E UC-NRLF E73 MSM GUIDE GIFT OF THE GUIDE SCIENCE FOR THE FIFTH GRADE WITH EXPERIMENTS BY PERCY E, ROWELL, M. S. DIRECTOR OF SCIENCE, THE A-TO-ZED SCHOOL BERKELEY, CALIFORNIA . CALIFORNIA THE A-TO-ZED 1913 ALL RIGHTS RESERVED COPYRIGHT, 1913, BY PERCY E. ROWELL Published July, 1913 MARIN JOURNAL PRESS BAN RAFAEL, CAL,. U. 8. A, PREFACE. This book, the first of a series of four, is written upon the basis that all science must rest upon the broad foundations of general knowledge. Many of the difficul- ties which have beset science teaching in the grades have been due to the fact that only a small field of science has been taught, and that the field has been too minutely studied. To confine the child of a lower grade to a study of a single group of phenomena, just because he is young, is to deprive him of natural opportunities of learning. There is no reason why all branches of science cannot be learned by children, if the beginnings are but presented according to their way of thinking. General knowledge is not necessarily superficial. The science which is most valuable to the child is that which explains the phenomena of the environment the science of common things the science of everyday life. No one branch of science can do this, nor can any one branch of science be properly taught without doing it. A blending of all branches of science, as a means for the best teaching of it in the grades, is inevitable. The teaching of science in the grades has been handi- capped by the supposed necessity for elaborate and cost- ly apparatus. Few of the experiments in this text require even the cheaper apparatus, while most of them do not require anything which really should be called apparatus. The use of common things to illustrate scientific truths 264303 VI PREFACE has also the decided advantage of bringing the science home to the child. He repeats his experiments at home, for he has the "apparatus", and the science becomes his, through the reproduction. The experiments, although very simple, do not merely verify the statements of the text, but they elab- orate and add to it. They are often the source of information, and thus the pupils become imbued with the desire for investigation the true scientific spirit. To obtain the best results the pupils should write up their experiments in brief manner and illustrate their work with simple drawings of the apparatus and objects which have been used. There has been no attempt at an exhaustive study ol any one thing. Many of the sections could he enlarged to produce a book in themselves. The attempt has been made, however, to show the balance which exists between vegetable and animal life, and the underlying principles which govern all animate as well as all inanimate exist- ence. If the conditions are such as to warrant the spe- cial and more comprehensive study of any of the sec- tions, the List for Teachers, which the United States Department of Agriculture has prepared, should be con- sulted. This list covers a vast field, not alone from the agricultural standpoint, but from that of general science. The work is cumulative, always building upon the old and constantly making use of it. Often the foundations for a section are laid many sections before, and thus the science lessons become one whole, a complete blending of the different parts being accomplished naturally, and without apparent effort on the part of the teacher or pupils. PREFACE V'H Teaching the applications of science to the industries and the arts will give the pupils the first insight into their own desires and capabilities. They will thus begin un- consciously to prepare themselves along the line of pre- vocational work. Later they will also realize the dignity of labor, and the science teaching may easily develop into the various branches of vocational work, and the pupils may be given the rare opportunity of viewing the field of human endeavor and of truly choosing their career in life. Many new texts and other publications have been freely consulted in the preparation of this book. Since much of the material has become common property, specific acknowledgment has not been made, but the author takes this opportunity of thanking the many pub- lishers who have so kindly supplied him with reference books. Especial thanks are due Mr. James B. Davidson, Superintendent of Schools of Marin County, California, and Mr. David R. Jones, City Superintendent of Schools of San Rafael, California, both of whom have read the manuscript and have given to the book the benefit of their experience. Thanks are also due Messrs Boggs, Davalos, and Persell who made many of the drawings. Acknowledgement is made through the text for other special obligations. The author alone is responsible for any mistakes which may have crept into the work. PERCY ELLIOTT ROWELL. Berkeley, California. July, 1913 CONTENTS Section Page 1. Time of Sunrise and Sunset . ( . . 1 2. Experiments . . 1 3. Direction. The North , . . . . 2 4. Circular Measurement , . . . . 7 5. Other Directions ; . