffin, etc. 
 
 The flashing point is the temperature at which a mixture of the 
 vapor of kerosene' and air can be set on fire. 
 
 Dry distillation of soft coal gives illuminating gas, ammonia, coal 
 tar, coke, etc. Dry distillation of wood gives wood spirit, acetic acid, 
 charcoal, etc. 
 
 Carbon dioxide is formed by the burning of carbon and its com- 
 pounds, by the breathing of animals, by the action of acids upon car- 
 bonates, by fermentation, by the action of baking powders, and by the 
 heating of limestone. 
 
124 CARBON AND ITS COMPOUNDS 
 
 It is a colorless gas, heavier than air, somewhat soluble; it neither 
 burns nor permits other things to burn. Carbon dioxide is used to 
 raise dough, as a fire extinguisher, and as the material needed to harden 
 plaster and mortar. By its presence in water it causes limestone to 
 dissolve. It serves as a food for plants. 
 
 Limestone is calcium carbonate', so are marble, coral, etc. When 
 limestone is heated very hot, lime remains. Lime and water combine 
 to give " slaked lime," or calcium hydroxide. Lime water is a solution 
 of calcium hydroxide. 
 
 134. Exercises. 
 
 1. What is the danger of sleeping in a room containing a stove? 
 
 2. When soda is put with tomatoes, effervescence takes place. 
 What gas is being formed, and why? 
 
 3. How could you remove the limestone of a bone, so that you 
 could tie the organic matter, which remains, in a knot? How could 
 you destroy the organic matter, and leave the mineral matter? 
 
 4. Would a carbon dioxide fire extinguisher be better for fires near 
 the floor or near the ceiling? 
 
 5. If a candle is put into an old well, and "goes out," what gas is 
 probably present? Is it safe for a man to enter such a well? 
 
 6. Mines are sometimes filled with "fire damp," and sometimes 
 with "choke damp." What gas is "choke damp?" 
 
 7. Open stoves "salamanders" containing burning charcoal 
 are often placed in freshly plastered buildings. How do they help 
 to harden plaster? 
 
 8. Where do clams, oysters, snails, etc., get the limestone out of 
 which they build their shells? Where does the limestone of our 
 bones come from? 
 
FIG. 109. 
 
 A magnetized needle or 
 bar takes a N-S position. 
 
 CHAPTER VIII 
 
 MAGNETS AND ELECTRICITY 
 
 135. Magnets. It was known to ancient peoples that 
 certain specimens of iron ore could draw to themselves 
 bits of iron or steel. These specimens came to be called 
 magnets, from Magnesia, in Asia Minor, 
 
 where they were found. Natural mag- 
 nets are also called lodestones, from 
 "lode," a vein of 
 iron. When a lode- 
 stone is suspended 
 so that it can move 
 freely, it points north and south. 
 If a bar of steel is rubbed with a lode- 
 stone, it becomes magnetic itself, and 
 likewise points north and south when 
 suspended (Fig. 109) . A slender mag- 
 netized needle or bar is the essential 
 part of a mariner's compass. The 
 compass was known before the days of 
 Columbus (Fig. 110). FlG . m . 
 
 Each end of a magnet 
 attracts iron filings. 
 
 136. The Poles of a Magnet. If a 
 
 magnetized steel knitting needle is dipped into iron filings, 
 the filings are attracted by the needle only at its ends 
 (Fig. 111). If the needle is broken in two, each piece is a 
 
 125 
 
 FIG. 110. 
 
 The Thirty-two "Points" of 
 a Mariner's Compass. 
 
126 MAGNETS AND ELECTRICITY 
 
 magnet. If each half is broken in two, we have four 
 magnets, each with a north-seeking and a south-seeking 
 end, or pole. Finally, if we lay the four pieces down end 
 to end, so that the north-seeking end of one piece touches 
 the south-seeking end of the next piece, all the four pieces 
 together will again form one magnet, which will attract 
 iron filings only at the two ends. 
 The law of magnets is : 
 
 Like poles repel each other; opposite poles attract. 
 
 If we bring the north-seeking end of a bar magnet near 
 the south-seeking pole of a suspended magnet, they will 
 attract each other; but if the two north- 
 seeking ends are brought together, 
 there will be repulsion between them 
 (Fig. 112). 
 
 FIG. 112. 
 
 137. Magnetic Substances. A mag- 
 net of steel retains its magnetism for a 
 long while; hence it is called a permanent magnet. It 
 
 will, however, lose its magnetism if s 
 
 heated. 
 
 If one pole of a magnet is held near a 
 piece of soft iron, such as a nail, the nail FlG 113> 
 
 itself becomes a magnet (Fig. 113), and A n ^ n h d el d f 
 attracts iron filings or another nail. But ^f becomes a mag ~ 
 when the nail is removed from the mag- 
 net, its magnetic properties disappear. Thus, while steel 
 can be permanently magnetized, soft iron forms only a 
 temporary magnet. 
 
THE MAGNETIC FIELD 
 
 127 
 
 It is not necessary for the magnet to touch the nail in order that 
 the nail may become a magnet. If the two are simply brought near 
 each other, the nail takes on magnetic qualities. We say it is mag- 
 netized by induction. Before a bit of iron is drawn to a magnet, it is 
 magnetized by induction, and its N-seeking pole is attracted by the 
 S-seeking pole of the magnet, while its S-seeking pole is repelled by the 
 S-seeking pole of the magnet. 
 
 The metals cobalt and nickel are also attracted by a magnet, but 
 less than iron. One oxide of iron, the magnetic oxide, is also attracted, 
 but rust is not. 
 
 138. The Magnetic Field. That a magnet can affect 
 a magnetic needle, or a piece of nickel or iron, without 
 touching it, shows that a magnet affects surrounding 
 space; that it has about 
 it a " region of influence. " 
 This region is called the 
 magnetic field (Fig. 114). 
 It extends in all direc- 
 tions from the magnet, 
 but the strength of mag- 
 netic attraction, like that 
 of gravitation (cf. 20), 
 becomes less as the dis- 
 tance from the magnet 
 
 increases. The magnetic needle may be enclosed in glass, 
 but this does not cut off the magnetic field. Air is not 
 necessary, for the magnetic influence is felt in a vacuum. 
 
 We can readily trace the magnetic field, in cross section (Fig. 114), 
 by placing the magnet under a sheet of glass or cardboard, and sprin- 
 kling iron filings upon the glass or cardboard cover. When the cover is 
 tapped gently, the filings arrange themselves end to end in the magnetic 
 
 FIG. 114. 
 
 The filings arrange themselves parallel with the 
 magnet's "lines of force. " 
 
128 
 
 MAGNETS AND ELECTRICITY 
 
 field. If we use a cover of fresh blue print paper, and expose it to 
 light with the filings in place, the position of the filings will be printed on 
 the paper. 
 
 139. The Earth a Magnet. The earth itself is a 
 great magnet, having its north and south poles. It is to 
 these magnetic poles, not to the geographical poles, that 
 
 the compass needle 
 points. The north mag- 
 netic pole is now in 
 Northern Canada, inside 
 the Arctic Circle. It is 
 slowly moving westward. 
 
 30W 
 
 FIG. 115. 
 
 The North Magnetic Pole, the " Line of No Vari- 
 ation," and the "Declination" in Different 
 Parts of North America. 
 
 The latest determination 
 of the position of the north 
 magnetic pole was made by 
 Amundsen, the Norwegian 
 explorer, in 1905; he found 
 it to be in latitude 70 5' N., 
 and in longitude 96 46' W. 
 (Fig. 115). This is the same 
 Amundsen who discovered 
 the earth's south geographical 
 pole in 1912. 
 
 Since the earth's north 
 magnetic pole is not the same as its north geographical 
 pole, a compass will point due north only at certain places. 
 The "line of no variation" is shown, for North America, 
 in Fig. 115. For all places east and west of this line the 
 compass shows a variation, or declination, from true north, 
 and the amount of variation must be known if the com- 
 pass is to be used accurately. In the eastern part of the 
 
EXERCISES 129 
 
 United States and Canada the compass points west of 
 north ; in the western part, east of north. 
 
 Columbus knew of the declination of the needle, and 
 kept a record of its amount for many places in the Atlantic ; 
 but to his sailors it was a source of great uneasiness, for 
 they thought that the very laws of nature were changed 
 in the new regions they passed through on 
 their long voyage. 
 
 Dipping Needle. If a magnetized needle is supported 
 so that it will swing in a vertical plane (Fig. 116), instead 
 of horizontally, it is called a dipping needle. Its north- 
 seeking end will then dip noticeably in the northern hemi- 
 sphere. Over the north magnetic pole it will stand verti- 
 cal, the north-seeking end being downward. At the south 
 magnetic pole the north-seeking end of the compass points 
 upward. It is plain that the compass cannot tell north and south 
 directions at the earth's magnetic poles, because there the magnetic 
 force is all vertical. 
 
 140. Exercises. 
 
 l.-If you had a compass and a bar magnet, how could you tell, 
 without suspending the bar magnet, which of its ends was north- 
 seeking? 
 
 2. How would a dipping needle behave at the "magnetic equator"; 
 that is, on a line half-way between the earth's magnetic poles? 
 
 3. How would a dipping needle behave if brought near a large 
 deposit of iron? How would a compass behave? 
 
 4. We believe that in a magnet the iron molecules are themselves 
 magnets, set end to end. Draw a sketch of such an arrangement, 
 marking the poles of each small magnet N and S respectively. 
 
 5. When a steel bar is held in the direction taken by a dipping 
 needle, that is, pointing to the earth's magnetic pole, sharp blows on 
 one end of the bar cause it to become a magnet. Suggest the reason. 
 
130 MAGNETS AND ELECTRICITY 
 
 6. How could ships be steered in the right direction, out of sight of 
 land, without the use of a compass? 
 
 7. Why are some magnets made in horseshoe form? 
 
 141. Electric Charges from Friction. If a glass rod is 
 rubbed with silk, the rod will attract light bodies, such 
 as paper, pith balls, cork, etc. (Fig. 117). If 
 a pane of glass is placed upon two books, 
 and rubbed with silk (Fig. 118), bits of paper 
 or cork that are placed under the glass will 
 be set in motion. A stick of sealing wax, or 
 a hard-rubber ruler or comb, has the same 
 power after it has been rubbed with fur or 
 flannel or hair. The silk, flannel, and hair 
 FIG. 117. become electrified, as well 
 
 The charged . , -, 11 
 
 rod first at- as the glass, wax, and rub- 
 tracts and * ' 
 
 ber. In fact, any two 
 unlike substances are FIG. us. 
 
 "charged" by rubbing; a part of the ^JjJk^Lifetft 
 muscular energy used up in the rub- ^ e n ath move up and 
 bing is changed into electric charges. 
 
 The ancient Greeks knew that amber, a fossil gum, 
 would attract bodies after being rubbed. Amber was called 
 "electron"; hence our words, electric, electricity, etc. 
 
 142. Conductors and Insulators. Dr. Gilbert, the 
 physician of Queen Elizabeth, found that some bodies 
 could be electrified by rubbing, and that others could not. 
 So he divided bodies into "electrics" and "non -electrics." 
 Because metal rods, held in his bare hand while being 
 rubbed, were not charged, he called metals "non-electrics." 
 If he had held the metal in a dry wooden or silk handle, 
 
ATTRACTION AND REPULSION 
 
 131 
 
 he could have electrified the metal as well as the glass. 
 His own body acted as a conductor, and the charge passed 
 through it to the earth. We now call bodies conductors, 
 or non-conductors. 
 
 Non-conductors are also called insulators, from the Latin, insula, 
 an island. A charge formed on one end of a glass rod remains where it. 
 was produced; but if one end of a metal rod is rubbed, the whole rod is 
 charged. The glass is an insulator, the metal a conductor; but both 
 are "electrics." Some of the best conductors are: metals, charcoal, 
 water vapor, and wet substances generally. Some of the best insula- 
 tors are: dry cotton, wool, wood, silk, glass, wax, rubber, and shellac. 
 Since the earth is a good conductor, a charged conductor will lose its 
 charge if it is not insulated from the earth. 
 
 143. Attraction and Repulsion. If an electrified body 
 is brought near bits of paper, they are first attracted, and 
 then repelled. This phenomenon is studied 
 most easily if an "electric pendulum" is 
 used. One is shown in Fig. 119. It is sim- 
 ply a ball of pith, or of cork, suspended by 
 a thread which insulates it. If a glass rod, 
 charged by rubbing it with silk, is held near 
 the ball, the ball is attracted to the rod. 
 After it has obtained a charge from the rod, 
 it is repelled. If a stick of sealing wax, 
 charged by rubbing it with flannel, is now 
 brought near the charged ball, the ball is 
 attracted. .Since the charged sealing wax attracts what 
 the charged glass repels, we say that the glass and wax 
 are oppositely charged. 
 
 If we call the charge on the glass positive (+), that on the wax is 
 negative ( ). It will be found that the silk has received a negative 
 
 FIG. 119. 
 
 Like charges repel 
 each other. 
 
132 MAGNETS AND ELECTRICITY 
 
 charge by being rubbed with glass, while the flannel rubbed with wax 
 or rubber receives a positive charge. 
 
 The laws of charged bodies are like those of magnets (cf. 136) : 
 
 1. Charged bodies attract uncharged bodies. 
 
 2. Bodies having unlike charges attract each other. 
 
 3. Bodies having like charges repel each other. The space sur- 
 rounding a charged body is called an " electric field" (cf. 138). 
 
 144. Induction of Charges. We have learned ( 143) 
 that an uncharged body is charged by contact with a 
 charged body. It may also be charged by induction, 
 without contact. A simple apparatus for showing this 
 is an egg shell covered with_tin foil (Fig. 120). If a posi- 
 tively (+) charged glass rod is brought 
 near the shell without touching it, the 
 shell will be electrified by induction. An 
 uncharged cork ball will be attracted 
 by either end of the shell. If the glass 
 rod is removed, the charges disappear. 
 We say they neutralize each other. We 
 
 FIG. 120. can charge the shell permanently if we 
 
 Egg tnd 1 un gedby remove one of the charges induced by 
 
 the glass rod. To do this we hold the 
 
 rod near the shell, as before, and then touch with the 
 
 finger the end of the shell farther away from the rod. 
 
 The repelled positive charge passes through the hand and 
 
 body to the earth. If the glass rod is now removed, 
 
 the shell will have a negative ( ) charge. 
 
 145. Electric Discharge. If the finger is held near a 
 charged glass rod, sparks pass between the two. The 
 sparks are larger if the finger is held near a charged 
 
ELECTRICITY OF THE ATMOSPHERE 
 
 133 
 
 conductor, for the whole conductor is discharged at once. 
 The strain in the electric field is greatest around the points 
 of an object; hence a discharge takes place very easily 
 from points, but less readily from blunt portions. When 
 the spark passes, the air is heated, and its rapid expansion 
 and contraction produce a sharp explosion." 
 
 146. Storing a Charge; the Leyden Jar. Apparatus 
 for storing frictional electricity (Fig. 121) is made of two 
 conductors (metal foil) separated by a non-conductor, 
 such as glass. If one conductor is 
 connected with a source of positive 
 charges, while the other conductor 
 is connected with the earth, the 
 negative charge of the second con- 
 ductor is held on the side of the 
 
 metal next to the glass, but the positive 
 charge of the second conductor is repelled 
 to the earth. If the earth connection is 
 then removed, we have a large positive 
 charge on one side of the glass, and a 
 correspondingly large negative charge 
 on the other side. 
 
 Earth 
 
 FIG. 121. 
 An Electric Condenser. 
 
 Ear 
 
 FIG. 122. 
 
 The Leyden Jar; an 
 Electric Condenser 
 and Storing Appa- 
 ratus. 
 
 The most common form of the apparatus is 
 the Leyden jar (Fig. 122); this consists of a glass 
 bottle, partly covered, both inside and outside, 
 with metal foil. If we charge the j ar with frictional 
 
 electricity, and then almost connect the two foils by some conductor, 
 
 a strong spark discharge takes place. 
 
 147. Electricity of the Atmosphere. Benjamin Frank- 
 lin showed that a lightning discharge was only a large 
 
134 
 
 MAGNETS AND ELECTRICITY 
 
 spark of electricity. One day in June, 1752, when a 
 thunderstorm was coming on, he sent up a kite having 
 at its top a pointed wire. On the lower part of the string 
 he had a key, and the kite-string was insulated from the 
 earth (Fig. 123). 
 
 When the kite-string became wet, so that it could con- 
 duct electricity, Franklin obtained sparks from it. The 
 
 sparks were ex- 
 actly like those 
 obtained by fric- 
 tion. 
 
 When two 
 charged clouds 
 approach each 
 other, the strain 
 in the "electric 
 field" between 
 them becomes so 
 great that, finally, 
 the charge bursts 
 through. This is 
 lightning (Fig. 
 124). If the 
 charge passes be- 
 tween a cloud and 
 
 the earth, we say that the lightning strikes. The two 
 clouds, or a cloud and the earth, with the non-conduct- 
 ing air between them, thus form a huge Ley den jar. 
 
 Thunder is due to the rapid expansion and contraction 
 of the air heated by the lightning. 
 
 148. Lightning Rods. The electric charge " induced" on the earth 
 
 Insulator 
 
 FIG. 123. 
 
 Franklin's kite was "charged by induction" from a 
 charged thundercloud. Note the spark. 
 
EXERCISES 
 
 135 
 
 by a passing thundercloud is greatest in projecting objects, such as 
 trees, spires, and hilltops (cf. 145). Commonly the leaves of trees 
 conduct the charge from the earth quietly, as a "silent discharge," 
 and prevent the striking of lightning. Franklin reasoned that a 
 pointed conductor a lightning rod would perform the same ser- 
 vice for a house. To be a real protection a lightning rod should have a 
 large diameter, should have a large number of points, and should 
 extend far enough 
 into the ground so 
 that it will always 
 end in moist earth. 
 
 149. Exercises. 
 
 1. When hair is 
 combed or brushed 
 vigorously in cold, 
 dry weather, it often 
 ' ' fluffs out," showing 
 that the individual 
 hairs are repelling 
 one another. Ex- 
 plain. 
 
 2. If, in cold, 
 dry weather, you 
 ' ' skate " in your slip- 
 pers across a woolen 
 
 carpet or rug, and then bring the tip of your finger near a gas jet or 
 other metal object, a spark often passes between your finger and the 
 object. Explain why. 
 
 3. If you rub a stick of sealing wax with flannel, the wax receives a 
 negative ( ) charge. If the charged wax is brought near an un- 
 charged "electric pendulum," what happens? When the pendulum 
 is repelled, what kind of a charge does it have? If, now, you bring 
 near the charged pendulum a rubber comb which has been rubbed 
 with flannel, and you find that the comb repels the pendulum, what 
 kind of a charge is there on the comb? 
 
 A Lightning Discharge. 
 
 FIG. 124. 
 
 Field Museum of Natural History. 
 
136 
 
 MAGNETS AND ELECTRICITY 
 
 4. Why is it dangerous to stand under a tree in a thunderstorm? 
 
 5. Read about the life of Benjamin Franklin. What did he do for 
 science, for business, and for the American Colonies? 
 
 150. Electric Currents. Magnetism and frictional 
 electricity, the two kinds of electrical phenomena already 
 studied, are closely related to the third form, electric 
 currents. The study of currents begins with the electric, 
 or "voltaic," cell, a contrivance by which the energy set 
 free in certain chemical reactions appears in the form of 
 electricity, instead of as heat or light (cf. 51, 105, and 
 109). Methods of producing currents were first studied 
 by Galvani, in 1786, and by Volta, in 1792. 
 
 We have already learned (cf. 103) that zinc and dilute 
 sulphuric acid give hydrogen. The chemical change also 
 
 produces a substance called zinc 
 sulphate. Besides both of those the 
 reaction produces heat. But when 
 both zinc and copper are put into 
 dilute sulphuric acid (Fig. 125), 
 and the ends of the metals outside 
 of the liquid are joined, a current 
 flows through the wire, the metals, 
 and the liquid. The metals may 
 be joined by simply allowing them to touch each other. 
 The zinc wastes away, just as when it is used alone; but 
 in exchange we get the current. 
 
 A simple way to find out whether or not a current is passing through 
 the wire connecting the metals is to " taste" the current. We do this 
 by touching the tongue with the ends of the wires a little distance 
 apart. The current produces a sharp sensation. 
 
 Copper 
 
 Cop- Zinc 
 per 
 
 FIG. 125. 
 
 Two Forms of the Simple Cell. 
 The current flows in the di- 
 rection of the arrows. 
 
KINDS OF CELLS 137 
 
 In making a cell we may use other metals instead of zinc and copper. 
 We choose one metal that acts readily with the acid, arid one that does 
 not. Carbon plates are often used instead of copper ones. Both 
 plates must be conductors. Solutions of other acids, of bases, or of 
 certain salts (cf. 214, 218, and 220) may be used instead of the 
 dilute sulphuric acid. 
 
 To bring the free ends of the metals into connection, so that there 
 can be a current, is called ''making," or "closing, the circuit"; the re- 
 verse is called "breaking," or "opening, the circuit" (cf. 100). A 
 number of properly connected cells is called a battery. 
 
 151. Kinds of Cells. The voltaic cell is of little prac- 
 tical use in its simplest form, because it is soon weakened, 
 or stopped entirely (we say it is " polarized "), by the 
 bubbles of hydrogen that collect upon the copper plate. 
 The hydrogen is formed by the action between the zinc 
 and the acid. A description of DanielFs cell also called 
 the gravity cell will show one way in 
 which polarization is avoided. 
 
 In Darnell's cell (Fig. 126) the two plates, 
 zinc and copper, are given a "crowfoot" 
 shape to increase their surfaces. The cop- 
 per is placed at the bottom of the jar in a 
 saturated solution of copper sulphate (blue 
 vitriol), while the zinc, which is in the upper A Gravity, or 
 part of the jar, is surrounded by dilute sul- Daniell> G ' eU * 
 phuric acid. The copper sulphate solution is the heavier, 
 and remains at the bottom; hence the name ' t gravity " cell. 
 
 The action of the cell is as follows: The zinc reacts with the dilute 
 sulphuric acid, giving zinc sulphate and hydrogen. The hydrogen 
 moves toward the copper plate; but in passing through the layer of 
 copper sulphate the hydrogen is used up, and copper is deposited in its 
 
138 
 
 MAGNETS AND ELECTRICITY 
 
 FIG. 127. 
 
 Sal Ammoniac Liquid and 
 Dry Cells. 
 
 place. Thus polarization is prevented. Daniell's cell is much used 
 for the operating of telegraph instruments (cf. 155). 
 
 152. Sal Ammoniac Cells. Sal ammoniac cells (Fig. 127) are 
 used where a strong current is needed for a short time, as for ringing 
 
 telephone and house bells. The liquid used 
 is a water solution of sal ammoniac, or am- 
 monium chloride (cf. 112). The conduc- 
 tors are a rod of zinc and a plate consisting 
 of carbon and manganese dioxide. 
 
 Dry Cell. A "dry" cell is enclosed in 
 a zinc jar, which serves as the zinc plate. 
 The space between the zinc and the carbon 
 is filled with a paste consisting of sal am- 
 moniac, manganese dioxide, charcoal, and water. The cell is closed so 
 that the water cannot evaporate. 
 
 153. Currents and Magnetism. As we learned in 
 150, we can test a circuit for the presence of a current 
 by bringing the free ends of the conducting wires in con- 
 tact with the tongue. Of course this will not do for very 
 weak or very strong currents. A second way of testing 
 for a current is to bring the wire of a closed circuit near 
 a magnetic needle or compass. The needle will be turned 
 from its N-S position. If the current is sufficiently 
 strong, and the bare conducting wire is dipped into iron 
 filings, some of the filings will cling to the wire. 
 
 Both of the last two tests show that a wire carrying a 
 current is surrounded by a magnetic field: that it is a 
 magnet. 
 
 154. Electromagnets. Since a conductor that is 
 carrying a current is surrounded by a magnetic field, we 
 
THE TELEGRAPH 
 
 139 
 
 should expect that a piece of soft iron placed inside a coil 
 of the wire would become a temporary magnet, just as 
 when it is in the field of a bar magnet (cf. 137). 
 Such magnets are called electromagnets. The 
 coil must be made of insulated wire, so that 
 the successive turns may not touch one an- 
 other. If they do touch, the current will not 
 pass through all the wire, but will be " short 
 circuited. " The greater the number of turns in 
 the coil the stronger the magnetic field will be, 
 and the stronger the electromagnet. But as 
 soon as the circuit is broken, the electromagnet 
 is demagnetized. 
 
 The coil of wire is called the helix; the iron is called 
 the core. A core made up of a bundle of small iron wires 
 makes a much stronger electromagnet than one in a single 
 piece. Telegraph instruments, telephone bells, electric 
 
 doorbells, fire alarms, 
 and many other de- 
 vices are operated by 
 electromagnets. 
 
 Earth_ j_ _ 
 FIG. 129. 
 
 A Simple Telegraph Instrument. When the key is 
 pressed, the circuit is made complete, and the sound- 
 er is drawn down by its electromagnet. 
 
 155. The Tele- 
 graph. The tele- 
 graph instrument 
 (Fig. 129) consists essentially of a' key for making and 
 breaking the circuit in an electromagnet, and thus pro- 
 ducing "clicks" in the sounder. The sounder is a small 
 lever (cf. 198) which is held by a spring against its upper 
 stop. Opposite the core of the electromagnet is a piece of 
 soft iron called the armature. When the key is pressed 
 
140 MAGNETS AND ELECTRICITY 
 
 down, and the circuit is thus closed, the core is magnetized, 
 and draws the sounder to the lower stop. This produces 
 a " click." When the key is released, the sounder springs 
 back. 
 
 The current is usually supplied by a " gravity" battery. Only one 
 wire is needed, for the return circuit is through the earth (cf. 146). 
 There is no interference between these earth circuits, in spite of the 
 large number of messages passing at the same time. 
 
 In the original telegraph, as made by Morse in 1832, a moving strip 
 of paper was placed under the sounder. If the circuit was kept closed 
 a very short time, a dot was made upon the paper; if for a longer time, 
 a dash was the result. Combinations of dots and dashes made up the 
 alphabet. The " printing telegraph" is rarely used now, for messages 
 are taken much more rapidly by ear. 
 
 The telegraph code is as follows: 
 
 I - ---- 2 -- --- 
 
 m w -- 3 ---- -- 
 
 n -- x - - - 4 ----- 
 
 o - - y - - - - 5 ~ 
 
 p ----- z --- - 6 ...... 
 
 q ---- & ---- 
 
 r - -- , - --- 8 ----- 
 
 s --- ? ------ 9 ---- - 
 
 t - . ------ 
 
 156. The Electric Bell. The electric bell (Fig. 130) 
 has a push-button for closing the circuit and thus operat- 
 ing the electromagnet. The hammer of the bell and the 
 armature are attached to a spring. When the electro- 
 magnet attracts the armature, the hammer strikes the 
 bell. But at the same instant the circuit is broken, and 
 the spring throws the armature back against the stop. 
 The circuit is thus closed once more, and the armature is 
 again attracted. In this way the hammer is made to give 
 the bell a rapid succession of blows. 
 
ELECTRIC FURNACES 
 
 141 
 
 157. Changes Produced by the Current. The difficulty 
 which a current meets in passing through a conductor 
 is called resistance. Some substances are much better 
 conductors than others. Thus, a silver 
 
 wire is a better conductor, that is, has a 
 smaller resistance, than a platinum wire 
 of the same diameter. For any given ma- 
 terial, the smaller the diameter of the wire 
 the greater the resistance. The heating 
 effect of German silver wire of high resist- 
 ance is used in the electric heater, electric 
 pad, electric flat-iron, and electric stove. 
 In passing through a fine wire of platinum 
 or carbon, the current finds so much 
 resistance that it heats the wire 
 white hot, forming the incandes- 
 cent- electric light. If carbon 
 wire is used, it must be placed in a bulb free 
 from air, or the carbon will burn up (c/. 51). 
 The "arc" electric light (Fig. 131) consists of 
 two pencils of gas carbon (cf. 119) placed such 
 a distance apart that there is great resistance 
 at the gap between them. The heat produced 
 changes some of the carbon to the vapor state, 
 and makes the vapor white hot. The temper- 
 ature produced is about 3,800 C. 
 
 158. Electric Furnaces. An electric arc furnace (Fig. 
 132) is an arc lamp enclosed in a box made of high-melting 
 materials, such as fire clay, lime, or magnesia (magnesium 
 oxide; cf. 48). 
 
142 
 
 MAGNETS AND ELECTRICITY 
 
 The resistance furnace (Fig. 133) has two poles able to deliver a 
 powerful current. We "close the circuit" by packing between the 
 poles the materials that are to be heated. The resistance due to 
 
 the materials changes the energy 
 of the current into heat. In the 
 intense heat of electric furnaces 
 man has been able to turn metals 
 like gold and platinum into 
 vapors, and to prepare many 
 substances of great commercial 
 importance. Among these are 
 
 graphite (cf. 119), carborundum, a very hard abrasive (scouring 
 and polishing material), and calcium carbide, a gray solid that reacts 
 with water to give acetylene, the gas used in acetylene lamps (cf. 
 257). 
 
 FIG. 132. 
 Electric Arc Furnace. 
 
 159. Electroplating. We have learned that when the 
 electric current is passed through dilute sulphuric acid, 
 hydrogen collects at one pole, and oxygen at the other 
 (cf. 100). If the current 
 is passed through a solu- 
 tion of copper sulphate, 
 copper is formed at one 
 pole, and oxygen and sul- 
 phuric acid at the other. FIG 133 
 
 In this Case the COpper Resistance Furnace. The materials to be 
 
 sulphate is used up. But 
 if the pole at which the 
 current enters the solution is of copper, the copper sul- 
 phate is not used up. What happens is that copper wastes 
 away at one pole, and is deposited at the other. An 
 object placed at the receiving pole will be electroplated 
 with copper. 
 
 . 
 
 heated are poured through the hoppers 
 A, A, and the current is passed between 
 B and B. 
 
DYNAMO 
 
 143 
 
 Battery 
 
 FIG. 134. 
 
 The copper plate forming the + electrode (pole) 
 wears away, but an equal amount of copper is de- 
 posited on the impression of the type (the elec- 
 trode). In this way a copper film is formed which 
 is the exact image of the type. 
 
 This is the way in which electrotype plates of the pages of books are 
 made (Fig. 134). An impression of the type is prepared in wax, this is 
 covered with graphite (cf. 119) to make it a conductor, and the wax 
 mould is then made the 
 receiving pole in a cop- 
 per sulphate "electrolytic 
 bath." The copper de- 
 posit is an exact copy of 
 the type. It is, however, 
 very thin; hence it is 
 strengthened, at the back, 
 by a filling of melted 
 metal. The original type 
 is free to be used over and 
 over again in the setting 
 up of other pages of the 
 book. 
 
 Silver-plating (Fig. 135) is carried out in a similar way. The solu- 
 tion contains a silver compound, the pole that wastes away is of silver,, 
 and the object to be plated is made the receiving pole. 
 
 160. Dynamo. On a small scale, currents may be 
 produced by batteries (cf. 150) ; but for larger uses men 
 need more economical and more powerful generators. 
 
 These are commonly known 
 as dynamos. 
 
 We have learned that when 
 a bar of soft iron, or a bun- 
 dle of soft-iron wires, is put 
 into the field of a coil carry- 
 ing a current, the soft iron 
 
 becomes magnetized (cf. 154) . Equally important is the 
 fact that when a magnet is introduced into, or removed 
 from, a coil of insulated wire, a current is produced 
 
 Fia. 135. 
 Silver-plating. 
 
144 
 
 MAGNETS AND ELECTRICITY 
 
 in the wire, 
 kept moving. 
 
 The current flows as long as the magnet is 
 This is illustrated by Fig. 136. The moving 
 of the magnet causes the wire 
 constantly to pass through 
 new portions of the magnet's 
 field. 
 
 Instead of moving the 
 magnet within a fixed coil, 
 we can keep the coil in mo- 
 tion, while we leave the 
 magnet stationary. This is the principle of the dynamo 
 (Fig. 137). A revolving frame, called the armature, is 
 wound with many separate coils of wire. As each coil ap- 
 proaches and leaves the magnetic field, currents are pro- 
 duced in the wires. These are drawn off, as rapidly as they 
 
 FIG. 136. 
 
 A magnet moved into or out of a coil 
 produces a current in the coil. 
 
 FIG. 137. 
 
 A Direct Current Dynamo, Directly Connected with an Automatic Engine. Courtesy 
 of the Ridgway (Pa.) Dynamo and Engine Co. 
 
 are produced, through wires attached to the poles of the 
 dynamo. The dynamo current may be used for the pro- 
 duction of heat or light, or it may be run into the motors 
 of trolley cars, etc., and used to produce motion. 
 
ELECTRIC POWER 145 
 
 161. Electric Motors. The motor has practically the 
 same construction as the dynamo, but its action is that 
 of the dynamo reversed. That is to say, while in the 
 dynamo we cause the coils of the armature to revolve in 
 the field of the magnet, and thus produce a current, in 
 the motor we run a current into the armature, and cause 
 it to revolve, producing motion. The motion of the arma- 
 ture can be passed on, by gear wheels or by belts, to the 
 wheels of a street car, or of whatever is to be set in mo- 
 tion. In other words, in the dynamo we exchange mechan- 
 ical motion for an electric current; but in the motor we 
 exchange the current for mechanical motion. 
 
 Electric motors are used not only for the moving of vehicles, but 
 also for running the machinery of factories, sewing machines, washing 
 machines (cf. Fig. 194), 
 electric fans, vacuum 
 cleaners, etc. e 
 
 Electric Street Cars. 
 In the trolley car the 
 motor is generally under 
 the car, and the current is 
 
 supplied by the generators (dynamos) of a power house (Fig. 138). 
 The current is carried by a "feed wire" to the trolley wire, or third 
 rail, from which it passes to the motor of the car. The return circuit 
 for the current is through the car track. 
 
 162. Electric Power. Electric power may be generated 
 in dynamos by engines using coal, gasoline, petroleum, 
 etc., as sources of energy, or the power may come from the 
 wind, waterfalls, rapids, or dams. Niagara furnishes power 
 not only for many electric furnaces and for processes of 
 electrolysis, but for lighting cities like Buffalo and Roches- 
 
146 
 
 MAGNETS AND ELECTRICITY 
 
 ter, and for propelling, lighting, and heating trolley cars 
 within a considerable distance. The control of water 
 power is everywhere giving the energy needed for electric 
 power (Fig. 139). This is true of the great dam at As- 
 souan, in Egypt, the Gatun 
 dam of the Panama Canal, 
 and the dam across the 
 Mississippi, at Keokuk, 
 Iowa (Fig. 140). 
 
 163. Summary. Magnets 
 are natural or artificial. Natural 
 magnets are lodestones. All 
 magnets, when freely suspen- 
 ded, point toward the earth's 
 magnetic poles, unless they are 
 interfered with by large masses 
 of iron, or by local magnetic 
 fields. 
 
 Two magnetic poles of the 
 same kind repel each other; 
 those of opposite kind attract 
 each other. 
 
 Soft iron forms temporary 
 magnets; steel forms permanent 
 magnets. Iron, steel, magnetic 
 cobalt, nickel, etc., are magnetic; that is, attracted by 
 
 FIG. 139. 
 
 Water from a higher level falls through a 
 penstock against the guides of the turbine. 
 The guides direct the rushing water upon 
 the blades, causing them to revolve rapidly. 
 The whirling turbine turns the shaft and the 
 generator attached to it. 
 
 iron oxide, 
 a magnet. 
 
 A magnet attracts a magnetic body by first inducing it to become a 
 magnet. 
 
 The earth is a magnet, with two magnetic poles. These are found 
 by the dipping needle, as well as by the compass. 
 
 The compass has been of the greatest use in the development of 
 navigation and civilization. 
 
 Frictional electricity is commonly developed by rubbing two sub- 
 
SUMMARY 147 
 
 stances together. Conductors can be electrified only if held by means 
 of an insulator. 
 
 An electrified body attracts one not electrified, then charges it with 
 its own kind of electric charge, and then repels it. 
 
 The space around a charged body is an electric field. An insulated 
 body brought into the field is electrified by induction. 
 
 FIG. 140. 
 
 Generator Room of the Mississippi River Power Co. at Keokuk. A dam 4,649 feet long 
 extends across the river, and raises the water behind the dam. Some of the water 
 rushes through turbines, generating 200,000 horse power (cf. 26) of electricity. 
 About a third of this is carried to St. Louis, 137 miles away. 
 
 When the strain in the electric field between two oppositely charged 
 bodies becomes sufficiently great, a discharge takes place, usually as 
 a spark. Discharge takes place most easily from points. 
 
 An electric condenser consists of two conductors, such ^s metal 
 foil, separated by a non-conductor, such as glass. The common form 
 is the Leyden jar. 
 
 Franklin proved that lightning is a huge electric spark. His kite was 
 electrified by induction from the charged cloud. 
 
 Electric currents are usually generated in cells or by dynamos. 
 
 The simple cell consists of zinc, copper (or carbon), and dilute 
 sulphuric acid. The current flows from zinc to copper inside the 
 
148 MAGNETS AND ELECTRICITY 
 
 liquid, and from copper to zinc outside of the liquid. A group of con- 
 nected cells is a battery. 
 
 The simple cell is easily polarized by the hydrogen which collects 
 upon the copper (or carbon) plate. Polarization is prevented, in 
 Daniell's cell, by a layer of copper sulphate solution between the zinc 
 and the copper. In other cells oxidizing materials are put into the 
 solution, or mixed with the carbon. These convert the hydrogen into 
 water. 
 
 Wires carrying currents are magnets. Electromagnets are formed 
 when soft iron is put into coils carrying currents. 
 
 The telegraph is essentially an electromagnet, with a key for making 
 and breaking the circuit. 
 
 The electric bell is an electromagnet in which the armature carrying 
 the hammer continually breaks the circuit, causing the hammer to 
 vibrate back and forth. 
 
 The resistance which the current meets in passing through con- 
 ductors appears as heat. This is the principle of electric lighting and 
 heating devices. 
 
 Electroplating is due to the electrolysis of solutions of the com- 
 pounds of certain metals, such as copper, silver, gold, nickel, etc. 
 
 A dynamo is a device in which coils of wire, moving rapidly through 
 the fields of powerful magnets, produce a current. 
 
 A motor is a dynamo reversed. In it an electric current is changed 
 into mechanical motion. 
 
 Men get electric power on an enormous scale by changing the 
 mechanical energy of falling water into electric currents. 
 
 164. Exercises. 
 
 1. If piece of steel is held near a dynamo, it is pulled strongly 
 toward the dynamo. If held there for a short time, it becomes a 
 magnet. Explain both facts. 
 
 2. Write in the Morse code: Will visit your school Tuesday, 
 April 9. Leave short spaces between letters and longer ones between 
 words. 
 
 3. Read an account of the life of Morse, the inventor of the tele- 
 graph. 
 
EXERCISES 149 
 
 4. What is meant by the terms " triple plate, quadruple plate," 
 etc., as applied to silver utensils? 
 
 5. How could a slab of impure copper be purified by the electric 
 current? 
 
 6. How could coal be converted into energy at the mine, and this 
 energy distributed without the shipping of the coal? 
 
 7. When the lighting system of a trolley car is on the same circuit 
 as the power, the lights often burn low while the car is being started, 
 but burn brightly when the car is in motion. What does this show as 
 to the power required to start the car as compared with that needed to 
 keep it moving? 
 
 8. What advantages has electric power over steam power for factory 
 use? For the home? 
 
CHAPTER IX 
 
 LIGHT AND SOUND 
 
 165. Luminous Bodies. Every object that we see 
 " is seen/' or " is visible/ ' because light from the object 
 enters the eye. When the visible body itself produces the 
 light, the body is said to be self-luminous. Self-luminous 
 bodies are usually very hot. This is the case with the sun, 
 a lamp flame, an arc electric light. However, most 
 visible bodies are not self-luminous; but they shine, or are 
 seen, by light which they receive, and then reflect to the 
 eye. We say that non-luminous bodies are illuminated 
 by luminous bodies. The moon is a non-luminous body. 
 Moonshine is sunshine reflected to us from the moon's 
 surface. An object seen by moonlight is thus seen by 
 sunlight that has been reflected twice: first from the 
 moon to the object, and then from the object to the eye. 
 When we take a lamp into a dark room, we see the objects 
 in the room, because they reflect lamplight to the eye. 
 
 166. Transparent and Opaque Bodies. Substances 
 through which objects are seen clearly are said to be 
 transparent. Such are water, glass, and air. A substance 
 that does not permit light to pass through it is said to be 
 opaque. Wood and iron are opaque. Certain substances 
 allow some of the light to pass, but objects cannot be seen 
 distinctly through them; such substances are said to be 
 
 150 
 
IMAGES THROUGH SMALL OPENINGS 151 
 
 translucent. Examples of translucent substances are 
 fog, ground glass, oiled paper, and thin china. Very thin 
 plates of all bodies, even metals, are translucent. Thus, 
 gold foil transmits a green light. 
 
 167. Light and Its Properties. Light is the cause 
 outside of us that produces the sensation of sight. Sun- 
 light produces other effects besides the lighting of objects. 
 Thus, if the skin is exposed to sunlight, it is not only 
 illuminated, but also warmed. In addition, chemical 
 changes are brought about in the skin, and it is tanned. 
 The energy of the sun thus appears as heat, light, and 
 chemical energy. 
 
 The velocity of light is very great: about 186,000 miles a second 
 (cf. 11). Sound waves travel through air at the rate of about 1,100 
 feet a second; but this is a snail's pace as compared with light. Be- 
 cause of the greater speed of light we see the flash of a gun before we 
 hear its report, and we see the lightning long before we hear the thunder 
 that accompanies it. 
 
 Light travels in straight lines through a transparent substance, if the 
 density of the substance is the same throughout. A single line of light 
 is called a ray, and a number of parallel rays make up a beam. A 
 sunbeam is an example. If a sunbeam enters a dark, dusty room, its 
 straight path is shown by the illuminated dust particles. On a foggy 
 night a street lamp sends out straight lines of light in all directions. 
 These observations show that light travels in straight lines. The same 
 thing is shown by the formation of images and shadows. 
 
 168. Images Through Small Openings. An easy way 
 to learn how images are formed is to let light pass through 
 the small opening of a " pin-hole camera." The camera 
 (Fig. 141) consists of a box with both ends removed. A 
 hole is cut in one of the remaining four sides of the box, 
 
152 LIGHT AND SOUND 
 
 and over this is pasted a strip of tin foil. A smooth pin- 
 hole is made in the foil. The inside of the box is black, 
 except for a white space just opposite 
 ,- : -_-n the tin foil. If the room is darkened, 
 - Jw> and a small, lighted candle is placed 
 FIG 141 before the pin-hole, an image of the 
 
 when light from an object candle is seen inside the box, on the 
 
 passes through a pin-hole 
 
 into a darkened box, the white screen: but the image is corn- 
 image is inverted. ' 
 
 pletely turned about. 
 
 The explanation is as follows: The candle flame is sending out 
 rays of light from a large number of points on its surface. Each 
 of these points sends a small beam through the pin-hole, and 
 the beam, when it strikes the white screen, makes an image of 
 the part of the candle flame from which it came. But all the beams 
 cross at the pin-hole. Hence the light from the top of the flame will 
 form the bottom of the image, and the light from the right side will 
 form the left side of the image, and the image is completely inverted. 
 A landscape seen through a very small point is also turned about. 
 
 169. Shadows. That light travels in straight lines is 
 shown, also, by the forming of shadows. When an opaque 
 body is put in the way of light rays, it cuts off the light 
 from the space behind it, producing a shadow. If the 
 source of light is very small 
 (S, Fig. 142), the shadow is 
 very distinct. But if the 
 luminous body has a consider- 
 able surface, and sends out n FIG. 142. 
 
 The shadow cast by an object that is 
 
 light from many points, the jJ^j^^arkSess point f light is f 
 shadow will have two parts: 
 
 one receiving no light at all, and the other getting light 
 from part of the luminous surface, but not from all of it. 
 
BRIGHTNESS, OR INTENSITY, OF LIGHT 
 
 153 
 
 We call the distinct shadow, which receives no light at all, 
 the umbra; the indistinct part surrounding the umbra is 
 called the penumbra. 
 Fig. 143 gives the 
 illustration : 
 
 FIG. 143. 
 
 The shadow cast b y an object that is illuminated by 
 the sun's surface consists of umbra and penumbra. 
 
 Let us suppose that 
 the moon, in the cone- 
 
 hnrPrl crmpp to tVP rio-Vit 
 rigm 
 
 of the earth, is entirely 
 cut off from sunlight. To an observer on that side of the earth the 
 moon would be entirely eclipsed by the earth's shadow (cf. 3). To 
 an observer on the moon the sun would be entirely eclipsed by the 
 earth. But if the moon were in the penumbra of the earth's shadow, 
 an observer on the moon would see the earth as a black body covering 
 part of the sun's disc, but not all. If an observer could stand just at 
 the tip of the umbra, and facing the earth, the sun's face would be just 
 exactly covered by the earth. 
 
 170. Brightness, or Intensity, of Light. We all know 
 that the distance of an object from a source of light affects 
 the amount of light received by the object, or the intensity 
 of the light. Now, if one boy holds his book twice as far 
 away from a reading lamp as another boy does, he receives, 
 not % as much light, but M as much light as the other. 
 A third boy, sitting three times as far away as the first, 
 receives only l / 9 as much light, and so on. 
 
 The reason for this is shown by Fig. 
 144. Two square cards, 1 inch and 2 
 inches on each edge, respectively, are 
 placed in vertical positions on the same 
 PIG 144 side of the lamp. The lamp should be 
 
 An object twice as far from the lamp Very Small, SO that its light shall COHie 
 as another gets only M as < , n A. / / e i nr\\ 
 
 much light. from practically one point (cf. 169). 
 
154 
 
 LIGHT AND SOUND 
 
 The area of the smaller card will be 1 square inch; of the larger, 4 
 square inches. If we place the smaller card 4 inches from the lamp, 
 and the larger card 8 inches (twice as far) from the lamp, then the 
 shadow cast by the first card will just cover the second card. This 
 means that the light which falls on 1 square inch at distance 1 is 
 spread out over 4 square inches at distance 2. Therefore the intensity, 
 or brightness, of the light on the more distant card is not H of the 
 brightness on the nearer card, but H X H, or 3^ as great. 
 
 171. Candle Power. The intensity of the light given 
 off by lamps is always stated as so many " candle power." 
 This is because the unit of intensity is the illuminating 
 power of a standard candle. The standard candle is of 
 sperm fat, weighs Ye of a pound, and burns at the rate of 
 120 grains (7.78 grams) an hour. 
 
 We get the candle power of a lamp 
 by using a photometer (Fig. 145). This 
 consists of a piece of oiled paper or 
 cardboard, supported in a frame, and a 
 pencil that can be set upright near the 
 frame. The work must be done in a 
 room that is dark, except for the lamp 
 and candle to be compared. These two 
 are lighted, and placed so that the two 
 shadows of the pencil shall fall on the oiled screen side by side. The 
 distance of the lamp or candle is then altered, so that the shadows are 
 equally dark. Suppose that the distance between the candle and its 
 shadow is 1 foot, and that between the lamp and its shadow, 4 feet. 
 We square each of these numbers; that is, we multiply each by itself. 
 The square of 1 is 1, and that of 4 is 16. So the lamp has an illuminat- 
 ing power 16 times as great as that of the candle. We say it is a " 16 
 candle-power " lamp. 
 
 172. Exercises. 
 
 1. At about 525 C. iron becomes red hot. Is iron illuminated 
 
 FIG. 145. 
 
 How to get the "candle power" of 
 an electric light. 
 
DIVISION OF THE LIGHT STRIKING A BODY 155 
 
 or self-luminous when we see it below this temperature? When we see 
 it above this temperature? 
 
 2. What reasons have we for believing that the moon is not self- 
 luminous? 
 
 3. Classify the following substances as transparent, translucent, or 
 opaque: ice, snow, alcohol, milk, iron, the material of our finger nails, 
 skin, tissue paper, carbon dioxide, a solution of blue vitriol. 
 
 4. I see a carpenter, down the street, driving nails; but the sound of 
 each blow comes to me just as I see the hammer raised for the next blow. 
 Why? 
 
 5. A flash of lightning is seen 10 seconds before the thunder is heard. 
 How far away is the thunder cloud? 
 
 6. Sirius, the brightest of the fixed stars, is about 8 light-years 
 distant (c/ 11). How many miles is this, if we call the speed of light 
 200,000 miles a second? 
 
 7. What are the positions of the sun, the moon, and the earth when 
 we have " new moon "? When we have " full moon "? At which of 
 these times may we have an eclipse of the moon? At which an eclipse 
 of the sun? 
 
 8. Why is the shadow cast by a light of small diameter, such as an 
 electric bulb, so distinct? 
 
 9. I sit 5 feet from a lamp, while my brother is 1 foot from the 
 lamp. How much more light does he get than I? 
 
 10. In a photometer (Fig. 145) a candle at a distance of 1 foot casts 
 a shadow just as dark as one cast by a lamp 6 feet away. What is the 
 lamp's candle power? 
 
 173. Division of the Light Striking a Body. When 
 light meets a body, several things may happen : 
 
 (1) The light may be thrown back reflected in 
 a regular way and in certain definite directions. 
 
 (2) It may be reflected irregularly dispersed in 
 all directions. 
 
 (3) It may pass through the body it meets. 
 
 (4) It may be absorbed by the body. 
 
156 
 
 LIGHT AND SOUND 
 
 FIG. 146. 
 
 The angle of incidence is equal to the angle of 
 reflection. 
 
 Usually two or more of these results take place at the 
 same time. 
 
 174. Reflection of Light. If you throw an elastic 
 ball, such as a tennis or golf ball, vertically downward 
 against a horizontal sidewalk, you expect it to bound back 
 vertically upward. But if you throw the ball downward in 
 an inclined direction, as A C of Fig. 146, it bounds off in 
 
 another inclined direc- 
 tion CB. Except for the 
 effect of gravity on the 
 ball (cf. 21) the angle 
 made by AC with CD 
 (angle A CD) is of the 
 same size as the angle 
 made by CB with CD 
 (angle BCD). The first angle (A CD) is called the angle 
 of incidence (i. e., falling upon); BCD is the angle of 
 reflection (i.e., bending back). The rule is: 
 The angle of incidence equals the angle of reflection. 
 Light and sound are reflected in the same way as the 
 ball. If A of Fig. 146 represents a small opening through 
 which a beam of light is admitted into a dark room, and 
 if the reflecting surface at C is a smooth plane mirror, you 
 will see the reflected beam only when your eye is placed 
 somewhere on the line CB. 
 
 175. Mirrors. 'A mirror, or looking-glass, is a good 
 reflector of light, because at its back there is a thin layer 
 of a metal, usually silver. You have noticed that when you 
 look at any object, including yourself, in a mirror, the right- 
 hand side of the object becomes the left-hand side of the 
 
MIRRORS 
 
 157 
 
 R 
 
 FIG. 147. 
 
 image of the object. If an open book is held toward a 
 
 mirror, the image has the printed matter backward. A 
 
 watch showing 9 A. M. forms an image in N 
 
 which the hands are where we expect ~ 
 
 them to be at 3 p. M. Let us see how 
 
 the regular reflection of light produces 
 
 images. 
 
 Suppose that MR of Fig. 147 represents a The eye sees an object in 
 
 ... ,. the direction from which 
 
 vertical mirror, and that a point or some object the light of the object 
 is at 0. Rays of light from 
 strike the surface of the mirror everywhere; but only 
 the ray that meets the mirror at F passes to the eye, 
 according to the rule of reflection (174). But the eye 
 sees only in the direction from which the light ray 
 comes as it enters the eye; so appears to be in the 
 imaginary position O f (read this: prime). 0' is just as 
 far back of the mirror as is in front of it. Now suppose 
 that the object is not one point, but many points. An 
 
 The image of arrow is a convenient form of object (Fig. 148). The 
 
 fna J p C ia e ne image of the arrow is of the same shape as the arrow 
 
 skuTup "but itself, but reversed sidewise. 
 
 Ibt^ieft A piece of polished plate glass (Fig. 149), if 
 looked at at the right angle, will be a mirror, 
 
 and yet be a transparent body at the 
 
 same time. If a bottle of water is 
 
 placed behind the glass, and a burning 
 
 candle in front of it, we see both objects 
 
 in the direction from which their light 
 
 comes to the eye. Hence the candle 
 
 and the bottle appear to be in the 
 
 same place, behind the plate glass, Athickgl asspiat 9 e acts both 
 
 and the candle seems to be burning in transmitter^ fight ; a thl 
 
 . -i candle seems to be burn- 
 
 tne Water. ing in the water. 
 
 FIG. 148. 
 
158 LIGHT AND SOUND 
 
 176. Diffused Light. When a reflecting surface is 
 rough, the light striking it is dispersed in all directions. 
 It is by diffused light that we see most objects. Daylight 
 is sunlight dispersed by reflection from the ground, trees, 
 houses, dust, clouds, etc. Moonlight is uniformly diffused 
 sunlight from the moon's surface. We see the " old moon 
 in the new moon's arms " by earthshine; 
 that is, by sunlight that has been re- 
 flected by the earth to the moon, and 
 has then come back to the earth. 
 
 FIG. 150. 177> Refraction of Light. Let us 
 
 If an object under water is ^ 
 
 looked at obliquely, it suppose that in Fig. 150 we have a 
 
 seems to be at one side of 
 
 and vessel partly filled with water, and that 
 we drop a stone (S) into it. To the 
 eye the stone does not appear to be S, but a little to one 
 side, and nearer the surface; that is, at S'. 
 
 The explanation is that water is denser than air (cf. 
 33), and that the light which comes from the stone to the 
 eye is bent at B, where it passes from water into air. It 
 is bent away from the direction of the line SB. Since we 
 see an object in the direction which its light has as it 
 enters the eye, the stone appears to be at S'. 
 
 Because light is refracted in passing from water into air, the water 
 of a pond or stream seems to be more shallow 
 than it really is, and a reed or an oar seems to be 
 bent where it enters the water. For a similar reason 
 a star near the horizon appears to be higher up 
 than it really is (Fig. 151). Its light is bent as 
 
 it enters the earth's atmosphere (cf. 38) from A ^Jj^ hori . 
 
 outside space. The amount of bending increases as zon appears to be 
 
 ,, higher up than it 
 
 the star's light approaches the earth, because the really is. 
 
COMPOSITION OF WHITE LIGHT 
 
 159 
 
 FIG. 152. 
 
 Forms of lenses. 
 
 air becomes more and more dense (cf. 41). A heavenly body is, 
 therefore, never where it seems to be, except when it is at the zenith; 
 that is, directly overhead. 
 
 178. The Lens. A lens is a piece of transparent mate- 
 rial, usually glass, having two curved surfaces, or a curved 
 and a plane surface. Six 
 forms of lenses are shown in 
 Fig. 152. When rays of light 
 pass through a lens, they are 
 bent toward the thickest part 
 of the lens. This is shown in 
 Fig. 153. Parallel rays coming from the left would thus 
 be brought together, or " brought to a focus/ 7 at F, on 
 the opposite side of the lens. If, on the other hand, light 
 were produced at the point F, and its rays went through 
 
 the lens, they would be made parallel. 
 
 Focus is from the Latin, and means 
 
 " hearth." 
 
 Burning Glass. The double-convex lens of 
 
 Fig. 153 would bring parallel heat rays, as well 
 
 as sunlight, to a focus at F. It would then be 
 called a " burning glass." Paper, or a match, at F could be set on 
 fire. 
 
 Refraction of Sound. If a lens were constructed of the right mate- 
 rial, it could refract sound waves (cf. 190), and bring them to a focus. 
 The ticking of a watch might then be heard at this focus, although not 
 at places much nearer the watch (Fig. 154). 
 
 179. Composition of White 
 Light. At first thought it may 
 seem likely that white light, such 
 as that of the sun, is simpler in 
 
 FIG. 153. 
 
 The lens brings the par- 
 allel rays to a focus. 
 
 FIG. 154. 
 
 Sound waves can be brought to 
 a focus like light waves. 
 
160 
 
 LIGHT AND SOUND 
 
 Fia. 155. 
 
 A glass prism breaks up white sunlight into 
 light of seven well-marked colors. 
 
 its composition than colored light; but this is not so. If 
 a beam of sunlight is admitted through a narrow slit (A) 
 into a dark room (Fig. 155), an image of the opening will 
 be made upon the screen at B. But if a glass prism (P) 
 is put in the path of the sunbeam, the image of the slit 
 will not be a simple line, but a series of lines side by side; 
 that is to say, a band. The image will not be white, but 
 will consist of bands of different colors. As the prism is 
 
 placed in Fig. 155, the 
 violet band is highest, 
 while the red band is 
 lowest. The reason is 
 that violet light is bent 
 mosfc by the prism, and 
 red, least. The order of 
 the colors will be: violet, 
 indigo, blue, green, yellow, orange, and red. The initial 
 letters make the fanciful word VIBGYOR. 
 
 When platinum, iron, etc., are heated, they first become red hot, and 
 last of all white hot. This suggests that we get the red rays first because 
 they have the slowest rate of motion. Only when the temperature has 
 risen are the violet rays added which are necessary to give pure-white 
 light. The red rays have the longest waves; the violet waves are 
 shorter, but move much more rapidly. 
 
 APPROXIMATE LENGTH OF LIGHT WAVES, IN MILLIMETERS 
 
 Violet. 000397 Yellow 000589 
 
 Indigo 000431 Orange 000656 
 
 Blue 000480 Red 000688 
 
 Green 000527 
 
 If a reversed prism is placed so as to catch the colored 
 bands produced by the first prism (Fig. 156), the colors 
 
THE RAINBOW 161 
 
 will be brought together again, and the rays produced 
 will be white, as they were before refraction. So we can 
 prove, both by breaking up white sunlight and by putting 
 its colored parts together, that it is composed of many 
 rays of different colors. The colored band produced by 
 the single prism is called the solar (i. e., the sun's) spectrum. 
 It was first studied with great 
 care by Isaac Newton, in 
 1672. 
 
 FIG. 156. 
 
 i or\ TO. T> * l TU ~ Reversed Prism. Sunlight that has been 
 
 loll, ine KainDOW. ine broken up can be recombined to 
 
 ,, , give white light. 
 
 finest solar spectrum we see 
 
 in Nature is the rainbow. In order to see a rainbow we 
 must look at falling rain, and the sun must be behind us, 
 and 42 degrees, or less, from the horizon. Half the dis- 
 tance from the zenith (c/. 177) to the horizon is 45 de- 
 grees. On a small scale a rainbow may often be seen in the 
 spray of a waterfall or of a lawn sprinkler. In Nature two 
 bows are often seen together: a primary one, red on the 
 outside of the arch and violet on the inside, and a secon- 
 dary one, outside the primary one, and with the colors of 
 the primary rainbow in reversed order. 
 
 In forming a rainbow each drop of water acts both as a lens and as 
 a mirror. It refracts the sun's rays as they enter the drop, reflects 
 them from side to side within the drop, and then refracts them as they 
 re-enter the air. 
 
 From the outside of the rainbow arch only red rays reach our eyes. 
 The drops inside the arch send to us, in order, orange, yellow, green, 
 blue, and indigo rays. The lowest drops send the violet rays. 
 
 A halo, or ring of light, around the moon or the sun is probably due 
 to a similar bending of light rays by the thin, icy clouds of the upper 
 part of the atmosphere. 
 
162 
 
 LIGHT AND SOUND 
 
 heat (cf. 183) 
 
 181. Absorption of Light; Color. Certain substances 
 do not allow light to pass through them, and do not 
 reflect it; what, then, becomes of the light? We say it is 
 absorbed (173). It is really changed almost entirely into 
 
 Lampblack, or soot, is a good absorber 
 of light; silver is an almost perfect re- 
 flector (cf. 57 and 175; also Fig. 
 157). 
 
 We see most objects by the light they 
 reflect (cf. 165 and 174). The color 
 of an object thus depends upon the color 
 of the reflected rays, or, in the case of a 
 transparent body, upon the color of the 
 light that passes through the body. A 
 red body sends red rays to the eye, and 
 absorbs all other rays. If it reflects 
 nearly all rays, it is light gray. If it 
 absorbs all, it is black. 
 Two colors that yield white light when mixed are called comple- 
 mentary colors. Such are red and blue-green, yellow and blue-indigo, 
 orange and light blue, green-yellow and violet. Color is not really a 
 property of bodies, but a sensation which they produce upon ourselves. 
 What we call color is the sensation that a body produces when we see it 
 in ordinary daylight. We all know how different the same colors ap- 
 pear in daylight, gas light, and the electric arc light. A blue ribbon will 
 not appear blue unless the light by which it is illuminated contains 
 blue rays. Daylight contains blue rays. But the light of sodium 
 vapor (cf. 109) contains only yellow rays. In such light all objects 
 are either yellow or black. For the same reason a blue object held in 
 the red light of a photographer's " dark room " appears black. 
 
 182. The Sky and Its Colors. The normal color of the 
 sky is blue, except when the atmosphere contains too 
 
 FIG. 157. 
 
 Two Air Thermometers. 
 The air in the black- 
 ened bulb becomes 
 warmer than that in 
 the colorless, or sil- 
 vered, one; the black 
 bulb absorbs the more 
 light and heat. 
 
CHANGE OF LIGHT INTO HEAT 
 
 much dust. Atmospheric dust may be ordinary, solid 
 dust, or fine particles (mist) of water or ice (cf. 268). 
 Sunlight dispersed by this dust is " white' ' daylight (cf. 
 173 and 176). Near the sun and near the horizon the 
 sky is ordinarily light gray. Sunrise and sunset colors 
 are due to the rays that are refracted least (cf. 179) ; 
 hence the indigo and blue of the zenith shade into 
 yellow, orange, and red near the horizon. 
 
 Sky coloring is caused not only by reflection and refraction, but also 
 by an effect which thin clouds of fine particles have in breaking up sun- 
 light into its spectrum. The same effect is produced by a glass plate 
 ruled with many parallel lines, say 15,000 to the inch. The phenome- 
 non is called diffraction. As with the prism, violet rays are bent most 
 and red rays least. 
 
 In 1883 the volcano of Krakatoa, Java, suffered a violent explosion, 
 and so much dust was driven into the upper air that it spread around 
 the whole globe. It produced brilliant sunset effects for 3 years. 
 
 183. Change of Light into Heat. From the study of 
 the spectrum we learned that the violet rays move most 
 rapidly and the red least rapidly. Below the red rays 
 there are rays moving too slowly to give out light of any 
 color, yet having a great deal of energy. These long 
 waves can be changed into heat just as light waves can. 
 Glass will not cut off the light waves, but it will cut off the 
 longer heat waves. We can prove this easily by holding 
 a pane of glass between the hand and a hot stove. Now, 
 when sunlight has been absorbed, and is then radiated 
 again (cf. 66), it no longer consists of the short light 
 waves, but of the long heat waves. The glass of green- 
 houses or hot-beds thus acts as a trap for the sun's energy; 
 for it permits the light waves to pass into the soil; but 
 
164 LIGHT AND SOUND 
 
 when the light waves have been changed into heat they 
 cannot escape. 
 
 The water vapor and impurities of the air act like glass 
 in making prisoners of the light waves and thus raising the 
 temperature of the earth. Without this the chill that 
 would follow the rapid radiation of heat from the earth 
 would quickly put an end to all animal and vegetable life. 
 
 184. Light and Life. The energy of the sun is stored 
 up not only by the earth's atmosphere, but also by the 
 action of plants. Plants containing chlorophyll, the green 
 coloring matter of our common vegetation, are able by 
 the aid of sunlight to build up complex organic sub- 
 stances, such as sugar, starch, cellulose, etc. (c/. 310). 
 Plants build up these substances out of carbon dioxide 
 and water. Oxygen is set free (cf. 52). Energy is re- 
 quired, for this is chemical work, and the sun supplies it. 
 When the material produced by the plant is afterwards 
 used as fuel or food, it reunites with the oxygen; the energy 
 reappears as body heat, muscular force, etc. In a very 
 real sense, therefore, plants store up the sun's energy for 
 their own use and for the use of animals. 
 
 185. Exercises. 
 
 1. Stand before a vertical mirror, and look at the image of your 
 hand while you write your name. What is the result? Explain it. 
 
 2. A mirror on a dresser is 30 inches above the floor. How do you 
 tilt the mirror if you want a full length view of yourself? Why do you 
 step back from the dresser? 
 
 3. Why is the broken top of a wave white (" white cap "), while the 
 unbroken wave is blue, green, etc.? 
 
 4. If you lay a small piece of thick glass over the middle part of a 
 
COMPOUND MICROSCOPE 165 
 
 piece of wire, and then look at the wire obliquely, the wire seems to be 
 broken at the edges of the glass. Try it, and give the reason. 
 
 5. If you look obliquely downward at a fish on the bottom of a pond, 
 is the fish where it seems to be? Is it nearer you or farther away? 
 Draw a figure to show why. 
 
 6. Why do we see the sun after it has really set, and before it has 
 really risen? 
 
 7. Investigation has shown that forest fires are sometimes caused by 
 glass bottles left by campers; explain. 
 
 8. Do we ever see a rainbow at midday? Explain why. 
 
 9. A mercury vapor electric lamp contains almost no red rays. What 
 effect has this upon the color of objects? 
 
 10. For what reasons can vegetables be raised so much earlier in a, 
 box covered with glass (a " cold frame ") than in the open air? 
 
 186. Simple Microscope, or Magnifying Lens. The 
 simple microscope (Fig. 158) consists of a convex lens 
 that will bring light to a focus. The object to be magni- 
 fied (here the arrow a b) is placed 
 
 between this focus and the lens. The 
 
 figure shows that the image (a' b') 
 
 will appear to be farther from the 
 
 lens than the object is, and that it The lens e*he object ap _ 
 
 will be right side up and enlarged. pear ""tSSSSt " not 
 
 187. Compound Microscope. The compound micro- 
 scope (Fig. 159) consists of (1) a concave, i. e., hollowed 
 out, mirror to collect and direct light rays; (2) an object 
 lens, or objective ; and (3) an eye-piece. The inside of the 
 microscope tube is black, to prevent light from being re- 
 flected back and forth. 
 
 The object to be magnified (a b} is fastened in a glass " slide," and 
 is lighted up by rays directed by the mirror. The rays from the object 
 
166 
 
 LIGHT AND SOUND 
 
 then pass through the object lens, and produce a reversed and inverted 
 image near the eye-piece. Just as the simple magnifying lens enlarges 
 an object placed near it, so the eye-piece enlarges the 
 image a b' , and it appears to be further magnified to 
 the size a" b" (read this: a second, b second). 
 
 Eye ,PTece 
 
 188. The Camera. The camera (Fig. 
 160) consists of a dark box having a movable 
 screen of ground glass (S). The tube con- 
 tains a convex lens. The image of the object 
 appears upon the screen, and may be looked 
 at through 0. When the image has been 
 " focused " on the screen, a " sensitized " 
 film or glass plate is put in place of the 
 screen. The chemical action of light 
 " prints " a picture of the object upon the 
 film or plate. 
 
 The sensitive film or plate is made by 
 completely 8 . image covering B> sheet of gelatine or of glass with 
 some compounds that are easily decom- 
 posed by light. Usually these are silver chloride or silver 
 bromide. After the film or plate has been exposed to light 
 from the object, the image is still invisible. It must be 
 " developed" by means of a solution of pyrogallic acid, 
 or some other " developer." Finally the image is " fixed." 
 Fixing consists in removing 
 the unchanged silver salt. 
 The material used is generally o 
 sodium thiosulphate, known | 
 popularly as 
 
 Objective 
 
 FIG. 159. 
 
 The compound 
 microscope makes 
 an object appear 
 much larger, but 
 
 hypo. 3 
 
 The result of these operations is 
 
 FIG. 160. 
 
 The camera is a device for focusing the 
 clear image of an object upon a sensi- 
 tive plate or film. 
 
HOW SOUNDS ARE MADE AND CARRIED 167 
 
 the negative (Fig. 161). In it the light parts of the object are dark 
 (opaque), and the dark parts are light. The photographer " prints " 
 the positive picture by placing the negative over sensitive paper con- 
 taining silver chloride, and exposing the two for some time to sunlight. 
 The paper will then be changed as the negative was. But as the dark 
 parts of the negative cut off the light, while the lighter parts permit 
 
 FIG. 161. 
 Negative and Positive Photograph. Negative by H. L. Schall. 
 
 it to pass through, the positive "print" contains light and shade in 
 the same relation as the object photographed. 
 
 189. How Sounds are Made and Carried. Just as light 
 is the cause that affects the optic nerve and gives us sight, 
 so sound is the cause that affects the nerve of the ear and 
 causes hearing. All sound is due to the motion of some 
 portion of matter. When a violin string is producing a 
 note, it is moving rapidly back and forth. We can prove 
 this by touching the string lightly with the finger. We 
 can prove the same thing in the case of a sounding tele- 
 phone or door bell. When we speak or sing, we force air 
 through the slit between the vocal cords (cf. 389), and 
 set them into rapid motion. When a vibrating tuning 
 
168 
 
 LIGHT AND SOUND 
 
 fork is put into water, it throws the water into sprays; 
 this shows that its sounding is due to its motion (Fig. 162). 
 
 Sounds are ordinarily carried by the air. If an electric 
 bell is placed inside a vessel of air (Fig. 163), and the air 
 is nearly all removed by an air pump, the sound given 
 out by the bell is feeble; but it becomes stronger again 
 when air is admitted. This shows that a vacuum would 
 not carry sound. But other kinds of matter besides 
 air carry sound. Thus the tap of a pencil or the scratch 
 of a pin against a long steam pipe is heard readily, if we 
 put the ear close to the pipe. Iron conducts sound 
 better than air. Water is also a better sound conductor 
 
 than air: the clashing together of two stones under water produces a 
 
 louder sound than in air. In air at C. 
 
 Fia. 162. 
 A sounding 
 body is in 
 rapid vibra- 
 tion. 
 
 sound travels about 1,100 feet in a second; 
 in water, about 4,600 feet, and in iron, 
 about 17,000 feet. 
 
 -f- 
 
 Fia. 163. 
 
 A bell ringing in a vacuum 
 would give forth no sound. 
 
 190. Sound Waves. When a 
 sound is produced (Fig. 164), it is 
 heard in all directions. This sug- 
 gests to us that sound waves start 
 as small spheres which get larger 
 and larger as they move outward from the sounding 
 body. But as the sphere grows larger, more and more air 
 must be set in motion. Naturally the motion of a given 
 volume of the air must become smaller and smaller. Fi- 
 nally the motion of the air is too 
 small to affect the ear. We say the 
 sound " dies out " with distance. 
 FIG. 164. How does the air move when it 
 
 s ?n g nd 8 p w h a e v rf,; 8p th e elr a8 is e aSe g r : carries sound? It caimot go as in a 
 
 na^compressed and e*- 
 
ECHOES 169 
 
 movement of a body of air; for we do not feel any motion 
 of the air from a sounding body. To understand the for- 
 mation of sound waves we must remember that air is elastic; 
 that is, it can be compressed, but will expand again when 
 released. The sudden jar given the air by a bell (Fig. 164) 
 pushes the air particles near the bell forward, producing a 
 layer of compressed air. This layer then expands, and 
 in doing so gives a rapid push to the next layer of air. 
 The sound wave thus proceeds outward as a series of 
 short, rapid compressions and ex- 
 pansions of air. 
 
 With a row of elastic balls (Fig. 165) we 
 can illustrate the way in which air particles 
 can give up their motion without going 
 forward. If we draw aside one of the balls, 
 and let it fall against the row, it gives its 
 motion to its neighbor. This gives its f ow . of balls : onlv the last 
 
 ball actually moves forward. 
 
 motion to the next ball, and so on down the 
 
 line. Only the last ball, which has no ball to which it can give its 
 
 motion, actually moves forward. 
 
 191. Echoes. Sound waves are reflected as light waves 
 are (cf. 174). If, on a quiet day, we shout toward some 
 wall, or barn, or cliff, our shout may be returned to us as 
 an echo. To succeed we must be far enough away to per- 
 mit the shout to cease before the reflected sound can come 
 back. In a small room the echo blends with the original 
 sound, and we do not notice it; but in a large room or 
 hall the echo of one word or sentence may come back just 
 as another is being spoken. The result is a confused mix- 
 ture of sounds. Echoes are often prevented by the hang- 
 ing of curtains or wires across the room. These break up 
 the disturbing sound waves. 
 
170 LIGHT AND SOUND 
 
 192. Noise and Tone. We distinguish clearly between 
 noises, which come from the confused mingling of sound 
 waves, and tones, which are the result of a rapid succession 
 of waves, all of the same sort, and coming at regular in- 
 tervals. It is this regularity that makes musical sounds 
 pleasant to the ear. By striking hard bodies, such as 
 dishes, stones, wires, car wheels, etc., we find that each 
 has its own definite tone. 
 
 By the pitch of a tone we mean whether it is high or low. 
 Pitch is caused by the frequency of the vibrations of what- 
 ever causes the sound. " Middle C " of a piano is brought 
 about by a wire that vibrates 256 times in a second. The 
 range of the human voice is from about 80 vibrations 
 (lowest bass) to about 1000 vibrations (high soprano) in a 
 second. 
 
 We can hear sounds due to a much greater frequency than we can 
 produce. Thus, the high notes of a violin, the noise of a cricket, and 
 the whistle of a locomotive are due to thousands of vibrations in a 
 second. When a sound comes from more than 40,000 vibrations per 
 second, the human ear can no longer hear it. 
 
 193. The Telephone. The principle according to 
 which the telephone " works " is shown in Fig. 166. M 
 and TV are two permanent magnets placed inside the wire 
 coils B and C. The circuit is through the coils, the wire 
 connecting them, and the earth. Before each magnet 
 there is a thin, iron disk (D and E) . If we make a sound 
 in front of D, the sound waves in the air make the disk 
 vibrate. As D moves back and forth in the " lines of 
 force " (cf. 138) of its magnet (M), it induces currents 
 (cf. 160) in the coil B. These currents are carried along 
 the wire, and appear in the coil C. Here they cause move- 
 
SUMMARY 
 
 171 
 
 FIG. 166. 
 The Simple Telephone. 
 
 ments of the lines of force of the magnet A 7 , and produce 
 vibrations in the disk E. The vibrations of E are just 
 like those of Z), and reproduce the sound we made at the 
 other end of the line. 
 
 In the modern telephone the " return circuit" is 
 through a second wire 
 instead of through the 
 earth. The receiver is 
 like the simple disk of 
 the figure, but the speak- 
 ing instrument ("trans- 
 mitter") is more complex. 
 The telephone was in- 
 vented in 1875 by Alexander Graham Bell, of Washington, 
 and Elisha Gray, of Chicago. 
 
 194. Summary. A visible body is either self-luminous or illuminated. 
 
 Bodies may be transparent, translucent, or opaque. 
 
 Light is the cause that produces sight. It moves in straight lines at 
 a speed of 186,000 miles a second. 
 
 An image formed through a small opening is inverted. 
 
 A shadow formed from a point of light is distinct, and composed of 
 an umbra alone. A shadow from a luminous surface has both umbra 
 and penumbra. 
 
 An eclipse of the sun occurs when the earth is within the moon's 
 shadow. An eclipse of the moon occurs when the moon is in the 
 earth's shadow. 
 
 Intensity of light is given in candle power. A photometer is an in- 
 strument for finding when the intensity of light from two luminous 
 bodies is the same. 
 
 Light striking a body may be reflected, dispersed, or absorbed; or 
 it may pass through the body. 
 
 Light is reflected at the same angle as that at which it strikes the 
 reflecting surface, but in a different direction. 
 
172 LIGHT AND SOUND 
 
 A plane mirror gives an image that is right side up, but has the right 
 and left sides reversed. 
 
 We see an object in the direction which its light has as it enters 
 the eye. 
 
 Daylight is dispersed sunlight. 
 
 Light that passes from one substance to another of a different 
 density is refracted. Because of refraction, objects in water are not 
 seen in their correct positions, and the heavenly bodies seem higher 
 above the horizon than they really are. 
 
 A lens with convex faces brings light rays, heat rays, and sound 
 waves to a point, or focus. 
 
 White light is a mixture of many colors. It is broken up into its 
 primary colors by a prism. The band of colors produced by sunlight is 
 called the solar spectrum. A rainbow is a spectrum on a large scale. 
 
 The color of a body is due to the rays it reflects. It absorbs rays of 
 all other colors. 
 
 Light rays are changed into heat rays when they are absorbed by the 
 earth and then given off. 
 
 Plants having chlorophyll use sunlight to prepare sugar, starch, etc., 
 out of carbon dioxide and water. 
 
 The simple microscope gives an enlarged, natural image. 
 
 The compound microscope consists of a mirror, an objective, an 
 eye-piece, and a tube. It gives an enlarged image which is completely 
 reversed. 
 
 The camera consists of a dark box, a screen, and a lens. It gives an 
 inverted, reversed image of reduced size. 
 
 Sounds are ordinarily carried by the air, but they may be carried 
 by water, metals, wood, etc. 
 
 Sound waves extend outward from the sounding body as enlarging, 
 spherical layers in which air is alternately compressed and expanded. 
 
 Echoes are reflected sound waves. 
 
 Noises are sound waves coming at irregular intervals. Tones are 
 waves, all of the same kind, and coming at regular intervals. 
 
 Pitch depends upon the frequency of vibration. 
 
 The telephone is constructed on the principle that vibrations of an 
 iron disk in the field of one magnet will produce corresponding vibra- 
 tions in an iron disk placed in the field of another magnet far away. 
 
EXERCISES 173 
 
 195. Exercises. 
 
 1 . Why does the photographer use red light in his dark room? 
 
 2. If you were to hold a suspended pith or cork ball near a sounding 
 tuning fork, what would happen? 
 
 3. Suggest why it is so much harder for a speaker to be heard in the 
 open air than in a hall. 
 
 4. A circular saw has a certain note when revolving rapidly. Why 
 does the pitch of the sound fall when the saw cuts into a board? 
 
 5. Why is the ringing of a bell so much clearer when the sound 
 comes " with " the wind than when it comes " against " the wind? 
 How does the wind affect the shape of the sound waves? 
 
 6. When is a room more likely to have echoes, when full of people, 
 or when empty? Why? 
 
 7. How are the marks upon a graphophone " record " changed into 
 sound? How are the records made? 
 
 8. How can sound waves be carried through a speaking tube? 
 
 9. Of what are " chimes " constructed? How are the different 
 notes secured? 
 
 10. Why can you hear a distant carriage better by putting your 
 ear to the ground? 
 
 11. What is the principle of the yell leader's megaphone? 
 
CHAPTER X 
 
 SIMPLE MACHINES 
 
 196. Need of Machines. Man uses a multitude of 
 devices, or tools, to enable him to do his work to better 
 advantage. Thus, he pries a stone or a log instead of 
 lifting it. If he needs to raise stones or bricks to the top 
 of a building, he employs a pulley with a rope over it ; by 
 pulling downward on the rope, he pulls the weight upward. 
 He splits logs with wedge and axe, and ploughs with a slop- 
 ing knife, or ploughshare. If he has to raise barrels into a 
 wagon, he rolls them up a sloping board instead of lifting 
 them. Wherever possible, he puts a wheel or roller under 
 a heavy object, so that he can move it without lifting it. 
 Finally, in order to fasten pieces of cloth or skin together, 
 he uses a needle or an awl. Since the thickness of this tool 
 increases very gradually, a little pushing forces the fabric 
 apart, and makes a hole for the thread. The forms of 
 tools have become more ingenious and complicated with 
 man's progress in civilization, but the simple principles 
 have been known for ages. These principles are repre- 
 sented by six simple contrivances, or machines : 
 
 (1) The Lever. (4) The Inclined Plane. 
 
 (2) The Pulley. (5) The Wedge. 
 
 (3) The Wheel and Axle. (6) The Screw. 
 
 197. Law of Machines. None of these machines nor 
 any of their improved forms can originate, or create,. 
 
 174 
 
LAW OF MACHINES 175 
 
 any energy. They simply make it possible for us to apply 
 force in a convenient direction, or at a convenient place. 
 Or they make it possible for us to exchange a small force 
 exerted through a considerable distance for a much larger 
 force exerted through a correspondingly shorter distance. 
 Thus, we give the head of a screw driver one complete 
 turn in order to get the screw to move forward only the 
 distance between two successive threads; but the force 
 we exert in overcoming the cohesion of the wood is enor- 
 mously greater than that which we ap- 
 ply to the head of the screw driver. 
 Again, we probably could not draw a 
 nail out of a board by pulling with all 
 our might, yet by the use of a claw 
 
 hammer (Fig. 167) we need to put forth 
 
 FIG. 167. 
 
 only a small effort to do the work. But A claw hammer is a 
 
 machine. 
 
 we must remember that in using ma- 
 chines we are making an exchange, not getting something 
 for nothing. 
 
 The exchange we make in using a sewing machine is the 
 opposite of that which we make in the screw and the 
 hammer. Sewing by hand is hard, not because it requires 
 much strength, but because it is slow. With a sewing 
 machine the seamstress can exchange her strength for 
 greater speed. 
 
 The law of machines is merely the statement of the 
 exchange we make in every machine. If we multiply 
 the power exerted (stated in weight units) by the dis- 
 tance through which the source of the power moves, 
 the product is just equal to the product obtained when 
 we multiply the resistance overcome, or the weight 
 
176 
 
 SIMPLE MACHINES 
 
 lifted, by the distance through which the resisting object, 
 or weight, moves. 
 Power X power distance = weight X weight distance. 
 
 198. The Lever. The claw hammer, pitchfork, and 
 crowbar are common forms of the lever. The fixed 
 support on which the lever rests is 
 called the fulcrum. If, in Fig. 168, 
 the distance from the fulcrum (F) to 
 the point at which the weight (R) is 
 attached is 1 foot, and the distance 
 from F to the point (P), where the 
 power is applied, is 2 feet, then the weight that can be 
 lifted at R is twice the power applied: 40 pounds at P 
 can support 80 pounds at R. If the distance from F to R 
 is 3 inches, and that from F to P is 51 
 inches, then 40 pounds at P can sup- 
 port 680 pounds at R. 
 
 FIG. 168. 
 A Lever of the First Class- 
 The fulcrum is between 
 the force exerted and the 
 resistance to be overcome. 
 
 FIG. 169. 
 Fish Scales: a Lever of 
 the First Class. 
 
 The balances (Fig. 9) are a lever. If the 
 
 two arms are of equal length, equal weights in 
 
 the two pans will just support each other. 
 
 In fish scales (Fig. 169) the arm holding the pan is the shorter, 
 
 hence a heavy object on 
 this pan can be supported 
 ' ' weighed " by a small 
 weight on the longer arm. 
 The weighted gate (Fig. 170) 
 and the well sweep (Fig. 171) 
 are other examples of the lever. 
 
 FIG. 170. 
 
 Weighted Gate. The stone nearly balances the 
 gate, so that very little effort is required to 
 lift the gate. 
 
 199. Classes of Levers. We divide levers into three 
 classes according to the way in which the fulcrum, the 
 
CLASSES OF LEVERS 
 
 177 
 
 
 FIG. 171. 
 
 Well Sweep : a Lever Used in Raising 
 Water from a Well. Courtesy of 
 the Ansco Co. 
 
 power, and the resistance are 
 placed with regard to one an- 
 other. In the crowbar and 
 balance the fulcrum is between 
 the other two. Such a lever is 
 of the first class. 
 
 In the nut-cracker (Fig. 172) 
 the resistance (the nut) is be- 
 tween the other two : the fulcrum 
 is at one end. This is a lever of 
 the second class (Fig. 173). 
 
 A wheelbarrow is also of the 
 second class. The fulcrum is the 
 axle of the 
 wheel, the 
 
 power is applied to the handles, and 
 the weight is between them. The 
 rule of machines applies here, just as 
 in levers of the first class. In making 
 the calculation we will not count the weight of the wheel- 
 barrow. If you place a piece of ice, 
 weighing 100 pounds, 1 foot from 
 the axle of the wheel, and grasp the 
 handles 5 feet from the axle, you 
 need exert a force of only 20 pounds 
 to lift the ice. 
 
 Levers of the 
 
 third class have the fulcrum at one 
 end, just as those of the second class 
 nave > but the power is applied be- 
 tween the resistance and the fulcrum 
 
 FIG. 173. 
 
 Lever of Second Class. The 
 resistance is between the 
 fulcrum and the power. 
 
 Lever of 'the' Third class. 
 ' 18 at P 
 
178 SIMPLE MACHINES 
 
 (Fig. 174). The tread of a grindstone and of a weaving 
 loom are examples of third class levers. So is the human 
 forearm (Fig. 277, 355). 
 
 200. Exercises. 
 
 1. To what class of levers do scissors belong? In cutting thick 
 cloth, or a wire, with shears, do you put the cloth, or wire, at the tips 
 of the shears or near the rivet? Why? 
 
 2. What kind of a lever is a pair of sugar tongs? The oar of a boat? 
 The handle of a hoe? A pitchfork? A pump handle? 
 
 3. If you were using a crowbar to roll a log along the ground, how 
 would you use the bar as a lever of the first class? How as a lever of the 
 second class? 
 
 4. If you support a 5 Ib. weight at one end of a bar 3 ft. long by 
 means of a 10 Ib. weight at the other end, where must the fulcrum be 
 placed? 
 
 5. An oar is 7 ft. long, and the handle is 1 ft. from the oarlock. How 
 far is the end of the blade from the oarlock? A boy pulls on the handle 
 with a force of 25 Ibs.; what force does the oar blade exert on the 
 water? Would there be any advantage in having the oar handle 2 ft. 
 from the oarlock? 
 
 6. Why is an oar blade made so broad? Upon what property of 
 water does the blade's usefulness depend? 
 
 7. When a woman is pushing with her toes against the treadle of a 
 .sewing machine, where is the power as regards fulcrum and weight? 
 
 What kind of a lever is the treadle in this case? What 
 kind is it when she uses her heel? In which case does 
 she have to do more work? How is the treadle attached 
 to the driving wheel? 
 
 201. Pulleys. In the simplest form of the 
 pulley (Fig. 175) we cannot lift more than 
 
 FIG. 175. the power we put forth; but we can raise the 
 weight by pulling downward. Such a pulley 
 is used for hoisting the sails of a ship, or for 
 
THE WHEEL AND AXLE 
 
 179 
 
 
 raising a flag on a flagstaff. By means of a 
 second pulley a horse pulling in a horizontal 
 direction can raise a weight vertically upward 
 (cf. Fig. 20, 26). 
 
 If we arrange two pulleys as in Fig. 176, two cords 
 support the weight, while only one is supported by the 
 power; hence a power of 1 pound can 
 support a weight of 2 pounds. We get this and One Fixed 
 advantage because the cord on which we 
 pull must descend twice as far as the weight rises. 
 If there^ are three cords (Fig. 177) supporting the 
 weight, and one supported by the power, 1 pound can 
 lift 3. 
 
 FIG. 177. 202. The Wheel and Axle. In the wheel 
 and axle (Fig. 178) the power applied on the 
 wheel must move a distance 
 equal to the circumference of the wheel, 
 while the weight attached to the axle 
 moves only the circumference of the axle. 
 The wheel in the figure has a circum- 
 ference 3 times that of the axle; therefore 
 
 1 pound on 
 the wheel 
 will support 
 3 pounds 
 on the axle. 
 
 The winch, or windlass (Fig. 
 179), is a form of the wheel 
 and axle in which the power is 
 applied to a crank. To raise 
 the weight a distance equal to 
 winch used for Raising of water. the circumference of the axle, 
 
 FIG. 178. 
 Wheel and Axle. 
 
180 
 
 SIMPLE MACHINES 
 
 the power must be exerted 
 through one complete turn of 
 the crank. A derrick (Fig. 180) 
 consists of a winch and a 
 system of cog wheels and 
 pulleys. 
 
 203. The Inclined 
 Plane. In climbing a 
 hill or mountain we pre- 
 fer to go up gradual 
 slopes instead of steep 
 ones, because in this way 
 we can raise the weight of our bodies with much less 
 effort. But in doing so we make an exchange: we travel a 
 much greater actual distance than 
 if we go " straight up." So, if 
 we wished to raise a 200 pound 
 barrel from the ground to a 
 wagon, we might lift it up directly; 
 but an easier way would be to roll 
 it up an inclined plane (Fig. 181). If the plane were 10 
 feet long and 3^ feet from the ground at the higher end, 
 the force required to push the barrel up the plane would 
 be 1 A of 200, or 66% pounds. We roll the 
 barrel 3 times as far as we wish to raise it, 
 but we need exert only J^ of the force. 
 This is the effort required if we exert force 
 parallel with the plane. 
 
 FIG. 182. 204. The Wedge. The wedge (Fig. 182) is 
 
 of im-iinedplane? 1 really two inclined planes with their bases placed 
 
 FIG. 181. 
 Inclined Plane. 
 
THE SCREW 
 
 181 
 
 together. It is made of hard wood or of iron, and is used to split logs 
 and stones, or sometimes to raise a heavy weight. If the length of the 
 wedge is 5 times its thickness, we drive it into the log 5 inches in 
 order to force the wood apart 1 inch. The axe is a wedge; so are the 
 pin and the needle (cf. 196). 
 
 205. The Screw. If we were going to the top of a 
 lighthouse 100 feet high, we might climb a vertical ladder 
 or rope, 01 we might go up gradually, on a long inclined 
 plane, rising, say, 1 foot in every 10. In the ascent by the 
 inclined plane we would walk 1000 feet in 
 order to rise 100 feet. The most compact 
 way of arranging an inclined plane is in a 
 spiral. This is done in the spiral staircases 
 of many lighthouses and towers. 
 
 Now, the screw (Fig. 183) is really a 
 long inclined plane with the ascent 
 arranged in a spiral instead of in a straight 
 
 T A 11 f i , 
 
 line. A small force can produce a large 
 
 - 'IT n 
 
 enect with the screw; for the power must 
 
 go a long distance in order to make the screw itself ad- 
 
 vance a very short distance. 
 
 The distance between threads is called the " pitch " of the screw. 
 Suppose that a screw having 12 threads to the inch is driven by a 
 screw driver having a handle 2 inches in diameter. 
 The handle has a circumference of 2X3 1 /?, or 6 2 /7 
 inches. The handle is thus turned through 6 2 /7 
 inches while the screw advances l /iz of an inch. 
 Hence the power moves about 75 times (6 2 /7 divided 
 by Vi 2 ) as far as the resistance or weight; a force of 
 3 pounds applied on the handle will exert a force of 
 about 225 pounds on the threads of the screw. 
 The screw is used not only for holding pieces of 
 
 great weights, such 
 
 as wagons or houses, 
 
 ^ or short distances. 
 
182 SIMPLE MACHINES 
 
 wood or metal together, and for lifting weights, but also for producing 
 great pressure. The letter-copying press (Fig. 184) and the vise are 
 screws used for this purpose. 
 
 206. Friction. The law of machines (cf. 197) does 
 not turn out to be exactly true in the actual use of a 
 machine, because some of the power exerted is used in 
 overcoming friction (cf. 24). But while friction repre- 
 sents lost effort, some friction is usually necessary in order 
 that a machine may " work." Thus, a barrel must 
 "stick " slightly to an inclined plane, or we cannot roll it 
 up; a rope passed over a pulley must adhere to the rim of 
 the pulley, or the pulley wheel will not turn when the 
 rope is drawn in. We all know how difficult it is to walk 
 upon a highly polished floor, owing to the lack of friction 
 between our shoes and the floor. Also, heavy objects 
 that are to be moved horizontally are placed on rollers or 
 wheels, if possible, because rolling friction is much less 
 than sliding friction. The wheelbarrow illustrates this 
 admirably, also the use of castors on bedsteads, tables, etc. 
 
 207. The Sailboat. Few discoveries of man have 
 helped him more in his rise to civilization than his ability 
 to travel long distances by water; this was made possible 
 largely by his discovery of the use of sails. 
 
 We can readily understand how a boat can sail " before 
 the wind": the sail merely provides a large area for re- 
 ceiving the pressure of the moving air. The sailboat not 
 only permits us to sail in the direction of the wind, but it 
 permits us to exchange rapid motion in this direction for 
 slower motion in some other direction. No sailboat, of 
 course, can go directly against the wind. 
 
THE SAILBOAT 
 
 183 
 
 Use of Keel. A wind blowing against a boat causes it to move in 
 
 the direction of the wind; that is, to " drift." To prevent drifting 
 
 we provide a boat with a "keel" 
 
 or a " centerboard." A keel is a strip 
 
 projecting from bow to stern on the 
 
 bottom of a boat. A centerboard is a 
 
 movable keel. The centerboard can 
 
 be lowered into the water when the 
 
 boat is in deep water, and drawn up 
 
 within the boat when the boat is in 
 
 shallow water. We can illustrate the 
 
 action of the keel by pushing a vertical 
 board side- 
 wise under 
 water. The 
 water re- 
 sists being pushed out of the way, just as air 
 does (cf. 27). 
 
 Use of Wind by the Sail. The sail (Fig. 
 186) is attached so that it can be let out at 
 right angles to the keel, or " hauled in " until 
 it is almost parallel with the keel. Let Fig. 
 187 represent a boat moving in the direc- 
 tion of the keel; that is, forward. The wind 
 is coming from the side, at right angles with 
 the keel. Such a wind is called a " beam 
 wind." It is plain that if the sail were let 
 out competely, no part 
 of the wind would be 
 
 FIG. 185. 
 
 Course of a boat "beating to wind- 
 ward." 
 
 FIG. 186. 
 
 A Sloop under Full Way. 
 Courtesy of Dr. C. F. 
 Millspaugh. 
 
 caught, and there could be no forward motion of 
 the keel. If the sail were drawn in completely, 
 the whole pressure of the wind would be against 
 the keel, and there would be only a sidewise 
 motion, provided the boat was not capsized. But 
 if the sail is set obliquely with the keel, as in Fig. 
 187, part of the force of the wind is used in push- 
 ing the boat sidewise (a motion resisted by the 
 
 FIG. 187. 
 Diagram of a Sailboat. 
 
184 
 
 SIMPLE MACHINES 
 
 Kite 
 
 _ String 
 FIG. 188. 
 
 keel), while another part pushes the boat forward. The more efficient 
 the keel is, the less does the boat drift; the " closer " does it sail "to 
 the wind." 
 
 208. The Kite. While in the sailboat the force of a 
 horizontal wind is changed partly to a force acting di- 
 rectly forward, in the kite a part of the 
 wind's force is made to act vertically 
 upward. If the kite (Fig. 188) is held 
 i Raising vertical, it gets all the force of the wind 
 that strikes it,. and moves off in a hori- 
 zontal direction. This takes place when 
 why the wind Makes a the kite string breaks while the kite is in 
 
 Kite Rise. 
 
 the air. The kite is then only a falling 
 body (cf. 21), acted upon by the wind and by gravity. 
 If the kite were held horizontal, it would catch no 
 part of the wind, like a boat with its sail parallel with 
 the wind. But if the kite is inclined to the wind, the 
 force of the wind is divided into 
 two parts, one of which presses 
 against the kite, and is resisted 
 by the string; while the other 
 part acts vertically upward, and 
 raises the kite into the air. 
 
 209. The Airship. Airships 
 may be of the balloon type 
 (Fig. 189), which rise because 
 they are filled with heated air or 
 other light gases; or they may 
 be aeroplanes monoplanes, 
 biplanes, hydroplanes, etc. 
 
 FIG. 189. 
 
 One of the first Dirigible Airships to 
 Fly in America. Note the whirling 
 propellor in front. Copyright, 
 The International Stereograph 
 Co., Decatur, 111. 
 
THE WINDMILL 185 
 
 which rise, as the kite does, because of the resistance 
 (inertia) of the air (Fig. 190). Only, while the kite uses 
 the inertia of air in motion (wind), the plane airship uses 
 air as matter which resists being pushed out of the way. 
 
 The explanation of the action of the air upon the aeroplane is prac- 
 tically the same as if the aeroplane were still, and the air were in rapid 
 
 FIG. 190. 
 A Modern Wright Flyer. Courtesy of Dr. Orville Wright. 
 
 motion. When the engine forces the planes rapidly forward, the force 
 (resistance) of the air acts in two parts, as with the kite. One of these 
 parts opposes the forward movement of the planes, and must be over- 
 come by the engine. The other portion of the air's resisting force acts 
 vertically upward, and raises the planes, against gravity, into the air. 
 
 210. The Windmill. One of the reasons why farming 
 has developed so rapidly in recent years is that windmills 
 
186 
 
 SIMPLE MACHINES 
 
 have come into such general use in pumping water for the 
 uses of the farm. The windmill relieves the farmer and 
 his family from the drudgery of pumping water, and 
 leaves them free for other labor. The windmill, like the 
 sailboat, kite, and aeroplane, works upon the principle 
 that if wind strikes a plane obliquely, part of the force of 
 
 the wind is exerted in producing 
 forward (or upward) motion. 
 In the windmill the planes (sails) 
 are attached to a hub (Fig. 191) ; 
 as the planes move forward, the 
 hub, or wheel, revolves. The 
 " pin-wheel " we used when 
 children is a miniature windmill. 
 
 For the pumping of water, the re- 
 
 FIQ volving wheel is attached to a piston 
 
 A Dutch Windmill. Copyright The which moves up and down in a pump 
 JatTrrimn n ot StereographC -' De - fcf- 42); water is thus raised out of a 
 
 well or cistern. On windy days the 
 
 windmill pumps the water into a raised tank, from which it can be 
 drawn when there is no wind, and the mill is quiet. 
 
 A recent article states that a village in Alaska, far within the Arctic 
 Circle, is to have its long night, of six months, illuminated by electri- 
 city. The average wind velocity at the village is 20 miles an hour, and 
 a large windmill will operate the dynamo that gives the current for the 
 light (cf. 162). 
 
 211. Summary. The complicated machines used by man are forms 
 of six simple machines: the lever, pulley, wheel and axle, inclined 
 plane, wedge, and screw. 
 
 A machine enables man to exert force more advantageously, but it 
 does not create any energy. 
 
 Power x distance power moves equals weight x distance weight 
 moves. 
 
EXERCISES 187 
 
 Levers are of three classes: 
 
 (1) The fulcrum is between the weight and the power. 
 
 (2) The weight is between the fulcrum and the power. 
 
 (3) The power is between the fulcrum and the weight. 
 Pulleys are wheels over which ropes can be pulled. 
 
 The wheel and axle is a form of the lever used for circular motion. 
 
 The wedge and the screw are really forms of the inclined plane. 
 
 Friction prevents us from getting the full amount of work out of a 
 machine; but some is necessary in order that machines may work at all. 
 
 A sailboat is a device for getting some forward motion out of any 
 wind except one that is " dead ahead." 
 
 The kite gets upward motion out of a horizontal wind. 
 
 The aeroplane gets upward motion by the pushing of its obliquely- 
 set planes horizontally against the air. 
 
 The windmill converts a horizontal wind into circular motion. 
 
 212. Exercises. 
 
 1. What kind of a machine is used for lifting window awnings? 
 A door transom? A weighted window sash? 
 
 2. How could you arrange a system of pulleys so that by pulling 
 downward with a force of 20 Ibs. you could raise 40 Ibs.? 
 
 3. If the crank of a winch (Fig. 179) makes a circle of 36 in. while 
 the rope is wound up 6 in. for each complete revolution of the crank, 
 how much force must I exert on the crank to lift a pail of water weigh- 
 ing 100 Ibs.? 
 
 4. What kind of a machine is a nail, a coffee-grinder, a carpenter's 
 brace and bit, a pendulum bob, a snow plow, a pin-wheel, a door knob, 
 a spoon, a spade, a chisel? 
 
 5. How do you hold your knife and your fork when cutting a tough 
 piece of meat? What kind of machine are these implements then? 
 What machine are the tines of the fork and the blade of the knife? 
 
 6. A man who can exert a force of 100 Ibs. wishes to raise a 300 Ib. 
 barrel into a wagon 3 ft. above the ground. He uses an inclined board; 
 how long must it be? 
 
 7. In loading a wheelbarrow, where should you put the load in order 
 to make the force needed for lifting as small as possible? 
 
CHAPTER XI 
 
 (Term^nTed Fruit Juice) 
 
 ACIDS, ALKALIES, AND CLEANING 
 
 213. Acids. We learned in 5 that no two sub- 
 stances have exactly the same special, or specific, prop- 
 erties. There are, however, many substances that are 
 alike in some particular property or properties. This is 
 true of the substances that make up the class we call 
 " acids," as well as of those we call " bases," or " alkalies." 
 The word " acid " means sour; sourness is a character- 
 istic property of most acids. The juices of ripe fruits 
 
 are sweet because they contain 
 sugar; but when they are ex- 
 posed to the air, the juices " fer- 
 ment": their sugar is changed 
 to alcohol and carbon dioxide. 
 This particular fermentation is 
 due to yeast (cf. 129). The 
 change does not, however, stop 
 here. When the fermented 
 juices, which now contain alcohol, 
 stand longer in the air, they be- 
 come sour, and we have cider vinegar, currant vinegar, 
 wine vinegar, etc. (Fig. 192). The cause of this second 
 fermentation is another plant, known as the " vinegar 
 mould," or " mother of vinegar." The sourness of vinegar 
 is due to acetic acid (cf. 124). In a pure form this is a 
 -colorless, sharp-smelling liquid, which freezes at 16 C., 
 
 188 
 
 FIG. 192. 
 Quick Vinegar Process. 
 
CLASSES OF ACIDS 189 
 
 and blisters the skin. Vinegar usually has only 3% or 
 4% of it. 
 
 The materials present in plants undergo other fermenta- 
 tions besides the one that gives acetic acid. Thus, "Dill " 
 pickles are small cucumbers fermented so as to give 
 lactic add; " sauer kraut " contains the same acid. Sweet 
 milk becomes sour because the milk sugar in it is changed 
 to lactic acid. Pure lactic acid is a thick liquid of very 
 sour taste. 
 
 214. Classes of Acids. It is not only by fermentation 
 of fruit juices that acids are formed. The fruits them- 
 selves, as well as other parts of plants, contain acids. 
 Tomatoes, cherries, rhubarb, etc., are strongly acid. Lem- 
 ons and oranges contain much citric acid; grape juice, 
 much tartaric acid; apples contain malic acid. All of the 
 acids already named in this chapter are compounds of 
 carbon with hydrogen and oxygen (cf. 123). These 
 acids are called organic acids (cf. 3). There are many 
 acids that contain no carbon at all, but have some other 
 element in place of the carbon. These belong to the class 
 of inorganic, or mineral, acids. Thus, nitric acid contains 
 nitrogen, combined with hydrogen and oxygen; sulphuric 
 acid consists of sulphur, hydrogen, and oxygen; phos- 
 phoric acid contains phosphorus, hydrogen, and oxygen. 
 These three acids are all thick, colorless liquids. They 
 are commonly " diluted " with much water. 
 
 All acids contain hydrogen, but not all have oxygen. Thus, hydro- 
 chloric acid (cf. 111) contains only hydrogen and chlorine. This is 
 the acid of the gastric juice (cf. 364). The gastric juice of man con- 
 tains about 0.22 of 1% of it; the adult dog has several times as much. 
 
190 ACIDS, ALKALIES, AND CLEANING 
 
 215. Acids and Coloring Matter. Besides having the 
 property of sourness, acids have a definite action on cer- 
 tain coloring matters, such as purple cabbage solution and 
 litmus. Acids often change the color of the dyes in our 
 clothing. Thus, " navy blue " fabrics are colored red by 
 the common acids of the laboratory. 
 
 Litmus is the coloring matter we generally use in testing 
 for acids. It is a blue substance obtained from certain 
 plants called lichens (cf. 324). Either the solution, or 
 filter paper that has been soaked in the solution, may be 
 used. The prepared paper is called litmus paper. Blue 
 litmus is changed to red litmus by sour plant juices and 
 by other acids. A substance which is able to change blue 
 litmus to red is said to have an " acid reaction." 
 
 216. Action of Acids with Metals. A third important 
 property of acids is that they corrode, or " eat," metals. 
 We have learned that hydrogen is made by the action of 
 some of the acids upon zinc, iron, etc. (cf. 103). When 
 the metals are so used, they are " eaten up," and disap- 
 pear. 
 
 Some metals, such as copper, do not act with dilute 
 acids to give hydrogen (cf. 150) ; but if the metal and the 
 dilute acid are kept in contact with air, the metal is 
 gradually corroded. Here the oxygen of the air acts with 
 the metal to give the oxide of the metal (cf . 48) ; the oxide 
 then reacts with the acid. Copper and lead cannot be 
 used for cooking utensils, because they act with the air 
 and the acids of fruits and other food, producing poisonous 
 compounds. 
 
 Copper is " eaten " very readily by dilute nitric acid. If a design is 
 
ACTION OF ACIDS WITH CARBONATES 191 
 
 painted upon copper with asphalt paint (Fig. 193), and the copper is 
 put into nitric acid, the part not covered by the asphalt is " etched " 
 by the acid. When the asphalt is removed, 
 the design stands out "in relief." 
 
 217. Action of Acids with Carbon- 
 ates. -The action of acids with car- 
 bonates may also be used as a test 
 for acids. Marble (cf. 132) and 
 hydrochloric acid react with much FIG. 193. 
 
 i T i T ^ 13 design may be etched 
 
 effervescence j because carbon dioxide on copper by dilute nitric 
 escapes as a gas (cf. 126). The 
 other product is calcium chloride. It may be obtained as 
 a white solid by the evaporation of its solution. 
 
 The limestone of bones, oyster and clam shells, and 
 of coral is rapidly eaten out by acids, and only the animal 
 material is left. As a result, bones that are treated with 
 acids lose their stiffening. The large amount of acid in a 
 dog's stomach enables him to digest bone. 
 
 Other carbonates react with acids as marble and limestone do. 
 Washing soda is sodium carbonate, which is made up of sodium, carbon, 
 and oxygen. Baking soda is sodium hydrogen carbonate, or sodium 
 bicarbonate (cf. 130). Both washing soda and baking soda effervesce 
 rapidly when an acid is added. The acid used may be tomato juice, 
 sour milk, or lemon juice, as well as a mineral acid (cf. 214). When 
 either of the two " sodas " is treated with hydrochloric acid, there is 
 formed, besides water and carbon dioxide, sodium chloride, or common 
 salt (cf. 108). Soda was formerly rare and expensive; but it is now 
 made, on an enormous scale, from common salt. 
 
 Wood ashes contain potassium carbonate, or " potash." The potash 
 is obtained from the ashes by the use of water. Potash reacts with 
 hydrochloric acid as soda does; but it gives potassium chloride instead 
 of sodium chloride. 
 
192 ACIDS. ALKALIES, AND CLEANING 
 
 218. Alkalies, or Bases. Bases are substances having 
 properties quite different from those of acids. They turn 
 litmus which has been colored red by acids back to the 
 blue color. All substances that do this are said to have a 
 " basic " reaction. The strongest (most active) bases 
 are called alkalies; hence a basic reaction is also called 
 an alkaline reaction. 
 
 The two strongest bases are commonly known as lye. 
 Better names are sodium hydroxide (caustic soda) and 
 potassium hydroxide (caustic potash). As the chemical 
 names show, these substances are composed of hydrogen 
 and oxygen, combined in the one case with the metal 
 sodium, and in the other with the metal potassium (cf. 
 109). Other common bases are ammonium hydroxide 
 ("ammonia water' 7 ; cf. 112) and calcium hydroxide 
 (slaked lime). Calcium hydroxide is the cheapest base. 
 It is made by adding water to calcium oxide (quicklime). 
 Quicklime is made by heating limestone (cf. 132). 
 
 Bases cannot be kept ;f exposed to the air; for they unite with its 
 carbon dioxide (carbonic acid; cf 126) to form the carbonates. Lime 
 that is " air slaked " is largely calcium carbonate. Solutions of potas- 
 sium and sodium carbonates have an alkaline reaction, and behave 
 like weak alkalies in other respects, because they react with water 
 to form small amounts of the hydroxides. 
 
 219. Caustic Soda and Caustic Potash. When sodium 
 carbonate (soda) solution is mixed with " milk of lime," 
 which is slaked lime " suspended " in lime water (cf. 132), 
 a chemical change occurs, and calcium carbonate is formed 
 as an insoluble powder. The sodium hydroxide (caustic 
 soda) remains in solution. 
 
NEUTRALIZATION; SALTS 193 
 
 Sodium carbonate -f calcium hydroxide give 
 (soluble) (soluble) 
 
 Sodium hydroxide + calcium carbonate. 
 
 (soluble) (insoluble) 
 
 The insoluble calcium carbonate settles, and the solu- 
 tion of sodium hydroxide can be poured off. When the 
 solution is evaporated, the sodium hydroxide remains as 
 a white solid. Potassium hydroxide is made in a similar 
 way. 
 
 Both of these solids are very soluble in water; they even 
 attract water from the air, becoming wet, like some 
 candies. They are changed back to carbonates by the 
 carbon dioxide of the air (cf. 218). Their water solutions 
 are " slimy " to the touch (cf. 109), and act vigorously 
 upon the skin, the fats, and other organic matter. The 
 taste of a very dilute solution of these " caustic alkalies " 
 is bitter. Strong solutions destroy the mucous membrane 
 of the mouth (cf. 359) as a hot body would. Hence the 
 name " caustic," meaning burning. 
 
 220. Neutralization; Salts. If caustic soda solution is 
 added drop by drop to hydrochloric acid containing lit- 
 mus, a point is found at which the litmus is neither red nor 
 blue, but has a lavender color. If blue or red litmus is put 
 into the solution, it is either not changed at all, or it be- 
 comes lavender. We say that the caustic soda has neu- 
 tralized the acid. 
 
 We can neutralize the hydrochloric acid by sodium 
 carbonate also; but in this case there is carbon dioxide 
 given off. If the neutral solutions are now evaporated, 
 each will give a residue of cubical, white crystals. The 
 
194 ACIDS, ALKALIES, AND CLEANING 
 
 taste and other properties of the residue show that it is 
 common salt. It is " neutral to litmus," .as we should ex- 
 pect from the method by which it was made. 
 
 If dilute nitric acid is neutralized with soda or with caustic soda, the 
 solid obtained is sodium nitrate; with dilute sulphuric acid the product 
 is sodium sulphate. If potassium carbonate or potassium hydroxide 
 were used with each of these acids, the products would be potassium 
 chloride, potassium nitrate, and potassium sulphate, respectively. Since 
 all of these substances are formed by the neutralization of an acid by a 
 basic substance, just as sodium chloride is, they are all called salts. 
 They have, in general, a salty taste, although there are decided dif- 
 ferences between the tastes. .Calcium hydroxide, or carbonate, if 
 neutralized with these acids, gives calcium chloride, calcium nitrate, 
 and calcium sulphate, respectively. 
 
 221. Tests for Certain Salts. To test for a substance, 
 as we use the word " test " in this section, is to find out 
 whether the substance in question is present or not. We 
 find this by the behavior of whatever is being tested. 
 Thus we can show that a solution contains an acid by 
 using the litmus test, and by the behavior of the solution 
 with metals, carbonates, etc. (cf. 214 to 217). Still, 
 these tests will not distinguish sulphuric acid from many 
 other acids. But if we apply the test for sulphates, in addi- 
 tion to the other tests, then there can be no doubt. Tests 
 " work " because no two 'substances behave exactly alike, 
 or have exactly the same properties (cf. 5). 
 
 In testing for a salt we ask ourselves two distinct ques- 
 tions : 
 
 (1) What metal does it contain? 
 
 (2) To what acid is it related; that is, is it a sulphate, a 
 chloride, or what? 
 
TESTS FOR CERTAIN SALTS 195 
 
 If a salt turns, out to be a calcium salt and also a car- 
 bonate, it must be calcium carbonate. If we get a test for 
 a sodium salt, and also for a chloride, the substance tested 
 must be sodium chloride. 
 
 1. Chlorides. We test for a chloride (including hydrochloric 
 acid) by dissolving the substance in distilled water, adding enough 
 dilute nitric acid to give the solution an acid reaction (cf. 215), and 
 by then adding a drop or two of silver nitrate solution. If a chloride 
 is present, there will be a white precipitate of silver chloride, an insoluble 
 solid. If we shake up the precipitate, it will clot together. If we pour 
 some of it upon filter paper, and expose it to sunlight, it becomes dark. 
 This last fact is the basis of modern photography (cf. 188). 
 
 2. Sulphates. We test for sulphates (including sulphuric acid) 
 by adding to the solution of the substance some dilute nitric acid, and 
 then a few drops of a solution of barium chloride or barium nitrate. If 
 a sulphate is present, there will be a, white precipitate of barium sul- 
 phate. 
 
 3. Nitrates. To test for a nitrate we first make a saturated solution 
 of ferrous sulphate. To about 5 c.c. of this solution, in a test tube, we 
 add a few drops of the solution to be tested, and mix it, by shaking, 
 with the ferrous sulphate solution. We then tilt the test tube, and pour 
 down its side about 5 c.c. of concentrated sulphuric acid. The heavy 
 acid slides underneath the solution, and when we hold the tube up-. 
 right, we find a brown layer or ring between the solution and the acid, 
 provided a nitrate is present. 
 
 4. Carbonates (either the solids or their solutions) are tested for by 
 means of dilute hydrochloric or nitric acid. Effervescence takes place, 
 and we prove that the escaping gas is carbon dioxide by passing it 
 into lime water. A white precipitate of calcium carbonate is formed 
 (cf. 126). 
 
 5. Phosphates. We test for phosphates in solution by adding to 
 the solution, first, a few drops of concentrated nitric acid, and then 
 a solution of ammonium molybdate. A yellow solid is precipitated, if 
 phosphates are present. 
 
 6. Iron Salts. Solutions suspected of containing iron are treated 
 
196 ACIDS, ALKALIES, AND CLEANING 
 
 ivith a few drops of concentrated nitric acid, and boiled for a few 
 minutes. Then a few drops of a solution of potassium thiocyanate or 
 .ammonium thiocyanate are added. A blood-red solution results; this 
 is pink if only a little iron is present. 
 
 7. Sodium Salts are tested for by the bright, yellow flame they give 
 when they are held, on a platinum wire, in the colorless gas flame (cf. 
 240). 
 
 8. Potassium Salts give a violet color to the colorless gas flame. The 
 color is seen best when it is viewed through blue glass; this cuts off the 
 yellow rays of sodium. 
 
 9. Calcium Salts. We test for a calcium salt by treating its solu- 
 tion with ammonia water and a solution of ammonium oxalate (the 
 ammonium salt of oxalic acid). A white precipitate of calcium oxalate 
 is formed. We pour off the liquid portion from the precipitate, and 
 .add dilute acetic acid to the precipitate. If the precipitate is really 
 calcium oxalate, it will not be dissolved. 
 
 10. Ammonium Salts. We test for ammonium salts by adding 
 them, in solution, to a small lump of quicklime, or about 5 c.c. of sodium 
 hydroxide solution, and warming the mixture gently. Ammonia is 
 ;given off, and can be known by its odor. 
 
 222. Exercises. 
 
 1. Why do we add soda to tomatoes in making " cream tomato " 
 ;soup? How do sour milk and soda " raise " biscuits? Why do straw- 
 berries curdle milk? 
 
 2. How could you tell whether a soil was " sour " or not? 
 
 3. Lime water is often added to milk before the milk is given to a 
 child or an invalid; why? 
 
 4. " Galvanized iron " is iron covered with zinc. Is it a safe material 
 for utensils in which fruits are cooked? Why? Is " tinned " iron 
 .safer? Why? 
 
 5. What base would you use if you wished to make some potassium 
 nitrate by neutralization? What acid would you use? How would 
 you tell when you had used just the right amount of each? 
 
 6. In moist weather, laboratory bottles sometimes lose their labels. 
 If this occurred, how could you tell whether a certain solid was, or was 
 
THE WASHING OF CLOTHING 197 
 
 not, calcium carbonate? Ammonium sulphate? Sodium nitrate? 
 Iron chloride? 
 
 223. The Washing of Clothing. We must now apply 
 what we have learned about acids, bases, and salts to some 
 
 FIG. 194. 
 
 Modern Laundry. The illustration shows an electric-power tub for washing ; one for rinsing ; 
 
 a hot mangle, or ironer; a cold mangle; electric irons, and laundry tub. Courtesy 
 
 of the Department of Home Economics, Cornell University. 
 
 common household practices. We begin with the washing 
 of clothing (Fig. 194). 
 
 Clothing that has been worn too long has a damp, 
 sticky feeling. It has this feeling because its pores are 
 clogged with the materials given off by the skin. These 
 consist of perspiration, of organic waste which the body 
 casts off through the skin, and of dead skin itself. When 
 these fill the pores of clothing, it is unfit to wear, whether 
 it looks dirty or not. The evaporation of the perspiration 
 regulates the temperature of the body (cf. 74), and the 
 clothing should aid, not hinder, this evaporation. The 
 reason why clean garments feel so comfortable is largely 
 because they have a fresh absorbing surface. 
 
198 
 
 ACIDS, ALKALIES, AND CLEANING 
 
 We should have clean bodies for the same reason that we should 
 wear clean clothing, if for no other; viz., in order that the pores of the 
 skin may be permitted to act freely in removing waste, and in evaporat- 
 ing the perspiration. 
 
 The washing of clothing thus has three objects: 
 
 (1) To remove dirt, and to open the pores of the clothing. 
 
 (2) To dry the washed clothing, and to give it a new absorbing 
 surface. 
 
 (3) To destroy the bacteria which are sure to accumulate in the 
 dirt of the skin and clothing. 
 
 224. Soap. To remove dirt we need not only water, 
 but soap. Soap is a salt, or a mixture of salts. The metal 
 
 (cf. 221) present in hard 
 soaps is sodium; in the old- 
 fashioned soft soaps (Fig. 
 195) it was potassium. The 
 acids to which the soaps are 
 related (cf. 221) belong to 
 the class of "fatty" acids, so 
 called because they are ob- 
 tained from the fats. Ex- 
 amples of the natural fats 
 are beef suet, mutton tallow, 
 and lard. Oils are liquid 
 fats. Strictly speaking, we 
 cannot call petroleum products or coal-tar products, 
 such as kerosene or benzene, oils at all. Palm oil, olive 
 oil, and cotton-seed oil are true oils. Soaps are made by 
 the boiling of fats and oils with alkalies. 
 
 When fat is heated with sodium hydroxide, it is " cut," 
 or "saponified." Saponify is from the Latin sapo (soap), 
 and means " to make into soap." As a result of the boil- 
 
 FIG. 195. 
 
 Old Way of Mnking Soap from Grease 
 and Potash L., e. Negative by T. B. 
 Magath. 
 
SOAP 199 
 
 ing with alkali, the fat disappears into solution ; it is changed 
 into the sodium salt (soap) and glycerine. Both of these 
 are soluble; but when salt is added to the solution the soap 
 is "salted out/' and floats on top of the solution. It is then 
 skimmed off, pressed, and cut into cakes. 
 
 FIG. 196. 
 
 Modern Way of Making Soap. The kettle is three stories high, and holds perhaps 275,000 
 Ibs. : enough to make, say, 700,000 bars of soap. Courtesy of Swift and Company. 
 
 In many modern soap factories (Fig. 196) the fat is 
 first heated with steam. The products are then glycerine 
 and the fatty acids. The soap is made from the fatty acids 
 and sodium carbonate (instead of the hydroxide). Gly- 
 cerine is a very valuable " by-product " of the soap fac- 
 tory. 
 
 Until a few decades ago soap was made in the home. In the spring 
 the winter's accumulation of wood ashes was pounded down into a 
 barrel, and set on a platform to be " leached," or extracted by water. 
 A hole was made in the ashes, water was poured into it, and the solu- 
 
200 ACIDS, ALKALIES, AND CLEANING 
 
 tion of potash that was formed trickled out into little troughs in the 
 platform. The solution was collected in kettles, and boiled down to 
 form the home-made lye. A kettle of fat was melted over an open fire, 
 the lye was added to this, and the two were cooked together, often for 
 two or three days. The resulting " soft soap " was put away in barrels 
 for the next year's use. 
 
 225. Action of Soap. When a sodium soap is dis- 
 solved, it is partly broken up, by the action of the water, 
 into sodium hydroxide and the fatty acids (cf. 218). 
 The sodium hydroxide acts upon the fats and oils of the 
 skin and clothing, and partly converts them into soaps, 
 so that they also are dissolved by the water. In using 
 soap we are using lye in a most convenient form, for its 
 caustic properties are so altered that it can cleanse fabrics 
 and the skin without injuring them. Toilet soaps are 
 " neutral to litmus," because an excess of fat is used, so 
 that the amount of free alkali is small. Laundry soaps 
 have more free alkali. 
 
 Soap has not only this chemical action, but the lather, 
 or suds, acts mechanically, entangling the undissolved fat, 
 dead skin, and dirt, and removing them. 
 
 226. Soap and Hard Water. We have already learned 
 (cf. 82) that the hardness of water is its soap-consuming 
 power. Hardness is due to dissolved salts, especially 
 calcium carbonate (limestone) and calcium sulphate 
 (gypsum). When soap is put into a hard water, it acts 
 with these salts, forming the calcium salts of the fatty 
 acids. These are insoluble, and separate as a scum, called 
 lime soap. If soap is used in sufficient amount, it will 
 soften such a water; but soap is too expensive. Besides, 
 
MATERIALS OF CLOTHING 201 
 
 the lime soap gets into the pores of the fabric, and in- 
 jures it. 
 
 If a soft water cannot be obtained in any other way, a method of 
 " softening " should be used. To remove permanent hardness from a 
 laundry water we often use soda or borax. Borax is sodium borate. 
 
 Sodium carbonate (or borate) + calcium sulphate give 
 (soluble) (soluble) 
 
 sodium sulphate + calcium carbonate (or borate). 
 
 (soluble) (insoluble) 
 
 The sodium sulphate left in the solution has no action with the soap. 
 Both temporary and permanent hardness may be removed at one opera- 
 tion by the correct amount of ammonia water or caustic soda. 
 
 Washing powders also precipitate hardness. They are usually soda 
 or potash, or dried soap containing an excess of alkali. 
 
 227. Materials of Clothing. Two common vegetable 
 fibers used for clothing and in the household are cotton 
 and linen. Cotton is the covering of the seed of the cotton 
 plant; while linen is found in the stalks of flax. Both are 
 chiefly cellulose (cf. 123). 
 
 Although cotton and linen are much alike chemically, 
 they are very different physically. Both consist of hollow 
 tubes (Fig. 197); but the fibers of cotton are flat and 
 twisted, while those of linen are nearly straight, and have 
 thick walls with a central opening. 
 Linen cloth is stronger than cotton, 
 but cotton is lighter and more elastic. 
 
 Cotton and linen are easily de- 
 stroyed by mineral acids (cf. 214), Woo( - 
 if these are strong or are allowed to Fiberg /'^ Linen 
 dry upon the fabric. They are not ering ol of thewooi! scaly 
 
202 ACIDS, ALKALIES, AND CLEANING 
 
 so easily harmed by alkalies. In fact, if cotton is treated 
 with strong alkali for a short time, and is then washed 
 thoroughly, it is actually made stronger, and has a glossy, 
 silky appearance. Cotton so treated is called mercer- 
 ized cotton. 
 
 Wool and silk (Fig. 198) are of animal origin, and con- 
 sist not only of carbon, hydrogen, and oxygen, as cellulose 
 does, but contain nitrogen also (cf. 
 123). They are the opposites of cotton 
 and linen in chemical behavior; for 
 they are not readily acted upon by 
 acids, but are easily destroyed by 
 FIG. IDS. alkalies. The fibers of wool are entirely 
 
 Co t c he siik"orm. ibers f different from those of linen and cotton. 
 Instead of consisting of long cells, wool 
 is made up of short, thick cells, with the projecting edges 
 of each lapping over part of the one next to it (Fig. 197). 
 The surface thus appears to be covered with horny scales 
 all lying in one direction. No method of washing wool 
 should be used that will force the cells closer together, 
 or the wool will shrink, and finally become stiff and 
 board-like. 
 
 228. Dyes. Dyes are colored compounds that are 
 either absorbed by the pores of a fiber, or combine chemi- 
 cally with the fiber to form a colored, insoluble compound. 
 Silk and wool are much more active chemically than cotton 
 and linen. Hence silk and wool can combine directly 
 with many more dyes. We can think of the process of 
 dyeing cloth as a reaction much like that which occurs 
 when an acid and a base unite to form a salt (cf. 220). 
 
PAINTS 203 
 
 Since cellulose combines with very few dyes directly, it and the 
 dye must be held together by a third substance, which can unite with 
 the cellulose on the one hand, and with the dye on the other. Such 
 a substance is called a mordant. Here, also, we can look upon the 
 dyeing process as a reaction between acids and bases; only there are 
 three substances in the reaction instead of two. The final, complex salt 
 is the dyed fabric itself. 
 
 Aluminum hydroxide is a common mordant. It is insoluble, and it 
 is sticky, like boiled starch. It is formed in the fibers of cloth when we 
 soak the cloth in aluminum acetate, and then in ammonia water. In the 
 making of calico the pattern is first printed on cotton cloth with a 
 mordant, and the cloth is then soaked in a dissolved dye. Tne dye com- 
 bines with the mordant, but not with the cloth alone. The uncom- 
 bined dye is washed out. If different parts of a pattern are printed 
 with different mordants, a number of colors can be made from 
 the same dye. 
 
 229. Paints. Common paint consists of linseed (flax 
 seed) oil and turpentine, mixed with " white lead," or 
 " zinc white/' and a pigment to give color. White lead, 
 etc., are compounds used to give the paint " body " or 
 "covering power." The turpentine not only thins the 
 paint, but assists in drying the oil. 
 
 When paint dries, its linseed oil is oxidized by the air to 
 a hard gum. Considerable heat is given off in the process; 
 hence heaps of cloths containing paint or linseed oil often 
 take fire without an apparent cause (" spontaneous com- 
 bustion "). Such cloths should never be left about a 
 building except in covered metal boxes. 
 
 To remove a paint stain from a fabric we need usually 
 remove only the linseed oil. This is soluble in benzine, 
 gasoline, etc. When we have removed the oil, we can 
 generally remove the white lead by brushing or rubbing. 
 
204 ACIDS, ALKALIES, AND CLEANING 
 
 When we use gasoline as a cleaning agent, we should 
 take great care to remain away from a fire. Especially 
 should we use care in rubbing silk that is wet with gaso- 
 line, lest the gasoline may be set on fire. 
 
 230. Removal of Stains. When we wish to remove a stain from a 
 fabric, we should consider whether the substance causing the stain 
 must be changed chemically, or whether it can be removed by physical 
 means. Thus, paraffin (" white wax "), the material of many candles, 
 especially of colored candles, is not a fat, and cannot be saponified by 
 lye and soap. It is, however, readily dissolved by benzine, gasoline, 
 or ether, and can thus be removed. An excellent way is to wet the 
 paraffin spot with benzine, and then to press it, by means of a flat iron, 
 between blotters. 
 
 Milk and cream stains, if fresh, are washed out with cold water. If, 
 however, they are old stains, the water of the milk will have evaporated, 
 leaving the fat in the fiber. To remove them we use soap and water, 
 or ammonia water, or we moisten the spot with benzine and press it 
 between blotters. Ammonia water, like soap and lye, saponifies the 
 fat and makes it soluble. 
 
 Iron rust must be removed by chemical means. It is a base (ferric 
 oxide or hydroxide) ; hence we use an acid to remove it. Dilute hydro- 
 chloric acid (cf. 111), lemon juice and salt, etc., are commonly used. 
 The acid must then be rinsed out and neutralized. 
 
 Ink stains are often hard to remove, because we cannot be sure of 
 what the ink is made. Fresh ink stains are usually taken out by fresh 
 milk. Old stains are soaked in water, and treated with oxalic acid 
 (10% solution). The acid is a poison. It should finally be rinsed out 
 with water, and neutralized by a mild base like borax or ammonia 
 water. 
 
 Old-fashioned inks contained iron compounds; hence stains caused 
 by them are treated like iron rust. 
 
 We must remember that most active chemicals, such as acids and 
 bases, affect dyes (cf. 215); hence they can rarely be used to remove 
 stains from colored fabrics. The cleaning agent should be used with a 
 piece of the goods, before it is applied to the garment. Acids spilled 
 
EXERCISES 205 
 
 on cloth should be washed out at once with water, and the spots treated 
 with a solution of baking soda, borax, etc. Ammonia should rarely 
 be used to neutralize acid spots on colored goods; it may react with the 
 dye, as well as with the acid we wish to neutralize. 
 
 231. Summary. Acids are the sour substances present in fruit, 
 vinegar, pickles, etc. They are either organic or inorganic. Inorganic 
 acids are also called mineral acids. 
 
 Acids act upon coloring matter, metals, carbonates of metals, bases, 
 and fabrics, especially upon cotton and linen. 
 
 Alkalies are the strongest bases. They turn litmus blue, destroy 
 skin and flesh, saponify fats, neutralize acids, and destroy fabrics, 
 especially wool and silk. 
 
 Neutralization is the chemical action between an acid and a base. 
 After neutralization the solution contains a salt. 
 
 Testing for salts consists in finding the metal present in them, and 
 the acid to which they are related. 
 
 Washing of clothing is for the purpose of removing dirt, opening the 
 pores of the cloth, and destroying bacteria. 
 
 Soap is the sodium salt of certain fatty acids; it is made by the boil- 
 ing of alkalies with fat, and is soluble in water. 
 
 Soft water and soap give alkali and organic acid in mild form. Hard 
 water first gives a lime-soap scum. Hard water is " softened " by soap, 
 soda, borax, ammonia water, etc. 
 
 Cotton and linen consist of long hollow fibers of cellulose. 
 
 Wool consists of short, thick cells having overlapping scales. 
 
 Silk and wool can be dyed directly more easily than cotton and linen. 
 
 Mordants are substances used to unite the dye to the fabric. 
 
 Paint generally consists of linseed oil, turpentine, a pigment, and 
 lead white, or some other substance with "covering" power. 
 
 Stains are removed sometimes by physical, and sometimes by 
 chemical means. 
 
 232. Exercises. 
 
 1. If you have spilled dilute hydrochloric acid upon woolen cloth- 
 ing, what should you use to neutralize the acid and to restore the color? 
 Would caustic soda do? Why? 
 
206 ACIDS, ALKALIES, AND CLEANING 
 
 2. Why is it not enough to wash clothing in cold water, even with 
 soap? Why is not enough to use hot water, without soap? 
 
 3. Commercial laundries sometimes use acids, such as hydrochloric 
 acid, for the washing of clothing; why is this not a good practice? 
 What fabrics especially are injured? 
 
 4. Why should wool be washed with mild soaps, and in warm, but 
 not hot, water? 
 
 5. How could you test a soap for an excess of alkali? 
 
 6. Why does not a soap give a lather as quickly in well water as in 
 rain water? 
 
 7. Why is " blueing" used in the laundering of white goods? 
 
 8. Why do not men make soap out of petroleum and lye? 
 
 9. Why should oily cloths piled in a heap take fire spontaneously, 
 while if outspread they do not? 
 
 10. What causes the "scum" that forms on the surface of an open 
 can of paint? Gasoline and benzine are cheaper than turpentine; are 
 they good substitutes for it? Why? 
 
CHAPTER XII 
 
 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 233. Modern Conveniences. In no respect does 
 modern life differ more greatly from that of the past 
 than in home comforts and conveniences. Ancient and 
 medieval peoples built larger monuments, and more 
 enduring tombs and temples, than we are building; but 
 the homes of the people were cheerless indeed when 
 compared with those of American cities to-day. Even the 
 wealthy could not always have heat, light, and water 
 in abundance; consequently the winter was full of dis- 
 comfort, houses were insanitary and dark, and filth and 
 dirt were everywhere the rule. The cleanliness, light, 
 and warmth of our houses, schools, and public buildings 
 are due to modern scientific discoveries and their appli- 
 cation. 
 
 234. Water in House and Town. We have already 
 considered the need of pure water (cf. 81 to 85, and 
 226) ; we must also remember that modern man needs an 
 abundance of water. In our houses we need it for drink- 
 ing, for cooking, and, as ice, for preserving food ; for bath- 
 ing the body, washing dishes and clothing, spraying 
 lawns and gardens, and carrying waste matter into the 
 sewage system. The industries of the city need it for 
 producing steam, for washing and rinsing on a large scale, 
 
 207 
 
208 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 as in laundries, tanneries, slaughter houses, starch fac- 
 tories, sugar refineries, gas works, petroleum refineries, 
 dye works, paper mills, etc. The community as a whole 
 needs it for protection against fire, and to carry away its 
 sewage. 
 
 Some cities pump water into "standpipes," or elevated 
 reservoirs, from which it flows, under pressure, into the 
 street " mains," and then into the houses; others use 
 force pumps of large capacity (cf. 42) ; others, still, have a 
 combination of both systems, using the reservoirs to assist 
 the pumps when there is the greatest demand for water, 
 as at meal-cooking time, or when there is a serious fire. 
 
 In order to get enough water, great cities go to enormous expense. 
 The Romans built great aqueducts (Fig. 199) to bring water from the 
 
 lakes of the Apennines to 
 Rome. New York City now 
 gets its water, through an 
 aqueduct, from the Catskills, 
 90 miles away. Denver is 
 fortunate enough to be sur- 
 rounded by mountains having 
 many streams of pure water; 
 this is allowed to flow through 
 pipes, by gravity, to the city. 
 Los Angeles gets its water 
 , from mountains many miles 
 
 How water may be carried under a river. 
 
 away. The cities on or near 
 
 the Great Lakes use lake water; but they take great care to prevent 
 the sewage from the city from polluting the water intended for the 
 city. Chicago has built an expensive " Drainage Canal" to carry 
 water from Lake Michigan into the Illinois River, and thus to empty 
 the city's sewage into the Mississippi instead of into the lake system. 
 Inland cities usually get their water supply from a near-by stream; 
 but such water needs careful filtration. 
 
 199 
 
HYDRANTS AND TRAPS 209* 
 
 235. Plumbing. In some cities water is sold to con- 
 sumers at a "flat rate/ 7 without regard to the amount 
 used. Other cities use a meter, or measuring device,, 
 which records the amount that actually flows from the 
 street mains into the house. The pipes, faucets, traps, 
 etc., through which water is carried to the different parts 
 of the house, or away from it, make up the plumbing of 
 the house. The word "plumbing" is from plumbum, 
 Latin for "lead." To make lead pipes, men force hot 
 lead, under great pressure, through steel dies having 
 ring-shaped openings. Nowadays iron pipes, as well 
 as lead ones, are used for plumbing. The iron is " gal- 
 vanized" to prevent rusting (cf. 222, Ex. 4). 
 
 Lead is used for pipes, sink linings, etc., because it is 
 not rusted readily (cf. 216). Lead pipes .are also easy 
 to bend around corners and into special shapes. Then, 
 too, they can be cut readily where necessary, and the 
 pieces joined by solder. 
 
 But the use of lead has one disadvantage, in that the fresh surface 
 of the metal is acted upon, and dissolved, by water. When lead is 
 taken regularly into the body, as in drinking water, it accumulates until 
 it causes sickness. Painters often have "painters' colic" because of 
 the lead compounds in paint (cf. 229) . Lead is not acted upon greatly 
 by pure water; but air and soft water, especially if carbon dioxide is 
 present (cf. 80, table), gradually " dissolve" it. Hard water acts. 
 upon the inside of the pipe after a time, and produces a coating that 
 does not dissolve. This protects the lead and the water. We should 
 always let water run for a moment from a new lead pipe, so as to make 
 sure that the water we drink is free from lead compounds. 
 
 236. Hydrants and Traps. Faucets, or hydrants, are usually of 
 brass, sometimes plated with nickel. They are generally of two kinds: 
 
 (1) Those having a movable, tapered plug with a hole in it. 
 
210 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 (2) Those in which the opening is closed by a rubber " plunger," or 
 "gasket." 
 
 Waste water, like that from a sink or bowl, is discharged into the 
 sewer pipe through a trap (Fig. 200). This is a bend in the pipe, 
 which remains full of water, and cuts off connection between the air of 
 the room and that of the sewer. Water should be 
 -From sink run every few days into sinks and floor drains that 
 are little used, so that the traps may always be full. 
 
 237. Kindling a Fire. The discovery 
 Drain Plug of fire came long before the dawn of history. 
 
 To Waste Pipe j. ... , 
 
 Fig 200. Many primitive peoples still start their 
 
 A Trap. fij. es ^y ru kk m g one pi ece of wood against 
 
 another. The friction gives the temperature needed to 
 set on fire the bits of bark, pitch, dry fungus, etc., that 
 serve as tinder (cf. Fig. 63, 76). A century ago the 
 kindling method used in Europe and America was to 
 strike steel or iron pyrites (a compound of iron and sul- 
 phur) against flint. In the flintlock musket this method 
 was used to kindle gunpowder. 
 
 The first practical friction matches were made about 
 1827. They consisted of wooden splints partly coated 
 with sulphur, and tipped with potassium chlorate, anti- 
 mony sulphide, and gum. Friction against a rough sur- 
 face produced heat enough to make the sulphur unite 
 with the oxygen of the potassium chlorate, and the heat 
 of the burning sulphur set the wooden splint on fire. The 
 "parlor" match has a tip containing paraffin or sulphur, 
 yellow phosphorus, and some oxidizing substance like 
 potassium chlorate or "red lead." Glue is used to make 
 all the substances adhere to the wood. 
 
 Parlor matches are ignited much more easily than 
 
THE FIREPLACE 211 
 
 sulphur matches; in fact, they often cause accidental fires. 
 Another serious trouble with the parlor match is that it 
 is deadly to the workmen (and these are largely women 
 and children) who handle it. They are frequently at- 
 tacked by a dreadful disease called "phossy jaw." For 
 these reasons many governments forbid the use of parlor 
 matches. 
 
 Safety matches are less convenient to use than other forms, because 
 they must be struck against the surface of the box; but they are not so 
 likely to take fire, and are much less dangerous to make. The reason 
 for this is that safety matches use red phosphorus, instead of the more 
 active yellow form, and that the phosphorus is on the striking surface 
 instead of on the splint itself. The striking surface is red phosphorus 
 and sand; the tip contains antimony sulphide, some oxidizing substance, 
 and glue. A " strike anywhere" match is now being made with phos- 
 phorus sulphide, a substance that does not cause the evil effects of 
 yellow phosphorus. 
 
 238. The Fireplace. It is hard for us to realize that 
 modern methods of heating are of such recent origin that 
 our grandparents, or certainly our great-grandparents, 
 lived at a time when all of these methods were little 
 known, and when the heating and much of the lighting 
 of the house was done by the open fireplace (Fig. 201). 
 No modern method of heating brings into the house the 
 cheer and sentiment that belonged to the fireplace; hence 
 men try, whenever possible, to use it as an ornament, no 
 matter what system they use for the actual heating. But 
 the fireplace is more than an ornament, for it is one of 
 the best means of ventilation (cf. 248), carrying out the 
 foul, cooled, lower air, and making room for the warmed, 
 fresh air that is so much needed for health and comfort. 
 
 The accessories of the fireplace were numerous. The necessary 
 
212 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 ones were the crane, a swinging frame from which the cooking utensils 
 were hung, and the andirons, or "dogs," used to hold the fuel up from 
 the hearth, so that the air might have better access. In large fireplaces 
 a huge "backlog" was used. This was placed at the back of the fire, 
 while smaller pieces of fuel were laid on the andirons, before it. The 
 
 Fig. 201. 
 The Fireplace of a Modern Living Room. 
 
 backlog often lasted for days, and from it the new fire was built in the 
 morning. 
 
 239. Stoves. In a stove the heat produced by burn- 
 ing fuel can be used in a more economical and convenient 
 way than in the fireplace. Stoves are usually of cast iron 
 or steel. The best surfaces for absorbing and radiating 
 heat are not highly polished and plated, but roughened 
 and black (cf. 181). In a cooking stove both the top 
 and the oven must be heated. To heat the oven evenly, 
 we rieed specially constructed flues, or outlets. If the 
 h'ot gases formed in burning are allowed to escape at once, 
 
GASOLINE AND KEROSENE STOVES 213 
 
 there is great waste of fuel; for only the top of the stove 
 is heated. But the cook stove has a "back damper" 
 which compels these gases to travel in a roundabout way, 
 heating a large surface of the oven before they enter the 
 pipe leading to the chimney. Wood and coal stoves have 
 a slightly different construction. 
 
 240. Gas Stoves. Gas stoves are rapidly taking the 
 place of wood and coal stoves, wherever gas can be ob- 
 tained. The gas used for lighting has a smoky flame, 
 and deposits soot. To avoid the soot, and to secure a 
 hot flame, we use the principle of the Bunsen 
 
 burner (Fig. 202). In this burner the gas 
 escapes through a pin-hole into a mixing tube. 
 The tube has air holes near the gas inlet. The 
 small, rapid current of gas draws the air into 
 
 these air holes, and the mixture of air and gas 
 
 burns at the top of the burner. The flame is Fi g . 202. 
 smaller than if the gas were burned directly; 
 but it is also hotter. Since the gas is mixed thoroughly 
 with air, the flame is smokeless. Smoke, or soot, repre- 
 sents wasted fuel. 
 
 If the supply of air taken in by the Bunsen burner is 
 too great for the amount of gas, there is a slight explosion 
 in the mixing tube, and the flame "strikes back" to the 
 narrow opening inside the burner. If we regulate the 
 gas supply and the size of the air holes, this will rarely 
 take place. In gas stoves the air holes are at the front, 
 near the openings through which gas enters. 
 
 241. Gasoline and Kerosene Stoves. The gasoline 
 burner is essentially a Bunsen burner. To light the 
 
214 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 gasoline stove we run some of the gasoline into a "cup," 
 and there burn it to heat the vaporizer. When the 
 vaporizer is hot, we allow the liquid gasoline to enter it 
 very slowly ; it is there changed to the gaseous form. Air 
 is drawn into the burner by the current of gasoline vapor, 
 and the mixture burns at the top of the burner with a 
 very hot flame, as in the case of gas. 
 
 The use of gasoline is attended with some danger unless the stove is 
 of good construction, and unless great care is taken in handling it. 
 People think of gasoline as a liquid. They should rather think of it as 
 a gas. It boils very low (60 to 70 C.), and what seems to be only a 
 little of the liquid may give a great deal of the vapor. The vapor 
 forms a very explosive mixture with air. Reservoirs should not be 
 filled when fires are anywhere about, and if any gasoline is spilled, 
 the room should be thoroughly aired before a burning body is brought 
 into it. 
 
 Kerosene burns with a smoky flame, and has a high boiling point 
 (150-250C.; cf. 121); hence burners using it must have hotter 
 vaporizers and a greater air supply than gasoline burners. 
 
 242. Electric Stoves and Heaters. The great advan- 
 tage of electric heating is leading to its use on a con- 
 stantly larger .scale (cf. 157). The electric flat-iron 
 (Fig. 194, 223) requires no hot range to heat it, nor any 
 particular room for its use, but may be used wherever 
 there is an electric "outlet." The electric stove needs no 
 flue, and heats without fuel or odor. The electric heating 
 pad is far superior to the hot-water bag, for it does not 
 grow cold. But electric heating appliances, like all others, 
 require care; if overheating occurs in the circuit, there is 
 serious danger of fire (cf. 258). 
 
 243. Hot Water and Steam Heating. The hot-air 
 furnace has been described already (cf. 67). It brings 
 
THERMOSTAT 
 
 215 
 
 Overflow Pipe- 
 
 warm air into the house, because it sets up convection 
 
 currents. Hot-water heating systems (Fig. 203) depend 
 
 upon the convection currents set up in cold water 
 
 when one part of the 
 
 water is heated. The 
 
 heating is done in a 
 
 furnace, and the water 
 
 heated, being lighter than 
 
 the colder water in the 
 
 pipes and radiators, rises 
 
 to take its place. The 
 
 cooler water flows back 
 
 to the furnace, to be 
 
 heated. A "standpipe" 
 
 in the attic keeps the 
 
 radiators full of water. 
 
 In steam heating, a furnace 
 is used to convert water into 
 steam, and the heat given off 
 by the steam, as it cools and 
 condenses (cf. 89), warms 
 
 the house. The hot water remaining after condensation returns to 
 the boiler to be reconverted into steam. 
 
 244. Thermostat. We have already learned that a 
 thermometer tells us temperature by registering the 
 difference in expansion between mercury and glass (cf. 
 62). We could also make a thermometer out of two 
 metals that expand different amounts when heated 
 through the same degrees of temperature. Thus, we can 
 rivet together a small bar of iron and one of brass so that 
 the resulting compound bar is straight when cold ; but when 
 
 Fig. 203. 
 Hot Water Heating System. 
 
216 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 the bar is heated, the unequal expansion of the two metals 
 will produce a curved bar. If we fasten one end of the 
 compound bar, leaving the other end free, the free end 
 will be able to push against a pointer, and so to record the 
 temperature. 
 
 In the thermostat (Fig. 204), an instrument used to 
 regulate the temperature of a room, the bar is made a 
 part of two electric circuits; it will permit 
 the current to flow in one circuit when the 
 room becomes too warm, and through the 
 other circuit when the room becomes too 
 cold. Electromagnets in the two circuits 
 control the supply of steam, hot water, etc., 
 turning it on or off as needed. 
 
 245. Exercises. 
 
 1. What is the source of the water in the city in 
 which you live? Is the water hard or soft? Is it 
 purified in any way before it enters the mains? How 
 large are the mains? Is your city water ever tested 
 for impurities? What have been the results of the 
 tests for the last two months? How much does your 
 family pay for water? How many cubic feet of water 
 does your family use in a month or in a quarter? 
 2. What is the form of the plumbing " traps " in your house? Are 
 they like the trap shown in Fig. 200? If your basement or barn has a 
 floor drain, find out the form of the trap, and describe it. 
 
 3. How are the outside faucets of your house emptied to prevent 
 the water in them from freezing in winter? Why not let the water 
 freeze in them? 
 
 4. Suggest some ways of kindling fire without the use of friction. 
 
 5. Show that the wood and coal cook stove is really an improved 
 form of fireplace. Show that the fireplace fire is an improved form of 
 the open fire built against a rock. 
 
 Fig. 204. 
 
 Thermostat. I f 
 the room be- 
 comes too warm, 
 the brass ex- 
 pands more than 
 the iron, and 
 turns the rod to 
 the right; so that 
 it makes a circuit 
 which cuts off 
 the heat. 
 
NEED OF VENTILATION 217 
 
 6. In what way are gasoline cans commonly distinguished from 
 cans for kerosene? Why? 
 
 7. What is the cause of the " pounding" often. heard when steam is 
 first turned on in a cold radiator? 
 
 246. Need of Ventilation. The changes that take 
 place in air during breathing have been given in 52. 
 Ventilation means the supplying of fresh air and the 
 removing of foul air. Our houses give us shelter, warmth, 
 and a host of comforts; but they usually rob us of air. 
 When the open fireplace was used, ventilation required 
 little thought; for the large volume of air that passed out 
 through the chimney was constantly replaced by fresh 
 air drawn in through cracks around doors and windows, 
 and even through chinks in the walls. But as men have 
 built tight-walled houses, used weather strips and storm 
 windows in winter, and replaced the fireplace by stoves, 
 furnaces, and steam and hot water heaters, this natural 
 ventilation has largely disappeared. It is a common 
 experience of doctors that many people who are healthy 
 enough in warm weather, when doors and windows are 
 open, have ' ' colds " and throat diseases when cold weather 
 comes on. One reason for this is that they seal up most 
 of the openings through which fresh air can enter and 
 foul air be removed. We must have good air in our 
 houses, or we, as a race, are doomed. 
 
 The way in which tuberculosis, or consumption, is now treated 
 shows the importance of fresh air. Instead of being protected from the 
 outer air the patient is now told to live in a tent, in the open air, 
 winter and summer, day and night. Pure air, with nourishing food, 
 has been found to be an almost certain cure for the disease in its early 
 stages. If the patient will do his part, it seems as though nothing can 
 
218 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 prevent our getting control of the " Great White Plague," as consump- 
 tion is called, in civilized communities. Many healthy persons, 
 realizing that their daily work gives them too little time in the open 
 air, sleep out-of-doors, even in winter. They do this, not only without 
 injury, but with great gain in health and vigor. 
 
 247. Methods of Ventilation. It has been calculated 
 that during one hour a healthy man will make about 
 4,000 cubic feet of air unfit for breathing. This is the 
 volume of a room 20 x 20 x 10 feet. Of course rooms are 
 not air-tight; hence all this air need not be forced into a 
 room artificially. The Massachusetts law provides that 
 at least 1,800 cubic feet of fresh air shall be furnished each 
 pupil each hour he is in school. If the amount of air 
 furnished to a schoolroom is below this, somebody ought 
 to take steps to get better ventilation. 
 
 Recent experiments show that the air of houses becomes 
 unfit to breathe, not so much because it contains im- 
 purities, as because it is stagnant. Slightly impure air, 
 if in motion, is better than highly pure air that is not 
 moving. In other words, the greatest need is circulation 
 of air. 
 
 Where steam or electric power can be obtained, as in city build- 
 ings, and in factories, heating and ventilation are often carried out 
 together. One method of such forced ventilation is to drive warm, 
 fresh air into the building by means of rotary fans, while the im- 
 pure air escapes through openings made in the walls and ceilings. 
 Another method is to remove the impure air by fans, and to admit 
 fresh, warm air through many small openings near the floor. Drafts 
 are thus prevented. The air is usually warmed by steam coils in the 
 basement. 
 
 The means of ventilation may also be used to cool buildings in sum- 
 mer, if the fresh air is first passed over ice. 
 
VENTILATION WITHOUT FANS 
 
 219 
 
 248. Ventilation without Fans. If there is no system 
 of ventilation in the house, each person owes it to himself 
 to provide fresh air for his breathing. Natural ventilation 
 depends upon the simple fact that heating air makes it 
 lighter, so that it rises, while cooling it makes it heavier, 
 so that it falls (cf. 67). We must remember also that 
 in winter the air of the house is warmer than the air out- 
 side; hence fresh air naturally enters 
 through the cracks at the bottoms of 
 doors and windows, while the warm air 
 of the house leaves at their tops. 
 
 Bedrooms. The windows of bedrooms 
 should be left open, unless storms make 
 this actually impossible. An excellent 
 plan, in stormy weather, is to lower the 
 upper sash a few inches. The outside 
 air then enters between the sashes, 
 while the air of the room leaves at the 
 top of the window. If a board having 
 partly boxed holes (Fig. 205) is placed under the lower 
 sash, the same result is reached. 
 
 Bedrooms should be aired thoroughly during the day. 
 The fact that a bedroom is kept cold does not mean that 
 its air is pure; cold air may be just as foul as warm air, if 
 it is not renewed often enough. 
 
 Gas stoves or kerosene stoves not connected with a 
 chimney are dangerous in closed rooms, since they produce 
 carbon dioxide and use up oxygen (cf. 127). 
 
 Schoolrooms. Schoolrooms that are not ventilated artificially 
 should have each of several windows open a little, rather than one open 
 wide. In this way strong air currents (" drafts") are avoided. If the 
 
 Fig. 205. 
 
 How to Ventilate a Bed- 
 room in Stormy 
 Weather. 
 
220 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 wind is blowing strongly, the openings should be on the side opposite 
 the wind. 
 
 When a large room is heated by a*stove, the stove should be sur- 
 rounded by a "drum," open at the top and bottom, and reaching from 
 near the floor to a point some distance above the stove-top. The 
 drum should be in two parts, hinged together, so that the stove may be 
 easily reached. The circulation of air in the room is then not left to 
 chance; for the drum not only protects those nearest the stove from 
 excessive heat, but it also sets up useful convection currents. These 
 bring cold air from the farthest parts of the room to the stove, heat it, 
 and then carry it away along the ceiling. The room is thus heated 
 evenly, and ventilated at the same time. 
 
 Healing Systems and Ventilation. The hot-air furnace brings in 
 fresh, warm air; but the removal of the cooled, foul air is left to the 
 cracks of the room. The fireplace, since its opening is near the floor, 
 is an excellent aid to the hot-air furnace. Stoves provide some ven- 
 tilation; since fresh air from outside must come in to take the place of 
 the air that goes through the stove. Hot water and steam heating 
 systems of themselves give no ventilation. 
 
 249. Need of Moisture in Air. One very important 
 constituent of fresh air must not be forgotten : its mois- 
 ture. We find air very comfortable, at any given tempera- 
 ture, if it has between 2 /5 and 2 /s of the water it can hold 
 at that temperature. Such air takes up the perspiration 
 at a moderate rate, and so regulates the heat of the body. 
 But if the moisture is more than 2 /s of what the air can 
 hold, we are uncomfortable; the perspiration does not 
 evaporate rapidly enough, and the air feels "sticky." 
 When too little moisture is present, the perspiration evapo- 
 rates too rapidly. The skin then becomes parched and dry. 
 
 As a result of artificial heating and ventilation the 
 amount of air moisture in a house is almost sure to be too 
 small. The reason for this is that the cold air entering a 
 
GLASS 221 
 
 house has its power of holding water increased by warm- 
 ing. The actual amount of water is not changed; but the 
 amount that the air holds as compared with what it is 
 able to hold is decidedly smaller. Hence it takes too 
 much moisture from our bodies. A well-known authority 
 says that the moisture in the air of a room should be such 
 that dew and frost are deposited on the inside of windows 
 in cold weather. If steam or hot water are used for heat- 
 ing, a shallow dish of water should be kept in the room. 
 In the hot-air furnace a water pan is provided inside the 
 air box. This should be kept full. 
 
 250. Light in the House. The problem of lighting 
 the house properly is a very serious one. Primitive 
 peoples, and even our own ancestors of a few generations 
 ago, could afford but little sunlight in their houses, free 
 as it is out of doors. This was because they had no cheap 
 transparent substance like our modern glass. They had 
 only oiled paper, or thin sheets of horn, isin-glass (the 
 mineral mica; cf. 285), etc. But the common people 
 could not afford, or get, much -of these materials; so their 
 houses were dark. The problem of sunlight is so impor- 
 tant to the general health, as well as to sight, that the men 
 who made cheap glass possible must be ranked among 
 the greatest benefactors of the race. Darkness in the 
 house means dirt and filth, and where these exist disease 
 and pestilence are sure to get a foothold. 
 
 251. Glass. Glass is made out of a mixture of sand, 
 limestone, and soda (or sodium sulphate instead of soda). 
 The mixture is melted in fire-clay pots about 4 feet high 
 
222 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 and 4 feet in diameter, and 
 forms a clear, transparent 
 liquid. When this is cooled, 
 it forms, before it hardens, a 
 pasty mass. While the glass 
 is pasty, vessels and other 
 objects can be made from it, 
 and it can be "blown" into 
 many shapes. 
 
 Window glass is made by work- 
 men who blow the pasty glass (Fig. 
 206) into the form of a cylinder, 
 
 and then cut the cylinder open lengthwise, so that it forms a sheet. 
 
 In a new process, glass is also drawn out by a machine into sheets 
 
 Fig. 206. 
 Blowing Window Glass. 
 
 Fig. 207. 
 
 Casting Plate Glass at the Saint Gobain Manufactory, France. 
 Scientific American Supplement. 
 
 From the 
 
ARTIFICIAL LIGHTING 
 
 223 
 
 of any desired width and of varying thickness (Scientific American 
 Supplement, No. 1689). 
 
 Plate glass is made by the pouring of melted glass upon hot iron 
 plates; heated rollers flatten it out (Fig. 207). 
 
 252. Artificial Lighting. Until about 1860 the only 
 common means of lighting were the fireplace, candles, and 
 oils. Among the oils used were lard, olive, and whale 
 (sperm) oils. The oils burn with a smoky flame; but by 
 the use of a wick they are drawn up (cf. 32), a little at a 
 time, and converted into vapor. It is this vapor that 
 burns. The oils have a very high boiling point; hence 
 there is little danger that the body of the oil will be set 
 on fire (cf. 122). 
 
 Candles. The materials used for candles are waxes, 
 fats, and paraffin. Waxes are high-melting fats, just 
 as oils are low-melting fats (cf. 224). The making of 
 
 Fig. 208. 
 
 Modern Way of Making Candles, In some of the candle-moulding machines more than 
 
 500 candles can be made at once. Courtesy of Roman and Company, 
 
 Cincinnati, Ohio. 
 
224 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 candles originally took place in the household, and in- 
 volved much painstaking work. A wick was dipped into 
 the melted fat, allowed to cool, and then dipped again, 
 until the desired thickness was obtained. 
 
 In modern candle-making (Fig. 208) the wick is set in a 
 mould, and the melted fatty material or paraffin (cf. 
 121) is poured around it in the mould. In former times 
 "snuffers" were required to remove the charred wick 
 inside the flame; nowadays, snuffers are not needed. 
 The reason for this is that in the modern candle one of the 
 threads of the wick is pulled more tightly 
 than the others. As a result the tip of 
 the wick curves outward to the edge of 
 the flame (Fig. 42, 49), where the air 
 oxidizes it completely. 
 
 Kerosene Lamps. The discovery of petroleum 
 in Pennsylvania in 1859 (cf. Fig. 98, 121) had 
 a decided effect upon the world's lighting and 
 heating problems; for it furnished gasoline, kero- 
 sene, paraffin, etc. Gasoline has too low a flash- 
 ing point (cf. 122) to permit its use with a wick, 
 in lamps. Kerosene cannot be burned with a 
 wick alone, as the true oils can (cf. 224) , because 
 it smokes. To increase the air supply, and so to 
 prevent smoking, kerosene lamps have chimneys. 
 The heated air and gases carried upward by convection create a draft; 
 thus fresh portions of air are drawn into the burner below the flame. 
 
 To increase the amount of kerosene that can burn in a given time, 
 and, therefore, to get a more intense light, men use central draft 
 burners. These have circular wicks (Fig. 209), and air is drawn to the 
 inside of the circular flame as well as to the outside of it. 
 
 253. Gas for Lighting. Illuminating gas is formed 
 when soft coal is heated in closed retorts (cf. 124), and 
 
 Fig. 209. 
 
 Central Draft Burner. 
 Air gets at the wick 
 both inside and out- 
 side. 
 
GAS PIPES AND FIXTURES 225 
 
 when steam is passed through a bed of hot hard coal or 
 coke. The second method gives water gas. At present 
 nearly all illuminating gas is water gas il enriched" with 
 gases obtained by the charring of petroleum; these make it 
 light-producing. 
 
 As illuminating gas comes to the consumer, it burns 
 with a brilliant, yellow flame. If burned from a circular 
 opening, it is smoky; but if we force it through 
 a narrow slit (a "tip"), it is almost smokeless, 
 because the gas has a large surface in contact 
 with the air. 
 
 254. Incandescent Mantles. To get a brighter light 
 than that of the ordinary gas flame, we may burn the 
 gas in a Bunsen burner, and put a "mantle" in its hot, 
 colorless flame. This is the principle of the Welsbach Fig - 21 ; 
 and other " mantle" lamps. The light comes from the A gas stream 
 incandescent (white hot) mantle (Fig. 210). 
 
 The best mantles contain the oxides of the two rare 
 metals cerium and thorium. The mantle is first knitted xi <j esto white 
 
 neat. 
 
 out of "stockingette." This is then soaked in a solution 
 containing cerium and thorium salts. When the stockingette is dried, 
 the solid salts fill its pores. The mantle is now set on fire. The 
 organic part (the thread) burns up, and the salts in its pores are 
 decomposed. The oxides of the metals remain as a thin, fragile shell. 
 Other gases, such as natural gas and gasoline vapor, can be used with 
 incandescent mantles. 
 
 255. Gas Pipes and Fixtures. Gas is stored by the 
 gas company in large tanks inverted in water. They are 
 loaded with weights, which, with the weight of the tanks, 
 cause the pressure of the gas. As gas is used up, the 
 tanks sink into the water; but they rise again when they 
 are refilled. 
 
226 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 Gas 
 
 The pipes that carry the gas underground to the con- 
 sumer are of iron; sometimes they are 3 or 4 feet in diam- 
 eter. The pipes from the street "main" into the house 
 and to the gas outlets are also of iron. The smaller pipes 
 are joined by screw joints, made gas-tight by some pasty 
 mixture, such as red lead and glycerine. The gas com- 
 pany tests the whole piping system of a house by pump- 
 ing air into it until there is considerable pressure. The 
 pressure is measured by a gauge, or manom- 
 eter (Fig. 211). The gas-fitter needs to be 
 careful, or he will break some of the joints 
 when he attaches the fixtures. 
 
 The "key," by which gas is turned on or off in a 
 fixture, is a tapering plug having an external, flat 
 handle. The plug fits into a hole with tapering sides. 
 To hold the plug tight in its socket, there is a short, 
 spiral spring. This is held in place by a screw that 
 presses against the body of the fixture. If the key or 
 its socket wears away, so that gas escapes around it, 
 the joint may be tightened by a slight turning of the 
 screw. We must remember that illuminating and 
 fuel gases usually contain much carbon monoxide, a very poisonous 
 gas, and that all leaks in the gas fixtures should be attended to im- 
 mediately. 
 
 256. The Gas Meter. In most houses the gas meter 
 is found in the basement. It is a metal box having, on its 
 face, dials like those of Fig. 212. When the hand on the 
 1 ' 5 cubic feet " dial has revolved 20 times, the hand on the 
 "1000 cubic feet" dial will have moved from to 1, and 
 will indicate 100 cubic feet. The hand on the "1,000" 
 dial must make one complete revolution to move the hand 
 on the "10,000" dial from to 1, and so on. Note in 
 
 Fig. 211. 
 The gas pushes 
 up the mercury 
 until the down- 
 ward pressure 
 of the mercury 
 equals the gas 
 pressure. 
 
ACETYLENE FOR LIGHTING 
 
 227 
 
 what direction each of the hands of Fig. 212 must have 
 moved to come to its present position; then write down 
 the meter "reading" shown in the figure. 
 
 The gas meter consists of two compartments the size of which is 
 controlled by two movable diaphragms, or disks. The diaphragms are 
 forced inward and outward by the 
 pressure of the gas from the city 
 "mains." A " slide valve " (cf. 24, 
 Fig. 19) changes the course which 
 the gas must take, so that the 
 compartments may be first filled, 
 and then emptied. As the dia- 
 phragms move back and forth, 
 they give their motion to the re- 
 cording hand of the dial. Since 
 the capacity of the compartments 
 is known, and the dial shows how 
 many times the compartments have been filled and emptied, the dial 
 also shows how many cubic feet of gas have passed through the 
 meter. 
 
 Fig. 212. 
 
 Gas Meter. The dials read up to 5, 1,000, 
 
 10,000, and 100,000 cubic feet, 
 
 respectively. 
 
 257. Acetylene for Lighting. Acetylene (cf. 120 
 and 158) is made by the action of water upon calcium 
 carbide. It contains a large proportion of carbon, and 
 burns with a very smoky flame. Hence the acetylene 
 burner must be different from an ordinary 
 gas burner. The most common form is 
 shown in Fig. 213. In this burner the 
 acetylene is mixed thoroughly with air, 
 and the two jets of burning gas are made 
 to strike each other. The result is an out- 
 spread, "fish-tail" flame. It is smokeless, 
 and of brilliant whiteness. 
 
 Fig. 213. 
 
 A Burner for Acety- 
 lene Gas. 
 
228 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 258. Electric Lighting. The principle of the arc and 
 incandescent electric lamps has already been given (cf. 
 157). The filaments of modern incandescent lamps are 
 made of the rare elements tungsten and tantalum, as well 
 as of carbon. Tungsten and tantalum lamps cost more 
 than carbon lamps; but they use much less electric energy 
 to produce a given amount of light. 
 
 It is very important to have a house properly " wired"; 
 for if wires that are close together lose their insulation, 
 we have the accident known as ' ' crossed wires," or ' ' short- 
 circuiting." If the wires were of large diameter, this 
 accident would not be particularly serious. But as copper 
 is expensive, the smallest possible wires are used, and these 
 are often unable to carry the "load" suddenly put upon 
 them. They become hot, and may set the house on fire. 
 To avoid the rise of temperature in a 
 circuit to the danger point, the electri- 
 cian places a "fuse box" (Fig. 214) 
 in the house. To "fuse" means to 
 "melt." 
 
 The fuse box contains a number of wires 
 made out of a low-melting mixture (alloy) of 
 metals. One of these is placed in each circuit. 
 If for some reason the amount of current in a 
 circuit becomes too great, the melting of the 
 fuse breaks the circuit, and prevents a fire. 
 
 The fuse box of a house usually contains, 
 also, the switch that controls all the electric circuits of the house. 
 When any repairing of wires or outlets is to be done, the house current 
 
 should be cut off by means of this switch. 
 
 ". . 
 
 259. The Electric Meter. The work done by the elec- 
 tric current (cf. 25) is measured in watt-hours, or in 
 
 USE METAL 
 
 Fig. 214. 
 A Fuse Box. 
 
SUMMARY 
 
 229 
 
 kilowatt-hours. The kilowatt is 1,000 watts (cf. 9: 
 kilogram, kilometer, etc.). A kilowatt is equal to 1.34 
 horse powers (cf. 26). A kilowatt-hour is an electric 
 power of one kilowatt working for one hour. It is the 
 common unit used by electric companies in selling power 
 to consumers. The watt is named for James Watt, the 
 inventor of the steam engine (cf. 24). 
 
 The common electric watt-hour meter is really a tiny, finely-built 
 electric motor (cf. 161). The "field" of the electromagnets of the 
 motor is produced by the current to be measured, and exerts force 
 on the "armature," causing it to revolve. The armature is delicately 
 
 KILOWATT HOURS 
 
 Fig. 215. 
 Electric Kilowatt-Hour Meter. 
 
 mounted, on steel balls and jewels. As the armature revolves, it gives 
 motion to clock gear-wheels, and these in turn move the hands of 
 the dials (Fig. 215). Note the direction in which the hand of each dial 
 has moved to bring it to its present position, and write down the read- 
 ing of the meter. 
 
 260. Summary. Modern conveniences are due to scientific dis- 
 coveries and their application. 
 
 We need an abundance of water for our houses, our industries, and 
 our community life. 
 
 Plumbing is the system of pipes, etc., that brings water to the 
 house, and carries water and waste away from it. 
 
 Traps keep sewer air out of the house. 
 
230 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 
 
 Matches raise combustibles to their kindling temperatures. 
 
 The fireplace is not only an ornament, but a means of ventilation. 
 
 Cooking stoves have roundabout flues through which the hot 
 gases must travel; these heat the ovens. 
 
 Gas stoves are Bunsen burners. 
 
 Gasoline must be treated like an inflammable gas. 
 
 Electric heaters are circuits with high resistance; they turn the 
 current into heat. 
 
 Hot-water heating depends on convection currents in heated water; 
 steam heating depends on the heat given 'off in .the condensation of 
 steam. 
 
 The thermostat depends upon the unequal expansion and con- 
 traction of different metals. 
 
 Ventilation is necessary for successful indoor living. It may be 
 natural or forced, but should not be left to chance. 
 
 Proper amount of moisture is as necessary as proper amount of air. 
 
 Cheap glass is a great civilizing agent. 
 
 For lighting, man uses candles, oils, petroleum products, gas, 
 acetylene, electricity, etc. 
 
 Incandescent mantles consist of oxides of certain metals. 
 
 The gas meter records the amount of gas that passes from the 
 " mains" to the house. 
 
 Electric circuits become hot from "short-circuiting." Fire is 
 prevented in such circuits by means of "fuse wires." 
 
 Electric power is sold by the kilowatt-hour. 
 
 Electric meters are small, finely-built motors. 
 
 261 Exercises. 
 
 1. What means of ventilation are there in your house? Are they 
 used? 
 
 2. If you open the door of a warm room, and hold a burning match 
 at the top of the opening, in what direction will the flame be drawn? 
 In what direction will it be drawn at the bottom of the doorway? 
 Explain. * 
 
 3. Show that the hot-air furnace is simply an improved form of a 
 heating stove surrounded by a "drum." 
 
EXERCISES 231 
 
 4. For what reasons is the size of the windows of our houses an 
 important matter from the point of view of public health? 
 
 5. What are the uses of plate glass? Find out what materials are 
 used in making optical glass; that is, glass for spectacles, lenses, etc. 
 
 6. How does it happen that so many candles are used nowadays, 
 when there are so many other ways of producing light? 
 
 7. If you "blow out" a candle or kerosene flame, you can relight it 
 by holding a lighted match some distance above the wick. Explain. 
 
 8. When a carbon incandescent lamp is old, its globe becomes very 
 hot while in use. Are you economical if you continue using it longer? 
 Explain why. 
 
 9. What kind of gas does your family use for lighting and heating? 
 How much does it cost per thousand cubic feet? How much did you 
 use last month? 
 
 10. What kind of incandescent lamps do you use at home? How 
 much does each cost? How long is the "life" of each lamp? For 
 what reasons is one of your electric lamps discarded? 
 
 11. What is the price of electricity per kilowatt-hour in your city? 
 How much did your family use last month? 
 
CHAPTER XIII 
 
 THE WEATHER 
 
 262. Causes of Weather. We have already learned 
 much about the earth's atmosphere: its composition, 
 density, and pressure (cf. 38 ff.); also about gases: 
 that they expand when heated, or when exposed to a 
 lower pressure; that they contract when cooled, or when 
 put under a higher pressure; that they give off heat when 
 compressed, but absorb it when expanded. We have also 
 studied about water: its three physical states, its great 
 heat capacity, and its presence in the atmosphere. These 
 topics form the basis of our study of the weather, and 
 should be reviewed carefully. By "weather" we mean 
 the changing conditions of the earth's atmosphere, such 
 as its temperature, its pressure, and the amount of 
 moisture it contains; the cloudiness or fairness of the sky; 
 the amount of rainfall or snowfall; the velocity of the 
 wind, and its direction. 
 
 As we look over this list of " conditions of the weather, " 
 we find that they are really the properties of two sub- 
 stances : air, as we find it in that great ocean, the atmos- 
 phere; and water, which enters the atmosphere so readily 
 by evaporation from seas, lakes, and rivers, and which 
 leaves the atmosphere again as clouds, rain, dew, snow, 
 and frost. 
 
 The average of all the weather conditions for any given 
 place is the climate of that place. 
 
 232 
 
CHANGES IN THE DENSITY OF AIR 233 
 
 263. Changes in the Density of Air. If we can imagine 
 that there is, near the earth's surface, a layer of air all of 
 about the same density, and if we also imagine that some 
 of this air becomes heated, we can understand how as- 
 cending air currents are produced (cf. 67). We say that 
 the heated air "rises"; what really happens is that the 
 surrounding, heavier air is pulled, by gravity, into the 
 place occupied by the heated, lighter air, and the heated 
 air is pushed up in the form of a current. The movement 
 of the air in currents must, of course, be more rapid than 
 the diffusion of gases (cf. 106), or the lighter air will be 
 mixed with the heavier air, and there will be no convection. 
 
 Air is made lighter, not only when it is heated, but also 
 when it takes up moisture. Steam has a lower density 
 than air (cf. Appendix, Table IV) ; hence air that is mixed 
 with much of it will be decidedly lighter than dry air at 
 the same temperature. 
 
 How high will an ascending air column go? It will rise 
 until it reaches a level at which its density is the same as 
 that of the air surrounding it. Then it will be flattened 
 out as horizontal currents (winds); in time these will 
 descend again to the earth. In this way we get ' ' circu- 
 lation" in the atmosphere. 
 
 Since the pressure of the atmosphere depends on the density of the 
 air, a barometer (cf. 40) placed in a region from which air is ascending 
 will show that the region is an "area of low pressure." The weather 
 observer reads the atmospheric pressure from his barometer, and uses 
 this pressure in ' ' forecasting " the weather ; but we must remember that 
 the barometer tells only the pressure of the atmosphere. If we wish 
 to draw any conclusions regarding the weather, we need other facts in 
 addition to the barometer reading. 
 
 The aneroid barometer is more convenient to carry about than the 
 
234 THE WEATHER 
 
 mercury barometer. It consists of a metal box from which the air 
 has been removed. One side of the box is connected by a system of 
 levers with a pointer that shows the atmospheric pressure. When the 
 pressure increases, the side of the box is pushed inward, and the pointer 
 moves forward. When the pressure becomes lower, the side of the box 
 springs back into place, and the pointer moves backward. 
 
 264. Heating of the Air. The final source of the heat 
 of the earth's surface is the sun (cf. 76). The sun's 
 rays give up part of their heat to the atmosphere as they 
 pass through it. But a much larger part of the sun's 
 heat reaches the earth's surface. This portion is partly 
 reflected back into the atmosphere and into space, and 
 partly absorbed (cf. 173 and 176) by the earth. The 
 part absorbed warms the land and the water for a time; 
 afterwards it is given back to the air. The total amount 
 of heat absorbed by the atmosphere has been estimated to 
 be about 70 per cent of the amount received from the 
 sun. Of course this absorption is only temporary; for in 
 the end the quantity received and the quantity lost are 
 practically the same. 
 
 The lower part of the atmosphere absorbs heat much 
 better than the upper part, and becomes warmer. The 
 reasons for this are that the lower air is denser, and that 
 it has more impurities : dust, smoke, clouds, carbon diox- 
 ide, and water vapor. All of these enable the atmosphere 
 to hold its heat. It is these good absorbers that make 
 the atmosphere a trap for the sun's energy, and a blanket 
 to prevent too rapid heating and cooling (cf. 183). 
 
 Air is also heated and cooled by its own contraction and expansion, 
 respectively (cf. 71). As it ascends, and therefore expands, it 
 becomes colder. This is the reason why ascending air currents finally 
 
MOISTURE OF THE AIR 235 
 
 reach levels beyond which they cannot go; they must spread out as 
 horizontal winds (cf. 263). When the cold, upper air falls to levels 
 having a greater density, the opposite effect is observed: the air is 
 compressed, and becomes warmer. Thus cold air that comes tumbling 
 down the slopes of the Alps into the Swiss valleys is often changed into 
 a hot wind (the/oe/m), because of its own compression. 
 
 265. Moisture of the Air. As we have already learned 
 (cf. 89), water changes into steam (evaporates) at all 
 ordinary temperatures. In the open air the amount of 
 evaporation usually seems to have no limit; this is true 
 because drafts arid winds constantly carry new portions 
 of air over the water, and remove the 
 air that has already taken up water. 
 But when we have an enclosed volume 
 of air over water, only a limited 
 evaporation of the water can take 
 
 place; this is the same as saying that, g 
 
 at a given temperature, only a limited Kg. 216. 
 
 , i , Bell Jar of Air over Water. 
 
 amount 01 steam can expand into a 
 given space or can mix itself with (diffuse into) a given 
 volume of air. Figure 216 shows such an enclosed 
 volume of air. At first water evaporates rapidly into the 
 air of the jar; but after a time the. amount of moisture 
 (steam) becomes no greater, no matter how long the 
 apparatus is allowed to stand. The water does not cease 
 evaporating, but the steam is condensed to water as rapid- 
 ly as the water is changed to steam. The condition of the 
 air, or the space, in the jar is then like that of a sponge 
 filled with water; we say that the air is saturated with 
 water vapor. If we raise the temperature, the air be- 
 comes unsaturated, although it was saturated at the lower 
 
236 THE WEATHER 
 
 temperature. More water will, therefore, change to 
 steam and mix itself with the air of the jar. But if we 
 lower the temperature of air that is saturated, enough of 
 the steam will be condensed to leave the air just saturated 
 at the lower temperature. 
 
 266. Humidity. The weight of the water that is present in a given 
 volume of air is called the humidity of the air. The humidity is stated 
 as so many grains of water for each cubic foot of air, or as so many 
 milligrams of water for each liter of air. A cubic foot of air or space 
 at 50 F. can hold 4 grains of water vapor; if saturated at 80 F., it 
 can hold 11 grains. The cubic foot saturated at 50 F. with 4 grains 
 of water is unsaturated at 80 F. It has, in fact, only yn, or 36 per 
 cent, of the amount needed to saturate it at 80 F. 
 
 The amount of water actually present in a volume of air or space, 
 divided by the amount the air or space would hold if it were saturated, 
 is called the relative humidity of the air or space. In the case given, the 
 relative humidity is 36 per cent (cf. 249 and 267). 
 
 267. Dew and Frost. Dew and frost are moisture 
 deposited directly from the air, upon cool objects. We 
 see dew formed when a pitcher of cold water "sweats" 
 on a hot day. In Nature, dew is commonly formed after 
 sunset, when the air and bodies near the ground radiate 
 their heat, and grow cool. Stones, grass blades, etc., cool 
 more rapidly than the air, and their temperature falls 
 below that at which the air is saturated. They therefore 
 cool the air near them, so that it deposits some of its 
 moisture upon them. The temperature to which air 
 must be cooled so that it will just deposit moisture is 
 called the dew point. If the dew point is below C., frost 
 is formed instead of dew. 
 
 A clear night favors the forming of dew and frost, 
 
FOGS AND CLOUDS 237 
 
 because the earth and the air cool more rapidly if clouds 
 are not present (cf. 264). A gentle breeze favors dew 
 formation, because it brings fresh supplies of almost 
 saturated air to the cooling objects. A strong wind is 
 not favorable, for it does not allow the air to remain long 
 enough in contact with the cool objects. 
 
 Fruit growers know that there must be air drainage 
 as well as water drainage in their orchards. If an orchard 
 is placed in a hollow, cold air will fall into it as water 
 would, and may cause damaging frosts, 
 while neighboring orchards situated on 
 the tops or slopes of hills may escape 
 injury. 
 
 The dew point may be found at any time by the 
 use of the apparatus of Fig. 217. A polished metal 
 beaker containing water is stirred with a ther- 
 mometer, and bits of ice are added from time to 
 time. The temperature reached when dew is Fig. 217. 
 
 just formed on the outside of the beaker is the 
 dew point. 
 
 We can use the dew point to determine the relative humidity of the 
 air (cf. 266). Such determinations are valuable in greenhouses, in 
 schoolrooms, and in your own house (cf. 249). Let us suppose that 
 the temperature of a room is 23 C. In the Appendix, Table VIII, 
 we find that the pressure of water vapor (cf. 89) at 23 C. is 20.9 mm. 
 This would be the pressure of the water vapor in the air at 23 C., if 
 the air were saturated with it. Suppose that we find the dew point 
 to be 10 C. Table VIII shows that at this temperature the pressure 
 of water vapor is 9.1 mm. The air of the room has, therefore, less 
 than half its capacity of water (9.1 divided by 20.9 is 0.44, or 44 per 
 cent, the relative humidity). 
 
 268. Fogs and Clouds. If the air just above the 
 ground is cooled below the dew point, its water is con- 
 
238 THE WEATHER 
 
 densed in tiny droplets, and we have a fog. If a fog is 
 formed some distance above the earth, we call it a cloud. 
 Some clouds consist of ice particles. 
 
 Clouds and fogs are not permanent, but may be ab- 
 sorbed again if the temperature of the air is raised above 
 the dew point, as it often is by the rising sun. But even 
 while a cloud lasts it is both losing water particles and 
 gaining them. Many persons think that clouds are lighter 
 than air, and float in the air. This is not so; cloud par- 
 ticles are heavier than air, and settle slowly toward the 
 earth. But as they reach a layer of unsaturated air, 
 they evaporate and disappear. This level, at which com- 
 plete evaporation takes place, is the bottom of the cloud. 
 Clouds also extend outward until their water particles 
 evaporate as rapidly as they are supplied. It is because 
 cloud material is constantly being formed at one place, 
 and is disappearing at another, that clouds change their 
 forms so readily. No one who has watched carefully the 
 forming of thunder clouds on a sultry afternoon can doubt 
 that they are really "springs" of water vapor, that rise 
 into the upper air, and then fall again in great, billowy 
 masses. 
 
 269. Forms of Clouds. The four principal forms taken 
 by clouds are the following: 
 
 (1) Cumulus clouds (Fig. 218); these are so called from the word 
 meaning "a heap," because they are rounded like heaps of wool. We 
 have the same meaning in the word "accumulate." Cumulus clouds 
 are formed by ascending air currents laden with moisture. They are 
 commonly seen on warm summer afternoons, at a height of one to five 
 miles, and often bring on thunderstorms and showers. 
 
 (2) Cirrus clouds (Fig. 219). Cirrus is from a word meaning 
 
FORMS OF CLOUDS 
 
 239 
 
 Fig. 218. 
 Cumulus Clouds. Copyright, International Stereograph Co. , Decatur, 111. 
 
 Fig. 219. 
 
 Cirrus Clouds "Mackerel Sky." Copyright, International Stereograph 
 Co., Decatur, 111. 
 
240 THE WEATHER 
 
 "feather." These clouds are distinguished by the distinct lines that 
 make them up. The lines may be arranged in many strange forms, 
 such as plumes, hazy streaks, etc. Cirrus clouds are the highest 
 clouds; they are often above five miles high, and consist of minute 
 particles of ice or snow. One arrangement of cirrus clouds is called a 
 "mackerel sky." 
 
 (3) Stratus clouds; these are so called because they occur in layers 
 {cf. 286). Stratus clouds are lower than the other two; usually from 
 half a mile to three miles high. 
 
 (4) Nimbus clouds, so called from nimbus, " a veil." These clouds 
 are cumulus or stratus clouds that are depositing rain or snow. 
 
 270. Rain and Snow. When the particles of water 
 mist that make up a cloud gather together into drops, 
 they fall into the air below the cloud. If this air is nearly 
 saturated, the drops continue falling until they reach the 
 earth as rain. If the conditions necessary for the forma- 
 tion of raindrops occur below C., snow flakes will be 
 formed (cf. 95, Fig. 76). 
 
 Cloudbursts. If the ascending currents of moist air are very strong, 
 as in thunderstorms and tornadoes (cf. 277 and 278), an enormous 
 quantity of water may be accumulated in the cloud. When this falls, 
 the rain is called a cloudburst. 
 
 271. Hail. Hail is made up of pellets or "stones" of 
 ice and snow in alternate layers. Hailstones probably 
 begin in the freezing of raindrops at lower levels. These 
 are carried upward by ascending currents, are dropped 
 downward, and are then carried upward again ; this treat- 
 ment is repeated many times. Thus the hailstones take 
 on layer after layer of covering, until they become too 
 heavy to be supported longer, and fall to the ground. 
 Hail does a great deal of damage, not only to window 
 panes, but also to fruit trees and crops. 
 
RAINFALL 
 
 241 
 
 272. Rainfall. Rain is caught for measurement in a 
 rain gauge (Fig. 220). This is really a funnel with a long 
 stem. The opening of the funnel has exactly 10 times the 
 area of a cross section of the stem, so that Vio of an inch 
 of rainfall gives a depth of 1 inch in the stem. The greater 
 depth of water in the stem makes the reading more accu- 
 rate. Snow is estimated as rain, the snow being allowed to 
 melt. About 10 inches of snowfall equals 
 1 inch of rain; but the relation is not 
 accurate for any particular case, since 
 snow falls in so many different degrees of 
 wetness. 
 
 Scientists have found that there are 
 several rules, or laws, of rainfall. Among 
 them are the following: 
 
 (1) Rainfall is less in the interior of 
 continents than on the coast. The 
 
 amount for each continent depends on how far rain 
 clouds can penetrate before a mountain barrier or 
 plateau condenses their moisture. 
 
 (2) The greatest rainfall occurs in the tropics. This is 
 due to the great capacity of hot air for moisture, or, better, 
 to the great evaporation that can occur at high tempera- 
 tures. 
 
 (3) When rainfall takes place on mountain slopes, the 
 sides get more than the base. This is true for the reason 
 that the moist air currents that bring the rain must go up 
 a certain distance before they are chilled enough to give 
 their greatest deposits. 
 
 Let us now consider some illustrations of these rules. No regions 
 are absolutely rainless, but half of the earth's land surface gets less than 
 
 
 I Receiv 
 Funru 
 
 1 
 
 H 
 
 / 
 
 
 
 
 Gauge- 
 
 Fig. 220. 
 Rain Gauge. 
 
242 
 
 THE WEATHER 
 
EXERCISES 243 
 
 20 inches of rain in a year, and is, therefore, considered unfit for farm- 
 ing without 'irrigation (cf. 42 and 297). The rainfall in Florida and 
 on the Gulf coast is over 60 inches a year. The sea coast of the state 
 of Washington has up to 100 inches. These abundant rains are 
 brought by warm, moist, ocean winds, which are cooled as they pass 
 over the land. In the Plains Region, just east of the Rocky Mountains, 
 the annual rainfall is below 20 inches; in the Nevada Desert, just east 
 of the Sierras, it is less than 5 inches. 
 
 The most wonderful rainfall in the world is in India, where the 
 average is 500 inches a year. This enormous amount is brought by 
 the southwest winds (monsoons) from the heated Indian Ocean, as 
 they ascend the land to the tops of the Himalayas. Beyond the 
 mountains the monsoon is a dry wind, and the plateau of Thibet, over 
 which it passes, is largely a desert. 
 
 273. Exercises. 
 
 1. Does the color of the soil have anything to do with the amount 
 of heat it can absorb? Why does the snow under specks of dirt melt 
 more rapidly than the clean snow beside it? Why does snow under a 
 heap of dirt melt so slowly? 
 
 2. Why does a high mountain top exposed to the sun become very 
 much hotter in the daytime than land in the valleys, but at night very 
 much colder? 
 
 3. A balloon that is at a certain height during the night usually 
 takes a sudden leap skyward at sunrise. Explain why. 
 
 4. Why does covering a plant at night prevent it from being frost- 
 bitten? 
 
 5. Would you feel any wind if you were in a region from which an 
 air current was ascending? Why? 
 
 6. Why is the seashore of a country cooler in summer and warmer in 
 winter than the interior? 
 
 7. Suppose that air containing moisture rises and expands until it 
 is cooled below the dew point; what effect does the condensing of its 
 moisture have upon its temperature (cf. 70)? 
 
 8. Suggest why a fog is formed more readily in a smoky atmosphere 
 than in a clear one. 
 
244 
 
 THE WEATHER 
 
 9. When you blow your breath into a cold glass bottle or lamp 
 chimney, you form a deposit of dew on the inside. Why? How cold 
 must the condensing object be? 
 
 10. Under what conditions can you " see your breath"? Why does 
 the condensed moisture disappear? 
 
 11. Find out how large a hailstone may become. 
 
 12. If a dish containing a mixture of salt and ice is left outside on a 
 cold day, it gathers little if any frost; but when it is brought into a 
 warm room, it condenses a great deal. Why? 
 
 13. Clouds are often formed on the headland shown in Fig. 107, 
 132, which travel with the wind (horizontally) a short distance, and 
 then disappear. Why are the clouds formed? Why do they disappear? 
 
 14. There is a steep ascent, in the form of hills or mountains, 
 practically the entire distance around the coast of Australia. Would 
 you expect the interior to be dry or moist? What are the facts regard- 
 ing Australia? 
 
 274. The Winds. The cause of winds is the inequal- 
 ities of atmospheric pressure. The air, being gaseous, 
 has great freedom of motion; so that, if the pressure be- 
 comes low at any given place, the surrounding, heavier 
 air crowds in from all sides, and buoys the lighter air 
 upward. These horizontal currents are the winds. 
 
 A fire, burning in the open air on a still day (Fig. 222), illustrates 
 
 ^ admirably the origin 
 
 of winds. The warm 
 air and smoke are 
 carried upward to a 
 certain level, and then 
 spread out horizon- 
 tally. At some dis- 
 tance they return to 
 the earth, and move 
 toward the fire as 
 strong drafts. The 
 
 FIRE 
 
 Fig. 222. 
 The winds are fomed like the currents about an open fire. 
 
REGULAR WINDS 245 
 
 horizontal currents at the earth's surface are the only parts of this 
 circulation that we ordinarily notice, but there are always horizontal 
 currents at higher levels, flowing in the opposite direction; and there 
 are downward currents to balance the ascending ones. 
 
 The force with which the wind will blow toward any 
 given place depends upon the difference in atmospheric 
 pressure between that place and the region about it. 
 Thus, if the barometer pressure at one place (A) on a 
 horizontal plain is 29.9 inches, and if two neighboring 
 places (B) and (C) have pressures of 29.8 inches and 29.7 
 inches, respectively, the velocity of the wind from A to C 
 will exceed that from A to B, or from B to C. We should 
 expect this to be so, since we know that water will flow 
 more rapidly down a steep incline than down a gentle one. 
 
 We can gather these facts together in one law of the 
 winds: 
 
 The winds blow because of the force of gravity, and always 
 from a region of high barometer pressure to one that is low. 
 The velocity of the wind is greatest where the change of 
 pressure is the most abrupt. 
 
 The instrument by which we measure the velocity of the wind is the 
 anemometer (pronounced an-e-mfan'-e-ter; the word is from anemos, 
 "wind," and meter, "measure")- It is a windmill with hollow, cup- 
 shaped sails; the speed with which it revolves is registered on a dial as 
 so many miles per hour. A light wind has a speed of less than 10 miles 
 an hour; it can just move the leaves of trees. A high wind, blowing at 
 25 to 40 miles an hour, sways the trees themselves. In a gale the wind 
 is over 40 miles an hour; in a hurricane or a tornado (cf. 278 and 279) 
 it is above 60 miles, and may reach 200 or more. 
 
 275. Regular Winds. On the land, the unevenness of 
 the surface and the different degrees of heating and cool- 
 ing at different places produce variable winds; but the 
 
246 THE WEATHER 
 
 ocean furnishes a free, unbroken path for air currents; 
 hence winds that blow over the ocean often keep their 
 direction for weeks and months at a time. Such regular, 
 long-continued winds are the trade winds of temperate 
 latitudes, and the monsoons of the Indian and West 
 Pacific oceans (cf. 272). 
 
 Land and sea breezes are also regular winds, due to the 
 alternation of day and night. By day, the air over the 
 land is warmed more than the air over the water. Con- 
 vection currents are thus set up on the land, which cause 
 an inflow of air from the ocean the sea breeze. At 
 night the land cools more rapidly than the ocean, and as 
 a result the ascending air current is over the water, 
 hence there is a flow of air from the land the land 
 breeze. 
 
 276. Cyclones. If the earth were not rotating on its 
 axis, winds would blow toward the area of low pressure 
 as directly as possible, in straight lines, as the spokes of 
 a wheel come together at the hub. But the rotation of 
 the earth causes the air to flow toward the ' l low " area by a 
 curved route. As a result of the curved paths of the 
 winds, the air at the center is set in a whirl. A dust 
 whirlwind illustrates, on a small scale, this circular move- 
 ment of air; a cyclone is a great whirl that may be 1,000 
 miles in diameter and 5 miles high. 
 
 In the northern hemisphere the direction of this whirl- 
 ing mass of air is opposite that of the hands of a clock. If, 
 in this hemisphere, you stand with your back to the wind, 
 the center of low pressure will be towards the left. In the 
 center of the cyclone there is comparative calm. 
 
THUNDERSTORMS 
 
 247 
 
 B 
 
 The whole area of low pressure moves in a definite 
 direction. In the northern United States this direction 
 is easterly; the cyclones begin in western Canada. The ve- 
 locity of the eastward movement is about 30 miles an hour. 
 
 Cyclones must not be confounded with tornadoes (cf. 
 278), which are smaller masses of very rapidly revolving 
 air, and which do great damage. True cyclones bring 
 the cold waves that sweep down upon us at more or less 
 regular intervals, both 
 
 in summer and in win- ^ / N N 
 
 ter, dissipating the ex- / \ 
 
 hausted air, and giving / / ^ 
 
 vigor to our people. 
 
 The curved path taken by 
 the wind in approaching a 
 "low" area is simply the 
 result of two motions ; one is 
 the straight-line motion of 
 the wind, by which it seeks 
 the "low"; the other is the 
 rotation of the earth from 
 west to east. The path of a 
 person on a revolving bridge 
 (Fig. 223) can be made to 
 
 illustrate the effect of these two motions. Suppose that the bridge is 
 standing still, and that you walk toward a street car at the opposite 
 end; your path is a straight line. But suppose that the bridge turns, 
 while you continue to walk toward the car. Your path on the bridge 
 will change its direction at every point: it will be a curve. 
 
 277. Thunderstorms. Thunderstorms are smaller 
 disturbances in the great cyclones; the frictional electricity 
 (lightning) that comes with them (cf. 147) is generated 
 by the rapid condensation of water vapor. The cause of 
 
 Fig. 223. 
 
 If you walk across a revolving bridge, keeping 
 
 your direction toward some object on the 
 
 opposite shore, your path will be 
 
 curved, somewhat like AC. 
 
248 THE WEATHER 
 
 the condensation is an ascending column of warm air 
 loaded with moisture. When this has produced a large 
 cloud (cf. 269), rain falls, and cools the ascending col- 
 umn below the temperature of the warm, moist air that 
 rises around it. The central, ascending column thus 
 becomes a cool, descending one, which draws down into 
 it the wet ascending currents, and precipitates their 
 moisture in violent rains. The thunderstorm has a center 
 of high pressure and low temperature; its circumference 
 has a low pressure and a high temperature. 
 
 278. Tornadoes. Tornadoes, or "twisters," are small 
 cyclones, as distinguished from the great, but not violent, 
 cyclonic storms (cf. 276). But while the tornado is of 
 small size, it is very violent and destructive. The wind 
 sometimes reaches a velocity of 200 miles, or more, an 
 hour, and no objects on the earth can resist it. Heavy 
 boulders are carried away hundreds of feet, and locomo- 
 tives are lifted from the rails. So great is the force of the 
 wind that frail objects, such as twigs and straws, are 
 driven into oak wood. 
 
 A tornado, as seen approaching, is a funnel-shaped cloud with the 
 small end downward. The lower end dangles along the ground in an 
 irregular way, touching it here and there. The path of the tornado 
 may be 50 feet to half a mile wide. The whole storm moves north- 
 easterly, in the northern hemisphere, at a rate of 25 to 40 miles an hour; 
 it generally exhausts itself in an hour or so. 
 
 In the great deserts, large whirlwinds carrying columns of sand 
 continue for hours at a time. Waterspouts are tornadoes over bodies 
 of water. Waterspouts at sea precipitate fresh water. This fact 
 shows that while a small column of water may be pushed up by atmos- 
 pheric pressure (cf. 40) toward the low pressure region of the water- 
 spout, most of the water in the waterspout comes from the air itself. 
 
WEATHER SERVICE OF THE UNITED STATES 249 
 
 279. Hurricanes. In the tropical part of the Atlantic, 
 north of South America, violent storms are developed, 
 called hurricanes. Similar storms in the Pacific and 
 Indian oceans are called typhoons. Both are great whirl- 
 ing masses of air, with a diameter of 300 miles or more, 
 in which the violence of wind and rain becomes enormous. 
 The "West India" hurricanes move northwestward until 
 they reach the southeastern coast of the United States; 
 then they move in a northeasterly direction, and, finally, 
 out into the Atlantic. They usually come in the months 
 of July to October, inclusive. 
 
 At the approach of a hurricane or typhoon, the sea and the air are 
 calm, and the barometer falls. Then the wind begins to blow, and 
 clouds and rain come on. The velocity of the wind increases to that 
 of the fiercest gale, or even to that of a tornado. If the center of the 
 hurricane passes over a ship, the sailors notice a sudden change from 
 black darkness and the most violent gale to a dead calm and a clear 
 sky. The barometer will now be very low. The ship is in the "eye" 
 of the storm, an area perhaps 20 miles in diameter. When this has 
 passed, the wind will break forth again, as suddenly as it stopped, but 
 it will be from the opposite direction. Then all the conditions that 
 were noticed when the storm came on will be reversed as the ship 
 passes out of the storm area. 
 
 The damage to shipping and to life because of hurricanes is very 
 great, both in the West Indies and in the southeastern states. It is not 
 only the wind and rain that are so destructive, but also the great 
 storm waves that are raised, and that sweep over all low-lying islands 
 and coasts. 
 
 Typhoons are still more extensive than hurricanes, because they 
 have a greater ocean in which to form and to move. 
 
 280. Weather Service of the United States. The 
 science of the weather is called meteorology (pronounced 
 me-te-or-ol'-o-gy). A Weather Service, or Weather Bu- 
 
250 THE WEATHER 
 
 reau, is especially needed in the United States, owing to the 
 great range of the country in latitude and longitude, and 
 the great variety of its weather conditions. The Bureau 
 is a part of the Department of Agriculture. 
 
 Many trained observers gather the weather conditions 
 each day, at 8 A. M. on the Atlantic coast and at 5 A. M. 
 on the Pacific. When their reports are telegraphed to 
 Washington, they give an instantaneous photograph of 
 the weather of the whole country. The facts reported by 
 the observers are simply the barometer height, tempera- 
 ture, rainfall or snowfall, direction and velocity of the 
 wind, etc. But the combined results, when placed upon 
 a map, make it possible for the expert at Washington not 
 only to tell what the weather is, but what it is likely to 
 be. Thus the coming of cold waves, of storms that are 
 likely to injure ships, of floods upon rivers, all can be fore- 
 told with more or less accuracy. That some forecasts 
 fail does not mean that the Weather Service is at fault, 
 but that all storms are not alike. But the forecasts 
 actually save to the people not only many lives, but 
 millions of dollars' worth of property annually: many 
 times the cost of the service. 
 
 The case of the Mississippi floods illustrates how the Service works. 
 If there are heavy rains in the Upper Mississippi Valley, there will be 
 serious floods along the lower course of the river. The " weather 
 man" knows the rainfall, and how much the river can carry off in an 
 hour; hence he knows what chance the river has of carrying all the 
 water it will receive. If more water is poured into it.that it can carry, 
 the level of the river must go up. The greatest floods of recent years 
 have occurred in 1897, 1903, 1912, and 1913. In the flood of 1912 the 
 Bureau predicted that the crest, or highest part, of the flood would 
 reach 54 feet at Cairo, 46 feet at Memphis, 53 feet at Vicksburg, 42 
 
WEATHER MAPS 251 
 
 feet at Baton Rouge, and 21.5 feet at New Orleans. The results agreed 
 remarkably with the predictions, although the predictions were for 
 floods 1 to 1 .5 feet higher than any previous record. Thus warned, the 
 people set to work to strengthen the banks and levees, to remove their 
 cattle and their families to places of safety, and to get all freight away 
 from the wharves. It is estimated that property to the value of 
 $16,180,000 was saved by these warnings. The cost of the river and 
 flood service for the entire country during 1912 was $80,000, or only 
 Yl of 1 per cent of the value of the property saved in this one flood. 
 
 In a similar way the Bureau gives warnings of coming frost, so that 
 whatever is possible may be done to save crops. When the weather 
 observer notes that a cold wave is coming, he sends word to the prin- 
 cipal city of his region. From this as a center, warning is sent by tele- 
 gram and telephone, by messenger, and by great signs placed on trains, 
 to all the producers of that region. 
 
 The warning which the Weather Bureau gives to shipping is also of 
 great importance, as we should realize if we could count the many 
 thousands of ships, large and small, that annually enter and leave our 
 ports on the Atlantic, the Pacific, the Gulf, and the Great Lakes. 
 Within 45 minutes after a storm is predicted, the warning is placed in 
 the hands of every ship captain in every lake and ocean port. Storm 
 'signals are also put up in all ports. As a result of the Weather Service, 
 the losses due to storms on the Great Lakes have fallen off two thirds. 
 
 281. Weather Maps. In the preceding section we 
 have learned how useful the weather service is. Let us 
 now see how "weather maps" are made. In the first 
 place, all the weather stations having the same barometer 
 height are joined by solid lines, as in Fig. 224, A. These 
 lines therefore show equal pressures, and are called isobars, 
 from isos, "equal," and barm, "heavy." If we examine 
 the map we shall see that the isobars curve, in irregularly 
 circular lines, about areas of low and of high pressure. 
 The pressure increases from the centers of the "lows" to 
 
252 
 
 THE WEATHER 
 
WEATHER MAPS 
 
 253 
 
254 
 
 THE WEATHER 
 
SUMMARY 255 
 
 the centers of the "highs." The "lows" represent cy- 
 clonic storms, and the "highs" the sharp, bright weather 
 that usually follows them. 
 
 Figure 224, A, J5, and C, are complete weather maps, as 
 issued by a local weather office. They show the isobars, 
 and also the isotherm for freezing; that is, the line joining 
 the places at which the temperature is 32 F. Note 
 carefully the progress of the "low" from March 13 to 
 March 15, and also the effect of the northwestern "high" 
 upon the isotherm of freezing. These maps show also the 
 temperature of individual stations, the direction of the 
 wind, and the amount of rain or snow. As they are 
 issued, they contain an official forecast for different parts 
 of the country. 
 
 282. Summary. The " conditions of the weather" are due to the 
 properties of the air and water of the atmosphere. 
 
 Ascending currents are pushed up by heavier air, which is pulled 
 downward by gravity. 
 
 A given volume of moist air is lighter than an equal volume of 
 dry air. 
 
 An ascending air column is an area of low pressure. 
 
 About 70 per cent of the heat received from the sun is temporarily 
 absorbed by the earth. The lower atmosphere does most of the ab- 
 sorbing. 
 
 Air is cooled by its expansion as it rises, and is heated by its com- 
 pression as it descends. 
 
 When a given volume of air or of space deposits its moisture as 
 rapidly as it takes up new moisture, it is said to be saturated with 
 moisture. 
 
 The humidity of air is the weight of water present in a given volume 
 of air. 
 
 Relative humidity is the amount present as compared with what 
 the space could hold if it were saturated. 
 
256 THE WEATHER 
 
 The dew point is the temperature at which air is just saturated with 
 moisture. 
 
 Frost is formed when the dew point is below C. It is not 
 frozen dew. 
 
 Clouds are fogs " up in the air." A cloud is limited to the region in 
 which water vapor can be condensed more rapidly than the condensed 
 moisture can evaporate. 
 
 Clouds are distinguished, according to their form, as cumulus, cirrus, 
 stratus, and nimbus clouds. 
 
 Rain occurs when water mist collects in drops that reach the earth. 
 
 Snow is formed when rain-forming conditions occur below C. 
 It is not frozen rain. 
 
 Hail usually has ice and snow in alternate layers. 
 
 Rainfall is measured by a rain gauge. 
 
 The mean annual rainfall of the United States varies from a few 
 inches in the deserts up to 100 inches in the state of Washington. 
 
 The circulation that forms the winds includes horizontal currents 
 at higher levels as well as at the earth, and downward as well as upward 
 currents. 
 
 Winds blow in curved paths toward regions of low pressure. The 
 velocity of winds is measured by the anemometer. 
 
 Regular winds are trade winds and land and sea breezes. 
 
 Cyclones are great whirlwinds in the air. They bring our "cold 
 waves," but are usually not destructive. In the northern hemisphere 
 they revolve in a direction opposite to that of the hands of a clock. 
 
 The curved path of the air in cyclones is due to its motion in straight 
 lines, together with the rotation of the earth. 
 
 A thunderstorm has a center of descending air (high pressure), which 
 draws into it ascending, moist air. 
 
 Tornadoes are small cyclones of great violence. 
 
 Waterspouts are tornadoes over bodies of water. 
 
 Hurricanes and typhoons are violent cyclones formed in the tropics. 
 
 Meteorology is the science of the weather. 
 
 The Weather Service of the United States collects the data regard- 
 ing the weather, and from them constructs daily weather maps. From 
 these it forecasts cold waves, floods, and storms, so that their harmful 
 results may be avoided as far as possible. 
 
EXERCISES 257 
 
 283. Exercises. 
 
 1. Clouds often move in a direction exactly opposite to that of the 
 prevailing wind; what may be the explanation (cf. 274)? 
 
 2. What is a weather vane? Its shape? Why has it this shape? 
 Why does a windmill (cf. 210) often have a vane? 
 
 3. Fishermen on the sea coast often sail out to the fishing grounds 
 at or before daybreak, and return about noon. Do the land and sea 
 breezes help them, or hinder them? 
 
 4. Suppose that a cyclone is 5 miles high, and has a diameter of 
 1.000 miles; how many times its height is its diameter? If, to show 
 these proportions, I make a circle out of wooden boards one inch thick, 
 how many inches in diameter must the circle be? How many feet? 
 
 5. If you were watching a barometer while a thunderstorm was 
 passing, what change in its height would you observe as the center 
 reached you? What would you observe in the case of a tornado? 
 
 6. Would your house be more likely to collapse inward, or outward, 
 if a tornado were to pass near it? 
 
 7. What kind of an air current do you think there is at the "eye" 
 of a hurricane? 
 
 8. In narrow bays a strong wind often " piles up" the water several 
 feet; explain. 
 
 9. Find out, if possible, what are the various flags used as weather 
 signals. 
 
 10. In what ways, in addition to making weather predictions, does 
 the Government seek to prevent loss of life and property at sea and 
 on the lakes? What recent invention has been of great assistance? 
 
CHAPTER XIV 
 
 ROCKS AND SOIL 
 
 284. The Earth's Crust. We have already learned 
 (cf. 38, Fig. 30) about the four parts that appear in a 
 cross section of the earth. The crust is merely that por- 
 tion of the core that is known to us; so far as we know, the 
 core contains the same materials as the crust, but in a 
 more compact form. 
 
 If we examine the crust, as it is exposed in a railroad 
 cut, a cellar excavation, or, best, in a quarry or gorge, we 
 find that it consists of two parts : 
 
 (1) The surface materials, or mantle rock; 
 
 (2) Bedrock. 
 
 Mantle rock is made up of such materials as clay, sand, 
 gravel, and pebbles, all of which are usually loose enough 
 to be worked by the spade and the pick. That upper 
 portion of the mantle rock which we can use for growing 
 crops is called soil. 
 
 Ordinary excavations may not be deep enough to go 
 through the mantle rock; but everywhere, and at only a 
 moderate depth, the mantle stops, and we have bed rock. 
 When bed rock is exposed at the surface, we have an 
 outcrop. 
 
 285. Some Common Rocks. Bed rock usually con- 
 sists of fragments of some mineral or minerals (cf. 102) 
 cemented together. The cementing material hardens, of 
 
 258 
 
SOME COMMON ROCKS 259 
 
 "sets," around and between the fragments, much as lime- 
 stone holds sand together in mortar. 
 
 The most common rocks are sandstone and limestone. 
 In sandstone, fragments of sand (quartz) are cemented by 
 iron oxide or silicic (pronounced sil-is'-ik) acid. Lime- 
 stone usually consists of masses, sometimes very small, 
 having the shape of shells and the hard parts of water 
 animals. These are compact, and cemented together by 
 calcium carbonate. Animal and plant remains, as we 
 find them in rocks, are called fossils. 
 
 When the cementing materials of a rock are removed, 
 the rock falls into its fragments. Sandstones are often 
 found that can be crumbled in the hand, owing to the 
 loss of cementing material. 
 
 Shale is a soft rock that splits easily into thin leaves. 
 It is made of flattened particles of clay, with cementing 
 material. 
 
 Granite consists of four minerals : quartz, feldspar, mica, 
 and hornblende. Quartz looks like glass, but is harder. 
 It crystallizes in hexagonal forms (cf. Fig. 75, 95). In 
 granite it forms small, shiny masses. The feldspar of 
 granite is usually pink or white. The mica forms shiny 
 masses that can be split off in very thin leaves (cf. 250). 
 The hornblende usually exists as black crystals. 
 
 The most easily attacked of the ingredients of granite 
 is feldspar; the carbonic acid of rain water decays it. So 
 the granite's quartz becomes sand, and its feldspar be- 
 comes clay. 
 
 Conglomerate is a gravel of various materials cemented 
 together. 
 
 We have artificial rocks as well as natural ones. In making articles 
 
260 
 
 ROCKS AND SOIL 
 
 out of artificial stone, men shape the rock material while it is soft and 
 plastic, and then bake, or "fire" it. The people of ancient Babylonia 
 and Assyria made their ordinary records, such as notes, deeds, and 
 mortgages, as well as the records of their history and literature, upon 
 clay tablets, and then baked the clay in the sun. 
 
 Earthenware articles, such as bricks, jars, and tiles, are made of 
 common clay, hardened by heat. If salt is put into the heating furnace 
 (kiln), the articles receive a glazed surface. 
 
 Porcelain and china are obtained by the " firing" of a mixture of 
 kaolin (a pure, white clay), quartz, and feldspar. The feldspar melts 
 first, and cements the mixture together. The first " firing" of porce- 
 lain and china articles takes place at a rather low temperature ; then the 
 
 glaze is added to the surface, 
 and the article is heated to a 
 high temperature, often for 
 several days. 
 
 Stoneware is much like por- 
 celain, but it has not been 
 heated to so high a tempera- 
 ture. As a result, it is opaque, 
 while porcelain is translucent. 
 The science of making articles 
 
 out of artificial stone is called 
 keramics. 
 
 Concrete is another artifi- 
 cial stone, made out of cement, 
 gravel, and water. The 
 cement and the water unite, 
 and cause the mixture to 
 "set." Cement is formed by 
 the heating of a mixture of 
 limestone and clay. 
 
 Fig. 225. 
 
 Niagara Falls are being undermined all the 
 time, because the soft shale is being worn 
 away by the water, and the hard lime- 
 stone falls into the Gorge. From 
 Hopkins, after Gilbert. 
 
 286. Classes of Rocks. If we examine many different 
 rocks, we shall find that we can divide them into two great 
 classes. One consists of rocks having a more or less 
 
CLASSES OF ROCKS 
 
 261 
 
 definite layer structure. A cross section, especially when 
 polished, shows multitudes of parallel lines. These rocks 
 are of different materials, a layer of one material covering 
 a layer of another material. Thus, the rock under the 
 Niagara River, at the Falls, is a hard limestone (Fig. 
 225). This rests upon a layer of soft shale. Sandstone 
 also forms one of the layers. 
 
 Each set of layers of rock of one kind is called a stratum. 
 The plural is strata. Rocks made up of strata are called 
 stratified rocks (cf. 132, 
 Fig. 107). They were 
 deposited, as sediment, 
 under water; hence they 
 are also called aqueous 
 rocks, and sedimentary 
 rocks. Limestone, sand- 
 stone, shale, and con- 
 glomerate are stratified 
 rocks. 
 
 Granite does not have 
 this layer structure, and 
 belongs to the class of 
 unstratified rocks. The 
 minerals present in gran- 
 ite are crystallized in 
 separate masses, and the 
 
 masses are closely interlaced. This is what we should 
 expect if quartz, feldspar, etc., had been melted together, 
 and then allowed to cool very slowly. 
 
 Other common unstratified rocks are basalt, lava, and pumice. 
 Basalt (Fig. 226) is often called ' ' trap rock." Lava and pumice have a 
 
 Fig. 226. 
 
 Giant's Causeway, Ireland; Made of Basalt. 
 
 Copyright, The international Stereograph 
 
 Co., Decatur, 111. 
 
262 ROCKS AND SOIL 
 
 structure like glass, and show no crystals. Slag is an artificial unstrati- 
 fied rock (cf. 119, Fig. 94). Since unstratified rocks were probably 
 in a melted condition when deposited, and therefore hot, they are often 
 called igneous rocks, from the Latin ignis, "fire." 
 
 Marble is an example of a third class of rocks. Marble 
 is calcium carbonate, like limestone; but instead of show- 
 ing a layer structure, it is crystalline, like igneous rocks. 
 We believe that such rocks were originally stratified, but 
 that they have been changed by heat and pressure. They 
 are called altered, or metamorphic rocks. Anthracite 
 oal is metamorphic coal, and slate is metamorphic shale. 
 Often all the stages in the change from stratified rocks to 
 apparently igneous rocks can be seen. 
 
 287. Origin of Stratified Rocks. In the preceding 
 section we learned that stratified rocks were formed as 
 sediment, under water, while igneous rocks were formed 
 by the cooling of melted minerals. How do we know this? 
 
 The best method of finding out how changes took place 
 in the past is to study the changes taking place to-day. 
 We know that running water can carry sediment, and that 
 when a stream empties into a body of water, such as a 
 lake or pond, its velocity is checked, and it deposits its 
 sediment in more or less horizontal layers. 
 
 Imagine a small stream emptying into a quiet pond. After a rain 
 the swollen stream will bring down mud, sand, and often fine gravel. 
 When it enters the pond, it drops its sediment, the largest particles 
 first, and the smallest ones last. The finest particles take a long time 
 to settle, and are spread out over the bottom of the pond. Then, after 
 a while, another rain comes, and a second deposit is placed over the 
 first one. The largest particles of the second deposit will be on top of 
 the finest particles of the first. In this way the sediment will take 
 on a layer structure, and a vertical cross section of it will show the 
 
ORIGIN OF IGNEOUS AND METAMORPHIC ROCKS 263 
 
 fine, parallel lines that are present in stratified rock. If now the 
 sediment were to become very thick, producing great pressure on the 
 lowest layers, and if a cementing material were present, the clay de- 
 posited in the pond might be changed to shale, and the sand to sand- 
 stone. 
 
 288. Origin of Igneous and Metamorphic Rocks. We 
 cannot observe the formation of igneous rocks as easily 
 as that of stratified rocks; but there are, even now, vol- 
 canic regions in which melted rock is being expelled from 
 the interior of the earth. 
 Sometimes the melted 
 rock hardens to a glassy, 
 brittle rock, forming ob- 
 sidian and lava (Fig. 227). 
 Sometimes the volcanic 
 material is full of gas 
 bubbles, and hardens to 
 form pumice. 
 
 New England has no 
 volcanic conditions to- 
 day, but there is every 
 evidence that it had them in the past ; for in many places 
 great dikes of igneous rock cross its other rocks, and these 
 are nothing but rock cracks that have been filled, from 
 below, with lava. In Oregon great areas of lava are 
 found on the surface. 
 
 Granite differs from lava and other igneous rocks in that it seems to 
 have been pushed into cracks and pockets entirely beneath the earth's 
 surface. Its minerals must have crystallized out during a long period 
 of very slow cooling. When we now find granite at the earth's surface, 
 we believe that the rock which once covered it has been worn away. 
 
 Fig. 227. 
 
 A Roman Mill; Made of Lava. Field Museum 
 of Natural History. 
 
264 ROCKS AND SOIL 
 
 It is evident that we must think of igneous rock as lying under all 
 other rocks. Time and again some of it has been liquefied, and has 
 penetrated into the cracks of stratified rocks, or has overflowed them. 
 As a result the stratified rocks near by were heated, and changed in 
 structure : they became metamorphic. 
 
 289. Weathering of Rocks. The earth's solid crust at 
 any given time is what it is because of two great agencies : 
 (1) the upbuilding agencies, and (2) the down-tearing 
 agencies. It is as though you were to set one man at 
 work building up your house, and another man at tearing 
 it down. The size and shape of your house would depend 
 upon the rates of speed at which the two men worked. 
 So it is with the earth. Agencies are at work building up 
 the land: igneous rock is pushed up from beneath, and 
 stratified rock is formed by deposit. But no sooner is 
 rock brought to the surface than it is attacked by the 
 air, by the surface water, and by plants and animals. In 
 this way bed rock, whether stratified or igneous, is 
 changed to mantle rock, and mantle rock to soil; then soil 
 is carried away by wind, rain, and stream, and deposited 
 as sediment ; the process of rock making begins over again. 
 The action of air and of the "weather" upon the crust of 
 the earth is called weathering. 
 
 Illustrations of weathering can be seen wherever rock (or any mate- 
 rial) is exposed to the air. At the base of every cliff there is a heap of 
 detritus, or talus, that has been broken off from the rock above. Around 
 every boulder in a field, if the ground is undisturbed, you can find chips 
 and dust that were once parts of the boulder. Polished marble 
 monuments become worn and rough, and limestone walls soon have 
 a surf ace that you can rub off. Artificial weathering is shown in the 
 wearing off of stone and cement sidewalks, floors, and steps, from 
 constant use. 
 
CAUSES OF WEATHERING 265 
 
 290. Causes of Weathering. The chief agencies of 
 weathering have already been named (cf. 289) ; they are 
 air, water, plants, and animals. Of these, air and water 
 are the most important. Both air and water produce (1) 
 physical changes (cf. 98) in rock, by wearing off and 
 carrying away rock material; and (2) chemical changes, 
 in that they actually alter the nature of the minerals of 
 the rock. Thus the carbon dioxide and water of the air 
 
 Fig. 228. 
 
 Sand Dune Being Carried by the Wind into the Grand Calumet River, at 
 Miller's, Ind. Negative by Geo. D. Fuller. 
 
 (carbonic acid; cf. 126) act chemically in decomposing 
 feldspar (cf. 285), in converting limestone into a soluble 
 compound (cf. 132), and in "dissolving" the cementing 
 material of many rocks, thus causing the rocks to crumble 
 Air can also act chemically upon rocks by oxidizing them 
 as it does iron (cf. 48). 
 
 We see the air (wind) acting as a mechanical, or physical, agent in 
 carrying off dust, and in moving the sand of a sandbank, or dune, and 
 
266 ROCKS AND SOIL 
 
 so shifting the whole bank (Fig. 228). A strong wind carrying sand 
 uses the sand as a cutting tool, just as a sand blast etches glass (cf. 43). 
 
 Water can carry along much larger objects than air, because it is 
 denser. Mountain torrents often roll down great boulders ; but usually 
 a river carries small gravel, sand, and the still finer particles that make 
 up mud and clay (cf. 287) . And just as wind carrying sand sculptures 
 rocks, so a river carrying sediment scours out its bed. 
 
 The expansion of water in freezing (cf. 70) is one of the most im- 
 portant causes of weathering. Most rocks are porous, and all have 
 cracks. When water freezes in the rock, the rock is forced apart. 
 It is a common experience that fragments fall from a cliff in the spring, 
 when we have frequent freezes and thaws, and when the frozen water 
 in the rock crevices melts, and releases the portions broken from the 
 cliff. 
 
 Plants have already been named as causes of weathering. The 
 decay of plants gives acids, and these attack rock (cf. 132 and 217). 
 Plant roots also act mechanically, tearing rocks apart, much as a tree 
 root breaks a sidewalk. 
 
 291. Drift. What is the origin of mantle 'rock and 
 soil? And why are soils so different? We have answered 
 these questions partly in our study of weathering. Mantle 
 rock and soil are decayed bed rock. But in this country 
 we find the mantle related to its bed rock in two entirely 
 different ways. In our southern states (except in the 
 Gulf Region) the mantle rock and the bed rock it covers 
 are of the same material. As we dig down we find the 
 rock less and less decayed, until we come to bed rock. If 
 there are boulders, they are simply harder parts of the bed 
 rock, which have not decayed as rapidly as the rest. In 
 such a case we must believe that the mantle rock was 
 formed, where it now lies, by the weathering of the bed 
 rock. Mantle rock of this sort is called residual mantle 
 rock or soil. 
 
DRIFT 267 
 
 But in the northern states the mantle is usually quite 
 different from the bed rock under it. Thus, we may find 
 a mantle of sandy soil directly over limestone, and clay 
 over sandstone. Moreover, the boulders (and there are 
 often many of them) are of materials that do not exist in 
 the bed rock of the region at all, but must have been 
 transported from a great distance. All mantle rock that 
 has been brought to a region, and not formed where we 
 find it, is called drift. 
 
 The agents that have brought drift, like the agents that produce 
 weathering, are Nature's " common workmen": chiefly air, water, and 
 ice. We have already learned that the wind can shift a great sand 
 bank (cf. 290), and that running water will carry away material from 
 one place, and then, when its velocity is checked, will deposit the 
 material at another (cf. 287 and 290). We do not need to study 
 rivers to learn how running water transports and deposits materials; 
 we can see its action after any rain. On every slope the rills that pour 
 down wear away the earth, and form grooves, or channels. The 
 transported pebbles, mud, etc., are deposited at the base of the slope. 
 A deposit of this sort, whether brought by a rill or by a great river, usu- 
 ally takes the shape of the Greek letter A (our D), and is called a 
 delta. The "Gulf Region" of this country is largely the delta of the 
 Mississippi. 
 
 But the peculiar drift of the northern states (a similar 
 drift is found in Europe) was not brought by air or by 
 water; we have abundant evidence that it was brought to 
 its present position by a great sheet of ice, which covered 
 the land for a time as the interior ice sheet now covers 
 Greenland. The ice brought fragments of igneous rock 
 from Canada, and left them in the United States. It 
 pushed before it great masses of clay filled with stones and 
 boulders, called "boulder clay," or "till." It carried 
 other boulders on its back. By means of great stones 
 
268 ROCKS AND SOIL 
 
 frozen into its base it marked the bed rock with grooves, 
 so that the direction of the ice streams can be clearly 
 traced. The time during which the ice lasted is called 
 the Glacial Period, and the material which the ice brought 
 with it is called glacial drift. 
 
 292. Erosion. We are now ready to give a name to 
 the total effect of the weathering process. We can see 
 that the land is everywhere being worn down, and that 
 the material formed in weathering is being carried by 
 rains into the rivers. This weathered material, together 
 with what the rivers themselves wear away, is being car- 
 ried into the sea. We must add to the down-tearing 
 agencies the action of the sea itself, as it wears away the 
 land by the pounding of its waves. This general cutting 
 down of the land level we call erosion, from the Latin 
 rodeo, "I gnaw." The agents of erosion are air and water 
 (including ice) ; they owe their physical energy to gravity, 
 the downward pull of the earth. 
 
 293. Exercises. 
 
 1. Is soft coal a rock? To which class does it belong? How was 
 it formed? Cf. 118. 
 
 2. Remembering that shale is hardened clay, and that clay "holds 
 water," what can you say of the conditions under which a deposit of 
 coal was formed, if we now find a layer of shale underneath it? 
 
 3. Old mortar is a mixture of sand and limestone. Which is the 
 cementing material? How can you remove it easily? 
 
 4. Why is sharp sand used in making mortar? Would sand 
 obtained from a lake beach be sharp? 
 
 5. How do pebbles become rounded? If you find a bank of rounded 
 pebbles some distance from any body of water, what do you con- 
 clude? 
 
SOIL 269 
 
 6. Glass scratches limestone, and is scratched by quartz; which H 
 the hardest of these three? How does the finger nail compare with 
 these substances in hardness? 
 
 7. Suppose that the rock directly under the Niagara River (Fig. 
 225) were suddenly to become a soft shale; what would be the effect 
 upon Niagara Falls? Do you think the Falls have always been where 
 they are now? Why? 
 
 8. Compare the composition of granite and of porcelain. Which 
 rock may be called the cementing rock of granite? 
 
 9. In what forms besides clay tablets did ancient peoples leave their 
 records? 
 
 294. Soil. Soils have as their foundation weathered 
 rock. Usually this is a mixture of sand and clay (cf. 
 285), and is called loam. Besides loam, a fertile soil 
 requires humus, or vegetable mould. This is the material 
 formed by the growth and decay of plants and trees; we 
 see it in the black top-soil of a forest. Growing plants 
 need humus as a food; but it is more than this, for it is 
 the means by which the minerals of the loam are prepared 
 for the use of the plant. The subsoil lies below the culti- 
 vated soil. On its qualities the qualities of the upper soil 
 depend. 
 
 Soil has not only the chemical materials of loam, humus, 
 air, and water, but it contains multitudes of the lower 
 organisms, such as bacteria (cf. 56 and 324). One who 
 studies the soil carefully soon realizes that it is not a dead, 
 inorganic mixture, but a world of life and activity. He 
 also learns that a fertile soil required centuries for its 
 development, and that if it is once destroyed, it cannot be 
 restored in a year or two. Every agriculturalist needs to 
 know what his soil contains, what it lacks, for what crop 
 it is suited, and how it ought to be handled, so that it will 
 
270 ROCKS AND SOIL 
 
 give as great a present yield as possible, without losing its 
 fertility for the future. And because all of us, no matter 
 where we live, depend upon soil products, we ought all to 
 be interested in the soil and its welfare. 
 
 295. Structure of Soil. We can classify soils as to the 
 way in which they were formed, and also as to their 
 structure. A sedentary, or residual, soil is one that was 
 formed where we find it (cf. 291). An alluvial soil is 
 one formed by deposit from water. Such is the soil of 
 the Gulf Region and of the Nile Valley. Glacial soils are 
 made up of glacial drift. 
 
 Soils that are very sandy are called light soils. They are easy to 
 cultivate, and they absorb water easily. But they also lose it easily, 
 so that their plants cannot live long in dry weather. Soils with an 
 excess of clay are called heavy soils. They take up water slowly; but 
 when they have taken it up, they hold it very firmly. A heavy soil, 
 on level ground, and in a region of good rainfall, is likely to be swampy. 
 Such soils often need to be drained by the digging of ditches and the 
 laying of " tiles," or pipes. If heavy soils are ploughed while too wet, 
 they cake, forming large, hard lumps separated by cracks. 
 
 The plant gets its food from that part of the soil that is 
 in solution; hence a soil must contain water. It must also 
 contain air for the respiration (cf. 52) of the roots and 
 underground stems. For these and other reasons the 
 size of the soil particles, and the distance they are apart, 
 are of great importance for the growing of crops. Be- 
 ginning with the largest, we may classify soil particles as 
 gravel, sand, silt, and clay. Dry clay particles form a 
 dusty powder, like flour. From a soil of the right degree 
 of fineness a plant can draw water even in dry weather, 
 because the water can be transferred, by capillary action 
 
TILLING THE SOIL 
 
 271 
 
 (c/. 32), from the place having more water to the place 
 having less. Hence the effects of a drouth are not felt 
 by the plant for a long time. 
 
 Besides the water that is held, by capillary action, 
 between the particles of the soil, each minute soil particle 
 has a film, or covering, of water, which it does not lose 
 entirely, even in dry weather. This water film, like 
 capillary water, is a solution containing the materials 
 needed by growing plants. 
 
 296. Tilling the Soil. Tillage is the working of the 
 soil by the use of implements. The implements may be 
 simple garden tools, such 
 as the spade and hoe, or 
 they may be plows, culti- 
 vators, and seeders, 
 drawn by horses or en- 
 gines. We till the soil 
 in order to improve its 
 structure, so that it may 
 retain water better, and 
 may permit plants to get 
 their nutriment from a 
 wider range. We also 
 use tillage to turn under 
 rubbish, manure, and 
 fertilizers, and to make 
 them part of the soil. Seeders deposit seeds and plants 
 in the position in which they are to grow. They usually 
 turn the soil at the same time. 
 
 Plowing (Fig. 229) consists in forcing a slanting knife or shovel,. 
 
 Fig. 229. 
 
 Egyptian Pbwing. Copyright, International 
 Stereograph Co., Decatur, 111. 
 
272 ROCKS AND SOIL 
 
 called a plowshare, to a certain depth into the soil, and then turning the 
 slice of soil over upon itself in the furrow. The slice is usually laid at 
 an angle of 25 to 50 (half a right angle is 45) with a horizontal plane, 
 ,so that the edge of the slice projects from the ground. Plowing not 
 only loosens the soil, and breaks it up, but it also brings to the surface 
 new material for the plant's growth. Modern agriculture has greatly 
 increased the depth of plowing, as well as its extent. Primitive peoples 
 
 Fig. 230. 
 A Disc Plow. The whirling discs are on the right. Courtesy of Deere and Co. 
 
 merely scratched the surface, and were able to till only a limited 
 area of land. 
 
 Cultivating is shallow plowing, or stirring, of a soil, usually after a 
 crop has begun to grow. Its purpose is chiefly to keep the surface soil 
 in a powdered condition, so that it will retain moisture. Cultivating 
 also destroys weeds. In dry farming frequent cultivating is carried 
 on; this produces a deep dust mulch, or covering, which prevents the 
 evaporation of water from the surface, and yet permits moisture to 
 rise from the subsoil by capillary action. 
 
 Plows and cultivators are of many types; each is good for a particu- 
 
IRRIGATION 273 
 
 lar kind of soil and a particular kind of work. Disc plows (Fig. 230) 
 have a revolving cutting instrument, called a disc, instead of a plow- 
 share. The friction is less than with an ordinary plow, because the 
 cutting tool rotates through the soil instead of sliding through it (cf. 
 206). 
 
 Gang plows consist of many plowshares attached to one frame. 
 They can be used on large, level areas, and are drawn by a large num- 
 ber of horses or by engines (tractors; Fig. 231). 
 
 Fig. 231. 
 
 A Gang Plow. This one has ten plowshares; behind it is a cultivator. 
 Courtesy of Deere and Co. 
 
 297. Irrigation. By irrigation we mean the adding of 
 water to a soil to make up for a lack of rain. Irrigation 
 may be carried on anywhere, but it is especially im- 
 portant in desert areas. In this country it is used to 
 supply water for farming and fruit-raising to the sections 
 having a small rainfall (cf. 42 and 272). Even in 
 almost rainless regions there is usually a lake or stream 
 that has a large amount of water during the rainy season, 
 or in the spring, when the snows melt in the mountains. 
 But in the summer, the growing season of crops, there is no 
 water. Men therefore impound the water in large reser- 
 
274 ROCKS AND SOIL 
 
 voirs at the time there is an abundance of it, and then let 
 it run off slowly during the dry period. Where natural 
 streams are wanting, irrigation canals carry the water from 
 the reservoirs to the farms. The reservoir is made by the 
 building of a dam across the outlet of a lake, or at some 
 suitable place in a stream. The water flowing over the 
 dam forms an artificial waterfall, which is often used for 
 power (qf. 162). 
 
 There are several methods of irrigation. One is to flood the land to 
 a certain depth, and then to allow the water to sink into the soil. The 
 flooding is repeated at intervals. Another way is to build pipes having 
 openings that throw sprays of water over the land; this is like rain. A 
 third way is to have furrows for the water, and to let it soak sidewise 
 into the growing area. 
 
 For that form of irrigation which we call " watering the garden" 
 the following suggestion is excellent: ''The hose should be used in a 
 manner to resemble rain. Give the garden a good soaking, and then 
 let it alone until your daily observation shows you that it has dried 
 out to a depth of from two to four inches from the top. Then repeat 
 the watering. The practice of frequent, shallow watering is wrong, 
 as it induces shallow rooting; when the watering is neglected, the roots 
 near the surface die, and the plants suffer. If a garden is properly 
 watered, the roots will go down some distance; if watering is too shal- 
 low, they will run along horizontally, just under the top of the ground. " 
 
 298. Fertility. The fertility of a soil is its crop-pro- 
 ducing power. This power depends upon the elements 
 in the soil, upon the physical condition of the soil, upon 
 the water supply, and upon other conditions. None of the 
 conditions named can make up for an unfavorable climate. 
 A soil that has all the conditions for growing corn in Iowa 
 may be barren, so far as corn is concerned, in Labrador. 
 
 It seems likely that at least 10 chemical elements are 
 
LOSS OF FERTILITY 275 
 
 taken from the soil by plants; hence these must be present 
 to make a soil fertile. Other elements are needed too, 
 such as carbon, hydrogen, and oxygen, but these are taken 
 from the air and from water. The 10 necessary elements 
 are: nitrogen, potassium, phosphorus, magnesium, sul- 
 phur, sodium, chlorine, iron, silicon, and calcium. Not 
 one of these is present in soil as an element, but each forms 
 a part of some compound. Thus, the potassium is a part 
 of clay; the silicon a part of clay and of sand; the nitrogen 
 a part of the proteids of the humus ; the phosphorus a part 
 of calcium phosphate. 
 
 While 10 soil elements are needed for plants, only 3 or 4 are used up 
 rapidly. These are nitrogen, phosphorus, potassium, and sometimes 
 calcium. It is often supposed that if any compounds of these neces- 
 sary elements are present, the soil is fertile. This is a mistake. The 
 elements must be in such compounds that the plant can absorb and 
 use them. One of the necessary conditions is that they must be in 
 compounds that are somewhat soluble; for it is the soil solution (cf. 
 295) that actually reaches the absorbing organs of the plant. How- 
 ever, these compounds must not be too soluble, or fertility will disap- 
 pear, because the rain will carry the compounds away. 
 
 In speaking of crops we must not forget the forest; for trees are a 
 crop, as well as rice or wheat. 
 
 299. Loss of Fertility. When we realize that plants 
 must be able to find certain elements in the soil, we can 
 see that the loss of these elements means the loss of 
 fertility. 
 
 Fertility is lost, in the first place, by the growing of 
 crops; for crops are grown in order that they may take up 
 the constituents of the soil, and work them up into food 
 for man and animals. This loss of fertility cannot be 
 avoided. But there are many other causes of loss that 
 
276 ROCKS AND SOIL 
 
 can be guarded against. One of them is the too rapid 
 removal of soluble compounds, by drainage. This is 
 often due to improper cultivation of sloping ground. 
 Nitrogen compounds, especially, disappear in this way; 
 for they are easily converted into nitrates of metals (cf. 
 220), which are very soluble. 
 
 Nitrogen leaves a soil not only because its compounds are dissolved, 
 but because they are decomposed, so that the nitrogen escapes back into 
 the atmosphere (cf. 55). It was found, in Minnesota, that a long- 
 continued cultivation of wheat upon a piece of land caused 6 times as 
 much nitrogen to leave the soil as was removed by the crops harvested. 
 
 If certain crops are grown too long upon a piece of land, its soil 
 becomes acid, or "sour." This is one of the common causes of loss of 
 fertility (cf. 302). Attempts to grow clover, alfalfa, etc., upon acid 
 soil are almost sure to fail. 
 
 300. Preserving and Restoring Fertility. While we 
 cannot help removing fertility when we remove a crop, 
 yet the loss is often much greater than it should be. 
 Farmers are learning that, as far as is possible, they must 
 put back upon the land everything not actually sold from 
 it. Hence they need to preserve carefully, and to use, 
 manure, the most common of farm fertilizers, so as to 
 restore humus to the soil. 
 
 Another great aid in the preserving of fertility is good 
 management. A farm cannot pay a profit if it sells the 
 fertility of its soil at a low price. The crops that are sold 
 should be those that take the least possible fertility from 
 the farm. The crops that take much fertility, and them- 
 selves bring a low price, should not be sold from the farm, 
 but should be converted into products that have a greater 
 market value. Thus, when grains are cheap, they should 
 
ROTATION OF CROPS 277 
 
 be used as cattle food, because the price received for farm 
 fertility as meat is usually greater than the price received 
 for it as grain. Besides, when cattle are raised, much of 
 the farm's fertility can be restored, as manure. 
 
 Dairying is profitable, both because dairy products bring a high 
 price, and also because they do not remove much fertility. If we sell 
 butter, for example, we are selling chiefly fat, composed of carbon, 
 hydrogen, and oxygen (cf. 224) ; that is to say, we are selling a product 
 made out of water and the carbon dioxide of the air (cf. 310). 
 
 301. Rotation of Crops. We can preserve the fertility 
 of a field by plowing it, and then letting it lie unused, or 
 ' ' fallow," for a year or two. But this is expensive, for the 
 field is bringing in no return. A better method is to 
 rotate, or change, its crops. In this way the same 
 elements of the soil are not removed year after year. 
 Sometimes rotation consists in sowing buckwheat, clover, 
 etc., and then, when they have grown, in "plowing them 
 under" (cf. 56). This treatment restores nitrogen to 
 the soil. Crops so used are called green manures. 
 
 The rotation of crops depends on the fact that different 
 crops remove different materials from the soil. Grains, 
 such as wheat, take up much phosphorus; grass takes up 
 little phosphorus. Corn is exhausting to the soil, for it 
 removes much of all three of the elements nitrogen, 
 phosphorus, and potassium. If the crop is changed at 
 intervals, the field that has lost a great deal of an element 
 has time to recover, and to get enough of that element into 
 a form in which the plant can use it. 
 
 Rotation has other good results. The root systems of plants are 
 different (cf. 316) ; hence one plant often breaks up the ground for 
 another. A long growing of the same plant in a field frequently 
 
278 ROCKS AND SOIL 
 
 allows plant diseases or harmful insects to get a strong foothold. 
 When the crop is changed, the new plant is usually immune; that is, 
 not affected by the disease. Certain weeds act in a similar way. 
 They grow readily in fields containing some one crop, and not so easily 
 along with other crops. It has also been found that many plants 
 leave in the soil substances called toxins, which act as poisons for the 
 same kind of plant in following years. 
 
 302. Artificial Fertilizers. Artificial, or commercial, 
 fertilizers are used when natural manures are not abun- 
 dant enough, or not of the right sort. As commonly used 
 they contain one, two, or all three of the elements nitrogen, 
 phosphorus, and potassium. One having all three ele- 
 ments is called a "complete" fertilizer. 
 
 The potassium compounds needed by the soil are ob- 
 tained from wood ashes (when these are to be had; cf. 
 217), or from deposits, as at Stassfurt, in Germany. 
 Recently some lavas, and some deposits in the West, have 
 been found that give potassium compounds useful for 
 fertilizers. 
 
 The phosphorus of fertilizers is in the form of phos- 
 phates, salts of phosphoric acid (cf. 214 and 221). 
 Rock phosphate and the ashes of bones both contain 
 calcium phosphate. They are sold in the form of a very 
 fine powder. 
 
 Calcium phosphate is very slightly soluble, so the 
 manufacturers of fertilizers often change it to acid calcium 
 phosphate by treating it with sulphuric acid (cf. 214). 
 The acid phosphate is called "superphosphate." In 
 purified form it is used for "acid phosphate" baking pow- 
 ders (cf. 130). Land plaster is the crude material 
 obtained when rock phosphate is treated with sulphuric 
 
SUMMARY . 279 
 
 acid. It contains much calcium sulphate, or gypsum. 
 Sometimes the name is used for powdered gypsum itself. 
 Nitrogen is obtained for fertilizers in a number of forms. 
 Some of it comes as sodium nitrate, or " Chili saltpeter," 
 from the western coast of South America. Ammonia and 
 ammonium compounds (cf. 112) are rich in nitrogen, and 
 are used as fertilizers. The waste obtained in slaughter 
 houses, such as scraps of meat, bones, hair, etc., is also 
 rich in nitrogen, and is converted into fertilizing material. 
 The use of such nitrogen compounds depends on the fact 
 that oxidizing bacteria (cf. 58 and 324) change a great 
 deal of the nitrogen into nitrates (cf. 220 and 299) for 
 the use of the food plants. 
 
 If a soil becomes acid, or "sour," it needs a basic substance (cf. 
 220) to make it "sweet." Lime and limestone are used for this, 
 purpose. These substances also have important effects on the struc- 
 ture of soil (cf. 295). A very sandy soil is not fertile, because its. 
 particles are too far apart, and do not retain water. Lime and lime- 
 stone help to cement the separate grains together (cf. 285), forming a 
 less porous soil. While they make a sandy soil less porous, lime and 
 limestone make a clayey soil more porous; they separate the particles 
 of clay, which cohere too closely, by forming a "nucleus," or center, 
 to which the clay particles can adhere. The soil particles are thus 
 made larger, and the soil more porous. 
 
 303. Summary. The earth's crust consists of mantle rock and bed 
 rock. Exposed bed rock is an outcrop. Soil is the portion of the 
 mantle that is used for growing crops. 
 
 Common rocks are sandstone, limestone, shale, granite, and con- 
 glomerate. 
 
 Rocks are stratified, unstratified, and metamorphic. 
 
 Stratified rocks are also called sedimentary, or aqueous, rocks. 
 They were formed, as deposits, under water. 
 
 Unstratified rocks are also called igneous rocks. They are found 
 
280 ROCKS AND SOIL 
 
 under all rocks, and often in the cracks of stratified rocks or as over- 
 flows over stratified rocks. 
 
 Metamorphic rocks are altered stratified rocks. . 
 
 Weathering is the decay of rock because of the action of the ' ' weath- 
 er." It is due to both physical and chemical action. 
 
 Detritus, or talus, is the weathered rock at the base of a cliff. 
 
 Mantle rock is either residual soil or drift. 
 
 Drift has been brought by air, water, or ice. Alluvial soil was de- 
 posited from water. 
 
 Glacial drift was brought by ice. In this country it is found as far 
 south as the mouth of the Ohio River. 
 
 Erosion is the general cutting down of the land level. The agents 
 of erosion get their energy from gravity. 
 
 Soil consists of loam, humus, and small organisms, such as bacteria. 
 It must also contain water and air. 
 
 According to their general structure, soils are either light or heavy. 
 
 Soil particles are classified as gravel, sand, silt, and clay. 
 
 Water is transferred through soil largely by capillary action. 
 
 Tillage is working the soil with implements. Plowing consists in 
 turning the soil over. Cultivating is shallow plowing. 
 
 Irrigation is the artificial watering of land. 
 
 The fertility of a soil is its power of producing crops. 
 
 At least 10 chemical elements are taken out of soil by plants, besides 
 the carbon, hydrogen, and oxygen taken from air and water. 
 
 The 3 soil elements that are used up most rapidly are nitrogen, 
 phosphorus, and potassium. 
 
 Fertility is lost by the growing of crops, by improper drainage, by 
 permitting a soil to become sour, by growing one crop too long, by 
 selling the fertility in the wrong form. 
 
 We can restore fertility by allowing land to ' ' lie fallow/ 7 by rotating 
 crops, and by using fertilizers. 
 
 304. Exercises. 
 
 1. Are wood ashes as good as lime for making an acid soil sweet? 
 Explain. 
 
 2. A year or two after a fire has ' ' burned over " land having an acid 
 soil there is often a wonderful growth of plants; why? 
 
EXERCISES 281 
 
 3. Does the freezing of the ground in winter play any part in pre- 
 paring a "heavy" soil for plant growth? Why? 
 
 4. Find out from some farmer or gardener what kind of a soil, sandy, 
 silty, or clayey, is best adapted to the growing of garden vegetables; of 
 corn; of grains like wheat and oats; of hay. 
 
 5. Humus absorbs water more readily than clay does, and less 
 readily than sand. What advantage is there in having humus in a 
 soil? 
 
 6. What is the economy of using the cream of milk for butter, and 
 feeding the skimmed milk to young stock, such as calves and pigs? 
 
 7. What is the economy of having birds on a farm? 
 
 8. Is there economy or waste in burning up the stubble of the farm? 
 Give both sides. 
 
CHAPTER XV 
 
 PLANTS 
 
 305. Plants and the Soil. The close connection be- 
 tween plants and the soil has already been spoken of 
 (cf. 298). Plants take out of the soil and the air about 13 
 elements; out of these elements the higher plants, build 
 up complicated and beautiful structures, known as roots, 
 stems, leaves, flowers, and seeds. We call these struc- 
 tures the organs of the plant (cf. 3). How is it that 
 plants are able to bring about this wonderful change of 
 the materials of soil and air into living plant material, or 
 plant ' ' tissue?" For the answer, in so far as men know it, 
 we shall need to go to textbooks of Botany. It is enough 
 to say that plants are living organisms, and that if we 
 put the embryo plant, that is, the plant which is enclosed 
 in the seed, into fertile soil, and leave it exposed to the 
 sunshine, the air, and the rain, it will sprout and grow. 
 Sooner or later it will become a full-grown plant, like its 
 parent, and will be able to carry on all the processes of 
 which its parent was capable. 
 
 306. Functions of Plants. When we enumerate the 
 organs of the higher plants, as we did in the preceding 
 section, we at once think of some special function, or duty, 
 which each performs for the plant. We can classify all 
 these special functions as parts of two general functions, 
 which all plants must carry out; for life depends upon 
 
 282 
 
FUNCTIONS OF PLANTS 283 
 
 them. Plants must feed, and for this purpose they must 
 have organs of nutrition. Then, if the species, or kind, 
 of plant is to survive, there must be organs for the pro- 
 ducing of new members of the species; these are the 
 organs of reproduction. Animals, as well as plants, must 
 carry out these two elementary processes successfully, if 
 they and their kind are to continue on the earth. The 
 higher plants carry out the process of nutrition in their 
 roots, stems, and leaves, and that of reproduction in 
 flowers and seeds. 
 
 But the plant, well as it may be fitted to live, is of no 
 consequence by itself. It must have proper surroundings, 
 such as soil, sunlight, air. The presence of other plants, 
 of the same or a different kind, and of animals, also 
 affects greatly the future of the plant. We call all these 
 surroundings of an organism, which help or hinder its 
 development, the environment of the organism. 
 
 It requires only a little observation to show us that the different 
 kinds of plants have become accustomed to certain environments. 
 Some do best in shady places, others in sunshine; some prefer sandy 
 soil; some, clay; some, humus. We say that each species, or variety, 
 has adapted itself to, or fitted itself for, its environment. 
 
 All the conditions, or influences, of the environment call out some 
 action on the part of the plant. We call the environment's influence 
 the stimulus (plural, stimuli; we have the same meaning in "stimu- 
 late"); the action of the plant we call its reply, or response, to the 
 stimulus. Thus, we say that light is a stimulus to our eyes, and sight 
 is the eyes' response. Light is a stimulus to the sunflower, too; the 
 turning of the sunflower toward the light is one way in which it re- 
 sponds to light. The environment is not always quite the same; so 
 plants are successful or unsuccessful according as they have, or have 
 not, developed parts to meet the conditions and changes in their envi- 
 ronment. 
 
284 
 
 PLANTS 
 
 the earth. 
 
 307. Germination of a Bean. When we put a seed into 
 the ground under proper conditions, it responds to the 
 stimuli it receives, by germinating. Germinating means 
 all the changes in the contents of the seed until the tiny 
 plant in the seed has become an independent plant, or 
 seedling. The bean gives us a convenient seed for study. 
 If it is soaked in slightly warmed water, say, over night, 
 the shriveled surface becomes distended, or filled, by the 
 water, which passes, by diffusion, through the "skin" 
 (cf. 106). If the bean is then placed in a box of earth, 
 set in a sunny window, and the earth is kept moist, growth 
 will begin. In a few days a curved "stem" will push up 
 When this straightens itself, it raises into the 
 air the two halves of the bean; between 
 them there is a pair of tiny leaves. At 
 the lower end of the small stem roots are 
 developed. As the bean seedling becomes 
 older, it forms pair after pair of true 
 leaves, always from a growing "tip"; the 
 "halves" of the bean become thinner, turn 
 green, and finally fall off. The plant is 
 now independent (Fig. 232). 
 
 What are the parts of the original 
 seed, and what change do they undergo in 
 germinating? We can answer these ques- 
 tions by studying the soaked bean before 
 planting. We find that the "halves" are enclosed in a 
 tough ' ' skin" ; this is the testa. All inside the testa is the 
 embryo. The "halves" are called cotyledons, or seed 
 leaves. They contain food for the embryo. It is for 
 this food that we eat the bean. Between the cotyledons 
 
 FIG. 232. A Bean 
 Seedling, with 
 Its Roots, Stem, 
 Cotyledons, First 
 Pair of True 
 Leaves, and Leaf 
 Bud. 
 
LEAVES 285 
 
 there is a tiny bud, called the plumule; this gives rise to 
 the stem and true leaves of the seedling. The cotyledons 
 are at one end of a minute, embryo stem, called the 
 hypocotyl (from hypo, i ' under, ' ' and cotyledon) . That end 
 of the hypocotyl which does not bear the plumule sends 
 out the roots of the seedling. 
 
 308. Other Seeds. The germination of other seeds is slightly 
 different from that of the bean. In many seeds the food of the embryo- 
 is not stored in the cotyledons, but in a space surrounding the embryo; 
 food so stored is called the endosperm. In the pea the cotyledons 
 remain within the testa, supplying the nutrition required by the 
 growing embryo and seedling. In the castor bean the cotyledons es- 
 cape, but they differ from those of the garden bean in that they become 
 large and green, and do the work of true leaves. 
 
 A large class of plants has only one cotyledon. These are called 
 monocotyls, while beans, peas, etc., are called dicotyls. Corn (maize) 
 is a monocotyl. In corn the embryo is at one side, just beneath the 
 testa. When the testa breaks open, the embryo sends its plumule- 
 upward, and the root end of the hypocotyl downward. The cotyledon 
 and the endosperm remain inside the testa. 
 
 309. Leaves. The expanded part of the leaf is called 
 the blade. In some plants the blade is attached directly 
 to the plant stem; in other plants there is a short stalk, 
 called the petiole. Sometimes the plant produces tiny 
 blades, called stipules, at the place where the petiole 
 joins the stem. 
 
 The blade is marked by a network of veins. If there is 
 a prominent central vein, this is called the midrib. Veins 
 are arranged in three general ways (Fig. 233). The 
 first leaf (on the left of the figure) is palm-veined; the sec- 
 ond, feather-veined; the third, parallel-veined. A leaf 
 
286 
 
 PLANTS 
 
 may be broken up into leaflets, as in the clover; it is then 
 called a compound leaf. 
 
 Where the heat of the sun is not too severe, as in temperate climates, 
 leaves are arranged on the stem in such a way that they shall receive 
 as much light as possible. Sometimes leaves alternate upon the stem; 
 sometimes two leaves are opposite each other. Often many leaves 
 
 FIG. 233. Leaves of the Maple, Birch, and Wild Lily-of- the- Valley . 
 
 are opposite one another; they are then said to be whorled. Often all 
 the leaves are attached at almost the same place on the stem, but take 
 the form of a rosette, so that all shall get light. 
 
 The leaf is made up of more or less spongy tissue, con- 
 sisting of layers of cells. The cells contain living, cell 
 material, or protoplasm (cf. 323), and a green material, 
 called chlorophyll (cf. 110). The outside of the leaf is 
 covered with a skin, or epidermis. This is usually color- 
 less. In the wall of the epidermis there are slits, which 
 can be varied in size by the plant; these are called sto- 
 mata (Fig. 234), meaning "mouths." The stomata are 
 the "breathing pores" of the leaf, and enable the plant 
 to take in air, and to give off the gases it does not 
 need. They also control the rate of evaporation of water 
 
THE WORK OF LEAVES 
 
 287 
 
 from the leaf. In leaves that take a horizontal posi- 
 tion the stomata are on the under side. Sometimes 
 there are as many as 100,000 to 
 each square inch. 
 
 ;: Guard CH 
 
 Opening 
 
 FIG. 234. Breathing Pore 
 (Stoma) of a Leaf. 
 
 Oxygen 
 
 310. The Work of Leaves. The 
 
 leaf has several very important du- 
 ties to perform. For one thing, it 
 controls the rate at which water 
 shall evaporate from the plant (cf. 
 309). Then it also serves as the 
 "breathing apparatus" of the plant, 
 taking in air, and giving off carbon 
 dioxide, etc. Its third great duty is to serve as the 
 
 "laboratory" of the plant. 
 Here carbon dioxide and 
 water are brought together, 
 and are combined chemically 
 in compounds that the plant 
 uses for food and for the 
 building of its tissue. These 
 compounds are sugar, starch, 
 etc. ; they belong to the class 
 known as carbohydrates 
 (cf. 184). 
 
 There is more oxygen in 
 the carbon dioxide and 
 water, taken together, than 
 is needed to form the carbohydrate; so the excess of oxy- 
 gen is given off into the air (Fig. 235). As a result, the 
 green plant takes up carbon dioxide from the air, and 
 
 Carbon dioxide 
 
 FIG. 235. The leaves act upon the carbon 
 dioxide, and produce oxygen. 
 
288 
 
 PLANTS 
 
 gives back oxygen in its place. In this way the process 
 by which the plant prepares carbohydrates is also the 
 process by which it purifies the air for the use of animals 
 (cf. 58). The making of carbohydrates out of carbon 
 dioxide and water requires chlorophyll and light (usually 
 
 sunlight). The combina- 
 tion generally takes place 
 in leaves; but other green 
 parts, such as stems, also 
 carry it out. 
 
 311. Modified Leaves. 
 Plants often have spe- 
 cial ways of supporting 
 themselves or of getting 
 food. Thus, plants with 
 slender stems have the 
 climbing habit. To carry 
 out new functions the 
 plant seems to have new 
 organs ; but if we examine 
 the plant carefully, we 
 shall find that the new 
 apparatus is simply one 
 of the original structures (stem, leaves, etc.), altered to meet 
 the new need. Thus, the morning-glory climbs because its 
 stem is sensitivej and twines around a support, such as a 
 string or a pole, Other plants have tendrils for support. 
 
 The tendrils of the pea are changed parts of its compound leaf 
 (cf. 309). Sometimes the tendrils, instead of twining about an erect, 
 straight object, twist themselves into the rough bark of a tree. But 
 
 FIG. 236. A Spreading Elm. Courtesy of the 
 Field Museum of Natural History. 
 
STEMS 
 
 289 
 
 in the ivy, which depends on brick or stone walls for support, the tendril 
 is still further changed to a sucker, or disk. Leaves are often changed 
 to thorns, as in the barberry. 
 
 But it is in the pitcher plants, the sundews, and the "Venus fly 
 traps" that we see the greatest change in leaves. In these plants the 
 leaves are altered so as to form wonderful vessels, or traps, for the 
 capturing of insects. The insects are digested by the plant. Here 
 the order of nature is reversed; for the plant consumes the animal, 
 instead of being consumed by the animal. 
 
 312. Stems. In our study of the bean (cf. 307) we 
 learned that the plumule becomes the leaves of the young 
 seedling. The growth of the plumule also produces a 
 
 FIG. 237. Under this "live oak" Sidney Lanier wrote "Marshes of Glynn." Note the 
 Spanish Moss on the tree. Courtesy of the Field Museum. 
 
 part connecting leaf and root; this is the stem, or stalk. 
 The leaves borne by the stem ordinarily appear only at 
 certain places, called the joints, or nodes. The jointed 
 structure of the stem is readily seen in the bamboo fish- 
 ing pole. The region of the stem just above the place 
 
290 
 
 PLANTS 
 
 where a leaf is attached is called the axil of the leaf. Buds 
 
 and branches are usually formed only in the axils of leaves 
 
 (cf. 315). 
 Stems are of many different sorts. Some are strong 
 
 and stiff, and able to bear a great deal of weight, as is the 
 
 case in trees; some run 
 along the ground, as in 
 the strawberry plant ; and 
 some seek a support, as 
 does the stem of the 
 morning-glory. 
 
 Branches usually are 
 in such positions that the 
 leaves get overhead light. 
 Even when branches be- 
 gin by growing upward, 
 they are commonly 
 pulled down by gravity, 
 as they grow larger, to a 
 more or less horizontal 
 position. 
 
 FIG. 238. A Hickory (Hicoria pecan). 
 Museum of Natural History. 
 
 Field 
 
 In trees the main trunk 
 sometimes grows straight up- 
 ward, as in the poplar and fir 
 
 (cf. Fig. 251, 327), and sometimes is divided again and again, as in 
 the elm (Fig. 236), oak (Fig. 237), beech, and hickory (Fig. 238). As 
 a result of the two kinds of branching, the general outline of a tree 
 may be either cone-shaped or spreading. 
 
 313. Structure of Stems; Wood. If we cut across a 
 growing woody stem, such as a lilac or a maple, we shall 
 be able to make out four distinct regions (Fig. 238a). 
 
STRUCTURE OF STEMS; WOOD 
 
 291 
 
 Epidermis 
 
 Heart 
 Wood 
 
 Annual 
 Ring 
 
 (1) An outer covering or skin, called the epidermis, as 
 in the leaf. 
 
 (2) Next inward, a layer of soft tissue, called the 
 cortex. This is generally green. 
 
 (3) A wood layer. 
 
 (4) A central portion, called the pith. When trees 
 are hollow, it is 
 
 usually the pith 
 and the wood 
 nearest to it that 
 have decayed. 
 
 From the pith 
 to the cortex 
 there are rays, 
 like the spokes of 
 a wheel. These 
 are called pith 
 rays, or medullary 
 rays. The pith 
 rays divide the 
 wood layer into 
 woody bundles. 
 
 The arrange- 
 ment just given is that present in all dicotyls (cf. 308) and 
 in plants like pines and firs (gymnosperms; cf. 327). In 
 plants having only one cotyledon in the seed, such as corn, 
 the woody bundles are not arranged around a pith, and 
 separated by pith rays, but are scattered through the stem. 
 
 Trees with the four regions just named can grow thicker 
 year by year; the wood is usually added in rings, called 
 annual rings (cf. Fig. 238a). If only one is produced in a 
 
 Sap Wood 
 
 Medullary Ray 
 
 FIG. 238a. Cross Section of a Woody Stem. 
 
292 PLANTS 
 
 year, then the number of rings indicates the age of the 
 tree (Fig. 239). Some of the "big trees" of California 
 are estimated to be between 2,500 and 3,000 years old. 
 They are often 35 feet in diameter and over 300 feet high. 
 
 Sawing of Wood. Logs of "soft" wood, such as pine, spruce, and 
 hemlock, are often floated down streams to the sawmills. Fig. 240 
 shows a log "boom," or enclosure, in which logs are kept until they are 
 
 FIG. 239. Felling a Great Tree. Courtesy of the Field Museum. 
 
 sawed. The log is hauled out of the water, and into the mill, by means 
 of a moving, "endless" chain. Here it is gripped by steel "dogs," 
 which hold it firmly to the log carriage. The carriage is then run up 
 to the saw. The saw first cuts off the rounded sides of the log, as 
 "slabs." In ordinary sawing, three sides are thus "squared"; then 
 the squared log is cut into boards by cuts made parallel to one another. 
 This is slash-sawing. 
 
 Radial, or rift, sawing is a cutting along lines from the outside of 
 the log toward the center. The cuts are thus made through the pith 
 rays (Fig. 240a). In slash sawing, the central board is the only one 
 
STRUCTURE OF STEMS; WOOD 
 
 293 
 
 cut in this way. Boards made by sawing through the pith rays are 
 better than slash-sawed boards, because they warp less, and have a 
 more even grain. Quarter sawing is radial sawing. The log is first 
 
 FIG. 240. A Log Boom. Courtesy of the Field Museum. 
 
 cut lengthwise into quarters, and boards are cut from the quarters as 
 nearly through the pith rays as is possible. The pith rays are the 
 ''silver flakes" that give to quarter-sawed oak its beautiful marking. 
 
 
 
 FIG. 240o. A Lengthwise Section through the Pith Rays, Showing the Ends of Quarter- 
 Sawed Boards. 
 
 Knots in boards are the remains of branches which grew on the 
 trunk when the tree was young. In old trees, these remains have 
 been entirely covered up by the annual rings. 
 
294 
 
 PLANTS 
 
 314. Sap. The water and dissolved food which the 
 root takes from the soil rise through the stem to the 
 leaves. This dilute solution is called sap. The sap 
 passes upward through the cells that make up the woody 
 
 layer of the stem. As the 
 tree grows older, the sap 
 leaves the inner wood, 
 which is near the pith, 
 and passes upward only 
 through the outer rings, 
 near the cortex. The in- 
 ner wood is called heart 
 wood ; the outer, sap wood 
 (cf. Fig. 238a). For lum- 
 ber, the heart wood is 
 greatly preferred, because 
 it does not warp as much, 
 or rot as readily, as sap 
 wood. 
 
 The sugar maple stores 
 away sugar in its woody 
 tissue. In the following 
 spring the water that rises from the roots dissolves the 
 sugar, producing maple sap. Men drill holes at intervals 
 into the sap wood, and insert spouts, down which the sap 
 drips into collecting buckets (Fig. 242). When the sap 
 is boiled down, it gives maple syrup and maple sugar. 
 
 315. Buds. Buds are structures for the building of 
 leaves, stems, and flowers (Fig. 243). Leaf buds are a 
 stem and its leaves in undeveloped form. While in the 
 bud, the stein is very short; so that its nodes are close 
 
 FIG. 242. Collecting Maple Sap. The buckets 
 ought not to be open, and there are too 
 many on the tree. Courtesy of U. S. Dept. 
 of Agriculture. 
 
ROOTS 
 
 295 
 
 together. On this account, the leaves, which on the 
 grown stem are far apart, overlap one another in the bud, 
 and form a compact bundle. This pro- 
 tects the tip of the branch until it is 
 ready to grow. The most common buds 
 are dry and shiny on the outside, and 
 are planned to keep out moisture. In 
 winter buds the inside of the leafy covers 
 is often wooly, in order to protect the 
 young leaves and stem from sudden 
 changes of weather (cf. 75). 
 
 Ovules 
 
 FIG. 243. Cross Section 
 of a Rose Bud. 
 
 The "growing tip" of each stem and branch has a terminal, or 
 *' end," bud. Buds that arise in the axils of leaves (cf. 312) are called 
 axillary buds. Buds that occur in unusual places, that is, not at the 
 tips of branches or in the axils of leaves, are called "unusual," or 
 adventitious, buds. The young shoots that are sent up by the stump 
 or the root of a tree are from adventitious buds. 
 
 316. 
 
 carried 
 
 Roots. The work of the leaves and the stem is 
 out in the air and the light; hence these parts 
 develop upward when the seed ger- 
 minates. But the duty of the root is 
 to hold the plant in a fixed place, and to 
 secure water and food for it from the 
 soil. Therefore roots ordinarily avoid 
 the light just as strongly as leaves and 
 stems seek it. Some roots, however, 
 such as those of water plants, carry on 
 their functions outside of the soil. 
 
 PIG. 241. Kinds of Roots. 
 
 The root that comes from the hypocotyl, and all that develops from 
 this root, is called the primary root. Sometimes the primary root goes 
 down in one main portion, called a tap root (Fig. 241). The dandelion 
 
296 PLANTS 
 
 and the turnip have tap roots. Often the roots are divided into many 
 branches, as in grass and corn. The roots that come from creeping 
 stems, such- as those formed at the nodes of the strawberry plant, are 
 secondary roots. 
 
 The root has a growing tip, protected by layers of cells. Near the 
 tip the root develops root hairs. These have delicate walls, and bring 
 the root into very close connection with the soil particles, so that it can 
 absorb water and nutriment (cf. 298) . 
 
 317. Underground Storage of Food. We have seen 
 (cf. 307) that many plants store away food for the next 
 generation in the cotyledons or the endosperm of the 
 embryo. Plants may be annuals, that is, may die down 
 to the ground each autumn, or they may be perennials, 
 which last from year to year. Many annuals store away 
 food, not in seeds, but in other plant structures. The 
 plant draws upon this supply in the following spring, when 
 rapid growth begins. Man has developed some of these 
 plants, so that they store away food for him. Often 
 the plant has an underground stem on which under- 
 ground leaves are developed for the purpose of stor- 
 age. The inner leaves become much thickened, and 
 the outer leaves take the form of tough, dry scales 
 that cover the inner leaves. Thus we get bulbs. The 
 onion and the lily are bulb-forming plants. An under- 
 ground stem is called a rootstock. The common ferns, 
 the wild ginger, the iris, and the bloodroot have root- 
 stocks. 
 
 When the underground stem becomes much enlarged, 
 it produces tubers, such as the potato. The surface of 
 the potato has little scales, which are imperfect leaves. 
 In the axils of these scales (cf. 312) are the "eyes" 
 
FLOWERS 297 
 
 of the potato. The eyes are buds which, when placed in 
 soil, produce new potato plants. 
 
 Not only the leaf and the stem, but also the root, may 
 become thickened, and be used for the storing of food. 
 The radish, turnip, parsnip, and carrot are thickened 
 tap roots; the sweet potato is a " fleshy" branching root. 
 
 318. Flowers We are now to study the flower, the 
 wonderful organ through which the higher plants repro- 
 duce themselves from generation to generation. 
 
 The complete flower has four sets of parts (Fig. 244), 
 and each of these is usually arranged in a whorl (cf. 309) 
 around the flower stalk. The C ar pe ,s 
 
 outer set is called the calyx, or 
 "cup," of the flower; its sepa- 
 rate parts are called sepals. The 
 next set of parts is called the 
 corolla ; each part of the corolla 
 is a petal. The third set con- 
 sists of the stamens, the organs 
 
 FIG. 244. Parts of a Flower. 
 
 that produce the pollen. The 
 
 innermost set is the carpels; these produce the seeds. 
 The top of the flower stalk, on which the parts of the 
 flower are arranged, is called the receptacle. 
 
 The corolla is usually the attractive, colored part of the flower. The 
 calyx is often highly colored also, but commonly it is green, like true 
 leaves. The flower is really composed of modified leaves (cf. 311). 
 The calyx and corolla are the most leaf-like parts, and enclose the 
 stamens and carpels, the real organs of reproduction. Often the calyx 
 or the corolla is in one piece, as a result of the joining together of the 
 sepals or the petals. We see this in the morning-glory and the bluebell. 
 
298 PLANTS 
 
 The stamen consists of two distinct parts : the stalk, or filament, 
 and the pollen case, or anther. In flowers that have the corolla in one 
 piece the stamens are often attached to the corolla. 
 
 The carpel of an ordinary flower consists, first, of a bulb-like seed 
 case, or ovary, in which tiny ovules, or " little eggs," are produced. 
 Above the ovary is a solid stem, called the style, which looks like the 
 neck of a flask. The tip of the style bears a sticky, outspread surface, 
 called the stigma. In many plants two or more of the carpels are 
 united, so that all the ovules are in one ovary. We call the whole 
 group of carpels the pistil. Thus, a simple pistil has only one carpel; a 
 compound pistil consists of two or more carpels. 
 
 The number of parts in flowers is important. Thus, there are usu- 
 ally 3 or 5 sepals, petals, stamens, and carpels. Often, however, the 
 number of stamens is twice that of the sepals. The number of petals 
 is also frequently doubled. The buttercup has 5 sepals, 5 petals, and 
 often over 30 stamens. In many flowers petals, or sepals, or both, are 
 entirely wanting. 
 
 319. Formation of Seeds. The structure of a seed 
 has been given in 307 and 308; let us now learn how 
 seeds are formed. Before the ovule in the carpel can 
 become a seed, it must be fertilized -by the pollen. When 
 the flower is mature, the pollen case splits, or breaks 
 open, and the pollen grains are carried by the wind or 
 by insects to the sticky surface of the stigma. Here the 
 pollen grain sends out a long tube that carries the fertilizing 
 pollen cells. The tube passes through the style into the 
 ovary, and then into the ovule. When the pollen tube 
 reaches the ovum, or ' l egg," within the ovule, the pollen cell 
 and ovum unite. The addition of the pollen cell to the 
 ovum causes the ovum to develop very rapidly, and it be- 
 comes the embryo (cf. 307). The ovule forms a hard coat 
 (testa) about the embryo, and any vacant space is stuffed 
 with food. The completely prepared ovule is then a seed. 
 
THE DISPERSAL OF SEEDS 299 
 
 The pollen used to fertilize a flower may come from the stamens of 
 the same flower, or from other flowers near or far away. The air is 
 often full of pollen grains. Many plants do not depend on chance for 
 fertilization, but develop structures that attract insects or birds. 
 These creatures then carry the pollen from flower to flower. Thus it 
 comes about that many flowers have a bright color and a sweet odor, 
 which tell the insect where food is to be found. For some creatures, 
 such as butterflies, the flower secretes a sweet liquid, called nectar. 
 Bees feed upon the pollen itself. The nectar is usually stored at a 
 place beyond the organs of reproduction, so that the visiting insect 
 must brush against these organs. The insect thus becomes loaded 
 with the pollen grains of one flower, and brushes them against the 
 stigma of the next flower it visits. 
 
 320. The Dispersal of Seeds. The parent plant is 
 usually not through with its labors when it has produced 
 the seed; it must still provide the place for the seed's 
 growth. Most plants have worked out a 
 method by which the seed shall be carried 
 away to new places. In some plants, as in 
 violets, the seed pod bursts open with con- 
 siderable force, scattering the seed to a dis- 
 tance. The seed pod itself is often arranged 
 so that it can be carried off by the air. Ex- 
 amples are the winged seeds of the maple 
 (Fig. 245), and the tufted seeds of the dan- 
 delion and thistle. Multitudes of seeds are 
 carried about by currents of water, even by those of 
 the ocean itself. Seeds like the " stickers" of the cockle- 
 bur and burdock are carried about by animals to a new 
 place for germination. 
 
 Fruits, which are the ripened ovaries or, sometimes, 
 other parts of the organs of reproduction, are also devices 
 
300 PLANTS 
 
 used by plants for the scattering of seed. The fruit is 
 carried away, and its fleshy part is consumed, while the 
 seed is scattered. Man has, of course, greatly developed 
 many natural fleshy fruits, just as he has developed roots 
 and stems (cf. 317). 
 
 321. Exercises. 
 
 1. Name some useful leaves of commerce. Name some useful 
 kinds of sap. What is made from each kind? 
 
 2. Why is it that so many perennial plants lose their leaves each 
 autumn? Name several perennials. 
 
 3. Suggest a reason why it is best that the sap should be less abun- 
 dant in winter than in summer (cf. 92). 
 
 4. Can you find a plumule in the peanut? What are the cotyledons 
 of the peanut? Cornmeal or peanuts kept in a paper bag often make 
 the bag greasy. Why? 
 
 5. Describe the veining of the leaves of the geranium, of the rose, 
 and of grass. Name some plants having compound leaves. 
 
 6. Name some trees with tap roots. Describe the root of the beet. 
 From what part of the beet is sugar prepared? 
 
 7. Why are logs for wood cut in winter rather than in summer? 
 Why are soft-wood logs kept under water until they are sawed? Does 
 wood shrink more evenly in the log, or in boards? What is kiln-drying 
 of wood? Why do house doors and windows "stick-" in summer, 
 although they are loose in winter? 
 
 8. Why is it possible for wood to 'Hake" stains? What besides 
 staining is done to make a wood with open structure more durable? 
 Why do men like "hard" woods for interior finish? What are several 
 common "hard" woods? 
 
 9. Ask a carpenter why shingles are made of cedar. Ask him why 
 shingles should be nailed with "cut" nails rather than with wire nails. 
 Why do cedar stumps last so long before they rot? 
 
 10. Why do forest flowers, like the hepatica, spring beauty, blood- 
 root, etc., bloom in the early spring? Why do some plants produce 
 /flowers_before they produce leaves? 
 
 L" 
 
CLASSES OF PLANTS 301 
 
 11. On what part of the strawberry are the seeds? Is the edible 
 *' berry" an enlarged ovary? What is it? Where are the seeds of the 
 raspberry? The currant? What has happened to the ovary in the 
 case of the apple? The cherry and peach? 
 
 12. Of what use are branches and leaves in electric storms (cf. 
 148)? 
 
 322. Classes of Plants. The plants we have been 
 studying are those highest in development the flower- 
 ing plants. These are composed of many parts, and carry 
 out their functions in complicated ways. There are 
 plants that perform these same functions in much simpler 
 fashion; they may have only a single living unit, or cell, 
 for the carrying out of all their functions. Between the 
 simplest plants and so high a plant as the daisy there are 
 all stages, or grades, of development. We therefore 
 divide plants, for the purpose of studying them, into 
 several groups, or classes, putting together all those that 
 have certain parts, or perform certain functions, nearly 
 alike, and then separating this class as sharply as we can 
 from the plants that do things in an essentially different 
 way. The divisions of plants, as we need to consider 
 them, are algae (pronounced aT-je), fungi (pronounced 
 fun'-jl), mosses, ferns, and seed plants. 
 
 323. Algae. The algae (singular, alga; the g is hard) 
 are chiefly water plants, and vary in size from a single, 
 tiny cell to great masses many feet long. They are green, 
 red, brown, etc., but all contain chlorophyll, and are able 
 to make their own food. A common alga is called pro- 
 tococcus; this is found as a green stain on the north side 
 of trees and fences. When the green material is examined 
 
302 PLANTS 
 
 with a microscope, it is found to consist of small cells 
 (Fig. 246). Often several cells adhere to one another. 
 The cell consists of a wall and of living substance within, 
 called protoplasm (pronounce this, pro'-to-plasm). The 
 denser part of the protoplasm is called 
 the nupleus of the cell. In the proto- 
 plasm are the grains of chlorophyll that 
 give the groups of cells their green ap- 
 pearance. 
 
 If the protococcus cells are examined 
 carefully, some will probably be seen 
 FIG. 246. Protococcus, that have dividing lines across them. 
 
 greatly magnified. 
 
 Each of the two halves may be divided 
 further, and the new cells thus produced may separate 
 from one another. As a result we have a whole group 
 of cells. Each cell contains its own protoplasm, nucleus, 
 and chlorophyll, and is an independent plant. This 
 formation of new cells is a method of reproduction. 
 It is called reproduction by cell-division. 
 
 Another alga is called spirogyra. This is a "scum" found in 
 ponds; its cells are attached end to end, so that they produce filaments, 
 or threads. The chlorophyll bodies are arranged in spirals. 
 
 Spirogyra carries out reproduction in a different way from proto- 
 coccus. Two cells in neighboring filaments bend their cell walls toward 
 each other, until they touch. Then the two walls between them dis- 
 appear, and the contents of one cell pass over into the other cell. The 
 materials of the two cells form a body called a spore. The spore, like 
 the embryo, endures through the winter, and then germinates, produc- 
 ing a new plant. The spirogyra is thus reproduced by a sexual method. 
 
 324. Fungi. Fungi (singular, fungus) form a large 
 group of plants that have no chlorophyll, and cannot, 
 
FUNGI 303 
 
 therefore, make their own food (c/. 310). They live by 
 attaching themselves to living plants or animals; or they 
 feed upon dead or decaying materials. An organism that 
 feeds upon other living organisms is called a parasite ; the 
 organism upon which a parasite feeds is called the host. 
 A fungus feeding upon decaying organic material is called 
 a saprophyte. 
 
 A yeast plant is a fungus having one cell. It is repro- 
 duced by budding (cf. Fig. 103, 129). Many centuries 
 ago "wild yeasts" were cultivated by man, and the result 
 is our ordinary bread yeast, or leaven. While feeding 
 upon the sugar of the dough, the yeast plant produces 
 carbon dioxide. This causes the dough to rise, and 
 makes bread porous and light. 
 
 Bacteria, also called microbes, or germs, are very small, 
 one-celled fungi found everywhere in air, water, and soil 
 (Fig. 247), and in the bodies of ^ , 
 
 plants and animals. They are re- 
 produced by cell-division, like pro- 
 tococcus. The cell walls of bacteria 
 usually have projections, called 
 cilia, by means of which the cells 
 swim about. It is bacteria that 
 make milk and fruit juices "sour/ 7 
 and cause meat to decay. These 
 changes are fermentations, like the 
 fermentations due to yeast. 
 
 Most of the bacteria that live about us are harmless, but others 
 cause diseases like typhoid fever, diphtheria, cholera, and consump- 
 tion, and must be looked upon as our worst enemies. Bacteria that 
 are of great importance to us are those that grow upon the roots of 
 
304 
 
 PLANTS 
 
 plants like clover, peas, and alfalfa (cf. 56), for they take nitrogen 
 
 from the air, and convert it into food for plants. 
 
 Moulds are fungi that grow upon fruits, bread, shoes, etc. We can 
 
 grow the bread mould readily by covering damp bread with a dish 
 
 (Fig. 248). 
 
 Mildews and rusts are fungi that 
 attack seed plants, and cause great 
 loss in fruit trees and grains. Mush- 
 rooms, toad stools, and puff balls are 
 also fungi. Lichens (cf. 215) are a 
 class of fungi that form spreading 
 masses, red, blue, yellow, etc., in 
 color, upon trees, rocks, and boards. 
 
 FIG. 248. Broad Mould (Mucor) wit! 
 a Fruiting Body that produces Spores. 
 
 325. Mosses. Mosses are much more highly de- 
 veloped plants than fungi and algae; for they have leafy 
 stems, and organs similar to roots, which hold the plant 
 up from the ground. In the common form of 
 
 the moss, little, erect stalks are formed (Fig. 
 249) for the organs of reproduction. The moss 
 does not produce flowers. 
 
 Mosses send out many leafy branches, and 
 so cover even bare rocks and mountain sides 
 with verdure. They can endure very dry and 
 very cold weather, renewing their growth as 
 soon as conditions are favorable. In cold 
 climates the moss of bogs and swamps is 
 changed to peat (cf. 118). This is mud 
 containing so much carbon that it can be used for fuel. 
 
 326. Ferns. Ferns are plants of still higher develop- 
 ment than mosses. Their peculiar and beautiful leaves 
 spring from underground rootstocks (cf. 317). Each 
 
SEED PLAXTS 
 
 305 
 
 "stem" is really a leaf stalk. The young leaf appears 
 to be rolled up in a spiral, and uncurls as it develops. 
 The leaf is a compound one (cf. 309), 
 with delicate and exquisite veining. 
 
 The reproductive organs of the ferns we 
 ordinarily see are the grain-like spots (sori) 
 on the back of the leaf (Fig. 250). In 
 some ferns, as in the bracken fern, the 
 edge of the leaf is rolled in to protect 
 these organs. 
 
 The leaf "stems" of ferns have woody 
 bundles (cf. 313) ; hence the leaves are sup- 
 ported easily, even when they grow large 
 and tall. In the tropics there are true ferns 40 feet high. 
 
 FIG. 250. Fern Frond 
 (Leaf) with Sori 
 (Fruiting Bodies). 
 
 327. Seed Plants. Only the seed plants produce 
 true seeds. The oldest seed plants, as the rocks of the 
 earth tell us, were relatives of the pine, spruce, and fir, 
 
 trees which we 
 call evergreens 
 (Fig. 251). In the 
 evergreens, the 
 seed is produced 
 on the carpel, but 
 not in it. Hence 
 these plants are 
 called gymnos- 
 perms (qf. 313), 
 that is, "plants 
 with the seeds 
 
 FIG. 251. Evergreens. In the center a Norway pine. The 
 "Christmas trees" are spruce and balsam fir. 
 
306 PLANTS 
 
 carpels of gymnosperms grow in groups, called cones. 
 These open when the seed is ripe, and allow it to 
 escape. Gymnosperms are also called conifers, that is, 
 "cone bearers." The cones that produce the seeds are 
 "pistillate" cones. Fertilization is carried out by pollen 
 produced in other cones called "staminate" cones. 
 
 The leaves of the common gymnosperms are not shed at the coming 
 of winter. After the new leaves have made their growth, the old ones 
 fall; but the tree is never without leaves. The leaves are usually 
 needle-shaped. In some cases, as in the ' ' Norway " pine, there are two 
 leaves in a whorl; in the " white" pine there are five. 
 
 The wood of the evergreens is "soft" wood. It is valued because 
 it is durable, even in the "weather," and because it is easily worked. 
 The wood of the white pine is especially prized. 
 
 The most common seed plants, those we have studied 
 in 307 to 320, do not have the seed "naked," but "in 
 a closed vessel." For this reason they are called angio- 
 sperms (pronounced an'-ji-o-sperms). The "closed ves- 
 sel" is the carpel. The most highly developed of the 
 angiosperms, such as the dandelion, daisy, aster, and 
 sunflower, have composite flowers. In these plants a 
 large number of individual flowers have "clubbed to- 
 gether," and grow upon a single stalk. The center of 
 the composite "flower" is called the disk. It contains 
 the disk-flowers a multitude of them each with a 
 closed corolla and a full set of reproductive organs. 
 Sometimes there are sepals, too. The next outer struc- 
 ture, which looks like a whorl of petals, is really a circle 
 of flowers ray-flowers with the corollas split open, 
 so that each looks like a strap. Outside of all are scales, 
 which look like sepals. 
 
DISTRIBUTION OF PLANTS 307 
 
 328. Economic Plants. The economic plants, or 
 plants useful to man, are very numerous and very im- 
 portant. Some have already been named. Out of trees 
 man gets lumber, and by grinding up certain woods he 
 gets the pulp for paper. Certain grasses, developed long 
 before the dawn of history, became wheat, oats, rye, 
 barley, etc. Indian corn was native to America, and was 
 developed by its primitive inhabitants. The potato is a 
 native of South America, but was developed, so that it 
 became edible, in Europe. The flax plant has given man 
 linen since the distant past. Cotton was known in ancient 
 Egypt, but its use on a large scale was impossible until the 
 invention of the cotton gin, which made cotton-raising 
 profitable in America. 
 
 Two of the great problems of agriculture in America 
 to-day are: (1) how the soil may be improved, so that it 
 shall give the greatest possible yields, and yet retain its 
 fertility; and (2) how our grain plants may be improved, 
 so that they shall bear most abundantly, shall be free from 
 pests and diseases, and shall be adapted to our varied 
 climate. To these problems we may add the problem of 
 the forests how they may be used without being 
 destroyed, and the problem of the fruit supply, a supply 
 that is making constantly increasing demands upon 
 gardeners, both here and in the tropics. 
 
 329. Distribution of Plants. Plants have distributed 
 themselves all over the earth; but there are certain great 
 factors, or conditions, that fix the regions where any 
 particular kind of plant can grow. The different kinds of 
 soil, and the amount of rainfall are two of these conditions 
 
308 
 
 PLANTS 
 
 (cf. 272 and 298); but the temperature is also very 
 important. As the earth is divided into temperature 
 belts, or zones, plants are also found distributed in belts, 
 or zones. The limits of temperature, below or above 
 
 FIG. 252. Cacti: the Cereus, Arizona. Negative by Geo. D. Fuller. 
 
 which plants find it hard to continue their existence, are 
 about 32 F. to 122 F., or C. to 50 C. 
 
 In the polar regions, lichens, mosses, and willows can 
 just support themselves. In the colder part of the 
 temperate zone there are conifers, such as spruce, fir, 
 hemlock; in the warmer part of the temperate zone 
 deciduous (leaf shedding) trees are more abundant. 
 Examples of these are the beech, maple, birch, oak, 
 hickory, and chestnut. In the tropical zone, the palm, 
 
SUMMARY 309 
 
 cypress, mangrove, magnolia, mahogany, and live oak 
 abound, and the forests are dense with climbing plants 
 and air plants. 
 
 Some of the most interesting ways in which plants 
 adapt themselves to their surroundings are seen in dry 
 climates like our western deserts. The greatest problem 
 of plants under these conditions is how to get the most 
 water, and how to lose the least. As a result they have 
 large and widely spreading roots, a thick skin, and a 
 small surface of leaves. The cactus (Fig. 252) is an 
 example of such plants. Its leaves are modified to spines, 
 because it does not need ordinary leaves; and the plant 
 body is a compact mass, so that there is little evaporation. 
 
 330. Summary. The organs of a plant are its roots, leaves, flowers, 
 etc., each of which has some particular function, or duty. 
 
 The two general functions of all living things are nutrition and re- 
 production. 
 
 The conditions and surroundings of an organism are its environ- 
 ment. The influence of the environment is a stimulus to the organism; 
 the change or action in the organism is its response to the stimulus. 
 
 Germination is the change from seed to seedling. 
 
 The seed of a bean consists of testa and embryo. The embryo con- 
 sists of two cotyledons, a hypocotyl, and a plumule. Nutriment stored 
 in an embryo, outside of the cotyledons, is called the endosperm. 
 
 Monocotyls have only one cotyledon. 
 
 Leaves consist of blade, petiole, and sometimes stipules. Veining 
 may be palm-, feather-, and parallel-vemmg. A compound leaf has 
 several leaflets. Leaves may be alternate, opposite, or whorled. 
 
 A leaf is covered with epidermis, through which there are openings 
 called stomata. Leaf tissue consists of cells. Cells contain proto- 
 plasm, and, in green leaves, stems, etc., chlorophyll. 
 
 The leaf is the laboratory of the plant. In it carbon dioxide and 
 water are built up into carbohydrates, and oxygen is set free. 
 
310 PLANTS 
 
 Leaves are modified to tendrils, suckers, thorns, spines, etc. 
 
 Steins consist of nodes, or joints. The kind of branching deter- 
 mines the shape of a tree. The stems of dicotyls consist of epidermis, 
 cortex, wood layer, and pith. Annual rings consist of the wood formed 
 in growing seasons. 
 
 Sawing may be slash-sawing or radial-sawing. Quarter-sawing is 
 radial-sawing. 
 
 Sap is the water and dissolved food that rises through the newer 
 wood (sap wood). 
 
 Buds are stems, leaves, and flowers in undeveloped form; they may 
 be terminal, axillary, or adventitious. 
 
 Roots may be tap roots or branching (fibrous) roots. 
 
 Food is stored in underground roots, leaves, and stems. Under- 
 ground stems are rootstocks; underground storage leaves form bulbs. 
 
 Flowers consist of calyx, corolla, stamens, and carpels. Sepals are 
 the parts of the calyx; petals, of the corolla. Simple pistils have only 
 one carpel; compound pistils, two or more. 
 
 The stamen consists of filament and anther. 
 
 The carpel consists of ovary, style, and stigma. 
 
 Seeds are formed after the pollen has fertilized the ovum. Seeds 
 are dispersed by violent bursting of the seed pod, by winged attach- 
 ments, by "stickers," and by fleshy fruits. 
 
 The chief classes of plants are algae, fungi, mosses, ferns, and seed 
 plants. 
 
 Algae are one-celled plants like protococcus, spirogyra, sea weeds, 
 etc. Their reproduction is by cell-division or by sexual methods. 
 Algae contain chlorophyll. 
 
 Fungi are moulds, yeast plants, bacteria, mildews, mushrooms, 
 lichens, etc. They contain no chlorophyll, and feed upon living, dead, 
 or decaying plants or animals. 
 
 Bacteria produce fermentations, as in the souring of milk, decay, 
 etc. Certain kinds produce disease. 
 
 Mosses have leafy stems, and root-like organs, but they do not 
 produce woody stems or flowers. 
 
 Ferns produce woody bundles in their leaves; but their stems are 
 underground. 
 
EXERCISES 311 
 
 Seed plants produce true seeds, and, in trees and shrubs, produce 
 woody stems. 
 
 Classes of seed plants are gymnosperms and angiosperms. 
 
 Composite flowers are the highest form of plant organization. 
 
 Economic plants are of great importance for man, in that they give 
 him food, clothing, shelter, and tools. 
 
 Plants are distributed in great zones, corresponding to the zones of 
 temperature. 
 
 \ 
 331. Exercises. 
 
 1. What precautions are necessary, in the canning of fruit, to keep 
 it from spoiling? Why? Why are meat, milk, compressed yeast, etc., 
 kept in cold refrigerators? 
 
 2. How do preservatives, like formaldehyde, borax, etc., prevent 
 the decay of food? If digestion is a series of fermentations (cf. 368), 
 will a food containing preservatives be easily digested? 
 
 3. Why do not fungi produce chlorophyll? When a potato sprouts 
 in a dark cellar, why are its leaves and leaf stalks white? How is 
 celery bleached? 
 
 4. Is it a good plan to put away fresh, warm bread in a covered 
 box? Why? 
 
 5. Do you think it possible that some of our wild grasses might be 
 cultivated so as to become useful grains? How could this be done? 
 What fruits have been developed by the cultivation of inferior or wild 
 varieties? 
 
 6. Many plants in the tropics have thick-walled leaves with tips 
 in the form of gutters. To what two sets of conditions have they 
 adapted themselves? 
 
 7. Why is it necessary for the leaves of evergreens growing in cold 
 climates to be thick and needle-shaped rather than thin and spreading? 
 
 8. What are some commercial uses of moss? 
 
 9. How does the cultivated rose differ from the wild rose? Ask a 
 gardener whether the cultivated rose can be reproduced from seeds. 
 
CHAPTER XVI 
 
 ANIMALS 
 
 332. What is an Animal? We have already studied 
 something of the relation between animals and plants. 
 Plants (those containing chlorophyll; cf. 310) change 
 carbon dioxide, water, and the minerals of the soil into 
 living material, which serves as food for the animal world. 
 In taking carbon dioxide from the air, plants remove a 
 waste product of animals, and restore oxygen in its place. 
 Thus they keep the composition of the air the same, year 
 after year. It was once supposed that plants did not 
 produce carbon dioxide. This is a mistake. Plants give 
 off carbon dioxide in their respiration, just as animals 
 do; but green plants take up much more than they give 
 off. Hence they seem not to produce any. 
 
 In general, we may say that an animal is an organism 
 that cannot build up its food out of mineral matter, while a 
 plant can. Plants having no chlorophyll (fungi) are excep- 
 tions to this statement (cf. 324). The lowest forms of 
 animals and plants are really so much alike that it is often 
 hard to say to which class a given creature belongs. The 
 fact that the higher animals can move about freely is not a 
 real difference; for many animals are attached to some 
 fixed place, while some plants have very rapid movements. 
 
 333. One-Celled Animals. In stagnant water or in 
 mud there is often found a bit of jelly-like substance that 
 
 312 
 
ONE-CELLED ANIMALS 313 
 
 shows, under the microscope, a peculiar power of chang- 
 ing its shape, and of moving about. This is one of the 
 lowest animals; it is called an ameba (Fig. 253), from 
 a Greek word meaning "to change." 
 The jelly-like creature consists of a 
 cell of protoplasm (cf. 323). At its 
 center the cell is grainy; this region 
 is the nucleus. The ameba thus con- 
 sists of one cell, like protococcus; but 
 it has no chlorophyll. It has no FlG< 2 S ag nffi n ed meba ' 
 organs, either. It moves by extend- 
 ing the cell wall at any region into a projecting lobe; 
 the cell contents then flow into the lobe. These lobes 
 are called "false feet." The ameba has no mouth; it 
 feeds by extending two lobes around an article of food, 
 and then withdrawing the cell wall. The protoplasm 
 simply envelops the food. The ameba excretes (throws 
 out) waste parts of its food merely by moving away 
 from them. When food is thus passed through the cell 
 wall, no opening is left; just as there is no break in the 
 tough, though fragile, film of a soap bubble when a needle 
 is put through it. 
 
 The reproduction of the ameba is also o'f the simplest 
 sort. The nucleus of the cell divides itself into two parts, 
 half of the protoplasm groups itself about each nucleus, 
 and at the line thus formed the cell divides ; there are now 
 two amebas instead of one. 
 
 A creature like the ameba forms a part of our own blood (cf. 378). 
 If you will examine a drop of blood, under the microscope, you will 
 see that it contains both red and colorless bodies. These are called 
 corpuscles, that is, ' 'little bodies." The colorless ones, called white 
 
314 
 
 ANIMALS 
 
 Cilia 
 
 Mouth 
 
 FIG. 254. Slipper Animalcule (Para- 
 mecium), magnified. View of the 
 Under Side. 
 
 FIG. 255. Bell Ani- 
 malcule (Vorticel- 
 la), magnified. 
 
 corpuscles, have the form and the simple structure of the ameba; but 
 they are not so active. 
 
 A more highly developed one-celled animal is called the " slipper 
 animalcule," from its shape (Fig. 254). Animalcule (pronounced, 
 
 an-i-mal-kul) means " little ani- 
 mal." The scientific name of the 
 creature is paramecium. In this 
 case the cell has 
 a permanent place 
 for feeding, called 
 the mouth, and the 
 mouth extends in- 
 ward, forming a gullet. The creature has a per- 
 manent shape, because its cell wall is more stiff than 
 that of the ameba. It swims about by waving the 
 thread-like extensions (cilia; cf. 324) of its cell wall. 
 A third one-celled animal is called vorticella, or 
 the "bell animalcule" (Fig. 255). Its shape is like 
 that of a bell with a long handle. It is called vor- 
 ticella because, by waving the cilia at its mouth, 
 it produces a vortex, or whirlpool, by which food 
 is carried into the cell. The cell wall is ex- 
 tended to form a " stalk," by which the creature 
 attaches itself to weeds, or to sticks and stones 
 in the bottom of ponds. 
 I 
 
 334. Simple Many-Celled Animals; 
 Hydra. If a water plant is placed in 
 a glass vessel of water, a hydra (Fig. 
 256) is often found attached to the 
 plant or to the sides of the vessel. 
 It is a brown or greenish creature half 
 an inch long, or less. 
 When it is not disturbed, the hydra extends several 
 thread-like "arms/' called tentacles, about in the water. 
 
 Endode.m 
 
 FIG. 256. Hydra, or Polyp. 
 Exterior View and Cross 
 Section. Magnified. 
 
SIMPLE, MANY-CELLED ANIMALS; HYDRA 315 
 
 If tiny bits of meat are dropped near them, the tentacles 
 direct the meat to the mouth. But food does not go 
 directly into the cell, as it does in one-celled animals. 
 We can see that this is not necessary, for the hydra's 
 body and tentacles are made up of two rows of cells. 
 The inner cells have the duty of digesting food, while the 
 outer cells serve to protect them. The digested food is 
 passed through the cell walls, from the inner cells to the 
 outer ones. The tentacles do not simply push food 
 toward the mouth, but some of their outer cells have 
 stinging weapons for paralyzing the hydra's prey. 
 
 Often the hydra may be seen budding, as yeast does 
 (cf. Fig. 103, 129). The young hydra remains attached 
 to the older one for a time, and then separates from it. 
 If a hydra is cut in two, each half produces the necessary 
 cells, and forms a new creature. The hydra is also re- 
 produced by a sexual method. There are not two sexes, 
 but some of the cells produce egg-like 
 bodies, and other cells on the same hydra 
 produce swimming cells that fertilize the 
 egg-like cells. When the two kinds of 
 cells unite, they form an embryo hydra. 
 This falls to the bottom of the water, and 
 in time develops into a full grown animal. 
 
 More highly developed forms of the hydra 
 have a great number of animals in a colony (Fig. 
 257) . The colony has root-like ' ' holdfasts, ' ' and FlG - 
 attaches itself to rocks. Hydra-like animals are 
 called polyps, from words meaning "many feet." The coral polyp 
 is a common form. Each coral polyp takes limestone from sea water, 
 and forms a hard internal structure (coral), which remains when the 
 
316 
 
 ANIMALS 
 
 FIG. 258. A Sim- 
 ple Sponge. 
 
 creature dies. The accumulations of coral rock limestone taken 
 from sea water in past ages are enormous in extent (cf. 132). 
 
 Sponges (Fig. 258) are many-celled animals less 
 well developed than hydras. The individual creature 
 has two cell layers separated by a gelatinous layer. 
 The gelatinous layer produces the tough, horny mate- 
 rial that we call " sponge." The animal is very soft, 
 and the horny structure keeps its body cavity open. 
 The cells have cilia, which produce incoming water 
 currents bearing food. The outer openings of the 
 body cavities form the tiny pores of the " sponge." 
 Our sponges therefore represent colonies of the 
 sponge animal with the horny material joined in a 
 large mass. Some sponges form skeletons of lime- 
 stone or of silica (the substance of powdered quartz), instead of horny 
 structures. 
 
 335. Starfishes. One of the interesting pastimes at 
 the seashore is watching the movements and other 
 activities of the starfishes (Fig. 259). The starfishes 
 belong in a class with sea-urchins, 
 sea-cucumbers, etc. This class is 
 more highly developed than 
 sponges and hydras. 
 
 The grown starfish is arranged 
 on a plan of 5. The central region 
 is round, and the "points of the 
 star," or "arms," branch out from 
 it. The covering of the animal 
 contains hard limestone knobs with 
 projecting spines. The body has a digestive system that 
 is distinct from the interior cavity (cf. 334) ; it has also 
 a simple nervous system, and the beginnings of a blood 
 system. 
 
 FIG. 259. Starfish. 
 
WORMS 317 
 
 On the lower (ventral) side of the "arms," or "rays," 
 the hard coverings are turned inward, forming five 
 grooves. Extending out of the grooves are many delicate 
 tubes ending in suckers. These " tube feet " can be 
 lengthened and shortened. The animal attaches itself 
 to rocks by means of the suckers, and then pulls itself 
 along. It moves in any direction. At the end of each 
 ray there is a tentacle, which is probably an organ for 
 smelling, and on each tentacle there is a red spot, which is 
 sensitive to light, and is, therefore, a very simple eye. 
 
 The exchange of gases (respiration) does not take place in all the 
 cells of the starfish, as in the simplest creatures, but in certain definite 
 spaces. These spaces thus form the beginnings of a breathing system. 
 The starfish is able to open the shell of the oyster, and to get at the soft 
 body within. It then turns a part of its stomach inside out over the 
 oyster, and digestion goes on outside of the body. The shell it simply 
 leaves behind. If a piece of a starfish is broken off, the cells that 
 remain produce new cells, and replace what has been lost. 
 
 336. Worms. The student must not think of caterpil- 
 lars, grubs, and "measuring worms" as worms; they are 
 the larva stage in the development of insects (cf. 339). 
 
 Dorsal Blood Vessel Muscles 
 
 ^P Esophagus 
 
 Pharynx 
 Brain 
 
 FIG. 260. The Earthworm. Several segments are omitted. 
 
 True worms do not change into anything else, but always 
 retain their " worm-like" form. Worms include earth- 
 worms (' ' angle worms ") , leeches, and many marine worms. 
 The most common of thesf is the earthworm (Fig. 260). 
 
318 ANIMALS 
 
 The earthworm has a long body, divided by crosswise 
 rings. The body has a definite head (anterior) end. If 
 we were to divide the body lengthwise, from top to bot- 
 tom, the two halves would be similar. We say that such 
 a body has two-sided (bilateral) symmetry. The earth- 
 worm has a mouth at the front of the under (ventral) side 
 of the body, and a body cavity the whole length of the 
 body. Waste material is excreted through openings in 
 each side of the body "rings." There is a nervous 
 system, with a brain at the front of the body. The 
 nerve cords are on the ventral side of the body; not, as 
 in higher animals, along the dorsal side (the back). 
 
 The earthworm has two sets of muscles in each "ring." 
 One set goes around the body. When this set contracts, 
 the ring grows smaller in diameter. The other set of 
 muscles is from front to back, in each ring. When these 
 contract, the ring grows narrower, and the whole body 
 becomes shorter. By extending a portion of the body, 
 by then holding on to the ground, and, finally, by con- 
 tracting the extended portion, the worm is able to move 
 along. 
 
 The earthworm's blood "circulates" in two lengthwise vessels. 
 Contractions take place at certain places called " hearts," and form 
 waves that pass through the vessels. Respiration, or communication 
 between the blood and the air, takes place through the body wall, 
 especially at certain thin places; there are no gills or lungs. Worms 
 are reproduced by the sexual method. If a worm's head or "tail" 
 is cut off, as often happens in the plowing or spading of ground, 
 each portion can replace the rings it has lost, and produce a perfect 
 worm. 
 
 In digging its burrows the earthworm swallows the soil, and extracts 
 whatever food the soil contains. Then it casts off the soil in little 
 
Kidrjey Ventricle 
 Posterior Adducto 
 
 Anterior Adductor 
 
 MOLLUSKS 319 
 
 heaps (" castings") at the opening of the burrow. In this way the 
 earthworm makes the soil porous, and brings subsoil to the surface 
 (cf. 296). 
 
 337. Mollusks. Clams and oysters are mollusks that 
 live in salt water. A very similar form, the mussel, 
 lives in fresh-water lakes and in streams. "Mollusk" 
 comes from a word meaning "soft," and is given to this 
 class of animals because of their soft bodies. 
 
 The mussel (Fig. 261) is found at the water bottom, 
 slowly plowing its way through mud or sand. It has a shell 
 made of two similar 
 parts (valves) ; these 
 are joined at the top 
 (the dorsal side of 
 the animal) by a 
 hinge. Inside the 
 shell is the mantle, 
 
 a Soft. mUSCUlar FlG - 26 1. Freshwater Clam, or Mussel; its Principal 
 
 Organs. 
 
 structure. This lines 
 
 each of the valves. The "foot" of the animal projects 
 from the anterior (head) end of the body. At the oppo- 
 site (posterior) end there are two openings called siphons. 
 The lower of these has organs like cilia, for forcing a 
 current of water through the body. The other siphon is 
 for outgoing water. The mussel's food, as well as its air, 
 comes to it in the water taken in at the lower siphon. 
 Between the mantle and the foot, one on each side, are 
 the gills, through which respiration takes place. 
 
 The halves of the shell are held together at the hinge by a tough, 
 horny ligament. The outer layer of the shell is made of the same horny 
 material. Inside this there is a layer of limestone, and on the inner 
 
320 ANIMALS 
 
 surface of the shell there is " mother-of-pearl/' which consists of alter- 
 nate, thin layers of limestone and horny material. The shell is made 
 (secreted) by the mantle. Some mollusks form pearls (which are' 
 mother-of-pearl in round masses), if some irritating substance comes 
 between the mantle and the shell. 
 
 The shell of the mussel springs apart when the animal is dead. 
 While alive, the creature holds the halves together by means of two 
 powerful muscles (anterior and posterior " adductors" of Fig. 261). 
 One end of each muscle is attached to the right valve, and the other 
 end of each to the left valve. When the muscles contract, the valves 
 come together with great force. The mussel, like the earthworm, has 
 a nervous system, with a brain at the anterior end of the body, over 
 the mouth. . 
 
 Mussels, clams, and oysters are called bivalves, because of the two 
 halves of their shells. Snails are called univalves, because the shell is 
 in one piece. Slugs are like snails, but they form no shell. To the 
 mollusks belongs, also, the devil fish, or octopus, the " nightmare of 
 the sea." 
 
 338. Crustaceans. Crustaceans are so called from 
 their hard body covering. The class includes crayfishes, 
 lobsters, crabs, barnacles, etc. (Fig. 262). 
 
 The crayfish, like the mussel and the earthworm, has 
 its parts arranged symmetrically. Like the earthworm 
 it has a number of joints, or segments, each of which 
 makes up a part of the length of the body. In the cray- 
 fish many of these joints have very well developed parts, 
 or appendages, popularly called "legs," "claws," "feel- 
 ers," etc. The hard covering of the body has already 
 been spoken of. This holds and protects the soft organs 
 within. At the posterior end (abdomen) the body cover- 
 ing is in several pieces; the remainder of the body, that 
 is, the head and thorax (chest), are inside one piece of 
 covering. The so-called ' ' legs ' ' and ' ' claws ' ' are attached 
 
CRUSTACEANS 
 
 321 
 
 at the thorax. The eyes are attached to ' ' stalks " on the 
 head. All these appendages consist of joints, so that 
 they may be bent. The segments of the abdomen have 
 smaller appendages for use in swimming. The jointed 
 abdomen can itself be 
 bent very easily. Thus 
 the crayfish is able to 
 make a very swift 
 backward motion (to 
 ' ' crawfish " ) by giving 
 its "tail" a downward 
 and forward stroke. 
 
 The crayfish has powerful 
 jaws for seizing and tearing 
 food, and a large stomach 
 containing a tooth-like struc- 
 ture for crushing food. 
 
 The blood is circulated 
 by a heart, which beats vig- 
 orously. The heart contains 
 only one chamber, and is set 
 into a receiving space. This 
 space contains blood brought 
 from the gills. When the 
 heart muscles contract, they 
 make the heart cavity smaller. The compressed blood in the cavity 
 then opens the valve leading to the arteries, and at the same time 
 closes the valve from the receiving space in which the heart is sus- 
 pended. When the heart muscles are relaxed, the pressure of the 
 blood in the arteries closes the valves opening out of the heart, and 
 the pressure in the receiving vessel opens the valves leading into the 
 heart. Hence the heart is refilled with blood that has passed through 
 the gills and been purified. This blood it pumps to all the organs 
 of the body. The gills are placed below the head-thorax covering, 
 
 FIG. 262. The Lobster. 
 
322 
 
 ANIMALS 
 
 and the water near them is kept in constant motion by little plates, 
 or " paddles." The motion of the water is produced by appendages 
 to which the plates are attached. 
 
 As the crayfish increases in size, it must have a larger "house;" so 
 it sheds its outer covering from time to time, and goes into hiding 
 until its new "shell" has grown. 
 
 339. Insects. Insects and spiders have the same 
 general structure as the crayfish, but they also differ from 
 it in many ways. The word insect means "cut into 
 parts," and indicates that these creatures are made up 
 of joints. True insects have a tough, horny covering, as 
 the crayfish has, but the head and the thorax are separate 
 instead of united. The legs are attached to the thorax. 
 When there are wings, as in flying insects, these are also 
 attached to the thorax. Respiration takes place in tube- 
 shaped air passages in the different segments of the body, 
 and not in gills. The muscles of insects are very highly 
 developed; we see the result in the jumping of the grass- 
 hopper and the flea. 
 
 One of the most fascinat- 
 ing things about insects is 
 the complete change, or 
 metamorphosis (pronounced 
 met-a-mor'-phos-is), which 
 they undergo as they de- 
 velop. Thus the eggs of the 
 
 FIG. 263. Stages in the Development of fly (Fig. 263) produce white, 
 
 crawling creatures (mag- 
 gots). We call the "worm-like" young of insects larvae 
 (singular, larva). After about a week of rapid feeding, 
 the larva of the housefly grows a "shell" about itself, in 
 
INSECTS 
 
 323* 
 
 Egg Mass 
 
 Larva 
 
 FIG. 264. The Mosquito. 
 
 which it undergoes its change. In this shell, or puparium, 
 
 it is called the pupa (pronounced pu'-pa), or chrysalis. 
 
 In about another 
 
 week the creature 
 
 emerges from its 
 
 shell a fly. 
 The egg of the 
 
 mosquito (Fig. 
 
 264) is deposited Pupa 
 
 in water, and 
 
 hatches to form 
 
 a "wiggler" (the 
 
 larva), which swims about in the water. The wiggler 
 
 breathes through the end of its "tail," and must come 
 
 to the surface for air. We can kill it by putting a film 
 
 of kerosene on the water, as the film cuts off its air 
 
 supply. The wiggler sheds its "skin" often, and thus 
 changes into the pupa. Finally the 
 flying mosquito comes out of the 
 pupa "skin." 
 
 Perhaps the most wonderful of 
 insect changes are those by which 
 the caterpillar becomes a chrysalis, 
 and the chrysalis a butterfly. Some 
 moths spin cocoons ; true butterflies 
 do not. 
 
 FIG. 265. A Wasp's Nest. 
 
 The most highly developed insects are 
 
 ants, bees, and wasps (Fig 265). In the case of the bees, some eggs 
 develop without being fertilized. These form the male bee, or 
 drone. The fertilized eggs produce female bees, but only a few 
 of the females the queens become capable of laying eggs. 
 
324 ANIMALS 
 
 The greater part of the females remain undeveloped, and are the 
 workers. 
 
 Ants, like bees, have a highly developed form of "society." Some 
 ants act as soldiers, and protect those that work. Certain ants cap- 
 ture other ants, and make them work. Other ants, still, have plant 
 lice for their "cows," and feed upon the liquids they produce. 
 
 Some of the insects, such as the bees and the larvae of the silk- 
 worm, are useful to man; but others, like the mosquito and fly, are 
 only a nuisance and a danger (cf. 424). But in numbers the insects 
 and spiders probably exceed all other animals put together. 
 
 340. Exercises. 
 
 1. What is the oldest part of the clam's shell? Of the snail's? 
 Read a description of the chambered nautilus. Who wrote a poem 
 about it? 
 
 2. What is the economic importance of the clam? From what are 
 pearl buttons made? What other materials are used for buttons? 
 
 3. Why does the earthworm come to the surface after a heavy rain? 
 Show that the earthworm is the "original plowman." 
 
 4. Why was an old-time doctor called a leech? 
 
 5. Give a list of at least 5 insects that are hurtful to man or to his 
 domestic animals. Extend the list, if you can. 
 
 6. Give a list of at least 5 insects that attack food plants or trees. 
 Extend the list if possible. 
 
 7. Give the ways in which man protects plants from the ravages of 
 insects. (Cf. also 301.) 
 
 8. Why are insects in the larva stage such greedy feeders? 
 
 9. Out of what does the silkworm spin its cocoon? The spider its 
 web? From what does the bee get its wax? Its honey? 
 
 10. How are insects helpful to plants? (Cf. 319.) 
 
 11. What is cochineal? What is its source? Its use? Answer 
 the same questions for sepia; for ambergris. 
 
 341. Fishes. The most striking difference between 
 fishes and all the animals already studied is that fishes 
 have an interior bony framework that supports the 
 
FISHES 
 
 325 
 
 body, while crustaceans, mollusks, etc., have an external 
 hard covering, if they have any hard structure at all. 
 In the animals that are below fishes in development the 
 11 trunk line" of the nervous system is in the lower region 
 of the body. In the fishes and those above them there 
 is a spinal cord ; it is in the upper region of the body, and 
 it is protected by a series of bones. Each bone in the 
 series is called a vertebra, and the whole series is called 
 
 First Dorsal Fin 
 
 FIG. 266. 
 
 Skeleton of a Fish. 
 
 the vertebral, or spinal, column (Fig. 266). Therefore 
 fishes and all higher animals are called vertebrates, while 
 the animals below them are called invertebrates. 
 
 The heart of the crayfish we found to consist of one 
 chamber, set in a space for receiving the blood that came 
 back from the body. In the fish we find a heart of two 
 chambers (an auricle, which receives blood from the 
 veins) and a ventricle, which forces blood into the arteries 
 (Fig. 267). The blood of fishes is red, because of the 
 presence of red corpuscles (cf. Fig. 286, 378). 
 
 The respiration of the fish takes place through gills. In higher 
 fishes, such as the perch, the gills are all placed under one hard cover- 
 ing, back of the head. In fishes not so well developed, such as the dog- 
 fish and shark, there are gill slits, one for each gill. In both kinds of 
 
326 ANIMALS 
 
 fishes water is taken in at the mouth, and passes outward through the 
 gill openings. This water contains dissolved oxygen (cf. 52) for 
 purifying the blood that comes to the gills. 
 
 The specific gravity of a fish is very nearly that of water. An ' ' air 
 bladder" enables the fish to change its specific gravity slightly, and to 
 sink or rise in the water, much as a submarine boat does (cf. 43). 
 When it compresses the air in the air bladder, the fish as a whole 
 becomes a little denser, and goes downward. When the compressing 
 
 Carotid 
 
 Arterj 
 
 FIG. 267. 
 Circulation of Blood in a Fish, with the Connecting Organs. 
 
 muscles are relaxed, the air expands; thus the body as a whole becomes 
 lighter, and rises. 
 
 The fish moves by means of the strokes of its powerful tail fin, as 
 well as by the strokes of smaller fins. The side fins aid the fish in 
 steering itself, while the fins on the upper (dorsal) and the lower 
 (ventral) sides of the body keep the fish right side up. In the lower 
 fishes, such as sharks, the upper lobe of the tail is much larger than the 
 lower; in higher fishes the tail is symmetrical. 
 
 The scales of fishes form a hard protective covering. They lap 
 over one another, and so permit the body underneath to bend. Sharks 
 have a tough skin covering without true scales. 
 
 342. Amphibians. The name " amphibians " (pro- 
 nounced am-fib'-i-ans) comes from amphi, meaning 
 "both," and bios, "life"; it refers to the fact that amphib- 
 ians live both on the land and in the water. Examples 
 of amphibians are frogs, toads, and salamanders. 
 
AMPHIBIANS 
 
 327 
 
 In amphibians, as in all animals above them, there is 
 not only a vertebral column, but there are four limbs, 
 the hard parts of which are parts of the bony skeleton. 
 The fore legs of the frog are small, and have four toes 
 each; the hind legs are long and strong, and each has 
 five webbed toes. The hind legs are, therefore, well 
 adapted for both jumping and swimming. 
 
 The frog's body (Fig. 268) is covered with a colored 
 skin, the outer layer of which it sheds in moulting. Each 
 
 FIG. 268. 
 Stages in the Development of a Frog. 
 
 of the frog's eyes is closed by an upper and a lower lid; 
 but the lower is the. more movable. Back of the eyes, on 
 the sides of the head, are two membranes ; these form the 
 outer ears. 
 
 The blood of amphibians, like that of fishes, is low in 
 temperature: these animals are "cold blooded." The 
 heart has two receiving chambers (a right and a left auricle) 
 and one ventricle. This is an advance beyond fishes 
 (cf. 341). 
 
328 ANIMALS 
 
 The young of frogs and toads undergo a metamorphosis (c/. 339). 
 As hatched from the egg they are "polywogs," or tadpoles. This is 
 the " larva" stage. Tadpoles are water animals, provided with gills 
 for breathing, and with a long tail for swimming. As they develop, 
 the tail becomes shorter, and the hind legs appear. The fore legs are 
 at first hidden by a fold of the skin that grows out to cover the gills. 
 The outer gills disappear, and inner gills and lungs are formed. 
 
 The tadpole lives upon vegetable food, but in changing into an 
 adult frog it changes its diet to, animal food, chiefly insects. The toad, 
 although it is first a tadpole, leaves the water entirely when it grows up. 
 In the winter time, frogs burrow into the mud at the bottom of ponds, 
 and live there (hibernate) through the cold weather without feeding. 
 To hibernate means to "pass the winter." 
 
 343. Reptiles. Reptile is from a Greek word meaning 
 "to creep," or "to crawl"; the Latin serpo, from which 
 "serpent" is derived, means the same thing. Reptiles 
 include lizards, chameleons, alligators, crocodiles, turtles, 
 and snakes. 
 
 Reptiles, like amphibians, are cold-blooded; but they 
 differ from amphibians in that they breathe, from the 
 first, with lungs. The heart of the crocodiles is higher in 
 development than that of other reptiles, for it has two 
 auricles (receiving chambers) and two separate ventricles 
 (chambers from which blood is pumped to the body and 
 the lungs). In this respect crocodiles are like birds and 
 mammals, including man (cf. 375). Other reptiles are 
 like amphibians. When there are two ventricles, the 
 pure blood from the lungs and the impure blood from the 
 body are not mixed in the heart. 
 
 Reptiles are covered with horny or with bony plates, or 
 both. The horny plates come from the outer skin, and 
 are usually "shed" and renewed, as in the case of snakes. 
 
BIRDS 
 
 329 
 
 Lizards have long bodies with a distinct head, neck, and 
 tail. Their feet have five toes each. Turtles have a 
 peculiar form, and move slowly, because of their protective 
 box of horny material. In temperate climates, reptiles 
 hibernate in winter. 
 
 Snakes have the remains of bones which show that their ancestors 
 once had limbs; but modern snakes have no limbs. In spite of this 
 they move rapidly. The body of the snake is so narrow that there is 
 little room for some of its internal organs, so these are altered. Thus, 
 one lung is very small, and almost useless. On the other hand, the 
 long muscular body is a wonderful structure for the seizing and crush- 
 ing of prey. Most small snakes are harmless. The dangerous ones in 
 this country are rattlesnakes, water moccasins, and copperheads. In 
 India there is a great python, and in South America, the anaconda, 
 which grows to a length of 30 feet. These kill their prey by crushing it. 
 
 Reptiles reached an enormous size in past geological times, as their 
 fossils tell us. There were then 
 swimming, walking, and flying 
 reptiles. 
 
 344. Birds. In certain 
 rocks there have been found 
 the remains (fossils) of birds 
 that are remarkably like 
 reptiles. They have a long, 
 jointed tail, as reptiles have, 
 and the tail feathers come in 
 pairs from these joints. In 
 modern birds (Fig. 269) the 
 tail joints are so much short- 
 ened that all the feathers 
 seem to come from one place. 
 
 Sternum 
 
 FIG. 269. 
 Skeleton of a Bird. 
 
 These fossil birds had teeth 
 
 like those of reptiles ; modern birds have only a horny beak 
 
330 
 
 ANIMALS 
 
 formed out of skin. In the ancient bird, the wing was 
 much like a simple fore limb, instead of the greatly altered 
 structure that we see in the wings of modern birds. 
 
 While modern birds still have some of the charac- 
 teristics of reptiles, .in other respects they have gone far 
 beyond them. Instead of being cold-blooded, birds have 
 a higher blood temperature than any other animal; viz., 
 from 100 F. to 110 F. Man's blood is at 98.6 F. 
 Horny scales, which cover reptiles, appear only on the 
 legs and feet of birds, while the main portion of the body 
 is covered with feathers. In flying birds the body is 
 wonderfully fitted for flight; in wading birds the neck 
 and feet are long; while in the case of swimming birds the 
 feet are webbed. The foot of a bird usually has four 
 toes. In climbing birds two of the toes are directed 
 forward and two backward. In perching birds three 
 
 toes are directed forward, 
 and one backward. 
 
 Crop 
 
 Pelvis 
 
 Stoma 
 
 The gullet of birds is enlarged 
 into a crop for the storing of food 
 (Fig. 270). The gizzard is the 
 muscular part of the stomach. In 
 grain-eating birds the inner lining 
 of the gizzard is hard and rough. 
 This rough lining, together with 
 the gravel and sand which these 
 birds eat, takes the place of teeth 
 in grinding and crushing the food. 
 The brain and the nervous system of birds are highly developed. 
 We ought to expect this from the wonderful ways in which birds adapt 
 themselves to their surroundings, and from the great care that they 
 give to their young. 
 
 Sternurq 
 
 Intestine 
 
 FIG. 270. 
 Digestive System of a Bird. 
 
MAMMALS 
 
 331 
 
 Much has been written of the usefulness of wild birds to man, and 
 this usefulness can hardly be exaggerated. Perhaps their greatest 
 service, aside from the pleasure they give us, is in the destruction of 
 insects that attack our food plants and trees. 
 
 345. Mammals. Mammals are so called because they 
 produce milk to nourish their young. The young are 
 brought forth alive, but require a period of care before they 
 are mature. While reptiles have a covering of plates, and 
 birds one of feathers, the skin of mammals forms a covering 
 of hair. The nails, claws, hoofs, and horns of animals, 
 including the quills of the porcupine, are all modified hair. 
 
 Mammals are all air-breathing, and live chiefly on the 
 land. Whales and porpoises are mammals that live in 
 the sea. The whale has lost its hind limbs, although there 
 are remnants of them under the surface of its body. The 
 whale's front limbs have 
 been changed to flaps, 
 to meet its needs as a 
 swimmer. The bat, also 
 a mammal, has learned 
 to fly. 
 
 A strange creature, the 
 duckbill, which lives in 
 Australia, is like birds 
 and reptiles, on the one 
 hand, and like mammals, 
 on the other. It lays 
 eggs, but it also forms Fl l 27 i , 
 
 An Opossum. The Field Museum. 
 
 milk for its young. One 
 
 group of mammals includes kangaroos and opossums (Fig. 
 
 271). These bring forth their young alive, but the young 
 
332 ANIMALS 
 
 are very feeble and immature. The mother therefore 
 keeps them in a pouch made of a fold of her skin, and 
 nurtures them with milk until they have become strong. 
 
 The nervous system of mammals is developed more highly than in 
 other animals. This is especially true of the size of the brain, and of 
 the folding of its surface. The folding increases the brain's area, and, 
 
 therefore, its capacity for de- 
 Esophagus (Tf 
 
 velopment. 
 
 The digestive organs of 
 mammals (Fig. 272) consist of 
 the mouth, gullet, stomach, 
 and intestines (bowels), with 
 many glands (cf. 358), such 
 as the liver. The structure of 
 Digestive organs of a Cow. the stomach is very different 
 
 for different mammals. In 
 
 herb-eating animals, such as the sheep and the cow, the stomach has a 
 lobe, or paunch, in which food can be stored. This storage stomach of 
 the ox holds about two bushels. After the animal stops its feeding, 
 the food returns to the mouth, and is chewed more finely (' ' chewing 
 of the cud"). Then the food passes on to the true stomach. Flesh- 
 eating (carnivorous) animals have a much simpler' stomach and a 
 shorter intestine than herb-eating (herbivorous) animals, because their 
 food requires less space for digestion. 
 
 346. Classes of Animals. In Chapter XV we learned 
 that we can put all known plants into groups, or classes, 
 according to the way in which each kind of plant meets 
 and solves the great problems of food getting, growth, and 
 reproduction. In the present chapter we have learned 
 that we can classify animals in a similar way. Just as 
 we trace the steps of development from the protococcus 
 to the daisy, so we can trace the steps from the ameba to 
 mammals. The ameba is as truly alive as a horse; why 
 
CLASSES OF ANIMALS 333 
 
 then do we think of it as a low animal? The answer is 
 that the horse has wonderful and special organs for par- 
 ticular duties, while the ameba has only one cell for all its 
 functions. In the ameba the cell is entirely independent 
 of other cells; in the mammal each cell has given up part 
 of its independence in order that a multitude of cells may 
 live together. 
 
 When many cells live together in an organism, each 
 cell does not need to carry out all the functions of the 
 organism; for there is a "division of labor" among the 
 cells, just as there is among the workmen of a successful 
 factory. We saw the beginnings of this "division of 
 labor" in the case of the hydra (cf. 334). As we ascend 
 the scale of animal forms, we find the division of labor 
 becoming more complete. Thus, the problem of food 
 digestion is worked out in a more and more excellent way. 
 The circulation of the blood, which begins in the con- 
 traction of some part of the blood tubes of an earthworm, 
 ends in the four-chambered heart of birds and mammals. 
 Respiration is first carried o'ut by all the cells; then by 
 some cells that have thinner walls. In higher creatures 
 these thin walls are greatly folded, so that they shall have 
 a large surface, and the result is the gill structure. In 
 amphibians we see the change from gills to lungs, while in 
 reptiles, birds, and mammals gills are not used at all. 
 
 We are likely to think that the mammals now on the earth have 
 always had their present forms. That this is not true is admirably 
 illustrated by the case of the horse. The fossils of the first horse show 
 that the animal was of about the size of a fox, and that it had five 
 toes to each foot. But the succession of fossils shows that the first 
 and fifth toes became mere splints, producing a three-toed animal as 
 
334 ANIMALS 
 
 large as a sheep. Then the second and fourth toes became splints, 
 while the splints of the first and fifth toes disappeared entirely. This 
 is the condition in the modern horse. Its hoofs are the enlarged nails 
 of the third (middle) toe, and there are splints that represent the second 
 and fourth toes. 
 
 347. Importance of Animals to Man. Primitive men 
 seem to have lived upon the fruits, seeds, and roots of 
 wild plants, and upon insects, worms, and small reptiles. 
 But when they invented weapons and tools, they were 
 able to kill large, wild animals, and to live upon meat. 
 It was an important day when, with traps and snares, 
 men began to capture animals alive; for they then began 
 the process of domesticating animals. The people of 
 Europe and Asia certainly learned to keep cattle, goats, 
 sheep, horses, and chickens, very long ago. As these 
 animals were protected by man, they gradually lost many 
 of their wild habits, and man, too, in depending upon 
 them, largely lost his need of hunting wild game. It was 
 natural, however, that men living near the ocean or 
 inland waters should continue to catch water animals, 
 such as fish, oysters, and lobsters, and these, especially 
 fish, still form the food of a large portion of the human 
 race. 
 
 Man learned to use his domestic animals not only for 
 their meat and milk, but also to carry himself and his 
 loads. To give his animals and himself a more certain 
 supply of vegetable food, he cultivated grains, fruits, etc. 
 As a result, he was able to cease his wandering over the 
 earth in search of pasturage, and to settle down upon 
 farms. Strangely enough, the horse probably originated 
 upon the American continent, but became extinct here 
 
SUMMARY 335 
 
 before man could use it. The ancestors of all the horses 
 in America have been brought here, from Europe or Asia, 
 since the days of Columbus. One reason why man's 
 progress was far more slow in America than in Europe 
 and Asia may have been that there were no beasts here 
 that could be readily domesticated as helpers of man. 
 
 Man has developed all the different varieties of chickens, dogs, cats, 
 pigeons, etc., as he has developed the .varieties of domestic plants; 
 namely, by selecting the individuals that possessed certain qualities 
 that he desired, and then breeding these individuals, generation after 
 generation, so as to make the desired qualities more and more promi- 
 nent. Thus horses are bred for different purposes, such as for racing, 
 for ordinary driving, for hauling loads in the city, and for farm work. 
 The horse that is good for one of these uses is not necessarily good for 
 any of the others. The types of cattle wanted for the commercial 
 production of milk and butter are different from those wanted for 
 meat. Sheep may be bred for the quality of their wool or the quality 
 of their flesh. Breeds of chickens that lay well are often unprofitable 
 as meat producers. The growth of scientific knowledge in the last 
 50 years has greatly increased the efficiency of animal breeding. 
 
 348. Summary. Animals cannot build up their food out of mineral 
 matter ; plants containing chlorophyll can. 
 
 In the ameba a single cell can carry out the necessary animal func- 
 tions. 
 
 The hydra consists of two layers of cells which have slightly differ- 
 ent functions. Each cell can, however, take up all the functions if 
 necessary. 
 
 Starfishes are much more highly developed than hydras. They 
 have the beginnings of a nervous system, a digestive system, a blood 
 system, a breathing system, and of organs of smell and of sight. 
 
 Worms have more symmetry than starfishes, and more highly 
 developed organs. Earthworms are of enormous value to the soil, 
 since they prepare it for plant growth. 
 
 Mollusks include oysters, clams, snails, slugs, and the octopus. 
 
336 ANIMALS 
 
 Crustaceans include crayfishes, lobsters, crabs, and barnacles. 
 They have three body regions: head, thorax, and abdomen. The 
 crayfish has a one-chambered heart and arteries, but no veins. Res- 
 piration is by gills. 
 
 Insects also have three body regions. Respiration is in air passages, 
 and not in gills. When insects undergo metamorphosis, there are 
 usually three stages: the larva, pupa, and adult stages. Insects 
 (including spiders) form the most numerous class of animals. 
 
 Fishes and all animals above them are called vertebrates. They 
 have a spinal cord and an interior bony framework. All animals below 
 fishes are called invertebrates. The heart of the fish is two-chambered, 
 its blood is red, and its gills are well developed. 
 
 Amphibians have limbs, and live partly on land and partly in 
 water. Frogs and toads hatch out as tadpoles. The heart of am- 
 phibians has two auricles and one ventricle. The adult breathes 
 with lungs. 
 
 Reptiles breathe only with lungs. The body is covered with horny 
 plates. The highest reptiles, the crocodiles, have a four-chambered 
 heart. 
 
 Birds show a great advance over reptiles, but have some reptilian 
 qualities. Their blood is, however, warm. The brain and nervous 
 system are highly developed. The body is covered with feathers. 
 
 Mammals have a covering of hair, and bring forth their young alive. 
 They are all air breathers. The brain and nervous system are the 
 highest among animals. Most mammals are either herbivorous or 
 carnivorous. Man is omnivorous; that is, he eats both vegetable and 
 animal food. 
 
 The high development of animals is due to the ' ' division of labor ' ' 
 among the cells. 
 
 Man has had a great influence in the development of economic 
 animals, and animals have had a powerful influence on the develop- 
 ment of man. 
 
 349. Exercises. 
 
 1. Name some invertebrates that are used as food by man. Which 
 is the most important in this respect? Are any amphibians used as 
 
EXERCISES 337 
 
 food? Any reptiles? Which class of mammals does man use as food, 
 the carnivorous or the herbivorous animals? 
 
 2. Find out about how many eggs your family uses weekly and 
 annually. Find out how many your city uses, and where the supply 
 comes from. 
 
 3. To what uses did primitive man put the skins and furs of ani- 
 mals? Name several of the ways in which we use them to-day. 
 
 4. How has the camel been useful to man? The reindeer? The 
 dog? How is the cat helpful to man? How is it injurious? 
 
 5. The Latin word for money, pecunia, from which we get our word 
 " pecuniary," comes from a word meaning "cattle." How did this 
 come about? 
 
 6. How have the tendons of animals (cf. 355) been used by man? 
 The bones? The horns? 
 
 7. What is ivory? For what is it used? What is the modern 
 substitute for it? 
 
 8. What is sperm oil, and for what is it used? 
 
 9. What is the source of the bristles of brushes? Did the Indian 
 have any use for the porcupine's quills? What other uses has man 
 for the hair of animals? 
 
 10. Name some economic products obtained from birds, aside from 
 their eggs and flesh. 
 
 11. What is the source of glue? Of gelatine? 
 
 12. Name several climbing birds. Perching birds. Swimming 
 birds. Wading birds. 
 
 13. Ask a farmer or a liveryman, if you do not know, why horses 
 are fed oats in addition to hay or grass. 
 
 14. Name some economic uses of fishes aside from the use of their 
 flesh as food. 
 
CHAPTER XVII 
 THE HUMAN BODY AND ITS FOOD 
 
 350. Chief Divisions of the Body. The science that 
 deals with the organs of plants and animals, and with the 
 functions of these organs, is called Physiology. The 
 science of the human body is called Human Physiology. 
 In Chapter XVI we learned that while in animals below 
 fishes (invertebrates) the parts supporting the body, if 
 there are any, are on the outside of the body, in fishes and 
 the animals above them (vertebrates) the framework of 
 the body is on the inside, and takes the form of a bony 
 skeleton. Along with this change in the body framework 
 there is also a change in the position of the nervous sys- 
 tem; in the vertebrates the important nerve centers are 
 all on the dorsal side (the back). We therefore think of 
 the body of a fish as having two spaces, or cavities: (1) a 
 dorsal cavity, consisting of the brain space (skull) and 
 the long narrow space (canal) inside the spinal column; 
 and (2) a ventral cavity. The ventral cavity is much the 
 larger, and contains the organs of respiration, circulation, 
 digestion, etc. 
 
 In mammals we make the same body divisions as in the 
 fish, but we divide the ventral cavity into two distinct 
 parts: (1) the thorax, and (2) the abdomen. 
 
 The diaphragm forms the dividing wall between these 
 two parts. In man (Fig. 273) these same divisions exist. 
 The thorax contains the lungs, the heart, some large 
 
 338 
 
CELLS AND TISSUES OF THE BODY 
 
 339 
 
 blood vessels, and the esophagus, by which food is carried 
 from the mouth to the stomach. Below the diaphragm is 
 the abdomen, which contains the stomach, intestines 
 (bowels), liver, kid- 
 neys, pancreas, spleen, 
 etc. The thorax and 
 abdomen together 
 form the trunk. 
 
 351. Cells and Tis- 
 sues of the Body. 
 
 The human body, like 
 that of any plant or 
 animal, is composed 
 of cells. These cells 
 are living, and con- 
 sist of cell walls and 
 protoplasm (cf. 323). 
 Like the ameba (cf. 
 333) they carry on 
 the fundamental pro- 
 cesses of life. They 
 feed, and they reject 
 the waste from their food. They also reproduce them- 
 selves by the process of cell-division (cf.. 323). Unlike 
 the cells formed by the division of an ameba, however, 
 the new cells of our bodies do not separate from the old 
 ones, but remain together. In this way the whole body 
 can grow, and new cells can at once replace those that die. 
 
 Since the cells of our bodies form a large community, the division 
 of labor is necessary (cf. 346). Hence we find special groups of cells 
 
 FIG. 273. 
 The Principal Organs of the Thorax and the Abdomen. 
 
340 THE HUMAN BODY AND ITS FOOD 
 
 set apart to do special kinds of work. A group of cells in which all 
 the cells do the same kind of work is called a tissue. Out of certain 
 tissues, or mixtures of tissues, the organs of the body are made. The 
 muscles contain muscle tissue, or groups of muscle cells, and nerves 
 contain nerve tissue, which consists of nerve cells. 
 
 One form of tissue is called connective tissue, because it connects 
 other cells. Its cells have slender, fine branches which extend between 
 the other cells, and hold all together. So muscles really consist of 
 muscle tissue held together by connective tissue. 
 
 352. Structure of Bones. Bones are made up of 
 branching, interlaced cells of connective tissue, stiffened 
 with limestone and calcium phosphate (cf. 302). The 
 limestone is about % of the weight of the bone. Among 
 the bone cells there are tubes, or "canals," containing 
 blood vessels and nerves. The outside layer of a bone is 
 very compact, and the whole bone has a tough covering 
 of connective tissue. This is called the periosteum, 
 meaning "around the bone." The animal matter (that 
 is, the connective and other tissues) of a bone may be 
 destroyed by burning. The ashes will contain the 
 mineral part. The limestone we can remove by soaking 
 the bone in some dilute acid, such as dilute hydrochloric 
 acid (cf. 128). The tough connective tissue will remain, 
 but the stiffening will be gone. Long bones have cavities. 
 They thus give the greatest possible strength, with the 
 least possible weight. 
 
 Cartilage is pliable, immature bone. It contains very little lime- 
 stone, and forms the skeletons of young animals. As limestone is 
 added, bones become more hard, but also more 'brittle. However, all 
 the cartilage in the body does not become hardened. Some remains 
 at the end of almost every bone, to diminish friction, and to prevent 
 the jarring of one bone against another. 
 
JOINTS 
 
 341 
 
 Pelvis 
 
 353. Joints. A joint is a place where bones come to- 
 gether. Some joints are intended to be bent freely; 
 these are called flexible, or movable, joints. Some joints 
 are not arranged for bending; these are inflexible, or im- 
 movable, joints. Some of the bones of the skull are held 
 together in inflexible joints. 
 
 Between inflexible joints there is usually a layer of 
 cartilage or of material much like it. Its use is shown 
 admirably in the backbone, where it forms pads between 
 the vertebrae. These pads permit the backbone to be 
 bent somewhat, and 
 act as cushions to 
 relieve the skull as 
 much as possible 
 from the jar caused 
 by walking and 
 running. 
 
 At movable joints 
 the bones are held 
 together by tough 
 bands, called liga- 
 ments, and the ends 
 
 of the bones are smooth and round. When muscles 
 pass over joints, they also assist in holding the bones 
 together. We distinguish three principal kinds of mov- 
 able joints (Fig. 274) : 
 
 (1) Those in which the movement is in two opposite direc- 
 tions only, as in an ordinary hinge; these are called hinge 
 joints. The knees, elbows, and fingers have hinge joints. 
 
 (2) Those that can be moved in any direction, as the 
 arm can at the shoulder. Such joints have the rounded 
 
 Patella 
 
 FIG. 274. 
 A Hinge Joint and a Ball-and-Socket Joint. 
 
342 
 
 THE HUMAN BODY AND ITS FOOD 
 
 I Bone 
 
 FIG. 275. 
 The Skeleton and its Parts. 
 
 end of one bone 
 fitting into the 
 socket of another, 
 and are called 
 ball-and-socket 
 joints. 
 
 (3) Those in 
 which one bone 
 glides over an- 
 other; these are 
 called gliding 
 joints. 
 
 354. The Skele- 
 ton. The human 
 skeleton -(Fig. 
 275) consists of 
 206 bones, which 
 together form the 
 frame work of the 
 head, trunk, and 
 limbs. The bones 
 of the head make 
 up the skull. 
 The cranium, or 
 "brain box," is 
 made up of 8 bony 
 plates joined to 
 gether. The face 
 is supported by 
 14 ' :nes, and 
 
THE SKELETON 
 
 343 
 
 Emensors 
 of Fingers 
 
 there are 3 little bones in each ear. This makes a total 
 of 28 bones in the head. 
 
 The backbone, or spinal column, consists of 24 bony 
 rings, or vertebrae (cf. 341). There are, in addition, 
 two bones at the base of 
 the backbone; these are 
 called the sacrum and the 
 coccyx. 
 
 Twelve of the vertebrae 
 have 2 ribs each. The 7 
 upper pairs of ribs are 
 joined in front to the 
 sternum, or breast bone, 
 and are called true ribs. 
 The 5 lower pairs of ribs 
 are called false ribs. The 
 3 upper pairs of false ribs 
 are joined to the lowest 
 pair of true ribs. The 2 
 lowest pairs of false ribs 
 are not attached, in front, 
 to anything, and are called 
 floating ribs. The shoulder 
 bones are 2 clavicles (collar 
 bones) and 2 scapulas 
 (shoulder blades). There 
 is also a hyoid bone at the 
 base of the tongue. The 
 lower end of the abdomen 
 is supported by the sacrum and coccyx bones of the 
 spinal column, and by the 2 pelvic, or hip, bones. 
 
 FIG. 276. 
 Surface Muscles of the Body. 
 
344 THE HUMAN BODY AND ITS FOOD 
 
 These 4 bones form the pelvis. There are altogether 
 58 bones in the trunk. 
 
 The four limbs have 30 bones each. Each arm has a humerus 
 (upper arm), radius and ulna (lower arm), 8 wrist bones (carpals), 5 
 hand bones (metacarpals) , and 14 finger bones (phalanges). Each 
 leg has a femur (thigh bone) , and a tibia (shin bone) and a fibula below 
 the knee. At the front of the knee is the knee cap (patella). In the 
 ankle there are 7 tarsal bones; in the foot, 5 metatarsals; in the toes, 
 14 phalanges. 
 
 A summary of the list of bones is as follows : 
 
 Bones of Head. 
 
 Cranium 8 Sternum 1 
 
 Face - 14 Hyoid 1 
 
 Ears 6 Clavicles- - 2 
 
 Scapulas 2 
 
 28 
 
 58 
 Bones of Trunk. Bones of Limbs. 
 
 Vertebrae 24 Upper limbs 60 
 
 Pelvis -------- 4 Lower limbs 60 
 
 Ribs 24 
 
 120 
 Total Number of Bones 206 
 
 355. Muscles and Tendons. The muscles are the 
 organs that move the animal body (Fig. 276), and at the 
 same time cover the skeleton with rounded flesh. They 
 constitute the lean part of meat. Muscles are made up of 
 long cells. Connective tissue, in the form of a white, 
 skin-like membrane, is present between the muscle cells, 
 and also holds the muscles in bundles. 
 
 The business of muscles is to grow shorter (to contract) 
 when commanded. By the shortening of all the cells, 
 
MUSCLES AND TENDONS 345 
 
 the muscle itself grows shorter. At a movable joint two 
 muscles usually act in opposition to each other, like two 
 springs on opposite sides of a door. If one muscle 
 shortens itself, the other grows longer. The two give a 
 forward and backward motion to the bone, like that 
 which we see when we raise and lower the forearm. 
 
 Tendons are the extensions of the connective tissue 
 of muscles; they bind muscles to bones. The tendons 
 are sometimes very long, and attach a muscle to a bone 
 at a distance. This is true in the hand. The thick 
 muscles that move the hand are in the forearm, while the 
 hand itself is slender and skillful. The long tendons that 
 extend to the hand and the foot are held down, near the 
 bones, by means of circular bands (ligaments) at the 
 wrist and ankle. 
 
 The bones act as levers (cf. 198 and 199). The fulcrum is the 
 joint. The weight is the member that is moved, and whatever it holds. 
 The power is the pull produced 
 by the end of the muscle or 
 tendon at the place where it is 
 attached to the bo'ne. To lift 
 your forearm (Fig. 277) the biceps 
 muscle of the upper arm (Fig. 276) 
 contracts, and pulls upon the 
 radius bone a few inches below 
 the elbow. The power is be- 
 tween the fulcrum and the weight; Fulcru 
 hence this is a lever of the third FlG 2 ?7. 
 
 claSS. Most of the levers in the A Third Class Lever in the Arm. The power 
 .,,.,, is supplied by the contraction of the biceps 
 
 body are of the third class. muscle. 
 
 Some muscles are under the control of the will (vol- 
 untary muscles), and some are not (involuntary muscles). 
 
346 THE HUMAN BODY AND ITS FOOD 
 
 Our bodies carry out the functions of digestion and circu- 
 lation without our wills: the muscles of heart and stom- 
 ach do not require our attention. But if you wish to 
 throw a baseball, or to " drive" a golf ball, or to sew or 
 write, your brain must call upon certain muscles to pro- 
 duce the proper motions. The body is held erect, and 
 the joints are prevented from collapsing by the action of a 
 multitude of muscles. 
 
 356. Injuries to Bones and Muscles. When bones are 
 broken, it is not only the mineral matter that breaks, but 
 the connective tissue, and the blood tubes and nerves as 
 well. When the broken pieces are held together by 
 bandages and splints, new cells of connective tissue unite 
 the broken edges, and restore the connections of the 
 nerves and blood vessels. The filling of the connective 
 tissue with minerals is the slowest part of the healing 
 process. When this takes place, the bone is said to 
 "knit" together. As a person grows older, more mineral 
 is deposited in the bones, and they become more brittle. 
 They therefore break more easily than in childhood, and 
 do not unite so readily if broken. 
 
 When the bones of a joint are separated, the bones are 
 said to be dislocated, or "out of joint." In this case the 
 ligaments and muscles at the joint are probably torn. 
 In a bad dislocation the muscles may draw up the bones 
 and prevent them from going back into place for some 
 time. The physician then puts splints on the joint to 
 hold it stiff until the ligament has time to grow together 
 again. The chief difference between a sprain and a dis- 
 location is that in a sprain the bones are not separated. 
 
KINDS OF FOOD 347 
 
 Tuberculosis (consumption) often attacks the joints. 
 At the hip it produces "hip disease. " 
 
 The chief injuries to muscles come from either overwork or under- 
 work. Most students take too little exercise, and are content to let 
 others play, while they themselves look on. The body should get 
 daily exercise, best out of doors. One should exercise until he just 
 begins to be a little tired; then he should rest. By gradually increasing 
 the amount of our exercise, all of us can build up vigorous bodies. But 
 exercise is useless unless we have good food, and long hours of sleep, and 
 unless we avoid alcohol and all other harmful stimulants. 
 
 357. Kinds of Food. As the cells of the body do their 
 work, some of their protoplasm is used up, and needs to 
 be replaced. Moreover, as the oxygen of the blood 
 comes to the cells, it "burns up" (oxidizes) some of the 
 cell material to give energy to the cells. There are, 
 therefore, two distinct reasons why we must have food : 
 
 (1) In order to give the cells material for their growth 
 and repair; 
 
 (2) In order to give them energy, so that they can do 
 their work. 
 
 So we may say that anything which gives the body the 
 materials for growth and repair, or which gives it heat or 
 energy, is food. 
 
 In spite of the fact that we eat many foods, we can re- 
 duce the kinds of food to five simple foods, or nutrients 
 (Fig. 277a; also Appendix, Table XII). The nutrients are: 
 
 1. Proteids. 4. Minerals. 
 
 2. Carbohydrates. 5. Water. 
 
 3. Fats. 
 
 Proteids are obtained from both animal and vegetable 
 food (cf. 56, 298, and 299). One form of proteids is 
 
348 
 
 THE HUMAN BODY AND ITS FOOD 
 
 albumin, present in the whites of eggs; another form is 
 casein, present in cheese and milk. A third proteid is 
 gluten, found in wheat and other grains; a fourth is 
 
 Potato 
 
 Sirloin Steak 
 
 Egg White Bread 
 
 FIG. 277a. 
 Nutrients in Some Common Foods. 
 
 legumen, found in beans, peas, and peanuts. Myosin, a 
 fifth proteid, is abundant in lean meat (muscles). Pro- 
 teids contain chiefly carbon, hydrogen, oxygen, nitrogen, 
 sulphur, and sometimes phosphorus. They are easily 
 
KINDS OF FOOD 349 
 
 changed to protoplasm by the cell, and are used especially 
 for the building up and repairing of the body tissues. 
 Proteids give off some energy when oxidized, but other 
 nutrients are better for this purpose. 
 
 Gelatine is extracted from bones when they are boiled with water. 
 Like the proteids, it contains nitrogen, and like them gives off some 
 energy when oxidized, but it is not a true proteid, for it cannot be used 
 in the building of body tissues. Substances like gelatine are called 
 albuminoids, meaning, "like the albumins." 
 
 Carbohydrates include the starches and sugars . 
 Starches come from corn, wheat, potatoes, and other 
 plants; sugars come from sugar cane, sugar beets, honey, 
 fruits, etc.. Carbohydrates contain carbon, hydrogen, 
 and oxygen only (cf. 123) ; no nitrogen. They are used 
 by the body for the energy (heat) that they furnish. The 
 body seems to be unable to use starch and cane sugar 
 directly. Starch must first be changed to maltose (malt 
 sugar), and this to dextrose (also called glucose, or " grape 
 sugar")- Cane sugar must be changed to dextrose and 
 levulose (fruit sugar). 
 
 Fats and oils contain carbon, hydrogen, and oxygen, 
 just as carbohydrates do (cf. 224). They are present in 
 such food materials as milk, butter, lard, olive oil, and the 
 fat of meat, as well as in eggs, corn, peanuts, etc. Fats 
 and oils, like carbohydrates, furnish heat and energy to 
 the body, but cannot build up protoplasm. The student 
 will see at once that we get these three nutrients (proteids, 
 carbohydrates, and fats) by eating the bodies or products 
 of animals and plants. 
 
 Our chief mineral food is salt; this is needed for important digestive 
 processes (cf. 364). Salt is present in many foods, and is used to 
 
350 THE HUMAN BODY AND ITS FOOD 
 
 season food. Iron compounds are needed to form a part of the blood; 
 we get them chiefly from vegetable food. Limestone and calcium 
 phosphate are needed by the bones (cf. 352). We get them in our 
 food and in hard water (cf. 132). 
 
 Water is needed in large amounts by the body. We realize this 
 when we remember that about 70% of the body is water. We get a 
 great deal of water even in our " solid" food (cf. 79). 
 
 Oxygen is not usually thought of as a food, because it does not 
 enter the body by the digestive organs; but the body must have an 
 abundant supply of it all the time to remain alive. 
 
 358. Organs of Digestion; Glands. The tube through 
 which food is passed for digestion is called the alimentary 
 canal, or digestive tract. It consists of the mouth, 
 pharynx (throat), esophagus (gullet), stomach, and the 
 large and small intestines. Altogether it is about 30 feet 
 long. 
 
 In order to digest food, liquids are poured upon it in 
 the mouth, the stomach, and the intestines. The liquids 
 are taken out of the blood for this purpose by organs 
 called glands. The origin of glands is as follows: 
 
 The alimentary canal, as well as the windpipe and 
 lungs, is lined with mucous membrane. This begins at 
 the lips, and is a continuation of the skin which covers the 
 outside of the body. It is pink from the network of blood 
 vessels beneath it, and produces a thin, clear liquid called 
 mucus. From this liquid it gets its name. The surface 
 of the mucous membrane is made up of a layer of flat cells, 
 called epithelial cells. Now, glands are made by the 
 folding in of epithelial cells in tubes or pockets (Fig. 278). 
 Blood vessels 'and vessels containing lymph, a substance 
 much like blood (cf. 379), are all about the glands; hence 
 it is only necessary for the epithelial cells to take what 
 
THE MOUTH 
 
 351 
 
 material they want from the blood. They then give off 
 this material to the gland pockets, and from the pockets 
 it is poured out into the organ for which it was intended. 
 A gland separating a liquid from the blood is said to 
 secrete the liquid, and the liquid is called a secretion. 
 The glands that secrete the digestive juice of the mouth 
 are called salivary glands, and the 
 secretion is saliva. The gastric 
 glands secrete gastric juice for the 
 stomach. 
 
 FIG. 278. 
 
 Diagram of a Simple and a 
 Complex Gland. 
 
 During chewing, 
 
 359. The Mouth. At the begin- 
 ning of the digestive tract is the 
 mouth. It contains the nerves of 
 taste, while just above it, in the nose, 
 are the nerves of smell. These two 
 senses therefore pass upon the quality 
 of the food at once. In the mouth 
 the food is broken up into bits 
 (chewed, or masticated) by the teeth, 
 the glands of the mouth secrete saliva; the mouth 
 1 ' waters." They often secrete it before food gets into the 
 mouth; the odor or thought of food is enough to put them 
 into action. The tongue rolls the food about in the 
 mouth, so that the teeth may chew it again and again. 
 Finally, when we wish to swallow the food, the tongue 
 pushes it back to the opening of the throat, or pharynx. 
 
 Saliva consists chiefly of water; this moistens the food 
 thoroughly before swallowing takes place. Some of the 
 solution of the food also gets to the nerves of taste. The 
 saliva is, however, more than water: it has an alkaline 
 
352 
 
 THE HUMAN BODY AND ITS FOOD 
 
 reaction (cf. 218) ; it contains certain salts, also ptyalin 
 (pronounced ti'-a-lin) , a ferment, or enzyme. 
 
 Ferments are substances that by their presence bring 
 about chemical changes (cf. 98). 
 
 Ptyalin begins the change of starch into sugar (cf. 357) ; hence a. 
 cracker becomes sweet when chewed. There are three pairs of salivary 
 glands in the mouth: one pair just under the tongue; another behind 
 the corners of the lower jaws; a third pair in front of the ears. 
 
 The tongue is a flat, movable organ made up of muscular tissue. 
 The back of it is attached to the bottom of the mouth. It has nerves 
 of touch, like those of the finger tips, and also nerves of taste. 
 
 The cheeks and lips are 
 made up of thin muscles 
 covered with skin on the out- 
 side and with mucous mem- 
 brane on the inside. 
 
 360. The Teeth. The 
 adult man or woman 
 has 32 teeth, set into 
 sockets in the jaw bones 
 (Fig. 279). The teeth 
 are of 4 kinds, called 
 
 incisors, canines, bicuspids, and molars. There are 2 
 incisors ("cutters") in each half of each jaw. They 
 are flat, sharp teeth used for biting off pieces of food. 
 Next to the incisors is the canine, or "dog," tooth. 
 This is sharper than the other teeth. In the dog and 
 other carnivorous animals it forms the tusk, or tearing 
 tooth. The fourth and fifth teeth are the bicuspids, so 
 called because each has 2 cusps, or points. The sixth, 
 seventh, and eighth teeth are the molars, or grinding teeth. 
 
 Molars Bicuspids 
 
 FIG. 279. 
 Teeth in the Lower Jaw. 
 
THE SWALLOWING OF FOOD 
 
 353 
 
 The child's first set of teeth ("milk teeth") is temporary. There 
 are 20 in the set. When the child is 6 or 7 years old, the first permanent 
 teeth appear. These are the first of the permanent molars. The 
 molars farthest back in each jaw 
 are "cut" last, and are called the 
 "wisdom teeth." 
 
 A tooth consists of a crown of 
 very hard enamel, and a neck and 
 root of material called dentine. The 
 roots are covered with " cement." 
 The interior of the tooth is called 
 the pulp cavity; it contains the 
 nerves and blood vessels of the 
 tooth. The teeth are precious, 
 and ought to be given every care. 
 They should be cleaned, every day, 
 with a soft brush, and if cavities 
 are formed they should be filled 
 by a good dentist. Hard sub- 
 stances, such as nuts, thread, and 
 brittle candy, should not be bitten; 
 for they may break the enamel. 
 If bacteria get into the interior of 
 the teeth, they cause a rapid decay. 
 
 361. The Swallowing of 
 Food. When food is ready 
 to be swallowed, the tongue 
 pushes it back to the pharynx 
 (Fig. 280). This is a mus- FiG.2so. 
 
 cular tube, about 4 inches Pat ^ Take |^ r F t he d Body byAirasThey 
 long, having a number of 
 
 openings. At its top there are 2 openings into the 
 nose, and 2 into the ears. The openings leading to 
 
354 THE HUMAN BODY AND ITS FOOD 
 
 the nose can be closed by the soft palate, which rises 
 up against them. The opening between the pharynx 
 and the mouth can be closed by two upright muscles, 
 which come together like the halves of a sliding door. In 
 passing from the pharynx, food must go over the ' l wind- 
 pipe," or trachea. We should soon be strangled if food 
 went into our windpipes; hence the larynx, at the top of 
 the windpipe, is closed by a cover, called the epiglottis. 
 When the food is in the pharynx, and the openings to 
 the nose, mouth, and windpipe are closed, the upper 
 muscles of the pharynx contract above the food, forcing 
 it downward into the esophagus. This is a tube about 9 
 inches long, lined with mucous membrane, and provided 
 with circular and with lengthwise muscles. The esopha- 
 gus muscles contract above the food, and force it down 
 into the stomach. 
 
 362. Exercises. 
 
 1. What advantages has the internal skeleton of vertebrates over 
 the hard external covering of insects and crustaceans? Has it any 
 disadvantages? 
 
 2. What advantages does man gain from his erect position? 
 
 3. Name several levers in the body. 
 
 4. How could you find out how much of the weight of a bone is due 
 to mineral matter? 
 
 5. What devices are there in the skeleton to prevent the jarring of 
 the softer parts of the body? 
 
 6. What kind of a joint do you think there is in your neck that 
 makes it possible for you to shake your head? To nod "yes." 
 
 7. What is the effect of high heels upon the position of the body in 
 walking? 
 
 8. What kind of a joint do the fingers have? What kinds has the 
 thumb? What are the structures in the hand that make it so skillful? 
 
THE STOMACH 355 
 
 9. Why does your head nod when you doze in your chair? 
 
 10. Do you think you are taller at night, or in the morning? Meas- 
 ure yourself, and explain what you find out. 
 
 1 1 . Give the reasons why sleep rests the body. 
 
 12. We are told that milk, and cereals such as oatmeal, are good for 
 young children, because they assist in bone making. What nutrients 
 must they supply? 
 
 13. Why do stones, sand, glass, etc., have no taste? 
 
 14. Why is the tongue provided with nerves of touch? 
 
 15. Why should a child's first teeth be cared for, even though they 
 are soon to be replaced by the permanent set? Why ought we to be 
 careful about bringing cold food, such as iced water, ice cream, and 
 cold melons, in contact with the teeth? 
 
 16. Why is milk called a " perfect" food? 
 
 17. Yeast contains the ferment invertase, which changes cane 
 sugar into grape sugar and fruit sugar (cf, 357). It also contains 
 zymase. How does this change the grape and fruit sugars? (Cf. 
 129.) 
 
 363. The Stomach. As we learned in 361, the 
 esophagus lies against the backbone, and passes through 
 the thorax into the abdomen. The stomach, at the 
 lower end of the esophagus, is wholly within the abdomen, 
 on the left side, and partly under the ribs. It is about 
 a foot long and about 4 inches in diameter. The stomach 
 is really an expansion of the digestive tract, like a lake 
 formed by the widening of a river. There is nothing to 
 close the entrance from the esophagus into the stomach, 
 but the opening (pylorus) from the stomach into the small 
 intestine is closed by a muscular ring while digestion is 
 going on in the stomach. 
 
 The method by which food is carried down the esopha- 
 gus has been partly explained in 361: the circular 
 muscles contract above the food. The esophagus is also 
 
356 
 
 THE HUMAN BODY AND ITS FOOD 
 
 FIG. 281. 
 Two Kinds of Muscles. 
 
 provided with lengthwise muscles (Fig. 281). As these 
 can be shortened by contraction, the esophagus can carry 
 out movements similar to those described for the earth- 
 worm (cf. 336). The lengthwise muscles shorten the 
 tube, and pull it over the food, while the circular muscles, 
 
 by contracting, form a 
 ring behind the food, and 
 push it along. 
 
 The stomach has both 
 of these kinds of muscles, 
 and in addition it has 
 oblique muscles. As a 
 result of the action of 
 these three kinds of 
 muscles, the food re- 
 ceived from the esopha- 
 gus is forced around and around in the stomach. It is 
 thus mixed thoroughly with the gastric juice, the 
 secretion of the glands of the stomach. 
 
 364. The Gastric Juice. The gastric juice is chiefly 
 water, but it contains the important ferments rennin and 
 pepsin, and also hydrochloric acid, in solution. From 5 
 to 10 pints are secreted daily. Rennin coagulates the 
 casein (a proteid; 357) of milk, forming "clots" like 
 those of sour milk. The proteids are insoluble in water, 
 and cannot pass from the alimentary canal into the blood ; 
 but the pepsin changes them into simpler substances, 
 called peptones and proteoses, which are soluble. 
 
 The hydrochloric acid of the stomach (cf. 214) carries out several 
 important reactions. Thus, pepsin acts best when hydrochloric 
 
THE INTESTINES 357 
 
 acid is present. Again, the food coming to the stomach is alkaline, 
 from the saliva it contains; the acid neutralizes this (cf. 220). Since 
 food is exposed to the air before we eat it, it contains a multitude of 
 bacteria, including those of fermentation. The acid destroys these, 
 and thus prevents fermentation and infection. We must not, however, 
 depend upon the hydrochloric acid to destroy all bacteria, for some, 
 such as those of typhoid, are not killed by it. 
 
 The action of the gastric juice changes food to a milky substance 
 called chyme; this is ready for digestion in the intestines. 
 
 365. The Intestines. As portions of food are changed 
 to chyme, the muscular ring at the pylorus is relaxed, and 
 the chyme enters the small intestine. Both the intestines 
 together form a tube about 27 or 28 feet long. This tube 
 is so long that it must be coiled in the abdomen (cf. 
 Fig. 273, 350) . Herbivorous animals have even longer in- 
 testines; that of the grown ox is about 150 feet long (cf. 
 345). In man the small intestine is about 22 feet long 
 and 1 inch in diameter; the large intestine is about 2 
 inches in diameter. Both of these have lengthwise and 
 circular muscles, like those of the esophagus. 
 
 Three glands discharge their secretions into the small 
 intestine; the glands are the intestinal glands (which 
 secrete the intestinal juice), the liver, and the pancreas. 
 All of these secretions have an alkaline reaction, and thus 
 differ from the gastric juice, which has an acid reaction. 
 
 The organs that are of the greatest importance in 
 absorbing the digested food of the small intestine, and in 
 transferring nutriment from the alimentary canal to the 
 blood, are the villi (singular, villus). These .are small 
 elevations that project from the wall of the small intestine, 
 and make its absorbing surface about 6 or 7 times as 
 
358 THE HUMAN BODY AND ITS FOOD 
 
 great as if it were smooth. Each villus contains a net- 
 work of small blood tubes (capillaries), and also lacteal 
 glands. The "food solution," called chyle, which the 
 small intestine prepares, goes into the epithelial cells of 
 the villi, and from these cells the blood tubes and lacteals 
 absorb it. The lacteal glands absorb the digested fats; 
 the blood tubes absorb the other kinds of food. 
 
 Between the small intestine and the large one there is a narrow 
 opening which allows food to pass. The large intestine begins at the 
 level of the right hip, passes up the right side to the diaphragm, then 
 across the abdomen to the left side, and down the left side. It does 
 some of the work of absorption, although it has no villi; but its chief 
 use is to discharge the solid waste from the body. It takes about 2 
 days, under normal conditions, for food to pass the length of both 
 intestines. 
 
 The vermiform appendix, which when inflamed produces appendi- 
 citis, is in the large intestine, near the place where the small intestine 
 and large intestine unite. It is a small, closed tube, about % of an 
 inch in diameter, and about 2 inches long. 
 
 366. The Liver. The liver is a dark-red organ weigh- 
 ing about 4 pounds (Fig. 282). It is on the right side of 
 the abdomen, under the lower ribs (see also Fig. 273, 
 350). The liver has several very important functions. 
 For one thing, it helps to remove from the blood the waste 
 nitrogen compounds formed by the destruction of the 
 cells. A second function of the liver is to make and 
 to store glycogen, a starchlike substance that is readily 
 changed to sugar when the body needs it. A third use 
 of the liver is to secrete bile, a yellow, bitter liquid, which 
 is emptied by the bile tube into the small intestine. 
 
 The bile is collected from the blood by a multitude of bile ducts. A 
 tube leads from the liver to the gall bladder, a sac that receives and 
 
THE PANCREAS 
 
 359 
 
 stores the bile when it is not needed. When the pylorus allows food to 
 pass from the stomach into the small intestine, the bile is poured out 
 for the food's digestion. 
 
 The bile lubricates the intestine, and helps all the operations of 
 digestion and absorption in the intestine. When bile is not secreted 
 
 Adjace 
 Lobules 
 
 Fig. 282. 
 Diagram Showing the Structure of the Liver. 
 
 properly, biliousness, accompanied by headache and indigestion, is 
 the result. 
 
 367. The Pancreas. We have already learned about 
 some of the ferments of the digestive tract: the ptyalin 
 of the saliva (cf. 359) and the rennin and pepsin of the 
 gastric juice (cf. 364). Important as these ferments are, 
 they are not so important as the ferments that are poured 
 into the small intestine in the secretion known as the 
 
360 THE HUMAN BODY AND ITS FOOD 
 
 pancreatic juice. The ferments of the pancreatic juice 
 are 
 
 (1) Amylopsin, which completes the digestion of starchy 
 foods ("amylum" means starch). 
 
 (2) Steapsin, which digests fats ("stear" means fat). 
 
 (3) Trypsin, which completes the digestion of proteids 
 (its name means " something that ' wears down/ or 
 digests"). 
 
 The pancreatic juice is a thin, watery liquid, like saliva. The 
 pancreas, which secretes it, is a tongue-shaped gland about 6 inches 
 long and one inch in diameter. It lies behind the stomach (see- 
 Fig. 273, 350). The pancreas of the lower animals, such as the pig, is 
 called sweetbread. The duct from the pancreas unites with that 
 from the liver, so both the bile and the pancreatic juice enter the 
 small intestine through the same opening. 
 
 368. Changes in Food by Digestion. Let us now look at 
 the process of digestion as a whole, and ask : ' ' What is the 
 fundamental thing that digestion in the mouth, stomach, 
 and intestines does?" The answer is that this digestion 
 makes food soluble, so that it can go through the wall of 
 the alimentary canal into the blood and lymph. Most of 
 the proteids do not dissolve in water; neither do the fats 
 and starch. Why do they not dissolve? We have already 
 learned that scientists believe that matter consists of 
 small particles called molecules (cf. 61). Now, chemists 
 believe that a part, at least, of the reason why proteids, 
 fats, and starch do not dissolve is that their molecules 
 are too large, and therefore too inactive. To make 
 these food materials dissolve, their molecules must be 
 broken down into smaller molecules. This is the work 
 that the ferments, or enzymes, perform in digestion. 
 
ABSORPTION, ASSIMILATION, AND STORAGE OF FOOD 361 
 
 We have already had illustrations of the action of these 
 ferments. Thus, the amylopsin of the pancreatic juice 
 changes the large molecules of starch to the smaller 
 molecules of malt sugar. In this form it is soluble. But 
 even the malt sugar molecule must later be broken up 
 into dextrose molecules for the use of the cells. Out of 
 the malt sugar molecule the ferment maltase produces 
 two dextrose molecules. The ptyalin of the saliva begins 
 the change of starch into sugar, but does not finish it. 
 The pepsin of the stomach, acting under acid conditions, 
 breaks up some of the complex proteid molecules into 
 peptones, which are soluble in the gastric juice. Proteid 
 digestion is not, however, completed in the stomach, so 
 the trypsin of the pancreatic juice, acting under alkaline 
 conditions, completes the process. In some similar way 
 the steapsin of the pancreatic juice changes the fats into 
 soluble form. It probably does this by decomposing the 
 fats into glycerine and acids. The acids formed are the 
 11 fatty acids" (cf. 224), such as stearic acid, oleic acid, 
 etc. Butter would give chiefly butyric acid (from butyrum, 
 "butter"). Of these fatty acids butyric acid is the only 
 one that is very soluble, in the strict sense of the word. 
 But the other acids are broken up, in the small intestine, 
 into very minute particles, so that they form a part of an 
 emulsion, like milk (cf. 91) . This emulsion can be taken 
 through the cell walls of the villi, and into the lacteal 
 glands (cf. 365). 
 
 369. Absorption, Assimilation, and Storage of Food. 
 
 Absorption (cf. 365) is not only the transferring of 
 digested food to the blood; strangely enough, the peptones, 
 
362 THE HUMAN BODY AND ITS FOOD 
 
 fatty acids, glycerine, maltose, etc., which are formed by 
 digestion, are not found in the blood. The blood does 
 contain fats, formed out of the glycerine and the fatty 
 acids ; proteids, formed out of the peptones and proteoses ; 
 and grape sugar, formed out of the maltose. From this it 
 may seem that absorption, so far as the fats and proteids 
 are concerned, undoes the work of the other stages of 
 digestion. But we must remember that the complex 
 molecules of our food are not the actual nutrients that the 
 cells can use, although they contain the "pieces" (small 
 molecules) out of which the body's fats and proteids can be 
 constructed. Digestion must be looked upon not simply 
 as a breaking down of large molecules, but also as a 
 recombining of the small molecules of digested food to 
 form the special fats and proteids of the body. 
 
 The last stage in the digestive process is called assimila- 
 tion, which means "making similar to." Assimilation 
 takes place at the cells. Here the proteid brought by the 
 blood and lymph becomes a part of the living protoplasm. 
 Here also, in some mysterious way, the cell protoplasm 
 causes the sugar and fat, and, to some extent, the pro- 
 teids, to unite with oxygen (cf. 52). It is this chemical 
 reaction that sets free the energy which the cells must 
 have to do their work, and which keeps the body warm. 
 
 Storage of Food. We eat only at intervals, while the body needs 
 food all the time. Hence there must be ways in which food can b3 
 stored up during the time of abundance, in order that the body may 
 have a supply to draw upon when its cells wear out, and its energy is 
 low. We have already learned that carbohydrates are stored up by 
 the liver (cf. 366) as glycogen. The muscles also store glycogen. 
 When dextrose is taken from the blood, by the cells, glycogen is 
 changed to sugar to keep up the blood's supply. 
 
OUR DIET 363 
 
 Fat is stored away in the spaces of connective tissue, as under the 
 skin (cf. Fig. 291, 392), between the muscles, and among the organs 
 of the abdomen. Fat so stored forms fat tissue. Animals that are 
 inactive in winter (hibernate ; cf. 342) usually store up a large amount 
 of fat to nourish their bodies during their long fasting. The blubber 
 of the whale is a thick layer of fat stored under the skin. The camel's 
 hump is fatty material that can be drawn upon when the animal has no 
 opportunity for feeding. 
 
 370. Our Diet. Does it make any difference what kind 
 of coal we burn under a steam boiler? If you were to ask 
 a wide-awake engineer such a question, he would prob- 
 ably answer (cf. 73) : ' ' Certainly it does. Some coals 
 give more heat than others. Some coals leave great 
 quantities of clinkers, while others burn up clean. And 
 the most expensive coal is not always the best." So it is 
 with the fuel of the body, our food. It makes a great 
 deal of difference what kind of food we eat, how it is 
 cooked and served, and what it. costs. We need to eat 
 some food for the energy it will give us, and some for its 
 power of building the worn-out tissues. Some apparently 
 good food is mostly waste, like the clinkery coal ; and some 
 food, though expensive to buy, has not a high nutritive 
 value. 
 
 The study of diet forms a science by itself; it is called 
 dietetics. Its experts are very careful to plan what they 
 call a "balanced ration," and a housekeeper should be 
 equally particular. A meal should not consist all of one 
 kind of nutrients, or some of the digestive organs, or their 
 ferments, will be overtaxed with work, while others will 
 have nothing to do. The housekeeper has a great 
 responsibility, not only for the health of the persons fed, 
 
364 THE HUMAN BODY AND ITS FOOD 
 
 but also for their efficiency in their work; that is, for what 
 they do as compared with what they could do. 
 
 A grown man, weighing about 154 pounds, and doing a moderate 
 amount of muscular work, needs from 60 to 115 grams (3 to 5 ounces) 
 of proteids per day. Part of these may be vegetable proteids. In 
 addition, he needs enough fats and carbohydrates to give him energy to 
 the amount of 3,000 or 3,400 large calories. A large calorie is 1,000 
 ordinary calories (c/. 64). This is about the amount of heat pro- 
 duced by the burning of 1 pound of carbon. We commonly get our 
 energy from cereals, bread, potatoes, sugar, fat, etc. 
 
 There is a great difference in the price of foods, when they are 
 considered as energy-producers. If corn costs !}/ cents a pound, 1 
 cent's worth of corn will give off 1,200 calories of heat, while 1 cent's 
 worth of codfish will give off only 20 calories, and 1 cent's worth of 
 oysters only 12 calories. Unless a family is careful, it may pay high 
 prices for food, and yet not be as well nourished as a family with a 
 simple and inexpensive, but well selected diet. 
 
 But we must remember that fresh vegetables, which give us almost 
 no proteid and fat, and but little carbohydrate, are very important 
 for the mineral salts they contain, and because they give bulk to our 
 food. We cannot estimate the value of a food in terms of proteids and 
 energy alone. 
 
 Whether food is cheap or expensive, it should be made 
 appetizing and nutritious by proper cooking and serving. 
 Cooking does not add to the nutrients of the food, but it 
 adds greatly to the digestibility. It softens and loosens 
 the tissues of food, and enables the digestive juices to get 
 at them. Proper cooking kills the parasites, such as 
 bacteria, that cling to food, and the trichinae (small 
 worms) and young tapeworms that are sometimes found 
 in raw meat. Meat is especially likely to be improperly 
 cooked. If it is fried or roasted, it should be seared on 
 the outside by being heated very hot at once; in this way 
 
ALCOHOL AND ITS EFFECTS 365 
 
 the nutritive juices are held inside. Overdone meat has 
 lost much of its value. Much frying in fat, of such food 
 as eggs, meat, and potatoes, is not good, for it covers the 
 food with a greasy coating, which the digestive juices of 
 the mouth and stomach cannot penetrate. 
 
 Here are some of the foolish things people do; then they wonder why 
 they have indigestion : 
 
 (1) They do not take enough exercise, yet they eat large amounts of 
 food. 
 
 (2) They do not eat enough food of the plain sort, but eat too much 
 of pickles, candies, cake, and pie. 
 
 (3) They take violent exercise too near meal time. If this comes 
 just before the meal, the body is too tired to digest food properly; if 
 after the meal, the body has not time to digest food before its energy 
 is needed for other purposes. 
 
 (4) They eat frequently between meals, never giving the stomach a 
 rest. If one is exercising hard, however, especially if he has not eaten 
 the slowly digestible food that " stays by," a "bite" between meals is 
 helpful. 
 
 5. People often drink very cold ("iced") water, and so chill the 
 stomach. 
 
 6. They do not eat slowly enough, so that the food is not mixed with 
 the saliva. 
 
 371. Alcohol and Its Effects The story of the injury 
 alcohol has done to men is a long and sad one, but at pres- 
 ent we shall consider only its effect upon the digestion and 
 assimilation of food, and its injury to the digestive organs. 
 When alcohol is poured over proteids, outside of the body, 
 it makes them coagulate, or harden, so that they will not 
 decay or ferment. This is a good thing in the preserving 
 of animal specimens, but it is not what we want in the case 
 of a food. For food, as we have learned, is eaten, not 
 
366 THE HUMAN BODY AND ITS FOOD 
 
 that it may be preserved, but that it may be broken down 
 by the ferments of the body. A strong drinker suffers 
 from stomach indigestion largely because his food has 
 been hardened and made -unfit for the body. Besides 
 injuring the food, alcohol paralyzes the stomach muscles, 
 so that they cannot mix the food thoroughly with the 
 gastric juice. 
 
 We learn that the using up of proteids at the cells pro- 
 duces body wastes (cf. 366 and 380). One of the most 
 important of these, and very injurious if retained in the 
 body, is uric acid. The cells pass uric acid over to the 
 lymph, and the lymph hands it over to the blood. The 
 blood carries it to the liver. Now, in health, the liver 
 changes a large part of the uric acid to urea, a soluble 
 solid that is removed from the body by the kidneys. But 
 alcohol, even the small amount in a glass of beer or wine, 
 may so upset the liver that the breaking up of uric acid 
 into urea is prevented, and the waste material is retained, 
 greatly to the injury of the body. 
 
 Those who defend the using of alcohol often tell us that 
 it is a food. It is true that a small amount of it can be 
 oxidized at the cells, and that this oxidation gives some 
 energy ; but it is also true that the cells are greatly injured 
 by it, and that for this reason it cannot properly be called 
 a food, but must be called a poison. The only reason for 
 which drinkers insist on calling alcohol a food is that they 
 want an excuse for satisfying the alcohol appetite. Alco- 
 hol undergoes no process of digestion. It passes at once 
 from the stomach into the blood and the lymph, and to 
 the cells. But there is too much alcohol for the cells 
 even in the amount taken by a moderate drinker. Now, 
 
ALCOHOL AND ITS EFFECTS 
 
 367 
 
 when real food is digested in an amount that is beyond 
 what the cells need, it can be stored. In this way sugar 
 and fat are stored (cf. 369). But alcohol cannot be 
 stored. That which cannot be oxidized at once becomes 
 simply waste, carrying harm wherever it goes. 
 
 Many patent medicines contain a great deal of alcohol 
 (Fig. 283), and people take them without realizing this 
 
 3 to 6% 
 
 Wine 
 6 to 10% 
 
 Some 
 Patent 
 Medicines 
 15 to 26% 
 
 A 
 
 Scotch 
 Whisky 
 39% 
 
 FIG. 283. 
 Amounts of Alcohol Present in Liquors and in Some Patent Medicines. 
 
 fact. A medicine containing alcohol will produce all the 
 effects of alcoholic liquors, and will develop an alcohol 
 appetite in persons who would not think of becoming 
 drinkers. Patent medicines may also contain injurious 
 drugs, such as opium, chloral, etc. An illustration is the 
 11 soothing syrup" that is often given to young children. 
 People ought to know that when they are giving a ' ' pare- 
 goric" soothing syrup, they are giving a preparation of 
 opium, and that the child becomes quiet, not because it is 
 cured, but because it is stupefied. The after-effects of 
 
368 THE HUMAN BODY AND ITS FOOD 
 
 such drugs are often very injurious. No medicine of 
 this sort should be taken or given unless a competent 
 physician prescribes it. 
 
 372. Summary. Physiology is the science that has to do with the 
 organs of animals and plants, and with the functions of the organs. 
 
 Man is a vertebrate. His body has a dorsal and a ventral cavity. 
 The dorsal cavity contains the brain and spinal cord. The ventral 
 cavity consists of the thorax and abdomen. These are divided by the 
 diaphragm. 
 
 The body is composed of living cells. A group of cells, all of which 
 do the same kind of work, is called a tissue. 
 
 Bones are made chiefly of connective tissue stiffened with limestone 
 and calcium phosphate. Cartilage is pliable, immature bone. 
 
 Joints are places where bones come together; they are movable or 
 immovable. 
 
 At movable joints bones are held together by ligaments. Movable 
 joints may be hinge, ball and socket, or gliding joints. 
 
 The skeleton consists of 206 bones. 
 
 Muscles are structures that move the body. Their duty is to grow 
 shorter. Muscles are made of muscle tissue and connective tissue. 
 
 Tendons are the extensions of the muscles' connective tissue. 
 
 The bones act as levers, muscles being the "power." 
 
 Muscles are voluntary or involuntary. 
 
 When bones of a joint are separated, the joint is said to be "dis- 
 located." In a ' ' sprain " the bones remain together, but the ligaments 
 are injured. 
 
 We eat food (1) to provide for cell growth and repair; (2) to provide 
 energy for the cells. 
 
 There are 5 simple foods, or nutrients: proteids, carbohydrates, 
 fats, minerals, and water. Proteids give material for the growth and 
 repair of- cells, also a little energy. Carbohydrates and fats give 
 energy. 
 
 The tube in which digestion occurs is the alimentary canal, or diges- 
 tive tract. Digestion is carried out by liquids taken from the blood 
 (secreted) by organs called glands. 
 
SUMMARY 369 
 
 The mou^h. contains salivary glands, which secrete saliva. Saliva 
 contains a ferment, ptyalin. 
 
 Ferments, or enzymes, are substances that by their presence bring 
 about chemical changes. 
 
 The teeth crush the food, and mix it with the saliva. 
 
 Food is swallowed by the action of the muscles of the tongue, 
 pharynx and esophagus. 
 
 Food enters the stomach from the esophagus, and leaves it at the 
 pylorus opening, entering the small intestine. 
 
 Gastric juice contains the ferments rennin and pepsin, and hydro- 
 chloric acid. Pepsin begins the digestion of proteids. 
 
 Digestion in the small intestine is carried out by the secretions of 
 3 glands. The intestinal glands secrete the intestinal juice. The 
 liver secretes the bile. The pancreas secretes the pancreatic juice. 
 
 The pancreatic juice contains the ferments amylopsin, steapsin, and 
 trypsin; these complete the digestion of carbohydrates, fats, and pro- 
 teids, respectively. Intestinal digestion takes place under alkaline 
 conditions. 
 
 Absorption in the small intestine takes place through the villi; 
 these contain blood tubes and lacteal glands. 
 
 The object of digestion is (1) to get the food into soluble form, and 
 (2) to get the large molecules of food substances into smaller molecules 
 that can recombine to form the molecules actually needed by the cells. 
 
 Assimilation is the bringing together of. food, oxygen, and 
 the cells. 
 
 Food is stored as glycogen (in the liver), and as fat. The stomach 
 acts as a temporary storage organ. 
 
 Dietetics is the science of our diet. We need a " balanced" diet, 
 containing the best possible proportions of cell-building and of energy- 
 producing material. 
 
 Good cooking and good serving are as important as proper kinds of 
 food. 
 
 Indigestion is often the result of our own carelessness. 
 
 Alcohol coagulates the proteids, and makes their digestion hard; it 
 therefore brings on stomach indigestion. It interferes with the action 
 of the liver, so that body wastes are left in the blood. 
 
370 THE HUMAN BODY AND ITS FOOD 
 
 Alcohol cannot be looked upon as a food, for it has the effects of a 
 poison. 
 
 Many patent medicines contain alcohol, and are as dangerous as 
 alcoholic liquors. 
 
 373. Exercises. 
 
 1. What nutrient in milk is coagulated when milk sours? What 
 stomach ferment clots it? What is a "full cream" cheese? What 
 nutrients does it contain? What ferment is there in the dessert called 
 " junket"? 
 
 2. What are the chief nutrients in bread, meat, sweet potatoes, 
 peanuts, fruit? 
 
 3. Name an easily digested fatty food. 
 
 4. Trace the course of meat through the alimentary canal until it 
 reaches the cells, naming the organs it passes through, and the change 
 each brings about. 
 
 5. Cases have been known in which surgeons have removed a pa- 
 tient's stomach, and attached the small intestine directly to the 
 esophagus. Could a person without a stomach digest all kinds of 
 food? What would be the chief disadvantage? 
 
 6. What changes occur in the absorption of food? 
 
 7. Name all the different functions of the liver that have been given 
 in this chapter. 
 
 8. Show that the energy of animal bodies comes, finally, from the 
 sun. 
 
 9. In what part of the digestive tract are fats digested? What 
 ferment is lacking if the body cannot digest them properly? What 
 ferments are lacking if potatoes cannot be digested? Meat? 
 
 10. What sugars does the body derive from cane sugar? From 
 malt sugar? 
 
 11. Why do we "raise" bread? How? Why is bread "heavy," 
 or "soggy"? What is the objection to our eating it? How is cake 
 raised? How is ' l angel food " cake raised? 
 
 12. Suggest a reason why "toasted" bread is so healthful. Why 
 are baked potatoes healthful? Why is a soft-boiled egg more digestible 
 than a hard-boiled one? 
 
EXERCISES 371 
 
 13. Why does soup alone not make a full dinner? When a man 
 doing physical labor eats too large a proportion of meat, he becomes 
 hungry long before meal time, while if he has a fair share of vegetables 
 and bread, his meal " stays by/' as he says, until the next meal. Ex- 
 plain why. 
 
 14. Strychnine contains carbon, hydrogen, oxygen, and nitrogen; 
 is it therefore a food? Why cannot alcohol be properly called a food? 
 
 15. Do you think that the following meal is "balanced," so far as 
 proteids, carbohydrates, and fats are concerned: soup, fried potatoes, 
 bread, and rice pudding? What do you say of the following menu: 
 ham and eggs, potatoes, nut salad, and mince pie? How about this 
 one: steak, baked potatoes, sliced tomatoes, and baked apples? 
 
 16. What is the value of a vegetable salad in a dinner? 
 
 17. Find, in a newspaper or magazine, a menu for breakfast, dinner, 
 and supper, and discuss it as to its food values and its economy. 
 
 18. What foods are omitted from an athletic training table, and 
 why? 
 
 19. Why can a dog digest bone? Why can he eat decayed meat, 
 while man can not? (Cf. 214 and 364.) 
 
CHAPTER XVIII 
 
 CIRCULATION AND RESPIRATION 
 
 374. The Circulation of the Blood. Just as the work 
 of Newton is the foundation of modern Physics, and 
 as Lavoisier's explanation of burning was the beginning 
 of modern Chemistry, so Harvey's discovery that the 
 blood circulates through the body was the starting point 
 of modern Physiology. Harvey, an English physician, 
 made his discovery about 1616. The blood has several 
 very important functions. The food that is digested in 
 the alimentary canal must be carried to the individual 
 cells all over the body (cf. 369); the blood carries it. 
 The oxygen that is taken into the body at the lungs must 
 also be taken to the cells; so the blood has the power of 
 carrying oxygen. The cells in the exposed parts of the 
 body (those near the skin, for example) must be kept 
 warm, so that the protoplasm can continue its work; 
 hence the blood is a carrier of heat, and keeps up the 
 body's temperature. The reaction between the food and 
 oxygen, which takes place at the cells, gives energy, but 
 it also produces waste materials (cf. 366 and 371). 
 These must not accumulate, or they will poison the body. 
 Hence the blood serves as the great sewer into which the 
 wastes of the cells are discharged. 
 
 A system carrying liquids through the body needs a 
 pump, or heart. The other organs of circulation are the 
 arteries, veins, and capillaries. There are also spaces 
 
 372 
 
THE HEART 
 
 373 
 
 between the blood tubes and the cells; these are filled 
 with lymph, a liquid much like the blood (cf. 379). 
 
 375. The Heart. The heart (Fig. 284) lies in the cavi- 
 ty of the thorax, almost surrounded by the lungs. The 
 smaller end is to the left of the 
 breast bone, but the larger end 
 is directly behind it. The heart 
 of a person is about as large as 
 his fist. The heart proper is 
 surrounded by a protective cov- 
 ering with a double wall. This 
 is the pericardium, meaning 
 "around the heart." Between 
 the two halves of the pericar- 
 dium there is a liquid that de- 
 creases the friction of the heart 
 in its movements. 
 
 The heart of man, like that 
 of all mammals (cf. 345), con- 
 sists of 4 cavities, or chambers. 
 These chambers are all needed, because the blood goes 
 through 2 distinct circuits, or "round trips." One of 
 these circuits is from the heart to the body, and then 
 back to the heart. This is the system, or body, circula- 
 tion. The other circuit is from the heart to the lungs, and 
 back again to the heart. This is the lung, or pulmonary, 
 circulation. The two upper cavities of the heart are the 
 right auricle and the left auricle (compare again the heart 
 of the crayfish, fish, frog, and bird) . The auricles receive 
 the blood from the body and lungs. The heart's two 
 
 Right Ventric 
 
 FIG. 284. 
 
 The Heart. Veins bring blood to 
 the auricles, and arteries carry it 
 away from the ventricles. Note 
 the valves, and the means of hold- 
 ing them shut. 
 
374 CIRCULATION AND RESPIRATION 
 
 lower chambers are the right and left ventricles. The 
 auricles force the blood into the ventricles; then the ven- 
 tricles exert the pressure that drives the blood to the 
 body and lungs. The ventricles have much thicker walls 
 than the auricles, because they have so much harder 
 work to do; and the left ventricle, which forces the 
 blood through the body circulation, has walls much 
 thicker than the right ventricle, which sends the blood 
 through the lungs. 
 
 The heart has 4 valves which permit its outlets to be opened and 
 closed. The valves are made of tough connective tissue, and are 
 strengthened by cords fastening them to the walls of the heart. Blood 
 pressing on one side of the valves makes them open, but when the 
 pressure is on the other side, they come together, and prevent the 
 blood from flowing backward. We are accustomed to think of the 
 heart as a pump; we must rather think of it as 4 pumps. Two valves 
 permit the blood to pass from the auricles into the ventricles, and two 
 more guard the openings to the two great arteries that carry the blood 
 to the lungs and body. The " beating" of the heart is due to the 
 pressing of its small end against the chest walls; this takes place at 
 each contraction of the ventricles. The heart of a child in its first 
 year beats about 120 times each minute. In the fourteenth year the 
 number of beats is about 85; in the adult, about 70 or 80. 
 
 376. Arteries and Veins. The tubes that carry blood 
 from the heart are called arteries; those bringing blood 
 to the heart are veins. The artery that carries blood 
 from the left ventricle (Fig. 285) is called the aorta; this 
 artery and its branches supply the body circulation. The 
 pulmonary artery, coming from the right ventricle, takes 
 blood to the lungs. 
 
 Arteries are made of 3 layers of tissue; the middle one 
 contains muscular fibers. Thus, while the arteries are 
 
ARTERIES AND VEINS 
 
 375 
 
 very strong, they are elastic. They expand as the blood 
 stream increases in size, and contract as it decreases. 
 Where arteries come near the surface of the body, the 
 wave of blood sent out at each 
 contraction of the left ventricle 
 can be felt as the pulse. The 
 pulse reading is usually taken at 
 the wrist. Since the arteries 
 are elastic, they act as exten- 
 sions of the ventricles, keeping 
 the blood under pressure even 
 when the ventricles are not con- 
 tracted. They can do this be- 
 cause of the heart valves, which 
 prevent a flow of the blood back- 
 ward into the ventricles. 
 
 Veins have thinner walls than 
 arteries, and are much less elas- 
 tic. Blood from the body circu- 
 lation enters the right auricle 
 through several large veins; 
 other veins bring blood from the 
 lungs to the left auricle. Blood 
 enters the auricles "by suction" 
 (cf. 42), much as lemonade 
 enters a straw when you remove 
 the air. When the auricle contracts, it forces its blood 
 into a ventricle. When the auricle is relaxed, its cavity 
 increases in volume, and the pressure in the cavity de- 
 creases. Blood cannot flow back into the auricle from 
 the ventricle, because the heart's valves prevent this. So 
 
 FIG. 285. 
 
 Heart, Lung, and Body Circula- 
 tion. Note the course taken by 
 the blood. 
 
376 CIRCULATION AND RESPIRATION 
 
 the pressure of the blood in the veins, while feeble, is 
 sufficient to force blood from the veins into the auricles. 
 The body has ways of helping the feeble blood pressure 
 in the veins. Many veins are so placed that they are 
 easily compressed by the body muscles that are near them. 
 Muscles in active use can thus hasten the flow of blood 
 in the veins. Veins of this sort have valves opening 
 toward the heart, but not away from the heart. Nature 
 takes care to have the blood go in the right direction. 
 
 377. Capillaries. The capillaries are the smallest of 
 the blood vessels (cf. 32), with an average diameter of 
 about 2^0 f an inch. While the purpose of the blood's 
 circulation is to get food and oxygen to the cells, and to 
 remove waste materials from the cells, yet the walls of 
 arteries and veins are too thick to permit the passage of 
 blood materials. It is only in the capillaries that the 
 walls are thin enough. 
 
 The capillaries extend to all parts of the body. They are in all 
 glands (cf. 358), for it is through the capillaries that glands get the 
 juices which they secrete; they are near the digestive organs, to take 
 the digested food into the blood (cf. 365) ; they are in the lungs, to 
 permit the blood to give off its waste carbon dioxide, and to take in 
 oxygen. 
 
 Capillaries may be looked upon as the tiniest branches of the 
 arteries, carrying blood to the body; they are also the small beginnings 
 of the veins, in which the blood is gathered for transportation back to 
 the heart. We can compare the flow of blood through arteries, veins, 
 and capillaries with the flow of a stream of water through a bed of 
 sand. The channel that brings the water is like an artery; the channel 
 through which it flows after passing through the sand is like a vein; 
 the thousands of tiny channels, by which the water finds its way 
 through the sand, correspond to the capillaries. 
 
THE BLOOD 
 
 377 
 
 378. The Blood. The blood consists of two parts. 
 One is a colorless liquid called the plasma ; the other is a 
 multitude of tiny bodies called corpuscles (cf. 341). 
 The plasma is made up of water and of dissolved mate- 
 rials. Among the dissolved materials are the blood 
 proteids, made out of the proteids digested by the body 
 (cf. 369). There are also fats, dextrose, salt, etc. 
 Besides the foods and minerals, the plasma contains 
 waste substances, chiefly carbon dioxide and urea. 
 
 The corpuscles (Fig. 286) are of 2 kinds, red and white. 
 The red corpuscles are much more numerous than the 
 white ones, but smaller. 
 As seen under the micro- 
 scope, a red corpuscle is 
 a thin, yellow cell (not 
 red), disc-like in shape. 
 The red corpuscles are 
 generally in groups, like 
 "stacks" of coins. The 
 groups appear red. Red 
 corpuscles contain protoplasm and a dark-red substance 
 called hemoglobin (from haima, " blood," and globe). 
 Hemoglobin forms a bright-red compound with oxygen; 
 this is oxyhemoglobin. It is as a part of this compound 
 that oxygen is carried from the lungs to the cells. Bright- 
 red blood is, therefore, blood with a good supply of oxy- 
 gen; dark-red blood is poor in oxygen. 
 
 White corpuscles are also single cells. Like amebas 
 (cf. 333), they have the power of changing their shapes 
 and of moving about. They can pass through the walls 
 of capillaries into the lymph (cf. 379). White corpuscles 
 
 Red 
 
 FIG. 286. 
 
 Blood Corpuscles, White and Red, greatly mag- 
 nified. 
 
378 CIRCULATION AND RESPIRATION 
 
 destroy disease germs that get between the eells> also the 
 germs in the blood. When you reeeive a wound that 
 penetrates the skin, they form a protecting; wall around 
 the wound, and usually keep germs from reaching the 
 remainder of the body. 
 
 When a wound bleeds, it is because a blood vessel has been cut. The- 
 blood at once seeks to close the opening by forming a thick mass, called 
 a clot. The clotting, or coagulating, material is fibrin; it is formed out 
 of fibrinogen, one of the proteids of the blood. This substance coagu- 
 lates, even at the blood's temperature, much as the white of egg coagu- 
 lates when heated. If a little absorbent cotton is placed on a wound, 
 its fibers help the fibrin, and the blood is coagulated more quickly. 
 
 379. The Lymph. The lymph is really another form 
 of the blood. It is made out of the plasma and white 
 corpuscles of the blood, which pass through the capillary 
 walls, and out of water and waste materials from the 
 cells. The lymph fills the spaces between the cells. We 
 have learned (cf. 377) that the capillaries give oxygen 
 and food materials to the cells, and that the cells give 
 waste materials to the blood. This is not strictly true; 
 the capillaries give their materials to the lymph, and the 
 cells really get their food supply from the lymph. In 
 the same way the cells discharge their waste into the 
 lymph, and the lymph passes it on to the capillaries. 
 Thus the capillaries and the cells really exchange material 
 through the lymph that is between them. 
 
 The lymph has no special pumping organ like the heart. For its 
 movement it depends upon the pressure of certain organs of the body, 
 such as muscles. In this respect the movement of lymph is like the 
 movement of blood in certain veins (cf. 376). The lymph is gradually 
 
RESPIRATION 379 
 
 collected Into two large tubes, called lymphatic ducts. By these it is 
 discharged into the blood. The lymph of the higher animals resembles, 
 in many ways, the colorless blood of the lower animals, such as insects. 
 In each case the absence of a pumping organ and of definite tubes 
 makes the circulation slow. 
 
 380. Excretion. As we have already learned (cf. 
 358), glands secrete liquids from the blood. If the secre- 
 tion is waste that needs to be expelled from the body, it 
 is called an excretion. Excretion is just as necessary as 
 ;any body function, for the wastes are poisons to the body. 
 The most important wastes to be removed, aside from the 
 solid waste of the alimentary canal, are water, carbon 
 dioxide, uric acid, urea, and certain salts (cf. 220). The 
 carbon dioxide is removed chiefly by the lungs. Most of 
 the other materials are in solution, and are removed 
 by the kidneys. There are 2 kidneys, and they are 
 attached at the back of the abdomen, one on each side of 
 the backbone. They have the shape of beans, and weigh 
 about 5 ounces each. The kidneys receive a large supply 
 of blood from the heart. After removing the waste, they 
 return the purified blood to the body. As the solution 
 containing body waste is collected by the kidneys, it is 
 passed on to the bladder, where it is stored until it is 
 expelled from the body. Alcohol drinkers are especially 
 liable to dangerous diseases of the kidneys (cf. 371); 
 Bright's disease is one of them. 
 
 381. Respiration. The need of respiration has already 
 been given, and respiration has been defined (cf. 52). 
 We need to respire 
 
 (1) To bring oxygen to the blood. 
 
380 
 
 CIRCULATION AND RESPIRATION 
 
 (2) To remove carbon dioxide from the blood. The 
 circulation of the blood brings about oxidation at the 
 cells, and also carries the carbon dioxide to the lungs. 
 The oxidation at the cells is internal respiration. The 
 exchange of gases between the air and the lungs is external 
 respiration, or breathing. The chief organs of external 
 respiration are the lungs, and the air passages which 
 connect the lungs with the air. To these we must add the 
 muscles and bones of the chest, which aid in breathing. 
 
 382. The Lungs. The lungs (Fig. 287) are two spongy 
 organs that hang in the thorax, and are surrounded by 
 
 two sacs of connec- 
 tive tissue. The sacs 
 are called pleurae 
 (singular, pleura). 
 The heart cavity is 
 between them. The 
 lungs are the meet- 
 ing place of air and 
 blood; hence we find 
 them to be a mass of 
 air passages and air 
 
 Diaphragm ^ / Cells OU tllC OUC hSilidj 
 
 and of blood vessels 
 on the other. Con- 
 nective tissue holds 
 these together. The lungs are lined with mucous mem- 
 brane, just as the other air passages are (cf. 358). The 
 entrance of air into the lungs, and its passage out of the 
 lungs, depend upon the expansion and compression of 
 
 FIG. 287. 
 
 The Lungs and Their Surroundings, Including the 
 Diaphragm. 
 
INSPIRATION 381 
 
 the lungs; hence the lungs are not rigid, but elastic. The 
 air sacs of the lungs number many millions. Their sur- 
 face in an adult has been estimated to be over 2,000 
 square feet. This is the floor area of a room 20 feet wide 
 and 100 feet long. 
 
 383. Exchange of Gases in the Lungs. A large ar- 
 tery (the pulmonary artery) carries dark-red blood from 
 the heart's right ventricle to the lungs. This blood is 
 spread out through the network of capillaries that is in 
 the air sacs, and loses its carbon dioxide. At the same 
 time it takes up oxygen, and becomes bright red. Then 
 it is carried, by the pulmonary veins, to the heart's left 
 auricle. This pumps it into the left ventricle, by which 
 it is forced, through the aorta, to the body. 
 
 The air that enters the lungs contains 21% oxygen, 78% nitrogen, 
 and 1% argon. As it leaves the lungs, it contains about 16% oxygen 
 and nearly 5% of carbon dioxide, water vapor, and other impurities. 
 The loss of oxygen is thus balanced by the gain in carbon dioxide. The 
 amounts of nitrogen and argon are not changed. About 1.2 pounds of 
 water and 1.5 pounds of carbon dioxide are exhaled from the lungs daily. 
 As the air exhaled is warm, and as the water is in the form of vapor, 
 the lungs aid the skin in removing heat from the body (cf. 395). 
 
 384. Inspiration. The external respiration (breath- 
 ing) consists of 2 acts: (1) inspiration, or "breathing in"; 
 and (2) expiration, or "breathing out." The entrance of 
 air into the lungs (inspiration) is brought about by the 
 enlarging of the chest. This permits the air in the lungs 
 to expand, and makes its density and pressure less than 
 that of the air outside. The outer air then rushes into the 
 lungs as it would into a vacuum (cf. 6 and 42). We 
 do not "suck" air into the lungs any more than we suck 
 
382 CIRCULATION AND RESPIRATION 
 
 soda water into a tube. What we really do is to produce 
 a ''partial vacuum," depending upon the air to make the 
 pressure in the lungs the same as that of the outside air. 
 
 The expansion of the chest is brought about in two ways. One of 
 them is the contraction of the diaphragm, the muscular partition that 
 separates the thorax from the abdomen. When the diaphragm con- 
 tracts, it pushes the organs of the abdomen downward, and makes the 
 thorax larger. This permits the outer air to rush into the lungs. The 
 second means by which the expansion of the chest is brought about 
 is by the action of the chest muscles. When the diaphragm moves 
 downward, these muscles pull the breastbone and ribs outward. 
 
 385. Expiration. The air taken into the lungs during 
 inspiration is expelled when the muscles of the chest and 
 diaphragm are relaxed. The ribs move downward and 
 inward of their own weight, and the organs of the abdo- 
 men, which were crowded together during inspiration, 
 expand again, and force the diaphragm up against the 
 lungs. As a result, the elastic air cells of the lungs, 
 which were "puffed out" with air, are now compressed, 
 and the air is forced back through the air passages. The 
 air that we inhale and exhale during ordinary quiet 
 breathing is called tidal air. It is about a pint (30 cubic 
 inches, or 500 c.c.) in volume. By making a conscious 
 effort we can take in and expel about 100 cubic inches 
 more air than in quiet breathing. The total capacity of 
 the lungs is about one gallon (231 cubic inches, or 4 liters). 
 An adult ' ' breathes," on the average, 18 times in a minute. 
 
 386. Exercises. 
 
 1. Trace the course of a drop of blood from the time it leaves the 
 left ventricle until it re-enters it. 
 
THE NOSTRILS AND PHARYNX 383 
 
 2. Is the heart a suction pump or a force pump? Why has the left 
 ventricle stronger muscles than the other heart chambers? 
 
 3. Why does the doctor ' ' take your pulse " when you are ill? Why 
 does he take your temperature? 
 
 4. What is meant by the ' ' transfusion " of blood? 
 
 5. Why is the blood in the veins ' ' blue blood ' ' ? How, in an accident, 
 can you tell that you have cut an artery rather than a vein? Which 
 would be the more serious, and why? On which side of a wound ought 
 an artery to be compressed, so as to stop bleeding, on the side toward 
 the heart or on the side away from the heart? How, in the case of a 
 cut vein? 
 
 6. Draw a sketch showing the cells of a capillary wall (a single layer, 
 end to end), and show how an ameba-like cell, such as a white corpuscle, 
 might get out. 
 
 7. What is the special duty of red corpuscles? Of the white ones? 
 What body fluid forms the " matter" of a blister? 
 
 8. If you were on a high mountain top, would there be as much 
 oxygen in every breath as at sea level? How do you think the body can 
 increase the oxidation of the blood at high altitudes? 
 
 9. When does the heart have more work to do, when we stand, or 
 when we lie down? Why? 
 
 10. Do you think continued and violent physical exercise would 
 have any effect on the size of the heart? Why? 
 
 11. When a boy or girl grows very rapidly, how is the heart's work 
 affected? Ought violent exercise to be indulged in at this time? 
 
 12. Why are you "out of breath" after running? 
 
 13. How does a very dry atmosphere affect the organs of respira- 
 tion? (Cf. 249). 
 
 14. Give the course of air in going from the nostrils into the lungs. 
 Give the course of the oxygen from the lungs, through the body cir- 
 culation, and back again to the lungs. 
 
 387. The Nostrils and Pharynx. The air that enters 
 the lungs goes through a passage consisting of several 
 parts; these are: the nasal passages, or nostrils, the 
 pharynx, or throat, the larynx, the trachea, or windpipe, 
 
384 
 
 CIRCULATION AND RESPIRATION 
 
 Tongu 
 
 and the bronchial tubes. All of these are lined with 
 
 mucous membrane. In the nostrils (ig. 288) the mucous 
 
 membrane is spread 
 out over a large sur- 
 face, and secretes a 
 great deal of mucus. 
 The nostrils, because 
 of their length, serve 
 to warm the air before 
 it reaches the wind- 
 pipe and lungs. The 
 mucus which they 
 secrete makes them 
 moist, and catches the 
 dust particles that are 
 in the inhaled air. 
 The air passages are 
 also lined, almost 
 
 everywhere, with cilia (cf. 333); these sweep back the 
 
 dust particles. 
 
 The pharynx was described in 361. It is separated 
 
 from the nostrils, when we swallow food, by the "soft 
 
 palate. " The two tonsils are in the sides of the pharynx, 
 
 under the lower jaw bone. 
 
 388. The Larynx and Trachea. The larynx (Fig. 
 289) is a box made out of pieces of cartilage placed at the 
 upper end of the trachea (windpipe). When we swallow, 
 the larynx is drawn upward against its cover, the epi- 
 glottis (cf. 361, Fig. 280) ; food passes over it in going to 
 the esophagus. We can feel one of the larynx cartilages 
 
 FIG. 288. 
 The Mouth and the Nasal Cavity. 
 
THE VOICE 
 
 385 
 
 Uryrw 
 
 (the ' ' Adam's apple ") at the front of the throat. During 
 breathing, the larynx drops down, and there is free com- 
 munication between the nasal passages 
 and the trachea. 
 
 The trachea is a rounded tube about 
 an inch in diameter. It holds its shape 
 because of a number of pieces of cartilage ; 
 these are bent in the shape of a C. The 
 trachea divides into two passages, or 
 bronchi, one of which goes to each lung. 
 The bronchi divide and subdivide into 
 the bronchial tubes. The smallest of 
 these end in the air cells of the lungs. 
 
 FIG. 289. 
 
 The Larynx, the Tra- 
 chea, and the Bron- 
 chial Tubes. 
 
 389. The Voice. The larynx not only 
 forms the opening from the throat to the 
 trachea, but it also holds the chief organs 
 of the voice, the vocal cords (Fig. 290). The vocal cords 
 are two strips of connective tissue fastened to the cartilages 
 
 Producing Sound 
 
 Quiet Breathing 
 
 FIG. 290. 
 The Vocal Cords. 
 
 of the larynx. When not in use they are drawn aside, 
 leaving a V-shaped opening. The cords are brought into 
 use by means of muscles. These act on the cartilages of 
 
386 CIRCULATION AND RESPIRATION 
 
 the larynx, and bring the edges of the cords near each 
 other. The air that passes through the larynx makes the 
 cords vibrate, producing sounds. The sounds are soft or 
 loud according to the amount of air used. . 
 
 The pitch of the voice (cf. 192) depends chiefly upon 
 the degree of tightness of the vocal cords, and upon their 
 length. When the cords are tightly drawn, and short, 
 they vibrate more rapidly than when loose and long; 
 hence they produce sounds of higher pitch. A man has 
 a larger larynx than a woman has, and his vocal cords are 
 larger and longer. As a result his voice is of lower pitch. 
 
 390. Speech. We use the vocal cords in ordinary speaking and 
 singing, yet we can "whisper" words without using the vocal cords 
 at all. We make the whispered words with the throat, tongue, teeth, 
 and lips. When we want to give loudness and pitch to our words, we 
 force the necessary amount of air over the vocal cords. The throat, 
 mouth, and nostrils also strengthen the sounds that come from the 
 vocal cords. The quality of a voice is that peculiarity which distin- 
 guishes one voice from another. By means of it we recognize the 
 voices of our friends. Voice quality depends on the special shape of 
 the air passages and mouth in each person, and on the peculiar way in 
 which each of us uses them in speaking and singing. 
 
 Vowels, or "vocals" (a, e, i, o, u, and y) are the vocal-cord sounds 
 that are changed least by the mouth, tongue, lips, etc. ; consonants are 
 greatly altered forms of these sounds. 
 
 391. Care of the Organs of Respiration. In our 
 
 breathing, as in eating and drinking, we are taking ex- 
 ternal material into the body. If there are disease germs 
 in this material, they have opportunity to develop and to 
 cause disease. We therefore need to guard against 
 throat and lung diseases, as well as against typhoid. The 
 
CARE OF THE ORGANS OF RESPIRATION 387 
 
 surest way to keep the organs of respiration in good health 
 is to learn good methods of breathing, and to breathe 
 good air (review 246 to 249). Our breathing should be 
 "full," and not "shallow"; that is, it should give all the 
 lung cells opportunity to carry on the exchange of gases, 
 and not only a part of them. It is the unused portions 
 of the lungs that are most liable to disease. We should 
 stand and sit erect, with the abdomen drawn in, and the 
 chest expanded, at every inspiration. If we are confined 
 indoors because of our work, we should go out of doors, 
 or to an open window, every little while, and should 
 breathe deeply of fresh air. 
 
 We should all breathe through the nostrils, and not 
 through the mouth. The nostrils remove dust and the 
 disease germs that cling to it (cf. 387), while mouth- 
 breathing permits the germ-covered dust to enter the 
 throat, windpipe, and lungs. Mouth-breathers are espe- 
 cially likely to have throat and lung diseases. Some 
 children have growths in the nasal passages ("nasal 
 polyps") or in the pharynx ("adenoids"); these close 
 the nasal openings to the lungs, and cause mouth-breath- 
 ing. All such growths should be removed by a competent 
 surgeon, for they often bring on, not only throat and lung 
 diseases, but also deafness; and they make many a child 
 appear stupid, when he is really ill. 
 
 Colds require the greatest care, for they lower the power of the 
 body, especially of the organs of respiration, to resist disease, and make 
 these organs fall an easy prey to pneumonia, consumption, diphtheria, 
 etc. The practice of deep breathing is a great aid in preventing colds. 
 
 Tobacco smoke irritates the throat and lungs by clogging up their 
 delicate membranes with soot. Cigarettes, especially, are harmful 
 
388 
 
 CIRCULATION AND RESPIRATION 
 
 to the organs of respiration. Their smoke contains not only the poison 
 of tobacco (nicotine), and poisonous gases like carbon monoxide 
 ("coal gas"), but also very irritating organic compounds called 
 aldehydes, which bring on the "hacking" cough of the cigarette user. 
 
 Alcoholic liquors are likely to bring on weakness of the lungs, so that 
 the drinker is easily attacked by pneumonia and consumption. 
 
 Tight clothing is a serious hindrance to good breathing. If clothing 
 is too tight about the chest, the chest cannot be enlarged properly in 
 inspiration. If it is too tight at the waist, it compresses the diaphragm, 
 the ribs, and the organs of the abdomen, and makes full breathing 
 impossible. 
 
 392. The Skin. The skin .(Fig. 291) serves as an out- 
 side covering for the body, protecting it from hurts, and 
 from the germs of disease that are constantly in the air. 
 
 It consists of 2 layers: (1) 
 the true skin, or dermis; 
 (2) the outer skin, or cuticle. 
 The cuticle is also called the 
 epidermis, meaning, "upon 
 the dermis" (cf. 309). , 
 
 The epidermis consists of 
 transparent cells, and has no 
 nerves or blood vessels. It 
 forms a tough outside cover- 
 ing. The lower layer of epi- 
 dermis cells is in contact with 
 lymph (cf. 379), and from 
 it gets the nutriment that is 
 needed for the making of new 
 cells. These take the place of those rubbed off at the 
 surface (cf. 223). Where the skin is put to rough use, 
 as in the palms of the hands and the soles of the feet, the 
 
 Fia. 291 
 Layers of the Skin, Greatly Magnified. 
 
THE HAIR AND NAILS 389 
 
 epidermis becomes thick, forming a callus. A corn is a 
 thick layer of epidermis cells formed at one spot. It 
 hurts because it is pressed, by the shoe, into the true skin 
 beneath. 
 
 The dermis, or true skin, is much thicker than the 
 epidermis. It is made up of tough fibers of connective 
 tissue, and has blood vessels and nerves. The surface of the 
 dermis has little elevations called papillae, some of which 
 contain the bodies that bring about the senses of touch 
 and of temperature (cf. 410). On the inner side of the 
 hands and fingers the papillae are arranged in rows . A layer 
 of fat is generally found under the dermis (cf. 369). 
 
 The color of the skin is due to coloring matter in the 
 lower layers of epidermis cells. When the skin is tanned 
 by wind and sun, the coloring matter is increased. 
 Freckles are spots of coloring matter in the epidermis. 
 
 393. The Perspiration. The perspiration is the liquid 
 poured out upon the. skin by the sweat glands (Fig. 291). 
 These glands are tubes coiled at their lower ends, and set 
 into the lower part of the dermis. Their purpose is to 
 cool the body (cf. 74). It is only when we are very hot 
 that the sweat collects on the skin in drops (sensible 
 perspiration). Ordinarily the perspiration is not noticed 
 (insensible perspiration). The sweat glands are under 
 the control of the nervous system ; much or little perspira- 
 tion is given off, according as the body needs to give off 
 heat, or to retain it. 
 
 394. The Hair and Nails. The hair and nails (Fig. 292) 
 are made of cells of the epidermis, but they have taken 
 
390 
 
 CIRCULATION AND RESPIRATION 
 
 Epidermis 
 
 special forms. A hair is a tiny tube, formed in a pocket of 
 the dermis. The part projecting from the skin, like the 
 epidermis itself, has neither blood vessels nor nerves. But 
 
 the inner end of the hair 
 is in the true skin, and 
 is kept growing by the 
 formation of new cells. 
 These are nourished by 
 the lymph of the dermis. 
 Tiny muscles in the hair 
 "pits" sometimes cause 
 the hair to "stand on 
 end/' causing "goose- 
 flesh." The hair covers 
 nearly the whole body. 
 
 FIG. 292. 
 Structure of the Nails and the Hair. 
 
 In the hair pits there are glands that secrete an oil for the hair; 
 these are the oil glands, or sebaceous glands. The oil softens the skin 
 and the hair. Brushing the hair helps the oil glands in their work, for 
 it spreads the oil along the outside of the hair. 
 
 Dandruff is a disease of the sebaceous glands and scalp. It is prob- 
 ably due to bacteria, and may spread from one person to another. 
 Only clean combs and brushes should ever be used for the hair. If 
 we pull a hair out without destroying the cell that produces it, a new 
 hair will grow. In baldness the cells lose the power of producing new 
 hair. The cause of all baldness is not known, but much of it seems to 
 result from dandruff, or from a lack of fat in the scalp. 
 
 The nails are plates of tough epidermis that grow out of 
 depressions in the dermis. They grow in length and 
 thickness as new epidermis cells are formed at their inner 
 ends, or roots. The older part of a nail is transparent; 
 the blood vessels beneath it make it appear pink. 
 
FUNCTIONS OF THE SKIN 391 
 
 395. Functions of the Skin. Some of the functions 
 of the skin have already been given. It is, first of all, a 
 covering for the body; it also contains the structures 
 that act upon the nerves of touch (cf. 392). In giving 
 off perspiration it is an organ of excretion, like the kidneys 
 (cf. 380). It is likewise one of the regulators of the 
 body's temperature: the skin and the lungs together 
 (cf. 383) enable the body to cast off the heat it does not 
 need. 
 
 The body remains at the normal temperature (98.6 F.) 
 whether we exercise or remain at rest, when the weather 
 is cold as well as when it is hot. This temperature there- 
 fore represents a condition of balance in the body's heat 
 supply: at 98.6 F. we gain heat and lose heat in equal 
 amounts. When we are warm, the blood rushes to the 
 surface of the body. The skin then radiates heat rapidly; 
 a rapid flow of perspiration also takes place. By these 
 means the blood is cooled, and the body's heat is lowered. 
 
 If the heat of the body needs to be saved, as when we are 
 in a cool room, the blood vessels near the surface grow 
 smaller, and less blood comes to the skin. Thus the body 
 loses less heat. If the lack of blood near the skin con- 
 tinues for a time, we feel cold. Then, if we are wise, we 
 'raise the temperature of the room, or wear warmer cloth- 
 ing. When the blood vessels remain tightly closed, as in 
 some forms of fever, we have a feeling of cold (a chill), 
 even when the body has heat that needs to be given off. 
 
 Bathing. The need of bathing has already been given (cf. 223). 
 The skin becomes covered with body wastes from the evaporated 
 perspiration, with oil from the sebaceous glands, with dust from the 
 clothing and the air, and with dead epidermis. The best kind of a 
 
392 CIRCULATION AND RESPIRATION 
 
 bath for removing this accumulation is a warm bath; it should be taken 
 at night, if possible. Warm baths taken in the daytime, unless they 
 are followed by a cold shower bath, or by a dash of cold water, may 
 make one liable to colds (cf. 391). A warm bath at night also aids 
 in bringing on a good night's sleep. 
 
 In the morning, when we wish to be aroused for the day's work, 
 especially if we must go out into the cold, a cold bath is the best. The 
 cold water gives the body a shock, in which the blood is driven inward 
 from the skin; but after a vigorous rubbing the skin glows. This is 
 due to the " reaction," as the blood re-enters the skin. 
 
 Many persons cannot endure the shock of a tub of cold water; they 
 do not have a proper reaction, and feel chilly. Such persons can, as a 
 rule, take a cold "sponge" bath, in which the water is applied rapidly 
 with a wet sponge or washcloth. Vigorous rubbing with a dry, rough 
 towel will bring about the " reaction." 
 
 396. Summary. The blood carries oxygen and digested food to the 
 cells, distributes the body's heat, and acts as the sewer for cell wastes. 
 
 The organs of circulation are the heart, arteries, veins, and capil- 
 laries; also the spaces containing the lymph. 
 
 The heart has 4 chambers, each of which can be made smaller by 
 the contraction of strong muscles. 
 
 The right auricle receives blood from the body circulation, and forces 
 it into the right ventricle. This, in its turn, forces the blood to the 
 lungs to be oxidized. 
 
 The left auricle receives purified blood from the lungs, and forces 
 it into the left ventricle. This forces it, through the artery called the 
 aorta, into the body circulation. 
 
 The valves of the heart make the blood flow in one direction. 
 
 Arteries carry blood from the heart; veins carry it to the heart; 
 capillaries carry it from arteries to veins through the body's tissues. 
 
 Arteries have very elastic walls, and are very strong. Some veins 
 have valves that open toward the heart; the circulation in such veins 
 is helped by the pressure of muscles near them. 
 
 The blood consists of the plasma and corpuscles. Corpuscles are 
 red, and white. Red corpuscles contain hemoglobin, which combines 
 
SUMMARY 393 
 
 with oxygen at the lungs. White corpuscles are like amebas. They 
 destroy bacteria. 
 
 The coagulated material of a blood clot, which closes a wound, is 
 fibrin, formed out of one of the proteids of the blood. 
 
 Lymph is a form of blood that exists outside of the organs of rapid 
 circulation. It has no red corpuscles. In supplying the cells, the 
 capillaries give their food material to the lymph, and this gives it to the 
 cells. 
 
 Excretion is the secretion of waste solutions, so that they may be 
 removed from the body. The chief excreting organs are the kidneys. 
 The skin excretes waste in the perspiration. 
 
 Respiration brings oxygen to the blood, and removes carbon dioxide 
 from the blood. 
 
 The chief organs of respiration are the two lungs and the air pas- 
 sages. The pleurae are sacs that surround the lungs. The lungs 
 contain a multitude of air cells. 
 
 In the lungs the air loses about % of its oxygen, and takes up car- 
 bon dioxide in its place. 
 
 In inspiration the chest is enlarged, and the outside air rushes into 
 the lungs. 
 
 In expiration the diaphragm and ribs are crowded against the lung 
 cavity, and force out the air. 
 
 The air passages include the nasal passages, the pharynx, the larynx, 
 the trachea, and the bronchial tubes. All are lined with mucous mem- 
 brane. 
 
 The larynx contains the vocal cords. In speaking and singing we 
 make sounds with the throat, tongue, lips, teeth, and nostrils, as well 
 as with the vocal cords. 
 
 We should have good habits of breathing, and should breathe good 
 air. Mouth breathing is dangerous. 
 
 Colds, tobacco, alcohol, and tight clothing are all sources of danger 
 to the organs of respiration. 
 
 The skin consists of epidermis and dermis. The sense of touch is 
 in the papillae of the dermis. 
 
 Perspiration is secreted (excreted) by the sweat glands of the 
 dermis. 
 
394 CIRCULATION AND RESPIRATION 
 
 Hair and nails are special forms of epidermis; they grow from pits 
 ("roots") in the dermis. 
 
 The functions of the skin are to cover the body, to assist in the sense 
 of touch, to excrete perspiration, and to help regulate the body's 
 temperature. 
 
 Bathing restores to the skin a fresh, clean surface, so that it can 
 carry out its functions. 
 
 397. Exercises. 
 
 1. With what organs of speech do you make the sounds of k, I, g, d, 
 t, m, s, and/? Find out how you make the sounds of all the letters of 
 the alphabet, and make a list of them, putting together all the letters 
 that seem more or less alike. 
 
 2. If you feel chilly, a few deep breaths, especially if you "hold 
 your breath" while the lungs are full, will make you warm. Tell why.. 
 
 3. Why should one go to bed when he has a bad cold? 
 
 4. What harm is done by the wearing of tight belts? 
 
 5. What is the danger in the taking of a hot bath, and then going: 
 out into the cold air? How may the danger be made less? 
 
 6. What are the uses of the finger nails? 
 
 7. How can a person's finger prints be used in identifying him? 
 
 8. Why is nasal catarrh so common a disease? 
 
 9. How does a dog cool his body when he is hot? 
 
 10. Alcohol drives the blood into the skin, giving a temporary feel- 
 ing of warmth. Is a drinker wise in "fortifying" himself with liquor 
 before going out into the cold? 
 
 11. Tramps often keep themselves warm in cold weather by putting 
 a sheet or two of newspaper inside their coats; explain. How could 
 you use this fact to keep yourself warm, if you found the bedding of 
 your room insufficient? 
 
CHAPTER XIX 
 
 THE NERVES AND THE SENSE ORGANS 
 
 398. The Nervous System. In studying a complex 
 structure like the human body, we need to consider it 
 part by part, and system by system. We must remem- 
 ber, however, that the body is not simply one structure 
 added to another, but that it is a complete organism, with 
 many parts acting together harmoniously. The eye, 
 hand, and foot have each a separate function, but all can 
 combine to do one thing, say, to make a "drop kick" in 
 football, or to run a sewing machine. The movements 
 of the eye, hand, and foot are under the control of the 
 will, but there are many activities of the body that pro- 
 ceed without our notice and without any effort of the 
 will. Examples of these are the beating of the heart, the 
 movements of the ribs and diaphragm in respiration, the 
 secretion of saliva, gastric juice, and bile when they are 
 needed. Our food is under our control until the muscles 
 of the throat have contracted in swallowing; after that it 
 is in the control of involuntary muscles. How does each 
 organ of the body know when to perform its function, 
 how much effort to put forth, and when to stop? The 
 answer is that the different organs are in communication 
 with one another, like the stations of a telegraph system, 
 or the houses on a telephone line. When there is a need 
 for the performing of a function, the organ concerned 
 receives notice of the need, and sets about doing its par- 
 
 395 
 
396 THE NERVES AND THE SENSE ORGANS 
 
 ticular work. When the demand is over, the organ re- 
 ceives notice, and stops its work. This regulation of the 
 body by communication between its parts is the work of 
 the nervous system. 
 
 The nervous system is studied in two divisions : 
 
 (1) The central nervous system, consisting of the brain 
 and spinal cord, and the nerves that start from these 
 structures; 
 
 (2) The sympathetic nervous system, which puts the 
 internal organs into communication with one another and 
 with the central system. 
 
 399. Nerve Cells and Their Structure. The parts of 
 the nervous system are made up of nerve tissue, just as 
 muscles are made up of muscle tissue. The unit of nerve 
 tissue is the nerve cell, or neuron (Fig. 293). This con- 
 
 Terminal 
 Brariches 
 
 Fig. 293. 
 A Neuron, or Nerve Cell. 
 
 sists of two parts, the cell body, or cell proper, and ex- 
 tensions of the cell body. The cell body looks much like 
 other cells, except that it has a grayish color. The ex- 
 tensions of the cell body are of two sorts. One of them 
 is the long, slender nerve fiber, or axon. Some cells have 
 one of these; others have two. Cells that have one axon 
 have also shorter extensions, or dendrites. Dendrites 
 
NERVE CELLS AND THEIR STRUCTURE 397 
 
 branch like the boughs or roots of trees, and so get their 
 name : dendron means ' ' tree. ' ' 
 
 The nerve fiber, or axon, consists of a central part 
 called the axis cylinder, and of two protective coverings, or 
 sheaths. The axis cylinder is an extension of the proto- 
 plasm of the cell body, and, like the cell body, is gray. 
 The coverings of the axis cylinder are usually white. A 
 bundle of nerve fibers is what we commonly call a nerve. 
 Nerve messages are carried by the axis cylinders of the 
 axons. A nerve message is also called a stimulus (plural, 
 stimuli; cf. 206) and a nerve impulse. 
 
 Nerve fibers are of 3 kinds, according to their use: 
 (1) those that carry messages from an organ to the brain 
 or spinal cord; (2) those that carry messages back to the 
 organs; (3) those that connect the other two. The nerve 
 fibers carrying messages to the brain are called afferent 
 fibers, or sensory fibers. They are called afferent fibers 
 from a word meaning "carrying to;" they are called 
 sensory fibers because they carry the stimuli received by 
 the senses to the central nervous system. Nerve fibers 
 of the second class are called efferent fibers, from a word 
 meaning "carrying away from." These fibers carry 
 messages from the central system to the organs. Efferent 
 fibers are also called motor fibers, because through them 
 comes the message telling the organ to act, or move. 
 The nerve fibers that connect afferent and efferent fibers 
 are called associating fibers. 
 
 Nerve tissue may be in separate neurons, or it may 
 consist of groups of neurons, called ganglia (singular, 
 ganglion, a "knot"). The brain and spinal cord consist 
 
398 
 
 THE NERVES AND THE SENSE ORGANS 
 
 of large groups of neurons; there are smaller groups in 
 different parts of the body. 
 
 Fissure 
 of Sylvius 
 
 Medulla Oblongata 
 or Bulb 
 
 400. The Brain and Its Parts. The brain is the 
 largest part of the nervous system (Fig. 294). It weighs 
 about 3 pounds; in exceptional cases, 4 pounds. In other 
 
 mammals there is 
 
 Cerebrum - ^^W^Jlfc- a distinct front 
 
 portion, or fore- 
 brain, called the 
 cerebrum. In 
 man this is the 
 upper portion. 
 There is also a 
 midbrain and a 
 hindbrain. The 
 hindbrain con- 
 sists of the cere- 
 bellum, the pons, 
 
 and the bulb. The bulb is also called the medulla oblongata. 
 The cerebrum is gray because of the cell bodies on its 
 surface (cf. 399). Its interior is white, and consists of 
 bundles of nerve fibers ("nerves")- The surface of the 
 cerebrum of an adult person has a great many folds, or 
 convolutions; these greatly increase its area. The in- 
 creased area of the cerebrum is needed as its cells increase 
 in number. A deep dent from front to back divides the 
 cerebrum into a right and a left hemisphere. All the 
 parts of the cerebrum are connected by nerve fibers, and 
 a multitude of fibers connect the cerebrum with the mid- 
 brain, hindbrain, and spinal cord, as well as with the 
 
 Fig. 294. 
 The Parts of the Brain. 
 
THE SPINAL CORD 399 
 
 sense organs. The cerebrum is the organ of the mind. 
 
 Through it we get the sensations of heat, light, sound, 
 touch, taste, etc., and the use of our voluntary muscles. 
 Twelve pairs of nerves (cranial nerves) pass from the 
 front of the cerebrum directly (that is, without going 
 through the spinal cord) to the head, neck, and trunk. 
 
 The midbrain is a rounded body lying under the cerebrum, and 
 connecting the forebrain with the hindbrain. 
 
 The cerebellum (meaning, "little cerebrum") is the largest body of 
 the hindbrain, and occupies most of the space inside the "base of the 
 skull." It is covered over by the back lobes of the cerebrum, and its 
 surface looks much like that of the cerebrum. The cerebellum seems 
 to have special control of muscular movements, making the muscles 
 contract properly and in pairs (cf. 355). It thus causes the move- 
 ments of the body to be orderly and regular. 
 
 The pons (from the Latin word for "a bridge") is in front of the 
 cerebellum, and consists largely of bands of nerve fibers. These con- 
 nect the cerebrum, cerebellum, and bulb. 
 
 The bulb, or medulla oblongata, is really the enlarged upper end of 
 the spinal cord, although it is within the cranium. It is below the 
 cerebellum, and consists of ganglia of the nerve cells and nerve fibers 
 that form the connection between the spinal cord and the brain. 
 
 401. The Spinal Cord. The spinal cord (Fig. 295) is a 
 column of nerve tissue about % of an inch thick; in the 
 adult it occupies the cavity of the spinal column down to 
 the bottom of the 20th vertebra. The cord is not round, 
 but has two lengthwise depressions (one in front and one 
 in back) that make a cross section of it look like a capital 
 H. The outside of the spinal cord is white, from the 
 coverings of its nerve fibers. The inside of the cord con- 
 sists of gray cells, and its section also resembles an H. 
 At its upper end the cord enters the skull, and is enlarged 
 
400 
 
 THE NERVES AND THE SENSE ORGANS 
 
 to form the bulb. The cord's lower end is continued in 
 large nerve trunks, which supply the hips and lower 
 limbs. 
 
 There are 31 pairs of nerves attached to the spinal cord. Each of 
 these joins the cord by a dorsal (back) and a ventral (front) root. The 
 two roots come together in a single " nerve" before they pass out of 
 the vertebrae, but their fibers remain separate, and have different 
 functions. The fibers of the dorsal roots are afferent, and carry 
 
 Efferent 
 Fibre 
 
 Spinal 
 Cord 
 
 Fig. 295. 
 The Spinal Cord and its Connections. 
 
 messages to the cord and brain; the fibers of the ventral roots are 
 efferent, and carry messages to the organs. 
 
 The spinal cord and brain are admirably protected by the vertebrae 
 and the cranium. They are surrounded by 3 membranes, which come 
 between them and the bones themselves. One of the membranes con- 
 tains a watery liquid; this acts as a cushion to prevent injury from 
 sudden shocks. 
 
 402. The Sympathetic System. We have seen that 
 the brain and spinal cord are the great nerve centers of 
 the body, and that they consist of a multitude of nerve 
 cells gathered together in large ganglia and nerve trunks. 
 Besides this central system, the body has another group 
 of nerve structures, called the sympathetic system. This 
 
THE SYMPATHETIC SYSTEM 401 
 
 system is smaller than the central system, but is very 
 important. It has for its special work the control of the 
 internal organs, such as the stomach, liver, etc. It also 
 controls the skin, with its blood vessels and sweat glands. 
 In addition, it has charge of other parts of the body that 
 are not reached directly by the brain and the spinal cord. 
 
 The sympathetic system gets its name from the fact that by con- 
 necting the different internal organs it sees to it that they act "in 
 sympathy with" one another. 
 
 While the ganglia of the sympathetic system are found in many 
 parts of the body, they are most abundant in two chains that are placed 
 in front of the spinal column, one on each side of it. The plexuses are 
 very complex ganglia of the sympathetic system. The solar plexus is 
 one of these; it has been called the " brain of the abdomen." It is 
 behind the "pit of the stomach," and is so important for all the com- 
 mon body functions that there is danger of instant death if it is injured. 
 For this reason a blow in the region of the stomach is very serious. 
 
 The sympathetic system is not independent of the 
 central system, but is a part of it. This is illustrated by 
 a simple case. When food gives a stimulus to the afferent 
 nerve fibers of the stomach, they carry the message to 
 certain sympathetic ganglia. The ganglia cannot turn 
 the message back to the gastric glands, directing them to 
 secrete the gastric juice; the ganglia must send the 
 message on to the central system. Then, if the demand 
 is a normal one, such as the call for gastric juice, the lower 
 parts of the central system (the spinal cord or the bulb, 
 for example) can send the efferent, or motor, impulses. 
 The return message goes through efferent axons and the 
 sympathetic ganglia to the secreting glands. In such a 
 case the upper brain (cerebrum) has no part in the 
 
402 THE NERVES AND THE SENSE ORGANS 
 
 operation. But if the sensation in the stomach is not a 
 normal one, but one of injury, the message goes to the 
 cerebrum, and we feel pain. 
 
 'This action of the sympathetic system upon the blood vessels of the 
 skin is well illustrated by the phenomenon of blushing. When we 
 have some unusual emotion (it may come from an insult or a com- 
 pliment), the sympathetic nerves cease, for a time, to control the blood 
 vessels that come to the skin. As a result, the blood rushes into them, 
 until the skin is red and hot. Then the sympathetic system gets back 
 its control over the blood vessels, causes them to contract, and turns 
 the excess of blood away from the skin. There is' a very close con- 
 nection between our emotions and the way in which our internal 
 organs carry out their work. Thus, unpleasant emotions, such as 
 anger, fear, and worry, seriously affect the digestive system. They 
 cause a partial paralysis of the nerve structures that control the 
 'digestive organs, and make good digestion impossible. 
 
 403. The Nervous System as a Whole. If we could 
 remove all the remainder of the body: muscles, bones, and 
 organs, leaving only the nerve structures, we should have 
 a " nerve skeleton," which would preserve the general 
 outline of the body. This is another way of saying that 
 *' nerves" go to all parts of the body. How are the 
 " nerve connections" made that put an organ (the foot, 
 for example) into communication with the brain? We 
 might guess at the answer, and say that the nerve fibers 
 (axons) are fastened together, much as pieces of rope are 
 spliced, or as wires are soldered together. But this does 
 not seem to be true. So far as we know, there is no 
 actual joining (or at most only a slight joining) of the 
 neurons. The axon has, at the end farthest from the 
 <?ell body, a number of short branches, called the end 
 
THE NERVOUS SYSTEM AS A WHOLE 403 
 
 brush. By the interlacing of the end brush of one 
 neuron with the dendrite of another neuron there is 
 formed a conduction pathway for the nerve impulse. We 
 can compare the interlacing of end brush and dendrite 
 with the interlacing produced when we put the fingers of 
 the one hand loosely between the fingers of the other. 
 
 From what we have just read we can understand that 
 the nerve pathway, along which an impulse must travel, 
 does not act like a continuous "wire," but like a wire 
 with "breaks" in it, or, at least, with places where there 
 is a great deal of resistance (cf. 157). Because there are 
 "breaks" in its path, some of them harder to cross, some 
 easier, the nerve impulse finds a preferred pathway. 
 This is the easiest path: the "path of least resistance." 
 In much the same way a stream of water flowing over 
 rocky soil, although it seems to have many courses from 
 which it can choose its channel, turns aside from all but 
 the one that offers the least resistance. We can also 
 compare the nerve impulse to a traveller. While the 
 traveller is inexperienced, one route looks as good as an- 
 other; but when he has travelled many times, he finds 
 certain "connections" easy, and always goes by the 
 routes that give those connections. 
 
 How are these " preferred pathways" laid out for our nerve im- 
 pulses? Some of them we inherit: the same impulses came to our 
 ancestors, and found the " paths of least resistance" long, long ago. 
 But others of these pathways are developed by experience. As some 
 certain stimulus moves again and again through the same chain of 
 neurons, it finds the path easier and easier to follow, until it finally 
 falls into that path, automatically, as soon as it starts on its journey 
 to or from the central system. 
 
404 THE NERVES AND THE SENSE ORGANS 
 
 The student may wonder how the afferent impulse that comes to the 
 central system can be "switched over" into the efferent neurons, and 
 sent back to the organs. The making of this connection is the work of 
 the associating neurons. If the proper associating neurons are in the 
 spinal cord, then the impulse will go no higher than the cord; it will be 
 turned over, at once, to the efferent neurons. For certain impulses 
 the associating neurons are in the bulb ; for others they are only in the 
 cerebrum. 
 
 404. Voluntary Action. We have already learned 
 (cf. 355 and 398) that the organs of the body are moved 
 by muscles, and that some muscles are under the control 
 of the will (voluntary muscles), while other muscles are 
 involuntary, carrying out their functions whether we 
 want them to or not. All the muscular action that 
 comes from the use of the will gets its impulse in the 
 cerebrum (cf. 400). If we see a pencil lying on the 
 floor, the sight of the pencil acts as a stimulus to the 
 cerebrum and to the mind. If we want the pencil, the 
 cerebrum sends the proper impulses to the muscles; we 
 stoop, and pick up the pencil. But it is not necessary for 
 us to pick up the pencil at all; we may prefer to step upon 
 it instead. Thus the mind has the power of choosing 
 what stimuli it will send back to the muscles. 
 
 405. Reflex Action. Reflex actions are involuntary 
 actions. They are called reflex, meaning "bent (or 
 turned) back," because the afferent impulses that start 
 them are turned back as efferent impulses. If the asso- 
 ciating neurons are below the cerebrum, we are not 
 conscious of either the stimulus or the response of the 
 organ (cf. 403). Of this sort of reflex actions are the 
 movements of the internal organs, such as the stomach, 
 
HABIT 405 
 
 heart, etc. These organs send word of their wants to the 
 central nervous system, and get back the efferent im- 
 pulse, without our knowing or willing anything about the 
 operation. Only when the organs are injured do the 
 impulses which they send get to the cerebrum, so that 
 we feel pain. This " sensation of injury" gets past the 
 lower part of the central system because it is unusual; 
 there are no associating neurons to turn it back until it 
 reaches the cerebrum. 
 
 But it is not only our internal organs that act reflexive- 
 ly; many of our external movements are not voluntary. 
 Thus, the blinking of the eyelids, which is for the pur- 
 pose of cleaning and moistening the eyeballs, is invol- 
 untary. If it were voluntary, we might forget to do it. 
 When you put your hand against a hot stove, you jerk 
 away the hand before you feel the pain. The "jerking 
 away" is a reflex act. It is so important for your body 
 that your hand shall not be burned, that a part of the 
 afferent impulse is switched over into the efferent chan- 
 nels without going to the cerebrum. But it is necessary 
 for your mind to know that hot stoves burn your hand, so 
 the message is also sent to the cerebrum, and becomes a 
 part of your memory. 
 
 406. Habit. Why is it that the control of so much 
 that the body does is left to involuntary, reflex action? 
 We can understand some of the reasons very readily. 
 In the first place, reflex action relieves the cerebrum and 
 the mind of a great deal of work. Then, by being freed 
 from the duty of controlling the internal organs, the 
 cerebrum has time to do a much higher kind of work for 
 
406 THE NERVES AND THE SENSE ORGANS 
 
 the body. It can be used for getting new impressions; 
 we can learn, and we can think. Memory belongs to the 
 cerebrum alone. But the work of getting new impressions 
 is very taxing to the cerebrum, so there is a device for 
 saving work here also. If we voluntarily perform a 
 certain act again and again, our memory becomes more 
 and more definite regarding the act, and the brain needs 
 to make less and less effort to have it repeated. So we 
 finally acquire the power of reflex action in doing a thing 
 that was at first entirely voluntary. Such acts are called 
 acquired reflex acts, to distinguish them from reflex acts 
 that are natural to us. We call acquired reflex acts 
 habits. 
 
 The power of forming habits is a great economy for the mind, for 
 the reason that the nervous effort required in the learning of a new 
 trick or trade, or in controlling our tempers, is too great to be kept 
 up always. So the mind, using its power of choice, directs the cere- 
 brum again and again to make the proper "connections" until the act 
 becomes reflex. After that time the mind depends on the acquired 
 " conduction pathways" to carry the correct impulses to the muscles. 
 
 While nature makes a good act easier and easier to perform, it visits 
 its punishment upon us if we perform bad acts, for they become easier 
 and easier, too. Finally, a bad act, which we performed at first only 
 by making a conscious effort, and which filled us with shame and 
 disgust, becomes a masterful evil habit that we find very hard to 
 break. We need to keep up our power of forming habits, and to use 
 that power, deliberately, to form good habits, so that it will be easier 
 and easier for us to do right, and harder and harder to do wrong. 
 
 407. Effects of Alcohol and Tobacco on the Nervous 
 System. We have already learned some of the effects of 
 alcohol and tobacco (cf. 371 and 391). Alcohol inter- 
 feres with digestion, injures the liver and kidneys, and 
 
EFFECTS OF ALCOHOL AND TOBACCO 407 
 
 prevents the removal of body waste. It makes the 
 drinker liable to lung diseases, such as consumption and 
 pneumonia. Because of these facts insurance companies 
 do not insure the lives of heavy drinkers at all. In 
 making out its rates, and the conditions under which it 
 will insure persons, an insurance company does not deal 
 with a few individuals, but with thousands of cases. You 
 may know a man who has drunk whisky, and lived to old 
 age. His case, by itself, proves nothing. But the in- 
 surance companies have kept records, now, for more than 
 half a century, and they know how alcohol affects men. 
 Their verdict is that the death rate among drinkers, even 
 moderate drinkers, is from 25 to 40 per cent higher than 
 among men who do not use alcohol. 
 
 Alcohol works injury, not only to certain organs, such 
 as those of digestion, but it attacks the whole body; it 
 does so through the most delicate organs of the body: 
 those of the nervous system. Alcohol injures the nerve 
 cells; in the steady drinker it causes them to break down, 
 and to become useless. Muscles that were under control 
 become uncertain, and the hands tremble. The user 
 of alcohol takes a drink to " steady" his nerves, but he 
 can steady them for only a little time. He thus develops 
 a habit that requires the constant use of alcohol, and the 
 alcohol injures his body more and more. In losing their 
 self control with regard to alcohol, many drinkers lose 
 their honesty and their abhorrence of crime. It has been 
 found true again and again that criminals drink strong 
 liquor to nerve themselves for horrible acts. 
 
 People sometimes say that the drinker injures only 
 himself, but this is not true. His friends and his family 
 
408 THE NERVES AND THE SENSE ORGANS 
 
 suffer with him, and he swells the numbers of the insane 
 and dependent people for whom society has to care, 
 but who can give back nothing in return. 
 
 We have already learned that the cigarette injures 
 the organs of respiration; its effect is much worse upon the 
 nervous system, especially upon that of young people. 
 Our nervous system must develop with our years. As 
 we acquire skill, new nerve structures are developed, both 
 in the organs and in the central system. The nerve cells 
 of the boy who uses cigarettes do not grow properly, and 
 the chances are against his "making good.' 7 Instead of 
 becoming alert and ready, he is more likely to lose ground, 
 and to become backward and indifferent. Only a small 
 per cent (less than 7) of the school children who smoke are 
 able to keep up their work. How can such children ex- 
 pect, later, to satisfy their employers or customers, and 
 to make a good living? It is not for nothing that the best 
 athletic trainers refuse to let athletes use tobacco. An 
 athlete needs steady nerves, "wind," strength, and the 
 ability to decide quickly; if he wishes to develop these 
 qualities to their fullest extent, he should let tobacco 
 alone. 
 
 408. Exercises. 
 
 1. What advantage does the body derive from a central nervous 
 system? What advantage does a telephone system derive from a 
 central station? Is there any disadvantage in either case? 
 
 2. Give other illustrations, besides the one given in 404, of the 
 fact that the mind can choose what stimuli it will send back to the 
 muscles. 
 
 3. How do you account for the fact that you can recall a "for- 
 gotten" event by a hard effort of the memory? 
 
THE SPECIAL SENSES 9 409 
 
 4. A foreigner who speaks our language perfectly when at ease 
 often falls into his native speech when excited. Tell why. 
 
 5. Why is the order for the closing of the eyelids, when we fear an 
 accident, not left to the cerebrum? 
 
 6. If the cerebrum of a person were removed, and he lived, could 
 any of his functions go on? What ones could not? 
 
 7. Why is the idea of goodness connected in our minds with clean- 
 ness? 
 
 8. How does a baby learn to speak with a rough voice, or with a 
 pleasant one? How does it learn to speak one language rather than 
 another? 
 
 9. Name several reflex actions of the external organs. 
 
 10. Suppose that you have a bad temper; in the light of what you 
 have learned about habit, suggest how you could get control of your 
 temper. What would you suggest to a person who always ' ' answers 
 back," as a way to cure himself of the habit? To one who uses 
 cigarettes? 
 
 11. Why does your mouth water when you smell a good dinner? 
 How do the salivary glands know when to secrete the saliva? Does the 
 11 watering" of the mouth serve any good purpose? 
 
 12. How are nerve impulses started, and to what organ are they 
 carried, when you "read over" your lesson for the first time? What 
 has occurred when you can recite it perfectly? 
 
 13. Why ought the performing of experiments with hydrogen, in 
 the laboratory, to help you get a better idea of this gas than merely 
 reading about it? Give the reasons. 
 
 409. The Special Senses. By the special senses we 
 mean touch, taste, smell, hearing, and sight. The organs 
 of the special senses are the skin, the mouth and tongue, 
 the nose, the ears, and the eyes. Each of these contains 
 afferent neurons that carry to the brain special messages 
 from the outside world. The eyes send light impulses, 
 the ears, sound impulses, the finger tips, feeling impulses. 
 As these impulses come to the brain, we, that is, our 
 
410 
 
 THE NERVES AND THE SENSE ORGANS 
 
 minds, must interpret them: we must know by our judg- 
 ment and our "common sense" what the impulses mean. 
 We say that the messages that come to the brain produce 
 sensations in the mind. The ability to interpret the 
 messages correctly comes to the mind through experience. 
 When the neurons in the finger carry to the brain an im- 
 pulse that is started by a needle point, the mind has the 
 sensation of touch, or of pain. The usual impulses sent 
 to the brain from the stomach produce in the mind the 
 sensation of hunger; the usual impulses sent by the 
 throat produce the sensation of thirst. We call the sensa- 
 tions that come from impulses within the body, general 
 sensations; those coming from im- 
 pulses outside of the body, we call 
 special sensations. 
 
 Tactile 
 Corpuscle 
 
 Fig. 296. 
 A Touch Corpuscle. 
 
 410. Touch. In the skin, and in 
 the mucous membrane of the tongue, 
 are little elevations ("papillae"; cf. 
 392) that contain the touch corpus- 
 cles (Fig. 296). Inside the touch cor- 
 puscles are the ends of the nerve 
 fibers. When we touch an object, the 
 changes in the pressure against the 
 touch corpuscles set up impulses in the nerve fibers. We 
 feel the object as smooth or rough, large or small, sharp 
 or blunt, hot or cold, hard or soft, according to the 
 account which the afferent neurons send to the brain. 
 
 The sense of touch is not equally good everywhere, as we well know. 
 Its acuteness depends on the number of touch corpuscles in a given 
 area. We can measure its acuteness by means of the tips of a pair of 
 
TASTE 
 
 411 
 
 dividers, or by two pins. The tongue can feel that there are two 
 points when they are only x /25 of an inch apart; the finger tips, when 
 they are about 1 /i2 of an inch apart. The back, however, feels the two 
 points as one, even when they are I 1 / '2 or 2 inches apart. 
 
 The sense of temperature is also in the skin and mucous mem- 
 brane. A chemist, in trying to find out whether a reaction causes a 
 rise of temperature, often holds to his lips the vessel with which he is 
 working, because the lips are especially sensitive to heat and cold. 
 
 411. Taste. The nerves of taste end in the mucous 
 membrane of the tongue and the back of the mouth 
 (Fig. 297). Only liquids and dissolved substances can 
 be tasted (cf. 359); solids 
 cannot get to the afferent 
 taste neurons. Some parts 
 of the tongue are much more 
 sensitive to taste than others, 
 and different parts of the 
 tongue recognize different 
 tastes. - There are sweet and 
 bitter tastes, sour and salty 
 tastes, and combinations of 
 these. Some of the nerves 
 of taste end in special struc- 
 tures called taste buds. The Tongue , 
 The "buds" contain little 
 cavities that open into the mouth; in the openings of the 
 cavities the "taste cells" come into very close contact 
 with the food solution. 
 
 The sense of taste can be greatly developed by use. Professional 
 "tasters" of tea, coffee, foods, etc., become very skillful. A good 
 sense of taste is a valuable protection to us, for it enables us to judge 
 
412 
 
 THE NERVES AND THE SENSE ORGANS 
 
 of the quality of food before we swallow it. What we call the ' ' taste " 
 of a substance is often a combination of smell and taste. Some of the 
 "strong" brands of cheese, for example, have a mild taste if we hold 
 our noses while eating them. 
 
 412. Smell. The sense of smell, like the sense of 
 taste, is at the opening of the alimentary canal. But the 
 sense of smell guards our organs of 
 respiration as well as those of digestion, 
 for it passes upon the good or bad 
 quality of the air we breathe. Smell 
 can recognize only gaseous substances, 
 and not all of those. Thus, air, 
 oxygen, and hydrogen are odorless. 
 The neurons that send odor impulses 
 to the brain end at the olfactory cells ; 
 these are in the upper part of the nose 
 cavity (Fig. 298). 
 
 Fig. 298. 
 
 Sense of Smell; the 
 Olfactory Cells. 
 
 Wild animals and primitive men have an 
 acute sense of smell, and can easily recognize 
 odors at some distance, but civilized man usually 
 has the sense in only a blunted form. For him 
 all odors are classified as pleasant or unpleasant, and he does not 
 distinguish them further. The trained scientist often develops his 
 sense of smell to a high degree, so that he is able to recognize sub- 
 stances by their odors even when very small amounts of the 
 substances are present. 
 
 413. Hearing; Structure of the Ear. We have already 
 learned that sound is due to the vibrations of some body 
 (cf. 189), and that the vibrating body sets up sound 
 waves in the air. The ear (Fig. 299) is the organ of 
 hearing; in it are the afferent neurons that respond to 
 
HEARING; STRUCTURE OF THE EAR 
 
 413 
 
 sound waves. The ear is usually considered under its 
 three divisions: (1) the outer ear; (2) the middle ear; 
 (3) the inner ear. 
 
 The outer ear is a funnel-shaped structure made 
 of cartilage and skin; it is used for the purpose of 
 collecting sound waves. The tube that leads to the 
 middle ear is called the auditory canal. 
 
 Cochlea 
 
 Eustachian 
 Tube 
 H/^" 
 Fig. 299. 
 Structure of the Ear; Section through the Temporal Bone. 
 
 The middle ear is a hollow in the temporal bone 
 (cf. Fig. 275, 354) ; it is called the ear drum, or 
 tympanum. Between the middle ear and the auditory 
 canal is stretched the membrane (tympanic membrane) 
 which corresponds to the "drum head." A chain of 3 
 small, connecting bones (cf. 354) stretches across the 
 middle ear. The first of them is attached to the 
 tympanic membrane, and the last reaches to the opening 
 of the inner ear. The middle ear is connected with 
 
414 THE NERVES AND THE SENSE ORGANS 
 
 the pharynx, or throat (c/. 361) by the Eustachian 
 (u-stak'-e-an) tube. This tube allows the air to press on 
 the inside of the tympanic membrane, and to balance the 
 pressure of the air in the auditory canal. Otherwise a 
 sudden change in the outside air pressure might burst 
 the tympanic membrane. When cannon are being fired, 
 persons standing near are instructed to hold their 
 mouths open, so that the air sjiock on the inner side of 
 the membrane may be equal to that on the outer side. 
 
 The outer ear gathers the sound waves, and the middle 
 ear passes the vibrations on to the inner ear, the real 
 organ of hearing. The inner ear is filled with liquids. 
 It is separated from the middle ear by a membrane; to 
 this membrane the last bone of the middle ear is attached. 
 As the membrane is made to vibrate, it gives its motion 
 to the liquids of the inner ear. The vestibule is the 
 first chamber of the inner ear. The cochlea (k5k'-le-a) 
 is like a snail shell, and this fact gave it its name. It is 
 the part of the ear that contains the fibers of the auditory 
 nerve. 
 
 Besides the cochlea and vestibule, the inner ear contains the semi- 
 circular canals. These are not part of the hearing apparatus, but 
 they are probably organs that tell the brain in what direction the body 
 is leaning, and so help in keeping the body balanced. 
 
 The ears should be cared for intelligently. Sharp objects should 
 not be put into them, and they should never be pulled or "boxed," for 
 fear that the "drum head" may be burst. The earwax is intended 
 to keep insects out of the ear, and should not ordinarily be removed 
 until it comes out of the auditory canal. Clean warm water will 
 remove earwax better than anything else. An unusually large secre- 
 tion of earwax sometimes causes dull hearing and deafness, but no one 
 except a physician ought to try to remedy the trouble. 
 
EYE SOCKETS AND LIDS 415 
 
 414. Sight. Light is the cause, or stimulus, outside 
 of us that produces the sensation of sight, or seeing 
 (cf. 167). The eye is the organ that is sensitive to the 
 light waves that come to us. But the eye is not merely a 
 "light spot," an organ to distinguish light from darkness. 
 It is a structure that enables us to perceive light that has 
 been changed by objects that reflect it, or refract, trans- 
 mit, or partly absorb it, so that we see the illuminated 
 objects in all their variety of light and shade, form and 
 color. The eye collects these modified light waves, bends 
 them so that they come to a focus, and out of them forms 
 an image on the retina (cf. 416). 
 
 415. Eye Sockets and Lids. The eye is admirably 
 protected. It is set into sockets in bones of the skull, so 
 that it is shielded on all sides except in front. The 
 sockets are lined with fatty tissue covered by a double 
 membrane. The fat and membrane not only make the 
 socket smooth, but they also form a soft cushion for the 
 eye ball, in case it is forced inward by a blow. 
 
 The eye is protected in front by the eyebrow, the eye- 
 lashes, and the eyelids. The bone forming the brow pro- 
 jects over the eye like a roof, protecting it against blows 
 from above. At the same time the hairs of the eyebrow 
 act like eaves troughs, and drain off perspiration, so that 
 it does not run down into the eye. The eyelashes shade 
 the eye from "high light," and keep out dust. The 
 eyelids move with incredible speed when the eye is in 
 danger (cf. 405), so that the "twinkling of an eye" is 
 really a very short space of time. Experimenters have 
 again and again owed the preservation of their eye- 
 
416 
 
 THE NERVES AND THE SENSE ORGANS 
 
 Sclerotic 
 Coat 
 
 sight to the fact that reflex action closed their eyelids 
 before the pieces scattered by an explosion could travel 
 to the eye. 
 
 The eyelids are lined with a very sensitive membrane, 
 the conjunctiva. The same membrane covers the front 
 of the eyeball. When we get a cinder into one of our 
 eyes, and it hurts badly, we ought to remember that 
 the pain is the conjunctiva's way of telling us that 
 the eye is in danger, and that we must remove the tres- 
 passing cinder. 
 
 . -- 
 
 416. Parts of the Eye. In many respects the eye is 
 like a camera (cf. 188). It contains a lens, called the 
 
 crystalline lens 
 (Fig. 300), a 
 "shutter," called 
 the iris, for regu- 
 lating the amount 
 of light that can 
 get into the eye, 
 a sensitive mem- 
 brane, the retina, 
 for receiving the 
 image, and an ar- 
 rangement, called 
 accommodation, 
 which changes 
 the focusing as objects are near or distant. 
 
 The crystalline lens divides the eye into two chambers 
 of unequal size. The smaller one is in front, and con- 
 tains a liquid called the aqueous (or "watery") humor. 
 
 Optic 
 Nerve 
 
 Fig. 300. 
 Parts of the Eye. 
 
PARTS OF THE EYE 417 
 
 The larger chamber is filled with a jelly-like liquid called 
 the vitreous (or "glassy") humor. These two humors 
 keep the eye round and full. They and the crystalline 
 lens together make up a double-convex lens (cf. 178), 
 and throw on the retina an inverted image of the object 
 seen. 
 
 The outside coating of the eyeball is tough and strong; 
 it is called the sclerotic (skler-ot'-ic) coat. It is opaque 
 everywhere except in front, where it becomes trans- 
 parent, and is called the cornea. The "white of the eye" 
 is the visible part of the sclerotic coat. The choroid 
 (ko'-roid) coat is inside of the sclerotic coat. It is dark in 
 color, and acts like the dark interior of a camera: it 
 absorbs light, and so prevents the light from being 
 reflected back and forth inside the eye. The iris is a part 
 of the choroid coat; it acts as a curtain for the eye, and 
 gives the eye its color. The pupil is an opening in the 
 center of the iris. It is controlled by two sets of muscles, 
 which open or close it, according to the amount of light. 
 In the cat the pupil becomes a narrow slit, when the light 
 is bright. 
 
 The retina (ret'-i-na) is the innermost coat of the 
 eye; it covers the back portion of the choroid coat. The 
 retina is very complex. By a delicate arrangement of 
 cells it arouses afferent light impulses in the neurons of 
 the optic nerve. The blind spot of the eye is the place 
 where the optic nerve begins to spread out to form the 
 retina. 
 
 The eyeball is held in place, and moved about, by means of 6 small 
 muscles. The transparent, front portion of the eye must be kept moist 
 and clean, hence the eye has lachrymal (lak'-rf-mal), or "tear," 
 
418 
 
 THE NERVES AND THE SENSE ORGANS 
 
 glands (Fig. 301). These secrete tears, and pour them over the eyes. 
 The tear glands are in the upper, outer corners of the eyes. Their 
 secretions are carried by a duct, or tube, into the nostrils. When the 
 tears are secreted in larger amounts than 
 the ducts can carry off, we "cry": the tears 
 overflow the lids. 
 
 Lachrymal 
 Gland 
 
 Nasal 
 Cavity 
 
 Fig. 301. 
 
 Relation of a Lachrymal 
 Gland to the Eye. 
 
 417. Accommodation. The crys- 
 talline lens and cornea together form 
 the most important focusing part 
 of the eye. The crystalline lens 
 differs from a glass lens in that it 
 is very elastic; if left to itself, it 
 becomes more convex. On this fact 
 accommodation depends. The lens 
 is held to the choroid coat by a ligament called the sus- 
 pensory ligament. Ordinarily this ligament is stretched 
 tight by the choroid coat, and flattens the lens. When the 
 lens needs to be more rounded, the ciliary muscles, which 
 are attached to the sclerotic coat, draw the choroid coat 
 forward. The result is that the suspensory ligament is 
 loosened, and the lens is allowed to become more convex. 
 This power of the eye to change the curvature of the lens 
 is accommodation. 
 
 The need for accommodation is plain if we know the properties of 
 light. When light from a distant object, such as a tree, comes to us, 
 the light rays are almost parallel; hence the lens, though flattened, can 
 bring the light to a focus on the retina (cf. Fig. 153, 178). But when 
 you look at a near object, the light rays from any point of the object 
 spread out, and make a large angle with one another; hence a lens 
 with a more rounded surface is needed to bring the rays to a focus. 
 As we become older, the crystalline lens loses its elasticity, and does 
 
NEAR- AND FAR-SIGHT 
 
 419 
 
 not become rounded when it 
 is released. We are, therefore, 
 likely to lose the power of accom- 
 modation. 
 
 418. Near- and Far-Sight; 
 Care of the Eyes. When a 
 normal eye is at rest, it is 
 in focus for distant objects. 
 For close objects, accommo- 
 dation must be used. A 
 " near-sighted " eye (Fig. 
 302) cannot see objects dis- 
 tinctly at more than about 
 10 inches' distance; when 
 the object is at a greater 
 distance, the focus is formed 
 in front of the retina. Hence 
 the light rays have crossed 
 before reaching the retina, 
 and the image is blurred. 
 The remedy for short- 
 sightedness is a concave lens 
 (cf. 178) of the right cur- 
 vature. This throws the 
 image farther back, upon the 
 retina. 
 
 In far-sighted vision the 
 object to be seen must be 
 more than 10 inches away; 
 otherwise the image will fall 
 behind the retina. Of course 
 
 Fig. 302. 
 
 Diagram of a Normal Eye, a Near- 
 Sighted Eye, and a Far-Sighted Eye. 
 The near-sighted eye needs a concave 
 lens; the far-sighted eye, a convex lens. 
 The dotted curved lines show where the 
 retina would be, if the defective eye were 
 normal. The dotted straight lines show 
 how the light rays are brought to a 
 focus by the proper eye-glasses. 
 
420 THE NERVES AND THE SENSE ORGANS 
 
 this is impossible, since the retina is opaque; but the 
 image on the retina is blurred, because the light is not 
 yet at a focus. The crystalline lens prevents far-sight, 
 if it has the power of accommodation. When this 
 power is gone, convex lenses are needed to help the 
 crystalline lens, and to make accommodation unne- 
 cessary. 
 
 Astigmatism (a-stfg'-mat-ism) is a defect of vision that is due to a 
 lack of sufficient curving, or a flatness, in some part of the cornea or 
 crystalline lens. The muscles of the eye keep trying to adjust the eye 
 and the lens so as to make a distinct image, and become worn out in 
 the attempt. Glasses for astigmatic eyes are made to correct the 
 particular trouble of each eye, and are of no use unless an expert 
 oculist fits them. There are few errors of vision that the oculist cannot 
 correct, and we should consult him at once if we have any difficulty 
 with our eyesight. Poor vision causes a constant strain upon the 
 eyes, with headaches, inflammation of the eyes, and nervousness. 
 Wonderful improvement in the general health often follows the 
 wearing of the right glasses, and the relieving of the eye from strain. 
 The eye is so delicate that if it is upset the whole nervous system 
 feels the effect. 
 
 Care of the Eyes. We should never rub the eyes with 
 the fingers unless we are certain that the fingers are clean ; 
 otherwise the eyes may become infected. We should 
 read only in a good light, but the light should not be too 
 bright, and should not be reflected directly to the eye. 
 Sunlight is too bright for reading. If we read or study by 
 lamplight, either our eyes or the lamp should be shaded, 
 best by a green shade. We ought not to read in a moving 
 train or street car for more than a little while. The jar- 
 ring of the car causes the book to shake, and the eye is 
 
SUMMARY 421 
 
 strained in trying to follow it. We ought not to read 
 while lying down; the position is awkward, and trying 
 to the eyes. 
 
 419. Summary. The body is one organism. The nervous sys- 
 tem regulates the body by providing communication between its parts. 
 The nervous system consists of the central and the sympathetic 
 systems. 
 
 Neurons are nerve cells. They consist of cell bodies, and of 
 nerve fibers, or axons. Dendrites are short extensions of cell 
 bodies. 
 
 A nerve is a bundle of nerve fibers. A nerve message is called a 
 stimulus, or nerve impulse. Nerve fibers are of 3 kinds: afferent 
 (sensory), efferent (motor), and associating. 
 
 Groups of neurons are called ganglia. 
 
 The brain consists of forebrain, midbrain, and hindbrain. 
 
 The cerebrum is the forebrain. It communicates with the body 
 through the midbrain, hindbrain, and spinal cord, but it has also direct 
 connection, by means of cranial nerves, with parts of the head, 
 neck, and trunk. 
 
 The cerebrum is the organ of the mind. 
 
 The hindbrain consists of the cerebellum, pons, and bulb. 
 
 The spinal cord is enclosed in the spinal column. Its out- 
 side consists of white nerve fibers; its inside of gray cell bodies. It 
 has many pairs of nerves; each nerve has afferent and efferent 
 fibers. 
 
 The sympathetic system consists of ganglia and nerve fibers that 
 control the internal organs and the skin. The sympathetic system 
 relieves the central system of much labor, but it cannot, of itself, send 
 back efferent impulses to the organs. 
 
 Nerve connections are commonly made by the interlacing of the 
 "end brush" of a nerve fiber with the dendrites of a neighboring cell 
 body. 
 
 The conduction pathway taken by a nerve impulse is the one that 
 offers the least resistance. 
 
422 THE NERVES AND THE SENSE ORGANS 
 
 The nerve organ to which an afferent impulse must go, before being 
 returned as an efferent impulse, depends on the position of the asso- 
 ciating neurons for that impulse. 
 
 Voluntary acts are directed by the cerebrum. 
 
 Reflex acts are either natural or acquired. Acquired reflex acts are 
 habits. Natural reflex acts have their associating neurons in organs 
 below the cerebrum. Habits have their associating neurons in the 
 cerebrum, but as parts of preferred pathways, so that the turning 
 back of the impulse in the right direction requires little or no effort 
 of the mind. 
 
 Alcohol injures the whole body by attacking the nerve cells. 
 
 Tobacco prevents the nervous system from developing properly, 
 and is, therefore, very injurious to young people. Cigarettes are worse 
 than ordinary tobacco. 
 
 The special senses are touch, taste, smell, hearing, and 
 sight. 
 
 Sensations are the interpretations, made by the mind, of the afferent 
 impulses that come to the brain. There are general and special 
 sensations. 
 
 Touch is due to nerve fibers in the touch corpuscles of the skin. It 
 is most delicate in the tongue and fingers. 
 
 Taste is the result of stimuli received by certain nerves that end 
 in the mucous membrane of the tongue and mouth. Only substances 
 in solution can give the stimuli. 
 
 Smell is due to impulses aroused in certain neurons by the olfactory 
 cells. 
 
 Hearing is the effect of sound impulses set up in the audi- 
 tory nerve. This nerve ends in the cochlea, a part of the inner 
 ear. 
 
 Sight is the sensation produced by light stimuli that are carried to 
 the brain from the retina. 
 
 The retina is the outspread end of the optic nerve. 
 
 The lachrymal glands secrete tears to wash the eyeballs. 
 
 Accommodation is the power of the eye to alter the curvature of the 
 crystalline lens, so that light from both near and distant objects may be 
 brought to a focus on the retina. 
 
EXERCISES 423 
 
 In near-sight the light rays are brought to a focus too far in front 
 of the retina. The remedy is concave glasses. 
 
 In far-sight the light rays are not brought to a focus at all. The 
 focus would be behind the retina, if this were possible. The remedy 
 is convex glasses. 
 
 The eyes should not be strained by being used in too bright a light, 
 too dim a light, or in awkward positions. If defective, they should be 
 cared for by a competent oculist. 
 
 420. Exercises. 
 
 1. Name as many sensations as you can, and tell what impulses 
 produce them. 
 
 2. "Saccharine" is a white solid having several hundred times the 
 sweetening power of sugar. A tiny amount, placed on the tongue, is 
 sweet; a larger amount is intensely bitter. Can you suggest a 
 reason? 
 
 3. How would you set about cultivating your sense of smell, so 
 as to make it acute? What do you think would happen in the 
 olfactory cells, if you were to do this? In the brain? 
 
 4. Name the organs through which a sound must travel before it 
 reaches the auditory nerve. 
 
 5. Stand before a mirror, in the dark, for a minute, and then sud- 
 denly turn on a light; what is the condition of the pupils of your eyes? 
 What happens as the light shines into your eyes? Tell why we are 
 dazed when we first come from the dark into a bright light. Why can 
 we not see so well when we first go into a dark room as we can after we 
 have been in it for a time? 
 
 6. Name all the structures through which a ray of light must go to 
 reach the optic nerve. 
 
 7. Read about the "compound" eyes of insects, and describe 
 them. 
 
 8. If it is true that the image on the retina is inverted, why do we 
 not see objects upside down? 
 
 9. A fly held near the eye looks as large as a man who is down the 
 street; how do we know it is not really as large? 
 
424 THE NERVES AND THE SENSE ORGANS 
 
 10. When a stick with a spark at one end is swung about in a circle, 
 the eye "sees" a continuous ring of light; why? Why does a meteor 
 (" shooting star") seem to have a "tail?" 
 
 11. Why does it rest the eye, after we have been reading, to look at 
 a distant object? 
 
 12. Adenoids, colds in the throat, etc., often cause deafness; what 
 part of the ear do they stop up first? 
 
CHAPTER XX 
 
 SANITATION 
 
 421. Bacteria and Disease. We have already learned 
 (cf. 324) that bacteria are plants belonging to the class 
 of fungi, and that they cause many fermentations, the 
 decay of dead animals and plants, and diseases that are 
 "catching," or contagious. All disease germs are not, 
 however, bacteria; some of them are minute one-celled 
 animals (protozoa). Thus, malaria and yellow fever are 
 caused by protozoa. It is impossible for us to escape 
 from germs, for they are everywhere about us: on the 
 ground, in the air, and in our houses; but, fortunately for 
 us, all germs do not cause disease. Most of them live 
 their own lives without interfering with ours. In the 
 outside air we should rarely meet with injurious germs 
 were it not that they escape from the bodies of animals 
 and of persons who are sick. So the germs we usually 
 have to fear are those that are carried, in food or by con- 
 tact, from animals to persons, or from one person to 
 another. 
 
 The "germ theory" of contagious diseases did not gain immediate 
 acceptance when it was first stated, for men could not believe that 
 organisms so small could do so much mischief. But the patient labor 
 of one investigator after another proved that the theory is correct. 
 We now know that germs are responsible for smallpox, measles, 
 diphtheria, scarlet fever, typhoid fever, tuberculosis, influenza (la 
 grippe), malaria, yellow fever, pneumonia, lockjaw (tetanus), mumps, 
 cholera, leprosy, the plague, etc., etc. It takes a definite kind of germ 
 
 425 
 
426 SANITATION 
 
 to cause a given disease; no other germ will "do just as well." But the 
 ways of different kinds of germs are not at all alike; it is often very hard 
 for the investigator to know just how each kind of germ gets into the 
 body, and how it does its work. Thus, it turns out that while a cer- 
 tain mosquito, called anopheles (a-nof'-e-les) , carries malaria germs 
 from one person to another, only the female anopheles sucks blood, and 
 is responsible for the spreading of malaria. 
 
 The science of germs, and of the way in which we can 
 deal with them, is bacteriology. The science of keeping 
 the body in good health is hygiene. The study of the 
 conditions and surroundings that make for the health of 
 the body and of the community, is sanitation. 
 
 422. How the Body Gets and Resists Diseases. 
 Germs, like other living organisms, grow rapidly when the 
 conditions for life (environment; cf. 306) are favorable. 
 They need animal or vegetable material for food; they 
 need moisture; they need a favorable temperature. 
 Germs often find these conditions in our solid food, in 
 milk, in water containing organic matter, in the filth of 
 the streets, and in the animals that make their home 
 with man. These animal companions of man are ver- 
 min, pets, and domestic animals. From food, and 
 water, and animals, then, disease germs are transferred 
 to man. In the body of man they find conditions favor- 
 able, and thrive enormously. The stomach secretion 
 kills many, but certain kinds are able to get through the 
 stomach (cf. 364). Some find favorable conditions in 
 the warm, moist cells of the throat and lungs; others, 
 still, get into the blood through cuts and scratches in the 
 skin. When we think of how constantly we come in con- 
 
HOW THE BODY GETS AND RESISTS DISEASES 427 
 
 tact with objects that contain harmful germs, we are im- 
 pressed with at least 3 things: (1) how efficient our skin 
 is in keeping out the invading army of germs; (2) how 
 important it is to wash the skin, especially that of the 
 hands, so that we may remove the germs before they 
 get into our food; (3) how necessary it is to keep the nasal 
 passages and the mouth (including the teeth) clean, so 
 that germs may not develop there, and spread disease to 
 the other parts of the body. 
 
 Why do not the germs of disease destroy man at once? 
 The answer is that there are two sides to the battle; the 
 body has its defenders, as well as its enemies. One of 
 these is the army of white corpuscles, which destroys 
 many of the disease germs that get into the blood. We 
 have already seen (cf. 378) that the white corpuscles are 
 like amebas, and that they are not only in the blood, but 
 get through the capillaries into the lymph. If a wound is 
 made in the skin or mucous membrane, the white cor- 
 puscles do their best to destroy the germs that enter the 
 wound. The body has not only the white corpuscles to 
 defend it, but also produces certain substances that act 
 as germicides ("germ slayers"). A great part of the 
 reason why we need to keep the body rested, well-fed, and 
 strong is that it may have an abundance of vigorous white 
 corpuscles, and that it may produce the right germicides 
 for the germs that attack it. Yet, in spite of everything 
 that the body can do, some dangerous bacteria may get 
 past the body's lines of fortifications; we then have a 
 disease. 
 
 The effect which disease germs have upon the body is 
 due not so much to the germs themselves as to the sub- 
 
428 SANITATION 
 
 stances that the germs produce. These substances are 
 violent poisons, called toxins; they injure the cells of the 
 body much as strychnine or other poisons would. Pto- 
 maines (to'-ma-ins), which cause so-called ptomaine 
 poisoning, are toxins produced in the decay of foodstuffs. 
 The disease germs that we take into the body when we are 
 "exposed" to a disease are not numerous enough to pro- 
 duce much toxin, so there is usually a period of time, 
 called the incubation period (incubation also means 
 "hatching"), during which the germs are multiplying, 
 and are producing enough of the toxins to give us the 
 symptoms of the disease. 
 
 423. How Germs May Be Destroyed. While the 
 disease germs that get into the body do not always cause 
 disease, because of the power of the white corpuscles and 
 the germicides to destroy them, we are not safe if we 
 depend on this power alone. We must do all we can to 
 destroy the germs before they enter the body. Hence 
 we cleanse the body and its clothing, and our dishes and 
 floors. Since food for man is often food for germs, we 
 cook or bake most of our food. The high temperature of 
 boiling water and of the oven destroys the germs. 
 
 To some of us the wiping up of dust ("dusting the 
 house") may seem an unnecessary performance. But if 
 a house is to be safe, the dust that collects must be re- 
 moved carefully; it may contain deadly germs. If a 
 house contains a great deal of heavy furniture and much 
 bric-a-brac, the labor of house cleaning is so great that 
 it may not be carried out often enough. The average 
 family needs to reduce greatly the quantity of its house 
 
HOW HOUSEFLY AND MOSQUITO AFFECT HEALTH 429 
 
 furnishings, if it is to make any real headway against dust 
 and the disease germs which the dust contains. 
 
 Light and air are nature's agents for the destruction of 
 germs "in the open"; we need these in our houses also 
 (cf. 246). One of the worst results of dust and dirt in 
 the house is that they cover up the germs, and prevent 
 light and air from getting at them. As we call the in- 
 vasion of our bodies, our homes, or our clothing, by harm- 
 ful germs, infection, so we call the 
 destruction of such germs disinfection. 
 The agents, or materials, that cause 
 germ destruction we call disinfectants. 
 The most common disinfectants of the 
 household are soap and hot water. 
 There are also chemical disinfectants 
 that are very useful for special pur- 
 poses (cf. 438). Disinfection by gases 
 is called fumigation. 
 
 424. How the Housefly and Mosquito 
 Affect Public Health. There is little or 
 no use in arguing the question whether 
 or not the fly does anything for man; 
 we have abundant evidence of what he Fi g . sos. 
 
 does to man. Flies grow, as maggots, in Foot of i a ngSn flyiWith 
 the body waste of animals; they feed in 
 all manner of dirty places; they enter sickrooms, and come 
 away loaded with disease germs (Fig. 303). Not only do 
 germs cling to the fly, but they are present in the dis- 
 charges of its body (' i fly specks ") . This evidence against 
 the fly is enough to exclude it from our tables, our dishes, 
 
430 SANITATION 
 
 and our faces. We should make every effort, by the use 
 of good screens, to keep flies out of our houses, and away 
 from our food. Especially should we protect little chil- 
 dren from them. 
 
 But while the slogan "Swat the fly!" rings through the 
 land, we must remember that the adult fly is largely what 
 we make it. It does not travel far. The germs that it 
 carries it gets from the neighborhood where it lives, and 
 where we live. To make a campaign against the fly 
 effective, we need to keep our neighborhood clean and 
 sanitary. Flies will not breed if there are no dirty places, 
 such as manure heaps and heaps of kitchen waste, in which 
 the adult fly can lay its eggs. Flies will not carry germs 
 from house to house if every house is properly screened, 
 and if we take care to destroy the disease germs that 
 come from sickness. Flies will not find food, out of doors, 
 if crumbs and dish water are not thrown into the yard, 
 and if garbage is carefully covered, removed, and de- 
 stroyed. So, to get rid of the fly and the long train of 
 troubles for which it is responsible we need not only to kill 
 it when we find it, but we must keep our neighborhood clean. 
 If we do this, the fly cannot develop and multiply there. 
 
 What is true of the fly is largely true of the mosquito. 
 Its breeding habits are well known (cf. 339, Fig. 264); 
 the eggs must be laid in water. In inserting its sharp 
 proboscis into the skin of a sick person, it becomes in- 
 fected, and then introduces the infection into the body of a 
 person who is well. The region about Rome has long 
 been filled with deadly malaria, but we now know that 
 people may live there without fear, if they are screened 
 against malaria mosquitoes. 
 
DANGER IN FOOD 431 
 
 Like the fly, the malaria mosquito is a "home product." It lives 
 very near the place where it was hatched. To get rid of it, we must 
 destroy its breeding places. Open cisterns, wells, rain barrels, water- 
 ing troughs, ditches, puddles, sagging eaves troughs, broken crockery, 
 and tin cans, anything that can hold water, all these give the mosquito 
 its opportunity. All unnecessary holders of water should be removed 
 or buried; the others should be carefully screened. Ditches should be 
 drained. Puddles, cisterns, and barrels that contain "wigglers" 
 should be treated with a little kerosene (cf. 339), and then screened. 
 Cities often suffer needlessly from mosquitoes, because the creatures 
 are allowed to develop in street catch basins. The catch basin receives 
 the water that comes from the street, and the water that remains in it 
 acts as a "water seal" to the street sewer, just as the "trap" does to 
 the house sewer (cf. 236) . If there is no rain for some time, and if the 
 catch basin is not "flushed out," the standing water permits the mos- 
 quito to breed. A little kerosene thrown into the catch basins would 
 rid the neighborhood of the nuisance. 
 
 425. Danger in Food. If the body were unprotected, 
 a single germ might cause a disease. But this is rarely 
 possible. A few germs are usually destroyed at once by 
 the blood. But a large number (many millions) may be 
 introduced into the body in a single bite of bad food, or 
 in a mouthful of infected water. So we need to be very 
 careful about the food we eat. Only persons with clean 
 hands and clean clothing should prepare and handle 
 food, and food should be stored only in clean, protected 
 places (Fig. 304). If customers were clean themselves, 
 and were particular about the cleanliness of what they 
 buy and use, their groceries, meat markets, bakeries, 
 fruit stores, candy kitchens, laundries, milk depots, etc., 
 would be clean too. 
 
 We must be particular, also, about tainted, or decayed, food. Over- 
 ripe fruit is always to be suspected. Many a household is so anxious 
 
432 
 
 SANITATION 
 
 not to waste food that it eats suspected food "to save it." This is the 
 worst kind of ' ' saving, ' ' for the food usually makes some one of the family 
 ill, and causes a waste a hundred times as great as any possible saving. 
 
 Fig. 304. 
 Exposed food, which is not protected from flies and street filth, is covered with germs. 
 
 Milk is especially liable to infection. Ever so many 
 epidemics of children's diseases, such as scarlet fever and 
 
DANGER IN FOOD 
 
 433 
 
 diphtheria, have been traced to an infected milk supply. 
 Milkmen having the diseases in their own families have 
 again and again been found delivering milk to other fam- 
 ilies. Typhoid fever and consumption are likewise spread 
 
 Only 
 Bottled 
 
 Buy Only From Clean Alii km en 
 Aiever Bug In Store 5vtarming With Flies 
 
 AlERE'6 A CflEAP/iO/IE-AlADE ICE- 
 
 FOR KEEPING BABY'S 
 
 Co*t: Less tha^n twenty -five, cent* 
 
 A- Wooden box. B-Tin collar, C-Tin pail with cover (pai I talUr than 
 milk bottle;. D- Sawdust packed around out.de o/ tin collar; E.- Paper feck- 
 <d en inside <? box cover, F- Ice packed around bottle o/ milk in pail. 
 
 Fig. 305. 
 There is need of ice to keep milk. Educational Poster, Chicago Health Department. 
 
 by infected milk. If we buy milk from a small dairy, we 
 should visit the dairy, or ask some competent person to 
 do so, to see if the conditions are sanitary, and if the cows 
 are healthy and well fed. If we buy in a large city, and 
 
434 
 
 SANITATION 
 
 cannot inspect the supply directly, we should ask the 
 health authorities to make frequent examinations of the 
 milk, so that we may be reasonably sure that it is safe. 
 
 Milk "spoils " most rapidly, of course, in warm weather, 
 just when babies suffer most from the heat. If to their 
 weakened bodies we add germ-laden milk, the results are 
 sure to be serious. The number of deaths of young 
 children, in summer, is very great, and many of them can 
 be prevented. Germs cannot develop so rapidly in cold 
 
 milk as in warm milk, 
 hence there should be a 
 refrigerator, of some sort, 
 in every family where 
 there are children (Fig. 
 305). Many cities fur- 
 nish free ice, or inexpen- 
 sive ice, to the very poor, 
 as this ' ' saves the babies . ' ' 
 
 Fig. 303. 
 
 The Wrong and the Right Kind of Nursing 
 Bottles. 
 
 In most cases children can 
 digest pasteurized milk (so 
 called from the celebrated 
 French scientist, Pasteur) . 
 
 The process of pasteurizing is simple and inexpensive, the apparatus 
 consisting only of a covered pail, with a hole in the cover for a 
 thermometer. The bottle containing milk is placed in the pail, 
 the pail is filled with water almost to the mouth of the bottle, 
 the cover and thermometer are put in place, and the pail is heated. 
 A temperature of 68.3 C. (155 F.) maintained for half an hour, 
 or of 77C. (170 F.) for 5 minutes, kills the disease germs of the 
 milk. The milk is then cooled rapidly, and stored in a refriger- 
 ator. The bottles used for the feeding of babies often spoil other- 
 wise good milk (Fig. 306). Those with a long, slender rubber tube 
 
DANGER IN FOOD 
 
 435 
 
 are especially dangerous, for germs collect in the tube, and are not 
 easily removed. It is on such details as this that the life of many a 
 baby depends. 
 
 Preservatives. Because chemicals destroy disease 
 germs, many dealers in foods, and, unfortunately, some 
 housekeepers, argue that chemicals may properly be used 
 to destroy the 
 germs in food, 
 and to prevent 
 natural decay. 
 Why not use sul- 
 phur dioxide to 
 preserve dried 
 apples, formalde- 
 hyde to preserve 
 milk and canned 
 corn, salicylic acid 
 to preserve fruit, 
 and borax to pre- 
 serve meat? The 
 answer is that 
 these preserva- 
 tives are, sooner 
 or later, poisons 
 to the body. The 
 least harmful 
 thing they do is 
 to prevent food 
 
 from digesting properly. We eat the food, but the body 
 does not get from it the necessary nutrients. Such food 
 is really wasted. 
 
 Fig. 307. 
 
 There is death in the public drinking cup. Educational 
 Poster, Chicago Health Department. 
 
436 
 
 SANITATION 
 
 Preservatives in milk are very injurious to children. 
 The small amount of chemicals may do only a slight dam- 
 age to a grown person, for milk is only a small part of his 
 food; but for the little child milk is almost the whole diet. 
 Milk that does not sour in 24 hours, or less, at a summer 
 temperature, needs to be tested for preservatives. 
 
 Fig. 308. 
 Sanitary Drinking Fountain. 
 
 426. Contaminated Cups, Money, Etc. Public drink- 
 ing cups are another source of great danger (Fig. 307); 
 many diseases can be spread by their use. The practice 
 of drinking from one "family" dipper is bad enough, but 
 how much worse it is for all the people, whether diseased 
 or well, to drink from the same cup when they are in 
 public buildings, or on the train, or at public fountains. 
 
TYPHOID AND SEWAGE 437 
 
 We ought to have our own drinking cups when we travel, 
 so that we shall not give a disease to any one else, nor run 
 the risk of catching one from others. We ought to have 
 our own cups at school, too, unless the school has a sani- 
 tary fountain (Fig. 308). To put into the mouth objects 
 that have been handled by others is just as bad as to use 
 dirty drinking cups. 
 
 Public towels and soap, as these are found in public washrooms 
 and in many hotels, are full of danger. . 
 
 All money, especially paper money, that has been carried about in 
 unclean pockets, and handled with dirty fingers, is "tainted." The- 
 examination of paper money by bacteriologists shows that the money 
 has, sticking to it, germs of almost every variety, including those of our 
 worst diseases. Hands should be washed after they have handled 
 money, and before they are used about food or the face. Certainly no 
 cashier ought to be expected to eat his dinner, and to "make change," 
 between bites, for customers. 
 
 427. Typhoid and Sewage. Typhoid fever is one of 
 man's most serious diseases. There are perhaps 250,000 
 cases of it in a year in the United States alone, with up- 
 wards of 25,000 deaths. The bacteria that cause it 
 (cf. 324) are taken into the body through the mouth, in 
 food or water. In the small intestine they multiply 
 rapidly, and produce toxins that pass into other parts of 
 the body. The body waste from the intestines and kid- 
 neys of a typhoid patient contains large amounts of the 
 germs. If the germs are not destroyed, they get into the 
 soil and into sewage. From the soil they may get into 
 garden vegetables, and may be carried, by seepage water, 
 into wells. The germs may get into milk from the water 
 with which milk cans are rinsed, or from some one who 
 
438 SANITATION 
 
 has the disease, or from some one who handles the milk 
 with dirty hands. If the sewage is emptied into the 
 stream or lake from which a community gets its water, 
 the whole community is in danger of having the disease. 
 Typhoid germs have been found in oysters that grew near 
 the outlets of sewers. In some, or all, of these ways the 
 typhoid germs of one who has the disease may find their 
 way into the alimentary canals of new victims. 
 
 An epidemic (the word means "among the people") that occurred 
 in 1885 in Plymouth, Pennsylvania, is often used to show the connec- 
 tion between drinking water and typhoid. Plymouth had 8,000 
 inhabitants, and obtained its water chiefly from a clear, pure mountain 
 stream. In the early spring, while there was still snow on the ground, 
 one man living near the stream, but far from the town, had typhoid 
 fever. His body waste was thrown on the ground, near the stream. 
 When the snow melted, the typhoid germs were carried into the stream, 
 and soon produced a dreadful epidemic in Plymouth. Within a few 
 weeks there were 1,104 cases of typhoid and 114 deaths. The cost of 
 this epidemic to that community was estimated as not less than half a 
 million dollars (Sedgwick). 
 
 Persons have been found who continue to harbor the germ long after 
 they recover from the disease, and who communicate the disease to 
 multitudes of others. Recently, a medical journal described an 
 epidemic in a western city, in which 85 persons had typhoid because 
 they ate " macaroni and cheese" that had been prepared by a " typhoid 
 carrier." The person in question was a woman 65 years old, who had 
 never consciously had typhoid fever and who was apparently in good 
 health. 
 
 428. Exercises. 
 
 1. Which house will have the better chance of fighting disease 
 germs successfully, the one with all-over, tacked carpets, or the one 
 with loose rugs? Why? The one in which a feather duster is used, 
 or the one in which the housekeeper removes dust with a damp cloth? 
 The one in which children are taught to wipe their feet outside of the 
 
EXERCISES 439 
 
 house, or the one in which street and barnyard filth is brought into the 
 house? 
 
 2. Why is it better to have little bric-a-brac on mantels arid walls, 
 rather than much? To have "open" plumbing, rather than plumb- 
 ing enclosed in wooden cupboards? To have a light, airy cellar, 
 rather than a dark, damp one? To do sweeping with a carpet sweeper, 
 rather than with a broom? What are the advantages of "vacuum 
 cleaning" apparatus? 
 
 3. Why should you not wipe your eyes with your fingers? Allow 
 your teeth to remain uncleaned? Cough with your face to the table? 
 Carry drinking glasses with your fingers inside the glasses? Turn 
 the leaves of a book with fingers moistened by saliva? Put pencils into 
 your mouth? 
 
 4. Which would you expect to be more contaminated with germs, 
 one-dollar bills or ten-dollar bills? Why? 
 
 5. Can a cistern be kept clean if birds are allowed to live on the 
 roof or in eaves troughs? 
 
 6. Name all the ways in which a community can guard itself against 
 typhoid fever. 
 
 7. Find out from a physician or a well-digger how a well should be 
 constructed and protected, so that surface water may not get into it 
 (cf. 81.) 
 
 8. How can the germs in drinking water be removed or destroyed? 
 (Cf. 83). Is ice ever dangerous to public health? 
 
 9. What do you think of the following as sanitary practices : Locat- 
 ing of bakeries in cellars? In tenement houses? Having milk depots 
 in cellars? Delivering milk in cans? Delivery of milk in bottles, but 
 in open wagons? Handling of milk bottles by the mouths of the 
 bottles? 
 
 10. Do you think it safe to put away furs, winter caps, underwear, 
 and clothing in a closet or trunk, without disinfecting them, and then 
 to wear them again in the fah 1 ? 
 
 11. What objection is there to having much furniture, and draperies, 
 bookcases, etc., in a sickroom? 
 
 12. What does sediment at the bottom of a milk bottle indicate? 
 Why ought the mouth of a milk bottle to be wiped before the bottle is 
 opened? 
 
440 SANITATION 
 
 13. Why should dish cloths and dish towels be sterilized often? 
 
 14. Find out when bread is delivered to a grocery in your neighbor- 
 hood, and watch the process. Write a description of the process, and 
 criticize it from the sanitary point of view. 
 
 15. In the same way study and criticize the handling of milk in your 
 own house and in that of some neighbor. 
 
 16. How is garbage disposed of in your neighborhood? Watch the 
 process of garbage collection, and criticize it. How could the house- 
 holder help in making the process more sanitary? How could the 
 collector help? 
 
 429. Tuberculosis, or Consumption. Consumption is 
 due to a germ (the tubercle bacillus), and is " caught" by 
 one person from another. Most persons, perhaps 90 out 
 of every 100, are attacked, at some time or other, by the 
 germ. Usually the body is able to overcome the disease, 
 and we do not know that we have been attacked. But 
 if the body once yields to the disease, we become weaker 
 and weaker, and less able to shake it off. It is one of the 
 triumphs of modern medicine that we know we can over- 
 come consumption if we treat it in its early stages. We do 
 not, therefore, need to give up if we have the disease, but 
 can use simple, easy means to be cured. The chief things 
 we must do are to live in the open air, to be warmly clothed, 
 and to eat an abundance of simple, nourishing food (cf. 
 246; also Fig. 309). If one has a suspicion that he has 
 tuberculosis, he ought not to hide the fact, nor to try 
 patent medicine " cures," but to see a physician at once. 
 When a large area of the lungs has become diseased, it is, 
 of course, harder for us to be cured; it may be impossible. 
 The tuberculosis germ is usually expelled from the body 
 in the sputum, or "spit," which the consumptive coughs 
 
TUBERCULOSIS OR CONSUMPTION 
 
 441 
 
 up from his lungs. This should never be scattered, but 
 should be entirely destroyed. The best way is to burn it. 
 
 By the modern method, consumption can be cured in any climate, 
 but a cold, dry climate is the best. To be cured, one does not, there- 
 fore, need to go away from a cold climate, as men formerly thought, 
 Neither is tuberculosis inherited, as men used to believe. The disease 
 can come only from the entrance of the bacilli into the lungs. But 
 people can inherit a weak resisting power, so that they need to use more 
 
 Fig. 309. 
 Open Air Cottage of a Tuberculosis Sanitarium. 
 
 care to avoid taking the disease than do the children of non-consump- 
 tive parents. One reason why members of the same family often get 
 the disease is that the germs are not destroyed with sufficient care, but 
 are allowed to spread through the house. They thus go from the sick 
 member of the family to those that are well. Sputum should not be 
 allowed to dry, and the dishes, linen, and clothing of the patient should 
 be thoroughly disinfected. 
 
 Tuberculosis germs remain in houses, and one family after another, 
 by living in an infected house, may furnish victims for the disease. 
 When we plan to move into a house, we ought to be interested, not only 
 in the view and the wall paper, but also in the sanitary history of the 
 house, so that we may know what risk we are taking by living in it. 
 
442 SANITATION 
 
 430. Spitting in Public. Public-health authorities 
 everywhere are trying to stop the practice of expectorat- 
 ing, or ' ' spitting," in public places. The habit is not only 
 disgusting and indecent, but dangerous. This is clear 
 from what we have learned of tuberculosis. If we 
 remember that a multitude of germs is expelled from the 
 body in the act of " spitting, " and that the germs cast 
 forth become a part of the dust that all passers-by must 
 breathe, we can see what a dangerous indulgence public 
 spitting is. 
 
 431. Colds. We often speak lightly of colds; if suf- 
 fering from one, we say we have "only a cold." But 
 colds need to be included in our list of serious diseases, if 
 for no other reason than that they are so common, and 
 that they lower the working ability of so many people. 
 Colds are also serious because they are often the begin- 
 nings of consumption, pneumonia, diphtheria, etc. The 
 cold does not cause these diseases directly, but it lowers 
 the power of the body to resist dangerous germs. 
 
 Colds are communicated from one person to another; the one who 
 has a cold ought to exercise care, so that he may not pass it on to others. 
 A cold that " hangs on" needs a physician's care, especially if it causes 
 difficult breathing and fever. If it is "only a cold," the avoiding of 
 drafts, care in clothing, and the eating of light food, especially of liquid 
 food, are usually all that is needed to cure it. The old saying is that 
 if you " stuff a cold" (that is, overeat), you will need to "starve out a 
 fever. " But if a cold makes us weak and chilly, a day or two spent in 
 bed will be of the greatest possible help. Time will actually be saved, 
 if we do not work when we are unfit for work. 
 
 We often "catch cold" after we have been overheated by the 
 wearing of too heavy clothing, or by living, even for a little while, in 
 
ANTITOXINS 443 
 
 rooms that are hot and poorly ventilated (cf. 247). A bad habit, 
 which too many of us have, is that of going into warm buildings, in 
 cold weather, without removing our outer wraps; when we go out 
 again, overheated, we are in danger of serious trouble. 
 
 432. Diphtheria. Diphtheria is often mistaken for a 
 cold; this fact is one reason why a cold should not be left 
 to chance, but should be treated by a physician. If a 
 child has a croupy cough that comes not only at night, 
 but also during the day, its throat should be examined at 
 once. Small, tough, grayish-white "patches" in the 
 throat indicate diphtheria. Membranous croup is diph- 
 theria in the larynx. 
 
 The germ of diphtheria is scattered abroad by the 
 violent coughing of the patient and by the discharges from 
 his nose and throat. All cloths containing the discharges 
 should be disinfected or burned. After one has had the 
 disease, he may have the germs in his throat for months, 
 and may give the disease to those with whom he comes in 
 contact. The germs may also get into the throat of a 
 healthy person, and yet be held in check because of the 
 person's " resisting power." This healthy person may, 
 however, infect milk, handkerchiefs, drinking cups, dishes, 
 etc., and pass the germs on to others who cannot resist 
 the disease. The cause of the severe illness in diphtheria 
 is usually its poisonous toxin, although sometimes the 
 throat is closed by the diphtheria membrane. Death 
 sometimes comes in two or three days. 
 
 433. Antitoxins. The word antitoxin means "against 
 toxin." When germs get into the body, they produce 
 toxins (cf. 422). To protect itself, the body produces 
 
444 SANITATION 
 
 not only white corpuscles and germicides, which kill the 
 germs themselves, but also substances that neutralize 
 the effect of the toxins. These are the antitoxins. For 
 every toxin that germs produce, the body probably forms 
 an antitoxin. In diphtheria the patient may not be able 
 to produce enough antitoxin to stop the disease, but if he 
 is helped by the addition of some diphtheria antitoxin to 
 his blood, he may win his fight against the germs. Like- 
 wise, if one who has been exposed to the disease is treated 
 with antitoxin, the germs may not be able to develop 
 enough of the toxin to cause the disease. 
 
 The diphtheria antitoxin is produced in the body of the horse. The 
 method is as follows: 
 
 Germs taken from some one who has the disease are allowed to 
 multiply in a rich nutrient like beef broth. They thus produce a great 
 deal of the toxin. The germs are then filtered out, and the liquid 
 containing the toxin is injected under the skin of a horse. The horse's 
 blood produces antitoxin to neutralize the toxin. As more and more 
 toxin is injected, more and more antitoxin is produced. The horse 
 becomes immune to, or "fortified against/' the Joxin. Then blood is 
 drawn from the horse, and is clotted and filtered. The resulting 
 filtered liquid is the antitoxin serum. When some of this is introduced, 
 under the skin, into the human body, it makes the body immune, or 
 at any rate helps in making it immune, to the toxin produced by the 
 diphtheria germ. 
 
 The records of many hospitals show that while before the days of 
 antitoxin there used to be 30 to 50 deaths out of every 100 cases of 
 diphtheria, the deaths since the introduction of antitoxin are only 
 from 11 to 18 in 100 cases. If the antitoxin is pure, and if it is used as 
 soon as the disease shows itself , there are practically no deaths. 
 
 434. SmaUpox. Typhoid, tuberculosis, and diph- 
 theria are germ diseases, but they are not accompanied by 
 
VACCINATION 445 
 
 a "breaking out" (eruption) of the skin. Smallpox 
 belongs to the eruptive diseases ; the sores, when they heal, 
 leave the "pock" marks that give the disease its name. 
 Up to the year 1800 almost everybody expected to have 
 smallpox; few seemed to have sufficient resisting power to 
 ward off the disease. The loss of life in smallpox epi- 
 demics was enormous: between the years 1700 and 1800 
 probably 600,000 persons, on the average, died of the 
 disease every year. But the practicing of vaccination 
 and the progress made in sanitary science have combined 
 to reduce the deaths from the disease to comparatively 
 small numbers. 
 
 Vaccination for smallpox was preceded by inoculation, which may 
 be defined as artificial infection. Inoculation consisted in putting 
 some of the " matter" from the eruptions of a smallpox patient under 
 the skin of a person who was well. The person inoculated chose to 
 have the disease when he was prepared for it, rather than when he was 
 not prepared. He usually had the disease in a mild form, and then 
 was immune for life. The method of inoculating well persons came 
 from China to Constantinople (we do not know when); from Con- 
 stantinople it spread, in about 1720, to Western Europe and to Amer- 
 ica. One disadvantage of this early method of inoculation was that 
 the persons treated could give the disease to others, hence they had to 
 be isolated, or kept apart. There were also some serious accidents 
 in inoculation, because men did not know of the existence of germs, and 
 therefore did not know the meaning of sanitary cleanliness. If the 
 " matter" introduced into the body of the well person was infected 
 with other germs, or if the instruments used were not clean, the person 
 inoculated "caught" other serious diseases. 
 
 435. Vaccination. The discovery of vaccination (vacca 
 means "a cow") by Jenner came in 1796. Jenner took 
 the "matter" formed in cowpox (smallpox of the cow), 
 
446 
 
 SANITATION 
 
 and introduced this "vaccine virus" under the skin of a 
 man. He thus found that he could produce in the man an 
 immunity to the disease. Vaccination (Fig. 310) usually 
 
 AFTER 
 
 Criminal negligence defaced 
 thb child for life. 
 
 A little SC^r* on the a^rrrz. will prevent 
 thousands of sc^rs on the fe>,ce. 
 
 Fig. 310. 
 Effect of Smallpox Educational Poster, Chicago Health Department. 
 
 produces a mild inflammation at the place where the 
 virus is introduced; this is due to the growth of the germs. 
 The germs from the cow are so much weaker than those 
 that come from a human smallpox patient that they can- 
 not produce the dreaded disease, but their presence in 
 
OTHER GERM DISEASES 447 
 
 the blood stimulates the body to produce the germicide 
 for the smallpox germ. 
 
 The germicide seems to remain in the blood for some time, perhaps 
 for years in some persons, and protects the body if other smallpox 
 germs enter. In some persons, however, the germicide disappears in 
 less than a year. We should be vaccinated every few years, or more 
 frequently if there is smallpox near us, in order that the germicide 
 may always be present in the body. If we are vaccinated by a good 
 doctor, with fresh vaccine virus, there is no danger. The doctor 
 should use only virus that has been purified, so that it cannot contain 
 other infecting germs. We should be vaccinated, not only for our own 
 sakes, but for the sake of others. The germs of smallpox live for 
 months in a dry condition; they may be preserved in books, clothing, 
 letters, etc. Hence we can never tell when we may catch the disease, 
 and give it to our friends and neighbors. We are not wiser than the 
 experience of the last 100 years. This experience teaches us that 
 while sanitary living helps to keep the germs down, it cannot help us 
 if they get into the blood, and if the blood has not prepared the proper 
 germicide for our defense. 
 
 Vaccination against typhoid fever is now being carried out with 
 success, especially to protect armies in the hard, insanitary conditions 
 under which they are often forced to live. The germs of typhoid are 
 cultivated until they have multiplied, and produced their toxins. 
 Then the germs are killed, and small amounts of the dead germs and 
 the toxins are injected under the skin of the person to be protected. 
 Vaccination against typhoid ought to be an additional precaution, not 
 a substitute for sanitary measures. 
 
 436. Other Germ Diseases. Scarlet fever and measles 
 are eruptive diseases, just as smallpox is. Both are 
 highly infectious, and both come chiefly in childhood. 
 The scarlet-fever patient often suffers little from the first 
 stages of the disease, but has very serious after-effects. 
 These may produce lifelong injury, even if they do not 
 
448 SANITATION 
 
 cause death. The discharges from the nose and mouth 
 are very infectious; so is the dead skin ("scales"), which 
 the patient "sheds" for some time after recovery. No 
 one recovering from the disease should be allowed at 
 large until the last traces of scaling have disappeared, or 
 he will scatter the infection broadcast. Measles is 
 infectious from the very first. It "breaks out" not only 
 in the skin, but in the mucous membrane of the mouth, 
 throat, and air passages. The eruption has a charac- 
 teristic "measly" odor. The after-effects of measles are 
 often very serious, for the disease leaves the throat and 
 lungs weak, so that there is danger of pneumonia and 
 consumption. It also weakens the eyes. Hence the 
 patient should not be allowed in a bright light, and 
 he should not be permitted to read until he has fully 
 recovered. 
 
 Pneumonia (nu-mon'ya) is one of our worst diseases, 
 especially in cities. It is caused chiefly by one kind of 
 germ, called pneumococcus (nu'-mo-kok-iis), which may 
 grow in any or all of the air passages. Pneumonia attacks 
 many of the larger animals and these may infect man. 
 The germs are carried from one patient to another in the 
 sputum, and in the discharges from the nose. The germs 
 of pneumonia have been found in the throat of most per- 
 sons, even of those that are healthy, but they are held in 
 check by the body's resistance. A severe cold, some 
 sudden exposure, or a weakening of the body, may give 
 them their opportunity (cf. 407). It is for us to keep the 
 body in good condition, and to exercise the lungs by 
 breathing deeply of fresh air (cf. 391), so that the germs 
 may not get a secure foothold. The danger in pneumonia 
 
OTHER GERM DISEASES 449 
 
 is partly due to the fact that the lung cells may be covered 
 up by the growth of the germs; the chief danger, however, 
 is from the toxin, which may stop the action of the heart. 
 
 We have already learned that malaria is carried by certain mos- 
 quitoes (cf. 424) ; yellow fever is carried in the same way. But while 
 one variety of mosquitoes (anopheles) carries the germ of malaria, an 
 entirely different variety (stegomyia; steg-o'-nrf-ya) carries the yellow 
 fever germ. Yellow fever has long been the pest of tropical and sub- 
 tropical countries, and has been greatly dreaded in our own southern 
 states. When the United States took up the administration of Cuba, 
 in 1898, it had before it the problem of a general " cleaning up," and of 
 getting rid of the yellow-fever mosquito. It had the same problem to 
 solve before it could dig the Panama Canal. If houses, especially 
 those in which there is yellow fever, are carefully screened against 
 mosquitoes, and if the breeding places of the mosquitoes are destroyed, 
 the disease can be kept under control. 
 
 Tetanus (tet'-a-nus), or lockjaw, is a disease we hear most about 
 after the celebration of an "insane" Fourth of July, when there have 
 been many accidents with toy pistols, firecrackers, toy cannon, and 
 fireworks. The skin is so good a protection for the body that although 
 tetanus germs are often on the skin they do not get into the body. 
 But flying particles of the "caps," wads, and paper of explosives carry 
 the germs through the skin. The toxin produced by the germs is very 
 powerful, causing a contraction and stiffness of the muscles, first of 
 those of the face, and afterwards of those of other parts of the body. 
 Hence the name "lockjaw." Tetanus germs grow in the ground, and 
 away from the air, hence they may be present on rusty nails and un- 
 clean garden tools. Wounds made by articles that have been in or on 
 the ground should be dressed carefully, by a physician if possible. 
 
 Rabies (ra'-be-ez), or hydrophobia, seems to be produced by pro- 
 tozoa that grow in the nerve tissue of the brain and spinal cord. The 
 disease is "given" to dogs and cats in the bites and scratches which 
 they receive from other creatures that have the disease. The infected 
 dogs and cats give the disease to man. 
 
 The Pasteur treatment for rabies is to cultivate the germs, so as to 
 
450 SANITATION 
 
 weaken them, and then to introduce the weakened germs into the 
 body. The body develops germicides that kill not only the weakened 
 germs, but also those that come from an infection. The first thing for 
 us to do, if we have received a wound from a suspected animal, is to go 
 at once to a physician to have the wound disinfected. The suspected 
 animal ought not to be killed, but captured, and confined for about 10 
 days. If it remains well, it cannot have the rabies, and cannot give the 
 
 SCARLET FEVER 
 
 HERE 
 
 All Persons Are Hereby Warned 
 NOT To Remove This Placard 
 
 UNDER PENALTY OF THE LAW 
 
 Fig. 311. 
 Quarantines should be respected. 
 
 disease. If all dogs could be muzzled for a few years, there would 
 probably be no more hydrophobia, for one dog could not infect another. 
 So-called madstones are of no use in curing the disease. 
 
 437. Quarantine. Quarantine (Fig. 311) is the isola- 
 tion, or setting apart, of a person having an infectious 
 disease, so that the disease may not spread to the com- 
 munity. Quarantine is also used in the case of goods, 
 plants, cattle, etc., if they are suspected of infection. In 
 the case of a ship coming to our ports, quarantine is the 
 
QUARANTINE 451 
 
 detaining of the passengers and goods on board the ship 
 until the health officials are satisfied that no infectious 
 diseases are being brought into the country. In the case 
 of a house, quarantine means the preventing of persons 
 from going into the house, or more especially from leaving 
 the house, for fear that they may carry disease to the 
 community. Quarantine means "forty," and comes from 
 the fact that governments of former times, not knowing 
 the incubation periods of germs, nor the time during 
 which infections were possible, detained suspected trav- 
 elers and goods for 40 days before admitting them into a 
 country. 
 
 Do we really understand what we have learned about 
 the spreading of disease by germs? If we do, we shall see 
 at once how valuable and how necessary it is for a city to 
 be able to quarantine persons suffering from dangerous 
 diseases. We shall also be able to see the value of isola- 
 tion even when it causes us personally great inconvenience. 
 Suppose that we have smallpox, or that a member of our 
 family has it ; we ought still to realize that the community 
 has a right to demand of us that we prevent the disease, 
 by all the means in our power, from spreading to those 
 about us. If we are recovering from scarlet fever, we 
 know we ought not to go to school, nor to mingle with 
 other people, until we are absolutely certain that the last 
 of the " scaling " is over. We also know that articles 
 such as milk bottles should not be taken away from a 
 house that is quarantined; they may be infected. By the 
 mingling of infected milk bottles with those going to other 
 houses, a whole neighborhood may be stricken. Sanitary 
 experts say that milk bottles should not be left at an in- 
 
452 SANITATION 
 
 fee ted house at all, but that the milkman should pour the 
 milk, out of doors, into vessels belonging to the house. 
 
 How shall a person having a dangerous germ disease be isolated? 
 In some cases it may be best for him to go to a hospital for contagious 
 diseases; in other cases he may be left in his own house, with his nurse, 
 but all other persons may be required to leave the house. In some 
 cases only room isolation, or confinement in a certain room, is advised. 
 In room isolation the cracks about the doors and transoms leading to 
 the remainder of the house should be closely sealed, and the nurse 
 should not mingle with the family. But room isolation is usually 
 unsatisfactory and dangerous, because it is not properly carried out, 
 and is not a real isolation. Real isolation in a room is not ordinarily 
 possible unless the house is a large one, and is so arranged that the 
 patient and the nurse can be removed to a really separate part of it. 
 
 The illustrations already given show us that the real value of isola- 
 tion, like that of other sanitary measures, depends on how it is carried 
 out. If we elect officers to provide a good quarantine, we must support 
 them when they are obliged to use force with some persons who refuse 
 to observe quarantine. Furthermore, we ourselves must obey the 
 regulations of our health department, not merely in the letter, so that 
 we may just escape punishment, but in the spirit, because we recognize 
 the fact that they are for the greatest good of all the people. 
 
 438. Disinfection. We have already learned (cf. 
 423) that disinfection means the destruction of harmful 
 germs. It applies to such familiar operations as the 
 boiling of milk and water, the filtering of water, and the 
 washing of hands and clothing, as well as to the treatment 
 of a wound with carbolic acid, or the fumigation of a room 
 with burning sulphur. Preservatives are disinfectants 
 put into food (cf. 425). 
 
 The need of careful disinfection during and after dis- 
 ease is much greater than people realize; because disin- 
 
DISINFECTION 453 
 
 fection is neglected, preventable diseases continue to 
 attack mankind. Some of the methods of disinfection 
 for particular diseases have already been suggested. 
 Thus, the sputum of a person having consumption or 
 pneumonia ought to be burned (cf. 429 and 436); the 
 cloths containing the discharges from the nose and throat 
 during scarlet fever and measles ought to be boiled in hot 
 water; dishes used by a patient, even if he has "only a 
 cold/' ought to stand in boiling water for some minutes, 
 so that the germs adhering to them may be entirely 
 destroyed. The need of disinfecting the body waste of 
 typhoid patients has not yet been appreciated sufficiently ; 
 it is through these wastes that water is polluted, and that 
 the disease is spread (cf. 427). Experience has taught 
 men that direct sunlight is an excellent germicide, hence 
 they have, from time immemorial, hung clothing and 
 bedding in the sunlight for disinfection. Of course a large 
 part of the disinfection that is carried out "in the open" 
 is due to air (cf. 58). Long-continued drying destroys 
 germs, as it does other living things. One way in which 
 salt acts as a preservative is that it removes water from 
 the cells of the germs that cause decay. Long-continued 
 cold also destroys germs ; strange as it may seem, explorers 
 in polar regions are not troubled with colds ; the germs of 
 colds cannot live there. 
 
 Substances having poisonous properties are also used to destroy 
 germs. One of the most frequently used of these chemical disin- 
 fectants is mercuric chloride. This is a compound of mercury and 
 chlorine; it is also known as bichloride of mercury and as corrosive 
 sublimate. It may be purchased in tablets that dissolve readily in 
 water. The " strength" of the solution is usually 1 part, by weight, 
 
454 SANITATION 
 
 of mercuric chloride to 1,000 parts of water. Common salt is mixed 
 with the mercuric chloride before the water is added. The solution is 
 very poisonous if taken internally, but it is very efficient in destroying 
 germs that are on the hands, on washable clothing, and on floors. 
 Mercuric iodide, a compound of mercury and iodine, is an even better 
 disinfectant than mercuric chloride, especially for surgical instru- 
 ments. It is mixed with potassium iodide to make it soluble. Its 
 ordinary name is biniodide of mercury. Strong acids and alkalies are 
 powerful disinfectants, but they are not used as much as they might 
 be because they act upon skin, clothing, etc. The most common acid 
 used in natural disinfection is the hydrochloric acid of the stomach 
 (cf. 364). In artificial disinfection carbolic acid is used. In winter, 
 carbolic acid is usually a solid; in summer it is a thick liquid. The 
 solid melts readily if it is set in a pan of warm water. The carbolic 
 acid disinfecting solution contains 2.5 to 5 grams of the acid in 100 
 grams of water. This would be 2 to 3 tablespoons full of acid to a pint 
 of water. The most common base, or alkali, used in disinfection is 
 "milk of lime" (cf. 132). Lye is also used. The disinfectant known 
 as chloride of lime, or "bleaching powder" (cf. 110), is made by 
 passing chlorine into slaked lime. 
 
 To disinfect a house by fumigation, gaseous germicides 
 are used. The two most common ones are sulphur 
 dioxide and formaldehyde. The sulphur dioxide is com- 
 monly made by the burning of sulphur "candles." The 
 candles used do not as a rule give enough sulphur dioxide 
 to destroy the germs ; they are also a source of danger, for 
 they may set the house on fire. Sulphur dioxide gas can 
 be obtained more safely if liquid sulphur dioxide, or the 
 solution of the gas, is poured out in saucers, and allowed 
 to evaporate. Sulphur dioxide is used to destroy vermin, 
 as well as germs. Formaldehyde is a compound of car- 
 bon, hydrogen, and oxygen (cf. 123) ; it is a much better 
 germicide than sulphur dioxide. One of the easiest ways 
 
SUMMARY 455 
 
 of getting the gas into a room is to sprinkle 40% ' ' forma- 
 lin " solution (a solution containing formaldehyde) upon 
 sheets placed in the room to be disinfected. The sheets 
 may be hung upon clothes lines. The room should be 
 closed tightly for several hours to give the disinfectant 
 time to complete its work. Separate articles may be 
 disinfected by placing them in a trunk, between cloths 
 wet with formalin solution. 
 
 Many accidents occur every year because some people 
 keep disinfectants in the family medicine closet, or have 
 them about the house, without a warning label. All such 
 substances should be kept by themselves, in a locked case, 
 and should be distinctly marked. They should also be 
 colored by the addition of a tiny amount of some bright 
 dye, so that no one will mistake them for something else. 
 
 439. Summary. Contagious diseases are caused by germs. Germs 
 may be bacteria or protozoa. The science of germs is bacteriology. 
 
 Hygiene is the science of keeping the body in good health; sanita- 
 tion deals especially with the health of the community.. 
 
 Germs grow in the body because they find favorable conditions 
 there. The body's defenders against germs that are in the blood are 
 the white corpuscles and the germicides. 
 
 The effect of germs is due to the toxins which they produce. From 
 the time we are exposed to a disease until we "come down" with it, the 
 germs are multiplying; this is the incubation period. 
 
 Germs can be destroyed, outside of the body, by cleansing the 
 body and its surroundings, by removing dust, by letting light and air 
 into our houses, and by disinfectants. 
 
 Disinfection is the destruction of harmful germs. Fumigation is 
 disinfection by gases. 
 
 Flies hatch in filth, visit dirty places, and infect our surroundings 
 and our food. Houses should be screened against them, those inside 
 
456 SANITATION 
 
 houses should be killed, and the neighborhood should be kept clean, sa 
 that they will not find food or breeding places. 
 
 Mosquitoes hatch in water, and live in damp places. One variety 
 carries malaria germs, another the germs of yellow fever. Their 
 breeding places should be destroyed. 
 
 . Food should be handled only with clean hands, and should be 
 stored only in clean places. Tainted food should be destroyed. Food 
 exposed to the dusty air of a city street will be infected. 
 
 Infected milk may spread consumption, typhoid fever, scarlet fever, 
 etc. Milk should be kept cold in summer. If it is suspected of in- 
 fection, it should be pasteurized. 
 
 Preservatives are disinfectants put into food. They should not be 
 used, as they injure the body. 
 
 Public drinking cups, money, public towels and soap, and pencils 
 that have been in somebody's mouth, are infected. 
 
 Typhoid fever germs enter the body through the digestive tract, 
 and develop in the small intestine. 
 
 Tuberculosis attacks the lungs of most people at some time or other. 
 It can be cured, if treated soon enough, by fresh air, sufficient clothing, 
 and nourishing food. 
 
 Spitting in public is dangerous to public health. 
 
 Colds should not be despised, but cured. 
 
 Diphtheria is often scattered by a healthy person who has the germs 
 in his throat, and who infects milk, drinking cups, dishes, etc. 
 
 Antitoxins are substances produced by the body to neutralize toxins. 
 
 Smallpox is an eruptive disease; it is prevented by vaccination. 
 " Vaccine virus" contains weakened germs; these stimulate the body 
 to produce the proper germicide. 
 
 Some other germ diseases are scarlet fever, measles, pneumonia, 
 yellow fever, tetanus, and rabies. 
 
 Quarantine is the isolation of infected persons or goods; it is neces- 
 sary for public health. 
 
 Health regulations should be observed and respected. 
 
 Disinfection destroys germs after a disease, so as to prevent a 
 repetition of the disease. 
 
 Chemical disinfectants are corrosive sublimate, carbolic acid, milk 
 of lime, chloride of lime, sulphur dioxide, formaldehyde, etc. 
 
EXERCISES 457 
 
 Disinfectants should be separated from medicines, so that they may 
 not be swallowed by mistake. 
 
 440. Exercises. 
 
 1. Give some of the objections to smoke in the air of cities. 
 
 2. If you remember that plants and animals build up complex 
 materials out of simple foods, what does the work of bacteria and 
 ferments seem to be? What, then, is the function of bacteria in the 
 economy of Nature? 
 
 3. What are the objections to the making of clothing in " sweat 
 shops" and in houses where families live? 
 
 4. What effect has the density of the population upon health and 
 the length of life? 
 
 5. Suggest how it is possible that the city may be made more health- 
 ful than the country. 
 
 6. To what danger are men exposed who work in factories where 
 metal articles are ground or filed? 
 
 7. What is the advantage, to a city, of a hospital for persons having 
 contagious diseases? What does your town or community do with its 
 smallpox patients? 
 
 8. Some people contend that rats and mice, like flies, are scavengers, 
 and are therefore useful to man. Are they economical scavengers from 
 the community's point of view? 
 
 9. Suggest how a house may be placed so as to get the greatest 
 possible amount of winter sunshine. 
 
 10. Give the objections to having unlighted clothes closets in a 
 house. 
 
 11. Medical books state that the period of isolation for scarlet fever 
 should be six weeks; what is the practice in your community? Is it 
 possible for a child in your community to go to school while another 
 child in the same house has scarlet fever? 
 
 12. Ask a physician or health officer about the number of cases of 
 infectious diseases in your town in the course of a year. Can you find 
 any reasons for the change in number from month to month? 
 
 13. Is inoculation ever used to protect animals from disease? Give 
 instances. 
 
458 SANITATION 
 
 14. In what sense is the growing of clover, alfalfa, etc., an inocula- 
 tion of the soil? (Cf. 56). 
 
 15. How does the formation of toxins in the soil resemble their 
 production in the blood? 
 
 16. If you were planning to disinfect a room with formaldehyde, 
 suggest how you would place books, so that the germicide could really 
 get at them; closets; bureaus and dressers; bedding; clothing. What 
 precautions would you take regarding cracks around doors, etc.? 
 
 17. Why does a dilute sugar solution, such as a fruit sauce, need to 
 be so carefully sterilized and kept away from the air, while a con- 
 centrated sugar solution, such as a preserve, does not? 
 
 18. Would you say that sanitary housekeeping is a simple or a 
 complex problem? Is it worth while? 
 
APPENDIX 
 
 TABLE I. THE METRIC SYSTEM. 
 
 1. Length. The unit of length is the meter (39 . 37 in.). 
 
 10 millimeters (mm.) = 1 centimeter (cm.). 
 10 centimeters =1 decimeter (dm.). 
 
 10 decimeters = 1 meter (m.). 
 
 1,000 meters = 1 kilometer (km.). 
 
 Note that the prefix "milli-" means 0.001, as mi7Z = 0.001 dollar; 
 "centi-" means 0.01, as cent = 0.01 dollar; "deci-" means 0.1, as 
 dime = Q. 1 dollaj. "Kilo-" means 1,000. 
 
 2. Square Measure, or Area. 
 
 100 square millimeters (sq. mm.) =1 sq. centimeter (sq. cm.). 
 100 square centimeters = 1 sq. decimeter (sq. dm.). 
 
 100 square decimeters =1 sq. meter (sq. m.). 
 
 3. Cubic Measure, or Volume. The unit of volume is the liter, 
 
 which is 1 cu. dm., or 1,000 c.c. 
 
 1,000 cubic millimeters (cu. mm.) = l cubic centimeter (c.c.). 
 1,000 cubic centimeters =1 cubic decimeter (cu. dm.). 
 
 1 cubic decimeter =1 liter (1.). 
 
 10 liters = 1 dekaliter (dl.). 
 
 10 dekaliters =1 hectoliter (hi). 
 
 10 hectoliters = 1 kiloliter (kl.). 
 
 4. Weight. The gram is the weight of 1 c.c. water at 4C.; 1 liter of 
 
 water at 4C. weighs 1 kilogram. 
 10 milligrams (mg.) =1 centigram (eg.). 
 10 centigrams =1 decigram (dg.). 
 
 10 decigrams = 1 gram (g.). 
 
 1,000 grams =1 kilogram (kg.). 
 
 1,000 kilograms = 1 metric ton. 
 
 459 
 
460 APPENDIX 
 
 TABLE II. EQUIVALENTS. 
 
 1. Length. 
 
 1 centimeter =0.3937 in. 
 
 1 meter = 39 . 37 in. = 3 . 28 ft. 
 
 1 kilometer = 1,000 m. = . 6214 mile. 
 
 1 inch =2.54 cm. 
 
 Ifoot = 0.3048m. 
 
 1 mile = 1 . 6094 km. 
 
 2. Area. 
 
 1 sq. cm. =0. 155 sq. in. 
 
 1 sq. m. =10.764sq. ft. = 1.196 sq. yd. 
 
 100 m. square =10,000 sq. m. = l hectare = 2. 47 acres. 
 
 1 sq. km. = . 385 sq. mile. 
 
 3. Volume. 
 
 1 cu. cm. = 0.061 cu. in. 
 
 1 cu. m. =35.315cu. ft. 
 
 1 liter =1,000 cu. cm. = 1.0567 qt. (U. S.). 
 
 4. Weight. 
 
 1 gram = 15. 4324 grains. 
 
 1 kilogram = 1 ,000 grams = 2 . 2046 Ibs. 
 
 1 metric ton = 1,000 kg. = 2,204. 6 Ibs. 
 
 1 short, or net ton =2,000 Ibs. 
 
 1 long, or gross ton = 2,240 Ibs. 
 
 1 grain - . 0648 gram. 
 
 1 ounce (avoirdupois) = 28 . 35 grams. 
 
 1 ounce (troy) =31 . 1 grams. 
 
APPENDIX 
 
 461 
 
 TABLE III. DENSITIES OF SOME SUBSTANCES. 
 
 Acetic acid* . 
 
 1.053 
 
 Magnesium . . 
 
 1.75 
 
 Alcohol (ethyl)* . 
 
 0.794 
 
 Marble .... 
 
 2.7 
 
 Aluminum . . , 
 
 2.67 
 
 Mercury (at 0C.) . 
 
 13.596 
 
 Brass 
 
 8.3 
 
 Nickel .... 
 
 8.57 
 
 Carbolic acid . 
 
 0.95 
 
 Nitric acid (cone.)* . 
 
 1.42 
 
 Carbon (charcoal) 
 
 1.6 
 
 Oil (cotton seed) 
 
 0.926 
 
 Carbon (gas) . 
 
 1.8 
 
 Oil (linseed) . . . 
 
 0.942 
 
 Carbon disulphide* . 
 
 1.27 
 
 Oil (olive) . . . 
 
 0.918 
 
 Chloroform* . 
 
 1.5 
 
 Oil (turpentine) . 
 
 0.873 
 
 Clay 
 
 1.9 
 
 Phosphorus (yellow) 
 
 1.83 
 
 Coal (anthracite) 
 
 1.26 to 1.8 
 
 Platinum .... 
 
 21.5 
 
 Coal (soft) . . . 
 
 1.2 to 1.5 
 
 Potassium . . 
 
 0.865 
 
 Copper .... 
 
 8.9 
 
 Sand (dry) ... 
 
 1.4 
 
 Cork 
 
 024 
 
 Silver 
 
 10.57 
 
 Diamond .... 
 
 . i 
 
 3.53 
 
 Sodium . . ' . 
 
 0.97 
 
 Ether* .... 
 
 0.72 
 
 Sulphur . . . 
 
 2.03 
 
 Gasoline .... 
 
 0.67 . 
 
 Sulphuric acid (cone.) 
 
 1.854 
 
 Glass 
 
 2.6 to 3.6 
 
 Tin ..... 
 
 7.29 
 
 Glycerine .... 
 
 1.27 
 
 Water at 0C. . . 
 
 0.999 
 
 Gold . , . 
 
 19.3 
 
 Water at 4C. . . 
 
 1.000 
 
 Hydrochloric acid 
 
 
 Water at 100C. . . 
 
 0.958 
 
 (cone.)* . . . 
 
 1.22 
 
 Water (sea) . . . 
 
 1.026 
 
 Ice ..... 
 
 0.918 
 
 Wood (hickory, dry) 
 
 1.00 
 
 Iodine . . . , . 
 
 4.95 
 
 Wood (maple, dry) . 
 
 0.64 
 
 Iron 
 
 7.8 
 
 Wood (white oak, dry) 
 
 0.86 
 
 Kerosene . ... 
 
 0.79 
 
 Wood (white pine, dry) 
 
 0.42 . 
 
 Lead ..... 
 
 11.35 
 
 Zinc 
 
 6.9 to 7.2 
 
 Limestone . . 
 
 3.2 
 
 
 
 At 15 C. 
 
462 
 
 APPENDIX 
 
 TABLE IV. WEIGHT (IN GRAMS) OF A LITER OF THE 
 DRY GAS AT oC. AND 760 MM. 
 
 Air 
 
 1.293 
 
 Marsh gas . " . 
 
 0.717 
 
 Ammonia .... 
 
 0.762 
 
 Nitric oxide . 
 
 1.34 
 
 Carbon dioxide . . 
 
 1.977 
 
 Nitrogen .... 
 
 1.256 
 
 Carbon monoxide 
 
 1.251 
 
 Nitrous oxide 
 
 1.97 
 
 Chlorine .... 
 
 3.18 
 
 Oxygen . . 
 
 1.429 
 
 Hydrochloric acid 
 
 1.61 
 
 Sulphur dioxide . 
 
 2.87 
 
 Hydrogen 
 
 0.0896 
 
 Steam 
 
 0.806 
 
 Hydrogen sulphide . 
 
 1.542 
 
 
 
 TABLE V. THE MELTING POINTS OF SOME SOLIDS. 
 
 Hydrogen 
 
 -256.5C. 
 
 Lead 
 
 327 
 
 Alcohol (ethyl) . . 
 
 -130 
 
 Zinc 
 
 419 
 
 Mercury .... 
 
 -39.5 
 
 Aluminum 
 
 657C. 
 
 Ice 
 
 
 
 Salt 
 
 820 
 
 Olive oil . . . . 
 
 3 
 
 Silver 
 
 961 
 
 Acetic acid 
 
 17 
 
 Copper .... 
 
 1065 
 
 Carbolic acid . 
 
 43 
 
 Gold 
 
 1071 
 
 Paraffin .... 
 
 55 
 
 Cast iron .... 
 
 1200 
 
 Sulphur .... 
 
 114 
 
 Pure iron .... 
 
 1550 
 
 Sugar (cane) . . . 
 
 160 
 
 Platinum .... 
 
 1775 
 
 Tin 
 
 232 
 
 
 
APPENDIX 
 
 463 
 
 TABLE VI. BOILING POINTS OF SOME SUBSTANCES. 
 
 Hydrogen 
 
 252C. 
 
 Alcohol, ethyl 
 
 78 
 
 Liquid air 
 
 -190 
 
 Water 
 
 100 
 
 Acetylene .... 
 
 - 72 
 
 Salt brine (saturated) 
 
 109 
 
 Ammonia .... 
 
 - 33 
 
 Turpentine 
 
 159 
 
 Sulphur dioxide . 
 
 - 8 
 
 Carbolic acid . 
 
 183 
 
 Ether 
 
 35 
 
 Camphor .... 
 
 205 
 
 Chloroform . 
 
 61C. 
 
 Glycerine .... 
 
 291 
 
 Gasoline .... 
 
 70 to 90 
 
 Kerosene .... 
 
 150 to 250* 
 
 TABLE VII. SPECIFIC HEATS. 
 
 Aluminum 
 
 0.214 
 
 Magnesium . 
 
 0.250 
 
 Asbestos .... 
 
 0.195 
 
 Marble .... 
 
 0.21 
 
 Brass 
 
 0.089 
 
 Mercury (solid) . 
 
 0.0319 
 
 Cadmium .... 
 
 0.0567 
 
 Paraffin .... 
 
 0.6939 
 
 Cement .... 
 
 0.20 
 
 Platinum .... 
 
 0.0324 
 
 Charcoal .... 
 
 0.16 
 
 Quartz . ... 
 
 0.188 . 
 
 Diamond .... 
 
 0.459 
 
 Salt 
 
 0.219 
 
 Copper . ... 
 
 0.0952 
 
 Silver 
 
 0.057 
 
 Glass . . . 
 
 0.1988 
 
 Sugar 
 
 0.274 
 
 Gold 
 
 . 0324 
 
 Sulphur 
 
 0.178 
 
 Granite .... 
 
 0.192 
 
 Tin 
 
 . 0562 
 
 Ice 
 
 0.55 
 
 Zinc 
 
 0.0955 
 
 Iron 
 
 0.114 
 
 
 
464 
 
 APPENDIX 
 
 TABLE VIII. VAPOR PRESSURES OF ICE AND WATER 
 AT DIFFERENT TEMPERATURES. 
 
 Temperature 
 
 Pressure in Milli- 
 meters of Mercury 
 
 Temperature 
 
 Pressure in Milli- 
 meters of Mercury 
 
 -10C. 
 
 2.0 
 
 29C. 
 
 29.8 
 
 - 5 
 
 3.0 
 
 30 
 
 31.6 
 
 
 
 4.6 
 
 31 
 
 33.4 
 
 10 
 
 9.2 
 
 32 
 
 35.4 
 
 11 
 
 9.8 
 
 33 
 
 37.4 
 
 12 
 
 10.5 
 
 40 
 
 55.0 
 
 13 
 
 11.2 
 
 50 
 
 92.2 
 
 14 
 
 11.9 
 
 60 
 
 149.2 
 
 15 
 
 12.7 
 
 70 
 
 233.8 
 
 16 
 
 13.6 
 
 80 
 
 355.5 
 
 17 
 
 14.5 
 
 90 
 
 526.0 
 
 18 
 
 15.4 
 
 99 
 
 733.2 
 
 19 
 
 16.4 
 
 99.5 
 
 746.5 
 
 20 
 
 17.4 
 
 100.0 
 
 760.0 
 
 21 
 
 18.5 
 
 111.7 
 
 1,140 
 
 22 
 
 19.7 
 
 120.6 
 
 1,520 
 
 23 
 
 20.9 
 
 133 . 9 
 
 2,280 
 
 24 
 
 22.2 
 
 159.2 
 
 4,560 
 
 25 
 
 23.5 
 
 180.3 
 
 7,600 
 
 26 
 
 25.0 
 
 201.9 
 
 12,160 
 
 27 
 
 26.5 
 
 213 . 
 
 15,200 
 
 28 
 
 28.1 
 
 224.7 
 
 19,000 
 
APPENDIX 
 
 465 
 
 TABLE IX. THE ELEMENTS AND THEIR SYMBOLS. 
 
 Aluminum 
 Antimony 
 
 Al 
 Sb 
 
 Molybdenum . . . 
 Neodymium 
 
 Mo 
 
 Nd 
 
 Argon . 
 
 . . A 
 
 Neon 
 
 Ne 
 
 Arsenic 
 
 .... As 
 
 Nickel 
 
 Ni 
 
 Barium 
 
 . . . . Ba 
 
 Niton (radium emanation) 
 
 Nt 
 
 Bismuth . 
 
 . . . . Bi 
 
 Nitrogen 
 
 N 
 
 Boron 
 
 B 
 
 Osmium 
 
 Os 
 
 Bromine 
 
 Br 
 
 Oxvcen 
 
 o 
 
 Cadmium 
 Caesium 
 
 . . . . Cd 
 Cs 
 
 Palladium 
 Phosphorus 
 
 Pd 
 p 
 
 Calcium 
 
 . . . . Ca 
 
 Platinum 
 
 Pt 
 
 Carbon 
 Cerium 
 Chlorine 
 
 . . . . C 
 . . . . Ce 
 . . . . Cl 
 
 Potassium 
 Praseodymium .... 
 Radium 
 
 K 
 Pr 
 R* 
 
 C hromium 
 
 Cr 
 
 Rhodium 
 
 Rh 
 
 Cobalt 
 
 Co 
 
 Rubidium 
 
 Rb 
 
 Columbium 
 
 Cb 
 
 Ruthenium 
 
 Ru 
 
 Copper 
 
 Cu 
 
 Samarium 
 
 Sm 
 
 Dysprosium 
 
 Dy 
 
 Scandium 
 
 So 
 
 Erbium 
 
 Er 
 
 Selenium .... 
 
 Se 
 
 Europium 
 
 . . . . Eu 
 
 Silicon 
 
 Si 
 
 Fluorine . 
 G adolinium 
 
 ..... F 
 Gd 
 
 Silver 
 Sodium 
 
 Ag 
 
 Na 
 
 Gallium 
 
 Ga 
 
 Strontium 
 
 Sr 
 
 Germanium 
 
 Ge 
 
 Sulphur 
 
 g 
 
 Glucinum 
 
 . . . . Gl 
 
 Tantalum 
 
 Ta 
 
 Gold . . 
 
 . . . . Au 
 
 Tellurium 
 
 Te 
 
 Helium 
 
 . . . . He 
 
 Terbium 
 
 Tr 
 
 Hydrogen 
 
 . . . . H 
 
 Thallium 
 
 T1 
 
 Indium 
 
 In 
 
 Thorium 
 
 Th 
 
 Iodine 
 
 I 
 
 Thulium 
 
 Tm 
 
 Iridium 
 
 Ir 
 
 Tin . . 
 
 Sn 
 
 Iron 
 
 . . . . Fe 
 
 Titanium .... 
 
 Ti 
 
 Krypton . 
 
 . . . . Kr 
 
 Tungsten 
 
 W 
 
 Lanthanum 
 
 La 
 
 Uranium 
 
 Ur 
 
 Lead 
 
 Pb 
 
 Vanadium 
 
 v 
 
 Lithium 
 
 Li 
 
 Xenon 
 
 Xe 
 
 Lutecium . 
 
 Lu 
 
 Ytterbium 
 
 Yb 
 
 M agnesium 
 
 . . . Mg 
 
 Yttrium 
 
 Y 
 
 Manganese 
 
 . . . . Mn 
 
 Zinc 
 
 7,n 
 
 Mercury . 
 
 . . . . Hg 
 
 Zirconium . . . , . 
 
 Zr 
 
466 
 
 APPENDIX 
 
 Bapiqd T ng 
 
 sapixQ 
 
 w 
 
 1 
 1 
 
 eaptpo! 
 
 sapixoipAjj 
 
 sapuonu 
 
 saptu'BXoo.uaj 
 
 saprae.fou.i9j 
 
 Bapiraoag 
 
 s 
 
 <!<j^fflfflOOOOOOMfefe^gggg^;pL l cZM^KMN 
 
APPENDIX 
 
 467 
 
 TABLE XI. HARDNESS OF SUBSTANCES. 
 
 We can compare the hardness of two bodies by rubbing them 
 together; the one having the greater hardness scratches or indents 
 the other. In the scale of hardness bodies usually have positions 
 between 1 and 10. The diamond is the only substance of hardness 
 10 (tf- 119). Substances that can be indented by the finger nail 
 have a hardness of less than 1 . A substance of hardness 6.5 is scratched 
 by a substance of hardness 7, but scratches a substance of hardness 6. 
 The list below is taken from the Smithsonian Tables, as they are given 
 in the "Handbook of Chemistry and Physics," published by the 
 Chemical Rubber Company, Cleveland, Ohio. 
 
 Substance 
 
 Hardness 
 
 Substance 
 
 Hardness 
 
 Talc . ... 
 Rock salt . . . 
 Calcite 
 Fluorite 
 
 1 
 
 2 
 3 
 
 4 
 
 Flint . . . . . 
 Galena. . . 
 Garnet .... 
 Glass 
 
 7 
 2.5 
 7 
 4 5 to 6 5 
 
 Apatite 
 Feldspar 
 Quartz 
 Topaz 
 
 5 
 6 
 
 7 
 8 
 
 Gold 
 Graphite .... 
 Gypsum .... 
 Hematite 
 
 2 . 5 to 3 
 . 5 to 1 
 1.6 to 2 
 6 
 
 Corundum 
 Diamond 
 
 9 
 10 
 
 Hornblende . 
 Iron 
 
 5.5 
 
 4 to 5 
 
 
 
 
 i 
 
 Agate 
 
 7 
 
 Lead .... 
 
 1 5 
 
 Alabaster .... 
 Alum . . 
 Aluminum 
 Amber 
 Anthracite 
 Antimony 
 Asbestos . 
 Asphalt . . . 
 Barite 
 
 1.7 
 2 to 2. 5 
 2 
 2 to 2.5 
 2.2 
 3.3 
 5 
 1 to 2 
 3 3 
 
 Magnetite 
 Marble .... 
 Mica 
 Opal 
 Orthoclase 
 Platinum .... 
 Pyrite 
 Silver 
 Steel 
 
 6 
 3 to 4 
 2.8 
 4 to 6 
 6 
 4.3 
 6.3 
 2.5 to 3 
 5 to 8 5 
 
 Bell Metal . . 
 Beryl . . 
 Bismuth . 
 Brass . . 
 Copper . . . 
 Dolomite . . . 
 
 4 
 7.8 
 2.5 
 3 to 4 
 2.5 to 3 
 3. 5 to 4 
 
 Stibnite .... 
 Sulphur .... 
 Tin 
 Tourmaline 
 Wax (0C.) . . . 
 Zinc 
 
 2 
 
 1.5to2.5 
 1.5 
 7.3 
 0.2 
 2.5 
 
468 
 
 APPENDIX 
 
 TABLE XH. PERCENTAGE COMPOSITION OF FOOD 
 MATERIALS. 
 
 Food 
 
 Water 
 
 Proteid 
 
 Fat 
 
 Carbo- 
 hydrates 
 
 Minerals 
 
 Value of 
 1 Ib. in 
 Large 
 Calories 
 
 Apples .... 
 
 83.2 
 
 0.2 
 
 0.4 
 
 15.9 
 
 0.3 
 
 315 
 
 Beans (dry) . 
 
 12.6 
 
 23.1 
 
 2.0 
 
 59.2 
 
 3.1 
 
 1,615 
 
 Beef (round) 
 
 68.2 
 
 20.5 
 
 10.1 
 
 .... 
 
 1.2 
 
 805 
 
 Beef (sirloin) 
 
 60.0 
 
 18.5 
 
 20.5 
 
 
 1.0 
 
 1,200 
 
 Bread .... 
 
 35.3 
 
 9.2 
 
 1.3 
 
 53.1 
 
 1.1 
 
 1,215 
 
 Butter .... 
 
 10.5 
 
 1.0 
 
 85.0 
 
 0.5 
 
 3.0 
 
 3,410 
 
 Candy .... 
 
 3.0 
 
 .... 
 
 .... 
 
 96.5 
 
 0.5 
 
 1,785 
 
 Cheese .... 
 
 30.2 
 
 28.3 
 
 35.5 
 
 1.8 
 
 4.2 
 
 2,070 
 
 Chicken .... 
 
 72.2 
 
 24.4 
 
 2.0 
 
 
 1.4 
 
 540 
 
 Cornmeal 
 
 15.0 
 
 9.2 
 
 3.8 
 
 70.6 
 
 1.4 
 
 1,645 
 
 Eggs . 
 
 73.8 
 
 14.9 
 
 10.5 
 
 
 0.8 
 
 721 
 
 Fish (salmon) . 
 
 63.6 
 
 21.6 
 
 13.4 
 
 .... 
 
 1.4 
 
 965 
 
 Milk 
 
 87.0 
 
 3.6 
 
 4.0 
 
 4.7 
 
 0.7 
 
 325 
 
 Mutton (leg) . . 
 
 61.8 
 
 18.3 
 
 19.0 
 
 
 0.9 
 
 1,140 
 
 Oatmeal .... 
 
 7.6 
 
 15.1 
 
 7.1 
 
 68.2 
 
 2.0 
 
 1,850 
 
 Oysters .... 
 
 87.1 
 
 6.0 
 
 1.2 
 
 3.7 
 
 2.0 
 
 230 
 
 Peanuts .... 
 
 9.2 
 
 25.8 
 
 38.6 
 
 24.4 
 
 2.0 
 
 2,560 
 
 Pork (fresh) . . 
 
 52.0 
 
 16.9 
 
 30.1 
 
 
 
 1.0 
 
 1,600 
 
 Potatoes (white) 
 
 78.3 
 
 2.2 
 
 0.1 
 
 18.4 
 
 1.0 
 
 385 
 
 Potatoes (sweet) 
 
 69.0 
 
 1.3 
 
 0.6 
 
 28.3 
 
 0.8 
 
 480 
 
 Rice 
 
 12.0 
 
 8.0 
 
 2.0 
 
 77.0 
 
 1.0 
 
 1,700 
 
 Strawberries 
 
 90.4 
 
 1.0 
 
 0.6 
 
 7.4 
 
 0.6 
 
 180 
 
 Sugar .... 
 
 
 
 
 100.0 
 
 . 
 
 1,850 
 
 Tomatoes 
 
 95.3 
 
 0.8 
 
 0.4 
 
 3.2 
 
 0.3 
 
 80 
 
 Walnuts (English) . 
 
 2.8 
 
 16.7 
 
 64.4 
 
 14.8 
 
 1.3 
 
 3,305 
 
GLOSSARY 
 
 abdomen 
 
 (ab-do'-men) 
 
 canine 
 
 (ka-nin') 
 
 acetylene 
 
 (a-set'-i-len) 
 
 capillary 
 
 (kap'-il-a-ri) 
 
 adenoids 
 
 (ad'-e-noid) 
 
 carnivorous 
 
 (kar-niv'-o-rus) 
 
 adventitious 
 
 (ad'-ven-tish'-us) 
 
 cartilage 
 
 (kar'-ti-laj) 
 
 afferent 
 
 (af'-er-ent) 
 
 casein 
 
 (ka'-se-m) 
 
 albumin 
 
 (al-bu'-mm) 
 
 centimeter 
 
 (sen'-ti-me-ter) 
 
 alga 
 
 (al'-ga) 
 
 centrifugal 
 
 (sen-trif'-u-gal) 
 
 ambergris 
 
 (am'-ber-gres) 
 
 cerebellum 
 
 (ser'-e-beT-um) 
 
 ameba 
 
 (a-me'-ba) 
 
 cerebrum 
 
 (ser'-e-brum) 
 
 amorphous 
 
 (a-mor'-fus) 
 
 chloride 
 
 (klo'-rid) 
 
 amylopsin 
 
 (am'-y-lop'-sin) 
 
 chlorine 
 
 (klo'-rin) 
 
 aniline 
 
 (an'-i-lm) 
 
 chlorophyll 
 
 (klo'-ro-fil) 
 
 antitoxin 
 
 (an'-ti-tox'-m) 
 
 chrysalis 
 
 (kris-a-lis) 
 
 aorta 
 
 (a-6r'-ta) 
 
 chyle 
 
 (kil) 
 
 aqueducts 
 
 (ak'-we-dukt) 
 
 chyme 
 
 (kirn) 
 
 aqueous 
 
 (ak'we-us) 
 
 cilia 
 
 (sil'-I-a) 
 
 avoirdupois 
 
 (av'-er-du-poiz') 
 
 clavicle 
 
 (klav'-i-k'l) 
 
 axillary 
 
 (ax'-il-la-ri) 
 
 coagulate 
 
 (ko-ag'-u-lat) 
 
 bacilli 
 
 (ba-sil'-i) ' 
 
 coccyx 
 
 (kok'-six) 
 
 bacteria 
 
 (bak-te'-ri-a) 
 
 cochineal 
 
 (koch'-i-nel) 
 
 barometer 
 
 (ba-rom'-e-ter) 
 
 cocoon 
 
 (ko-koon') 
 
 Bell, Alexander Graham. Born 
 
 composite 
 
 (kom-poz'-It) 
 
 1847. Inventor of the telephone. 
 
 conifer 
 
 (ko'-ni-fer) 
 
 biceps 
 
 (bi'-seps) 
 
 conjunctiva 
 
 (kon'-junk-ti'va) 
 
 bicuspids 
 
 (bi-kus'-pids) 
 
 contagious 
 
 (kon-ta'-jus) 
 
 bilateral 
 
 (bi-lat'-er-al) 
 
 corolla 
 
 (ko-r6T-a) 
 
 biniodide 
 
 (bm-i'-od-id) 
 
 corpuscle 
 
 (kor'-piis'l) 
 
 bronchi 
 
 (bron'-ki) 
 
 cotyledon 
 
 (kot'-i-le'-dun) 
 
 buoyant 
 
 (boi'-ant) 
 
 Crustacea 
 
 (krus-ta'-she-a) 
 
 cactus 
 
 (kak'-tus) 
 
 crystalline 
 
 (kris'-tal-m) 
 
 caisson 
 
 (ka'-son) 
 
 deciduous 
 
 (de-sid'-u-iis) 
 
 calorie 
 
 (kal'-o-ri) 
 
 decimeter 
 
 (des'-i-me'ter) 
 
 calorimeter 
 
 (kal'-o-rim'-e-ter) 
 
 dendrite 
 
 (den'-drit) 
 
 calyx 
 
 (ka'-lix) 
 
 dentine 
 
 (den'-tm) 
 
 
 469 
 
 
470 
 
 GLOSSARY 
 
 Dewar (du'-er) Sir James. Scottish 
 chemist who liquefied gases, espe- 
 cially hydrogen. Born 1842. 
 diaphragm (di'-a-fram) 
 dietetics (di-e-tet'-iks) 
 
 diphtheria (dif-the'-ri-a) 
 dirigible (dir'-i-ji-b'l) 
 
 dynamo (di'-na-mo) 
 
 efferent (ef'-er-ent) 
 
 effervesce (ef-er-ves') 
 electrolysis (e-lek-trol'-i-sis) 
 embryo (em'-bri-6) 
 
 enamel (en-am'-el) 
 
 environment (en-vi'-run-ment) 
 enzyme (en'-zim) 
 
 epidemic (ep'-i-dem'-ik) 
 
 epidermis (ep'-i-der'-mis) 
 epithelial (ep'-i-the'-li-al) 
 
 esophagus (e-sof'-a-gus) 
 fibrinogen (fi-brin'-o-gen) 
 formaldehyde (f6r-mal'-de-hid) 
 Franklin, Benjamin. American in- 
 vestigator, philosopher, and 
 statesman; 1706 to 1790. 
 Galileo (gal'-i-le'-o). Italian as- 
 tronomer and physicist; 1564 to 
 1642. 
 
 Galvani (gal-va'ne). Italian; one 
 of the discoverers of current 
 electricity. Lived 1737 to 1798. 
 ganglia (gan'-gli-a) 
 
 gelatine (jeT-a-tin) 
 
 germicide (jerm'-i-sid) 
 glycogen (gli'-co-jen) 
 
 gymnosperm (jim'-no-sperm) 
 Gray, Elisha. American electrician, 
 and inventor of the telephone; 
 1835-1901. 
 
 Harvey, William. English physi- 
 cian who discovered the circula- 
 
 tion of the blood. Lived 1578 to 
 1657. 
 
 hemoglobin (he'-mo-glo'-bm) 
 hepatica (he-pat'-i-ka) 
 
 herbivorous (her-biv'-o-rus) 
 hibernate (hi'-ber-nat) 
 humerus (hu'-mer-us) 
 
 hydroxide (hi-drox'-id) 
 hygiene (hi'-ji-en) 
 
 hyoid (hi'-oid) 
 
 hypocotyl (hi'-po-cot'-il ) 
 
 immune (i-mun') 
 
 incisor (in-sl'ser) 
 
 incubation (in'-kQ-ba'-shiin) 
 inertia (in-er'-shi-a) 
 
 inoculation (in-6k'u-la'-shun) 
 insulator (m'sQ-la'-ter) 
 
 intestine (m-tes'-tm) 
 
 invertase (in-vert'-as) 
 
 isolation (I'-so-la'-shun) 
 
 Jenner, Edward, M.D. Born 1749 ; 
 died 1823. English investigator 
 and physician. Discoverer of 
 vaccination. 
 
 kilometer (kil'-o-me'-ter) 
 lacteal (lak'-te-al) 
 
 la grippe (la grip') 
 
 larvae (lar'-ve) 
 
 Lavoisier (la'-vwa'-zya/), Antoine 
 Laurent. French chemist; 1743 
 to 1794. Proved that burning in 
 air is union with oxygen, 
 leaven (lev'-en) 
 
 legume (leg'-um) 
 
 Leyden (H'-den) 
 
 lichen (li'-ken) 
 
 Liebig (le'-bik; German "k" is 
 softer than in English) Justus, 
 Baron von. German chemist, 
 1803 to 1873. 
 
GLOSSARY 
 
 471 
 
 lymphatic (lim-fat'-ik) 
 medulla oblongata 
 
 (me-dul'-a ob'-lon-gah'ta) 
 membranous croup 
 
 (mem'-bra-nus krup) 
 meniscus (me-nis'-kiis) 
 
 metatarsal (met'-a-tar'-sal) 
 microbe (mi'-krob) 
 
 millimeter (mil'-i-fne'-ter) 
 monocotyl (mon'-o-cot'-il) 
 Morse, Samuel F. B. American 
 artist and inventor. Lived 1791 
 to 1872. Invented the telegraph, 
 mucous (mu'-kus) 
 
 muriatic (mQr'-i-at'ik) 
 
 myosin (mi'6-sin) 
 
 Newton, Sir Isaac. English philoso- 
 pher, and investigator in physics 
 and mathematics. Lived 1642 
 to 1727. Professor of mathemat- 
 ics at Cambridge University, 
 England. 
 
 nucleus (nu'-kle-us) 
 
 octopus (ok'-to-pus) 
 
 olfactory (61-fak'-to-ri) 
 
 omnivorous (om-niv'-o-rus) 
 opossum (o-pos'-um) 
 
 oxide (6x'-id) 
 
 palate (pal'-at) 
 
 pancreas (pan'-kre-as) 
 
 pancreatic (pan'-kre-at'-ik) 
 papilla (pa-pil'-a) 
 
 paramecium (par'-a-me'-shi-um) 
 Pasteur (pas'-tur') Louis. Lived 1822 
 to 1895. First a chemist, then a 
 founder of bacteriology. Direc- 
 tor of the Pasteur Institute, Paris, 
 patella (pa-teT-a) 
 
 penumbra (pe-num'-bra) 
 perennial (per-en'-i-al) 
 
 periosteum (per'-i-os'-te-um) 
 
 petiole (pet'-i-ol) 
 
 phalanges (fa-Ian'- jez) 
 
 pharynx (far'-inks) 
 
 phenomena (fe-nom'-e-na) 
 
 phosphorus (fos'-for-us) 
 
 photometer (fo-tom'-e-ter) 
 
 pistillate (pis'-ti-lat) 
 
 planets. The planets are heavenly 
 bodies that revolve about the sun. 
 Moons are secondary planets that 
 revolve about the planets, and 
 with them revolve about the sun. 
 The major planets are Mercury, 
 Venus, Earth, Mars, Jupiter, 
 Saturn, Uranus, and Neptune. 
 The mean distance from the earth 
 to the sun is 93,100,000 miles. 
 The distance of Mercury is about 
 0.39 of the earth's distance; that 
 of Venus, about 0.72; that of 
 Mars, about 1.52; of Jupiter, 5.2; 
 of Saturn, 9.54; of Uranus, 19.2; 
 of Neptune, 30. The "year," or 
 time of revolution about the sun, 
 is about 88 days for Mercury, 225 
 days for Venus, 687 days for 
 Mars, almost 12 years for Jupiter, 
 and almost 165 years for Neptune. 
 
 pleura (plu'-ra) 
 
 plumule (ploo'-mul) 
 
 pneumatic (nu-mat'-ik) 
 
 Polaris (po-la'-ris) 
 
 polyp (pol'-ip) 
 
 posterior (pos-te'-ri-er) 
 
 Priestley, Joseph. English writer, 
 clergyman, and chemist. Lived 
 1733 to 1804. Discovered oxygen 
 Aug. 1, 1774. 
 
 proboscis (pro-bos'is) 
 
472 
 
 GLOSSARY 
 
 proteid 
 
 (pro'-te-id) 
 
 stomata (sto'-ma-ta) 
 
 proteose 
 
 (pro'-te-os) 
 
 strychnine (strik'-nm) 
 
 protoplasm 
 
 (pro'-to-plazm) 
 
 sublimate (sub'-li-mat) 
 
 pulmonary 
 
 (pul'-mo-na-ri) 
 
 thermometer (ther-mom'-e-ter) 
 
 puparium 
 
 (pu-pa'-ri-um) 
 
 Torricelli (tor-ri-tchell'-y or 
 
 pylorus 
 
 (pMo'-rus) 
 
 tor'-re-chel'-le). Italian physi- 
 
 pyrometer 
 
 (pi-rom'-e-ter) 
 
 cist; inventor of the barometer. 
 
 python 
 
 (pl'-thon) 
 
 Lived 1608 to 1647. 
 
 quarantine 
 
 (kwor'-an-ten) 
 
 trachea (tra'-ke-a) 
 
 retort 
 
 (re-tort') 
 
 trichinae (tri-kl'-ne) 
 
 salicylic 
 
 (sal'-i-sil'-ik) 
 
 trypsin (trip'-sm) 
 
 salivary 
 
 (sal'-i-va-ri) 
 
 tuberculosis (tu-bAr'-ku-los'-is) 
 
 saponify 
 
 (sa-pon'-i-fl) 
 
 tympanum (tim'-pan-um) 
 
 saprophyte 
 
 (sap'-ro-fit) 
 
 urea (u'-re-a) 
 
 sebaceous 
 
 (se-ba'-shiis) 
 
 vaccmation (vak'-si-na'-shun) 
 
 secrete 
 
 (se-kref) 
 
 vacuum (vak'-u-iim) 
 
 sepal 
 
 (se'-pal) 
 
 vertebra (ver'-te-bra) 
 
 sepia 
 
 (se'-pi-a) 
 
 villi (vil'-I) 
 
 silica 
 
 (sil'-i-ka) 
 
 vitreous (vit're-us) 
 
 siphon 
 
 (si'-fon) 
 
 vitriol (vit'-ri-61) 
 
 solute 
 
 (so-luf) 
 
 Volta (v6r-ta), Alessandro, Count. 
 
 species 
 
 (spe'-shez) 
 
 Italian physicist and discoverer 
 
 spectrum 
 
 (spek'-trum) 
 
 of electric currents; 1745 to 1827. 
 
 spirogyra 
 
 (spi'ro-ji'-ra) 
 
 vorticella (v6r'-ti-ceT-a) 
 
 sputum 
 
 (spu'-tum) 
 
 Watt, James. Scottish inventor; 
 
 stalactite 
 
 (sta-lak'-tlt) 
 
 1736 to 1819. He first made 
 
 stalagmite 
 
 (sta-lag'-mlt) 
 
 instruments at the University of 
 
 stamen 
 
 (sta'-men) 
 
 Glasgow, and then invented the 
 
 staminate 
 
 (stam'-i-nat) 
 
 modern form of the steam engine. 
 
 steapsin 
 
 (ste-ap'-sm) 
 
 whorl (hwurl) 
 
 stipule 
 
 (stip'-ul) 
 
 zymase (zi'-mas) 
 
INDEX 
 
 (NUMBERS DENOTE PAGES) 
 
 Abdomen, 338, 401 
 
 Absorption of light, 155, 162 
 
 Acetic acid, 116, 117, 189 
 
 Acetylene, 114, 142, 227 
 
 Acids, 98, 188, 189, 454 
 
 Acids, action on carbonates, 119, 191 
 
 action on metals, 190 
 
 and coloring matter, 190 
 Acids, classes of, 189 
 
 Acetic, 116, 117, 189 
 
 Butyric, 361 
 
 Carbonic, 117, 265 
 
 Citric, 189 
 
 Hydrochloric, 95, 96, 98, 99, 105 
 
 Inorganic, 189 
 
 Lactic, 189 
 
 Malic, 189 
 
 Nitric, 189, 190 
 
 Oleic, 361 
 
 Organic, 189 
 
 Phosphoric, 189 
 
 Prussic, 116 
 
 Pyrogallic, 166 
 
 Sulphuric, 95, 189 
 
 Tartaric, 116, 189 
 
 Uric, 366 
 
 Acid reaction, 190, 357 
 Adhesion, 28 
 Aeration of water, 81 
 Aeroplane, 184 
 Afferent nerve, 397, 400, 404 
 Air, 4, 21, 38, 39, 46, 56, 64, 72, 81, 
 98, 232, 233, 234, 429 
 
 a non-conductor, 72 
 
 brake, 44 
 
 drainage, 237 
 
 in soil, 270 
 Airship, 184 
 Albumins, 55, 348 
 Alcohol, 56, 116, 119, 188, 355, 388, 
 406 
 
 Algae, 301 
 
 Alimentary canal, 350 
 
 Alkalies, 188, 192, 454 
 
 Alkaline reaction, 192, 352, 357, 361 
 
 Alloy, 8 
 
 Alluvial soil, 270 
 
 Alum, 90 
 
 Amber, 130 
 
 Ameba, 313, 339, 377 
 
 Ammonia, 105, 117, 279 
 
 water, 192, 201 
 Ammonium chloride, 54, 105 
 
 hydroxide, 192 
 
 salts, tests for, 196 
 Amorphous substances, 91 
 Amphibians, 326 
 Amylopsin, 360, 361 
 Anemometer, 245 
 Aneroid barometer, 233 
 Angiosperms, 306 
 Aniline, 116 
 Animalcule, 314 
 Animals, 52, 312, 332 
 Anopheles, 426 
 Anther, 298 
 Anthracite coal, 262 
 Antitoxins, 443 
 Appendix, 358 
 Aqueous humor, 416 
 Arc light, 141 
 Argon, 54 
 Artery, 372, 374 
 Artificial lighting, 223 
 Artificial rocks, 259 
 Assimilation, 361 
 Atmosphere, 38, 41, 56, 232, 234 
 Auricle, 373 
 Axil, 290, 295 
 Axon, 396 
 
 Backbone, 343 
 
 473 
 
474 
 
 INDEX 
 
 Bacteria, 55, 57, 76, 81, 203 
 
 and disease, 425 
 
 in soil, 279 
 Bacteriology, 426 
 Baking powder, 120 
 Balances, 11, 176 
 Ball-and-socket joint, 342 
 Balloons, 41, 99 
 Barnacles, 320 
 Barometer, 39, 233, 249 
 Basalt, 261 
 Bases, 105, 192, 454 
 Battery, 137 
 Bean, 284 
 Bed rock, 258 
 
 Bell, Alexander Graham, 171 
 Bell, electric, 140 
 Bell jar, 47 
 Benzene, 114 
 
 Bichloride of mercury, 453 
 Bile, 358 
 Birds, 329 
 Bivalves, 320 
 Black lead, 110, 142 
 Blacksmith's forge, 113 
 Bladder, 379 
 Blast furnace, 112 
 Bleaching powder, 104 
 Blood, 361, 372, 377, 381 
 
 circulation, 372 
 Blue Vitriol, 90 
 Boat, submarine, 44 
 Body, 1, 5 
 Body circulation, 373 
 
 human, 338 
 Boiler scale, 79 
 Boiling point, 86 
 Bones, 122, 340, 341 
 Borax, 201 
 Brain, 398 
 Bread, 120 
 Bright's disease, 379 
 Brimstone, 106 
 
 (see Sulphur) 
 Bronchial tubes, 384, 385 
 Buds, 294 
 Bulb, 398, 399 
 Bulbs, 296 
 Bunsen burner, 213 
 
 Buoyant force, 33 
 Bureau of Standards, 13 
 Burner, Bunsen, 213 
 Burner, central draft, 224 
 Burning, 39, 46 
 
 glass, 159 
 Butyric acid, 361 
 
 Caissons, 44 
 Calcium carbide, 142 
 
 carbonate, 118, 121, 195, 201 
 
 chloride, 191 
 
 hydroxide, 192, 194 
 
 in soil, 275 
 
 salts, tests for, 196 
 Calorie, 62, 66, 364 
 Calorimeter, 69 
 Calyx, 297 
 Camera, 166 
 Camera, pin-hole, 151 
 Candle, 49, 223, 224 
 
 power, 154 
 Capillaries, 372, 376 
 Capillary action, 30, 49 
 Carbohydrates, 347 
 Carbolic acid, 454 
 Carbon, 110 
 
 dioxide, 51, 94, 117, 118, 119, 120 
 
 disulphide, 106 
 Carbonates, tests for, 195 
 Carbon in soil, 275 
 Carbonic acid, 117, 265 
 Carborundum, 142 
 Carpals, 344 
 Carpels, 297 
 Cartilage, 340 
 Cartridge, 22 
 Casein, 88, 348 
 Casting of metals, 67 
 Caustic potash, 192 
 
 soda, 103, 192 
 Caves, limestone, 122 
 Cavendish, Henry, 96 
 Cell, 313 
 
 Cells and tissues, 339 
 Cells, electric, 136, 137 
 Cellulose, 116 
 Center of mass, 34 
 Centigrade scale, 61 
 
INDEX 
 
 475 
 
 Centrifugal force, 27 
 Cerebrum, 398 
 Charcoal, 51, 112 
 Charring, 110 
 Chemical, changes, 94, 362 
 
 engine, 120 
 China, 260 
 
 Chlorides, tests for, 195 
 Chlorine, 103, 104 
 
 in soil, 275 
 
 Chlorophyll, 104, 164, 286 
 Chrysalis, 323 
 Chyle, 358 
 Cigarettes, 387, 408 
 Cilia, 303, 384 
 Ciliary muscles, 418 
 Circuit, 96, 137 
 Circulation, of air, 218 
 
 of blood, 372 
 Citric acid, 189 
 Clam, 319 
 Clavicles, 343 
 Climate, 232 
 Clothing, 71, 197, 201 
 Clouds, 237, 238 
 Cloudbursts, 240 
 Coagulation, 378 
 
 filters, 82 
 Coal, 110 
 Coal tar, 117 
 Cohesion, 28, 65 
 Coke, 115 
 Colds, 387, 442 
 Cold storage, 85 
 Collision, a source of heat, 73 
 Color, 162 
 
 Coloring matter, 190 
 Combustion, 48 
 Compass, 125 
 Composition of water, 95 
 Compounds, 95, 96 
 Compression of gases, 68 
 Concave, 30 
 Concrete, 260 
 Conduction of heat, 63 
 Conductors, 131 
 Conglomerate, 259 
 Conifers, 306, 308 
 Connective tissue, 340 
 
 Convection, 63, 215, 220 
 
 Convex, 29 
 
 Coral, 122 
 
 Core of earth, 38 
 
 Corn, 277 
 
 Cornea, 417 
 
 Corolla, 297 
 
 Corpuscles, 313, 377, 410, 427 
 
 Corrosion of metals, 190 
 
 Cortex, 291 
 
 Cotton, 116, 201 
 
 Cotyledons, 284 
 
 Crabs, 320 
 
 Cranium, 342 
 
 Crayfishes, 320 
 
 Crearn, 88 
 
 Crops, 277 
 
 Crust of earth, 38, 258 
 
 Crustaceans, 320 
 
 Crystalline lens, 416 
 
 Crystals, 66, 89 
 
 Cultivating, 272 
 
 Current, electric, 136 
 
 Currents and magnetism, 138 
 
 Curvature, 418 
 
 Cyclones, 246 
 
 Cylinder, 23, 42 
 
 Dairying, 277 
 Daniell's cell, 137 
 Davy, Sir Humphrey, 114 
 Daylight, 158 
 Decay, 39 
 Delta, 267 
 Dendrites, 396 
 Density, 31, 32 
 
 of air, 233 
 Dermis, 388 
 Detritus, 264 
 Dextrose, 349 
 Dew, 236 
 Dewar bulbs, 56 
 Dew point, 237 
 Diamond, 110 
 Diaphragm, 338, 382 
 Dicotyl, 285, 291 
 Diet, 363 
 Dietetics, 363 
 Diffraction of light, 163 
 
476 
 
 INDEX 
 
 Diffused light, 158 
 
 Diffusion of gases, 100 
 
 Diffusion of liquids, 101 
 
 Digestion, 94, 350, 361, 362, 376 
 
 Dikes, 263 
 
 Diphtheria, 443 
 
 Dipping needle, 129 
 
 Disc plows, 273 
 
 Discharge of electricity, 132 
 
 Disease, 425, 426, 447 
 
 Disinfection, 429, 452 
 
 Dislocation, 346 
 
 Dispersed light, 155 
 
 Distillation, 80, 87, 115 
 
 Diving bells, 44 
 
 Drainage, 270, 276 
 
 Drift, 266 
 
 Drinking water, 77 
 
 Drop, 29 
 
 Drouth, 271 
 
 Drugs, 367 
 
 Dry cell, 138 
 
 Dry distillation, 116 
 
 Dust, atmospheric, 163 
 
 Dyes, 117, 202 
 
 Dynamo, 143 
 
 Ear, 413 
 
 Earth's crust, 258 
 Earthenware, 260 
 Earthshine, 158 
 Earthworm, 217 
 Echoes, 169 
 Eclipse, 3, 153 
 Economic plants, 307 
 Efferent nerve, 397, 400, 404 
 Effervescence, 118, 191 
 Electric bell, 140 
 Electric charges, 130, 131 
 
 currents, 136 
 
 furnace, 141 
 
 meter, 228 
 
 motors, 145 
 
 power, 145 
 
 stoves and heaters, 214 
 Electrical resistance, 73 
 Electrics, 130 
 Electrolysis, 95 
 Electromagnets, 138 
 
 Electroplating, 142 
 Elements, 97 
 
 in soil, 275 
 
 Elements, number of, 107 
 Embryo, 282, 284, 298 
 Emulsion, 88, 361 
 Endosperm, 285 
 Energy, 24 
 Enzyme, 352 
 Epidermis, 388, 391 
 
 of leaf, 286 
 
 of stem, 291 
 
 Epiglottis, 353, 354, 384 
 Erosion, 268 
 Esophagus, 354 
 Etching, 191 
 Ether, 116 
 
 Eustachian tube, 414 
 Evergreens, 305 
 Excretion, 379, 391 
 Expiration, 381, 382 
 Explosives, 22, 54 
 Eye, 415, 416 
 
 Fats, 116, 198, 223, 347, 358, 361, 
 
 363 
 
 Feldspar, 259, 261, 265 
 Femur, 344 
 Ferment, 352, 356 
 Fermentation, 119, 188, 303 
 Ferns, 301, 304 
 Fertility, 274, 275, 276 
 Fertilizers, 55, 278 
 Fibrin, 378 
 Fibula, 344 
 Filament, 298, 302 
 Filtering, 81, 82 
 Fire, 39, 46 
 Fire-damp, 114 
 
 engine, 43 
 
 Fire, kindling a, 210 
 Fireplace, 211 
 Fishes, 324 
 Flame, 48 
 Flashing point, 115 
 Floating body, 34 
 Floods, 250 
 Flowers, 297, 301, 306 
 Fly, 322, 429 
 
INDEX 
 
 477 
 
 Focus, 46, 159 
 
 Fogs, 86, 237 
 
 Food, 347, 353, 361, 363, 366, 431 
 
 and body heat, 71 
 Foot, 7 
 Force, 21, 24 
 
 centrifugal, 27 
 
 buoyant, 33 
 Forest, 275, 307 
 Formaldehyde, 454 
 Fossils, 259 
 
 Franklin, Benjamin, 133 
 Freezing mixtures, 89 
 Friction, 24, 182 
 
 electric charges by, 130 
 
 and heat, 73 
 Frog, 327 
 Frost, 91, 236 
 Fruits, 299, 307 
 Fuels, 72 
 Fumigation, 429 
 Fungi, 301, 303 
 Furnace, hot air, 64 
 Fuse, 228 
 
 Galileo, 20, 39 
 Gall, 358 
 Galvani, 136 
 Gang plows, 273 
 Ganglia, 397 
 Gas, carbon, 112 
 
 illuminating, 225 
 
 for lighting, 224 
 Gases, 54, 68 
 
 collection of, 45 
 
 expanding, 22 
 
 liquefying of, 68 
 
 properties of, 67 
 Gas meter, 226 
 Gasoline, 115, 214 
 
 engine, 23 
 
 and kerosene stoves, 213 
 Gas-pipes and fixtures, 225, 226 
 Gastric juice, 189, 351, 356 
 Germs, 303, 428, 437, 447 
 Gills, 52, 319, 325 
 Glacial drift, 268 
 
 period, 268 
 
 soil, 270 
 
 Glands, 350, 357, 376, 417 
 Glass, 43, 221, 222, 223 
 Glucose, 349 
 Gluten, 348 
 Glycerine, 199, 366 
 Glycogen, 358, 362 
 Granite, 259, 261, 263 
 Graphite, 5, 110, 142 
 Gravitation, 18 
 Gravity, 17, 18, 22, 29, 268 
 Gravity cell, 137 
 Gray, Elisha, 171 
 Gun cotton, 54 
 Gunpowder, 22, 54, 210 
 Gymnosperms, 291, 305 
 Gypsum, 279 
 
 Habit, 405 
 Hail, 240 
 Hair, 389 
 Halo, 161 
 
 Hardness of water, 79 
 Harvey, 372 
 Hearing, 409, 413 
 Heart, 373, 374 
 Heat, 52, 59, 62, 136 
 
 capacity, 70 
 
 sources of, 72 
 
 use of, by the body, 71, 347 
 Heating, 214 
 
 of air, 234 
 
 hot water and steam, 214 
 
 systems, 220 
 Hemoglobin, 377 
 Hinge joint, 341 
 Hornblende, 259 
 Horse-power, 25 
 Human body, 338 
 Humerus, 344 
 Humidity, 220, 221, 236 
 Humor, aqueous, 416 
 Humus, 269 
 Hunger, 410 
 Hurricanes, 249 
 Hydra, 314 
 
 Hydrants and traps, 209 
 Hydrocarbons, 114 
 Hydrochloric acid, 105, 189 
 Hydrogen, 95, 96, 98, 99, 103 
 
478 
 
 INDEX 
 
 Hydrogen in soil, 275 
 
 peroxide, 50 
 
 sulphide, 106 
 Hydrophobia, 449 
 Hydroxides, 192 
 Hygiene, 426 
 Hypocotyl, 285 
 
 Ice, 83, 84 
 
 box, 64 
 
 Igneous rocks, 262, 263 
 Illuminating gas, 116, 225 
 Image, 151, 157, 415 
 Incandescent mantles, 225 
 Inch, 7 
 
 Incidence, angle of, 156 
 Inclined plane, 174, 180 
 Induction, 127, 132 
 Inertia, 26 
 Infection, 429 
 Ink stains, 204 
 Inoculation, 445 
 Insects, 322 
 Inspiration, 381 
 Insulation, 228 
 Insulators, 131 
 Intestines, 357 
 Iris, 417 
 Iron, 50, 265 
 
 in soil, 275 
 
 rust, 204 
 
 salts, tests for, 195 
 Irrigation, 43, 273 
 Isobars, 251 
 Isotherm, 255 
 
 Joints, 341 
 
 Keramics, 260 
 Kerosene, 115 
 
 lamps, 224 
 
 stoves, 213 
 Kidneys, 366, 379 
 Kilowatt, 229 
 Kindling, a fire, 210 
 
 temperature, 68 
 Kite, 184 
 
 Lachrymal glands, 417 
 Lacteal glands, 358 
 
 Lactic acid, 116, 189 
 Lampblack, 112 
 Lamps, kerosene, 224 
 Land plaster, 278 
 Larynx, 383, 384 
 Laundry, 197 
 Lavoisier, 46 
 Lava, 261 
 Law of winds, 245 
 Lead, 190, 209 
 Leaves, 285, 286, 288 
 
 work of, 287 
 Legumen, 348 
 Lens, 159, 416 
 Lever, 174, 176, 177, 345 
 Levulose, 349 
 Leyden jar, 133 
 Lichens, 304 
 Liebig's condenser, 80 
 Ligaments, 341, 345, 418 
 Light, 141, 151, 159,429,453 
 
 in the house, 221 
 
 intensity of, 153 
 
 waves, 9 
 Lighting, acetylene for, 227 
 
 artificial, 223 
 
 electric, 228 
 
 gas for, 224 
 Lightning, 134 
 Light-year, 10 
 Lime, in soil, 279 
 
 kiln, 123 
 
 slaked, 192 
 Limewater, 51, 118 
 Limestone, 121, 259, 261, 340 
 
 in soil, 279 
 Linen, 201, 307 
 Linseed oil, 203 
 Liquefying of gases, 68 
 Liquid air, 56 
 Liquids, 66 
 Liquid, surface of, 29 
 
 ammonia, 84 
 Liter, 9 
 Litmus, 190 
 Liver, 357, 358 
 Lizard, 329 
 Loam, 269 
 Lobster, 321 
 
INDEX 
 
 479 
 
 Lodestones, 125 
 
 Luminous bodies, 150 
 
 Lungs, 52, 376, 379, 380, 381 
 
 Lye, 192, 200 
 
 Lymph, 350, 366, 373, 378, 379 
 
 Machines, 174 
 Magnesium in soil, 275 
 Magnetic, field, 127 
 
 poles, 128 
 Magnets, 17, 125 
 Magnifying lens, 165 
 Malic acid, 189 
 Maltose, 349, 361, 362 
 Mammals, 331, 338 
 Man, 334, 338 
 Manganese dioxide, 50 
 Manometer, 226 
 Mantle, incandescent, 225 
 
 rock, 256, 258 
 Maple, 294 
 Marble, 122, 191, 262 
 Marsh gas, 114 
 Mass, 18, 20, 32 
 
 center of, 34 
 Match, 6, 69 
 Matches, friction, 210 
 
 parlor, 210 
 
 safety, 211 
 Matter, 4 
 Measles, 448 
 Medulla oblongata, 398 
 Memory, 405 
 Mercuric iodide, 454 
 Meniscus, 30 
 Mercuric oxide, 46, 49, 
 Mercury, 29, 40, 46, 56 
 
 chloride, 453 
 
 fulminate, 22 
 Metacarpals, 344 
 Metals, 98 
 
 corrosion, 190 
 
 oxides, 190 
 
 Metamorphic rocks, 262, 263 
 Metamorphosis, 322 
 Metatarsals, 344 
 Meteorology, 249 
 Meter, 7, 8 
 
 Meter, electric, 228 
 
 gas, 226 
 
 water, 209 
 
 Metric system, 7, 9, 12, 13 
 Method, scientific, 2, 3 
 Mica, 221, 259 
 Microbes, 303 
 Microscope, 165 
 Midbrain, 399 
 Mildew, 304 
 Milk, 88, 432 
 Mind, 399, 410 
 Minerals, 98, 347 
 Mirrors, 156 
 Mixtures, 97 
 
 Modern conveniences, 207 
 Modified leaves, 288 
 Moisture of air, 235 
 Moisture in air, need of, 220 
 Molecules, 60 
 Mollusks, 319 
 Monsoons, 246 
 Moonlight, 150, 158 
 Mordants, 203 
 Morse, S. F. B., 140 
 Mortar, 123 
 
 Mosquito, 323, 426, 429 
 Mosses, 301, 304 
 Moths, 323 
 Motors, electric, 145 
 Mould, 304 
 Mouth, 351 
 Mucus, 350 
 Muriatic acid, 105 
 Muscle, 340, 344 
 Mushrooms, 304 
 Mussel, 319 
 Myosin, 348 
 
 Nails, 389 
 Natural gas, 114 
 Nature, 1 
 Nerve cells, 396 
 
 tissue, 340, 396 
 Nervous system, 395, 402 
 Neuron, 396, 404 
 Neutralization; Salts, 193 
 Newton, Sir Isaac, 17, 161 
 Niagara, 261 
 
480 
 
 INDEX 
 
 Nitrates, tests for, 195 
 Nitric acid, 189, 190 
 Nitrogen, 47, 53 
 
 in fertilizers, 279 
 
 in soil, 275, 277, 279 
 Nitroglycerine, 54 
 Nodes, 289 
 Noise and tone, 170 
 Nose, 383 
 Nucleus, 303, 313 
 Number of elements, 107 
 
 Obsidian, 288 
 Oils, 198, 349 
 Oleic acid, 361 
 Opaque bodies, 150 
 Opium, 367 
 Ores, 112 
 Organs, 3 
 Ounce, 12 
 Ovary, 298 
 Ovule, 298 
 Oxidation, 48, 52 
 Oxides, 48 
 
 of metals, 190 
 Oxygen, 46, 49, 50, 95, 96, 164 
 
 in soil, 275 
 Oyster, 319 
 
 Paint, 112, 203 
 Palate, 354, 384 
 Pancreas, 357, 359 
 Paper, 116 
 PapiUae, 389 
 Paraffin, 115, 204 
 Paramecium, 314 
 Parasite, 303 
 Patella, 344 
 Patent medicines, 367 
 Pearls, 320 
 Pelvis, 343 
 Penumbra, 153 
 Pepsin, 356, 359, 361 
 Peptones, 359, 362 
 Percussion, 22 
 Pericardium, 373 
 Periosteum, 340 
 Perspiration, 71, 389, 391 
 Petiole, 285 
 
 Petroleum, 114 
 Phalanges, 344 
 Pharynx, 353, 383 
 Phenomena, 2 
 Phosphates, 278, 340 
 
 tests for, 195 
 Phosphoric acid, 189 
 Phosphorus, 53, 210 
 
 in soil, 275, 277 
 
 oxide, 53 
 
 sulphide, 211 
 Photography, 195 
 Photometer, 154 
 Physical changes, 94, 265 
 Physical states of matter, 65 
 Physiology, 338 
 Pisa, Leaning Tower of, 19, 20 
 Pistil, 298 
 Piston, 23, 42 
 Pitch, 170, 386 
 Pith, 291 
 Planets, 27 
 
 Plants, 57, 266, 282, 283, 301, 307 
 Plasma, 377 
 Plaster, 123 
 Platinum, 96 
 Plexus, 401 
 Plowing, 271 
 Plumbing, 209 
 Plumbline, 20 
 Plumule, 285 
 Pneumatic hammer, 44 
 Pneumonia, 448 
 Polaris, 10 
 Poles of battery, 96 
 Pollen, 297, 298 
 Polyps, 315 
 Pons, 399 
 Porcelain, 260 
 Potash, 191 
 Potassium, carbonate, 191, 194 
 
 chlorate, 49 
 
 chloride, 191 
 
 hydroxide, 192, 194 
 
 in fertilizers, 278 
 
 in soil, 275, 277 
 
 permanganate, 50 
 
 salts, tests for, 196 
 Pound, 12 
 
INDEX 
 
 481 
 
 Power, 25 
 Preservation, 435 
 Pressure, atmospheric, 39 
 
 of air, 233, 248 
 
 reduced, 87 
 
 standard, 40 
 Priestley, 46 
 Printer's ink, 112 
 Prism, 160 
 Properties, 5, 6 
 Proteids, 55, 347, 356, 362 
 Proteoses, 356, 362 
 Protoplasm, 286, 302, 377 
 Prussic acid, 116 
 Ptomaines, 428 
 Ptyalin, 352, 359, 361 
 Pulley, 174, 178 
 Pulmonary circulation, 373 
 Pulse, 375 
 Pumice, 261, 263 
 Pumps, 39, 41, 42, 43 
 Pupa, 323 
 Pylorus, 355 
 Pyrometer, 14 
 Pyrogallic acid, 166 
 
 Quarantine, 450 
 Quarter sawing, 293 
 Quartz, 259, 261 
 Quicklime, 94, 192 
 
 Rabies, 449 
 Radial sawing, 292 
 Radiation, 63 
 Radius, 344 
 Rain, 57, 240 
 Rainbow, 161 
 Rainfall, 241, 250 
 Rain gauge, 241 
 Reaction, alkaline, 192 
 Receptacle of flower, 297 
 Reduced pressure, 87 
 Reflected light, 155, 156 
 Reflection, angle of, 156 
 Reflex action, 404 
 Refraction, of light, 158 
 
 of sound, 159 
 
 Relative humidity, 236, 237 
 Rennin, 356, 359 
 
 Reptiles, 328 
 
 Reservoirs, 274 
 
 Residual mantle rock, 266 
 
 Residual soil, 270 
 
 Resistance, 141, 142 
 
 Respiration, 39, 51, 52, 376, 379 
 
 Retina, 415, 417 
 
 Retort, 47 
 
 Ribs, 343 
 
 Rocks, 258, 259, 260 
 
 Rock salt, 102 
 
 Roots, 295 
 
 Rootstock, 291 
 
 Rotation of crops, 277 
 
 Rusting, 39, 48, 50 
 
 Safety lamp, miner's, 114 
 
 Sailboat, 182 
 
 Sal ammoniac, 105 
 
 Sal ammoniac cell, 138 
 
 Saliva, 351 
 
 Salt, 87, 89, 90, 91, 102, 349 
 
 Salts, 193, 194 
 
 tests for, 194, 195, 196 
 Sand blast, 43 
 Sand dune, 265 
 Sandstone, 259 
 Sap, 294 
 Saprophyte, 303 
 Saturation, 235 
 Scapulas, 343 
 Scarlet-fever, 447 
 Science, 1, 3 
 
 general, 3 
 
 Scientific method, 2, 3 
 Screw, 174, 181 
 Secretion, 351, 366, 377, 379 
 Sedentary soil, 270 
 Sedimentary rocks, 261 
 Seeds, 297, 298, 299, 301 
 Sense organs, 399 
 Senses, special, 409 
 Sepals, 297 
 Separator, dairy, 27 
 Serum, 444 
 Shadows, 152 
 Shale, 259 
 Sight, 409, 415 
 Silicon in soil, 275 
 
482 
 
 INDEX 
 
 Silk, 204 
 
 Silver chloride, 166, 195 
 
 Silver-plating, 143 
 
 Skeleton, 342 
 
 Skin, 388, 391, 410 
 
 Skull, 342 
 
 Sky colors, 162 
 
 Slaked lime, 118 
 
 Slate, 262 
 
 Slugs, 320 
 
 Smallpox, 444 
 
 Smell, 409, 412 
 
 Smoke, 213 
 
 Snakes, 328 
 
 Snow, 91, 240 
 
 Soap, 79, 197, 198, 200 
 
 Soda, caustic, 103 
 
 washing, 191 
 
 baking, 191 
 
 water, 118 
 Sodium, 103 
 
 carbonate, 198 
 
 chloride ; salt, 191, 194 
 
 hydroxide, 103, 192 
 
 in soil, 275 
 
 nitrite, 54 
 
 salts, tests for, 195 
 Soil, 258, 267, 269, 270 
 Solar plexus, 401 
 Solids, 65 
 Solubility, 89 
 Solute, 87 
 Solutions, 87, 88 
 Solvent, 87 
 Soot, 112 
 Sound, 167, 168 
 
 reflection of, 156 
 
 refraction of, 159 
 
 velocity of, 151 
 Sources of heat, 72 
 Space, 4, 5, 6 
 Specific heat, 70 
 Specific gravity, 31, 32 
 Spectrum, solar, 161 
 Speech, 386 
 Spinal cord, 399 
 Sponges, 315 
 Spore, 302 
 Sprain, 346 
 
 Stains, removal of, 204 
 Stalactites, 122 
 Stalagmites, 122 
 Stamens, 298 
 Starch, 116, 287,349 
 Starfishes, 316 
 
 Stars, apparent position, 158 
 Steam, 85 
 
 engine, 23 
 
 heating, 214, 215 
 Steapsin, 360, 361 
 Stearic acid, 361 
 Stems, 289, 290 
 Sternum, 343 
 Stigma, 298 
 Stipules, 285 
 Stomach, 355 
 Stomata, 286 
 Stoneware, 260 
 Stoves, 210 
 
 electric, 214 
 
 gas, 213 
 
 gasoline and kerosene, 213 
 Stratified rocks, 261, 262 
 Stratum, 261 
 Style, 298 
 Submarine boat, 44 
 Subsoil, 269 
 Substances, 5 
 Sugar refining, 87 
 Sugars, 116, 349 
 Sulphates, 194, 195 
 Sulphur, 5, 51, 106, 210 
 
 dioxide, 51, 106, 454 
 Sulphuric acid, 95, 189 
 Sulphur in soil, 275 
 Sun, 72 
 
 distance of, 9 
 Sunlight, 57 
 
 Suspended substances, 81 
 Switch, electric, 228 
 Sympathetic (nervous) system, 395, 
 400 
 
 Talus, 264 
 Tap root, 295 
 Tarsals, 344 
 Tartaric acid, 189 
 Taste, 409, 411 
 
INDEX 
 
 483 
 
 Teeth, 352, 427 
 Telegraph, 139 
 Telephone, 170 
 Temperature, 62 
 Tendons, 345 
 Testa, 284 
 Tests for salts, 194 
 Tetanus, 449 
 Thermometer, 14, 60, 61 
 Thermos bottles, 56 
 Thermostat, 215 
 Thirst, 410 
 Thorax, 338, 373 
 Thunder, 134 
 Thunderstorms, 247 
 Tibia, 344 
 Tincture, 87 
 Tinder, 210 
 Tissue, 339, 396 
 Tobacco, 387, 406 
 Tonsils, 384 
 Tornadoes, 247, 248 
 Torricelli, 39 
 Touch, 409, 410 
 Toxins, 278, 428 
 Trachea, 354, 383, 384 
 Trade winds, 246 
 Translucent bodies, 151 
 Transparent bodies, 150 
 Traps and Hydrants, 209 
 Trichinae, 364 
 Trolley cars, 145 
 Trypsin, 360, 361 
 Tubercles, 55 
 Tuberculosis, 347, 440 
 
 treatment of, 217 
 Turbines, 146 
 Turpentine, 203 
 Turtle, 328 
 Tympanum, 413 
 Typhoid, 437, 447 
 Typhoons, 249 
 
 Ulna, 344 
 Umbra, 153 
 Units of length, 7, 9 
 Univalves, 320 
 Uric acid, 366 
 
 Vaccination, 445 
 
 Vacuum, 6, 20, 40, 67 
 
 Vaporizer, 214 
 
 Vaseline, 115 
 
 Velocity, 22 
 
 Vein, 372, 374 
 
 Veins, of leaves, 285 
 
 Ventilation, 217, 218, 219, 220 
 
 Ventricle, 373 
 
 Vertebrates, 325 
 
 VilU, 357 
 
 Vinegar, 188 
 
 Vitreous humor, 417 
 
 Voice, 385 
 
 Volcanic conditions, 263 
 
 Volta, 136 
 
 Voltaic cell, 136 
 
 Volume, 6, 7 
 
 Voluntary action, 404 
 
 Vorticella, 314 
 
 Washing, of clothing, 197 
 
 powders, 201 
 
 soda, 191 
 Water, 28, 232, 347 
 
 hardness of, 79, 121 
 
 composition of, 95 
 
 electrolysis of, 95 
 
 expansion, 266 
 
 gas, 225 
 
 hard, 200 
 
 in house and town, 207 
 
 in soil, 270 
 
 occurrence of, 76 
 
 purity of, 77 
 
 Waters, natural, composition of, 77 
 Waterspouts, 248 
 Watt, James, 25, 228 
 Waves, 163 
 Waxes, 223 
 Weather, 232 
 
 Bureau, 249 
 
 forecast, 251 
 
 Weathering of rocks, 264, 265 
 Weather maps, 251 
 Weather service in U. S., 249 
 Wedge, 174, 180 
 Weight, 4, 5, 10, 18 
 Weight, units of, 11, 12 
 
484 
 
 INDEX 
 
 Wells, pollution of, 78 
 
 Wheat, 271 
 
 Wheel and axle, 174, 179 
 
 Whirlwind, 246, 248 
 
 White lead, 203 
 
 Wind, 22, 57, 233, 245, 246 
 
 Windmill, 185 
 
 Wind, use of, 183, 184, 185 
 
 Wood, 116,291,294 
 
 Wood alcohol, 116, 117 
 
 Work, 24, 25 
 
 chemical, 164 
 Worms, 317 
 
 Yard, 7 
 
 Yellow fever, 449 
 Yeast, 119, 188 
 Yeast plant, 303 
 
 Zenith, 159 
 
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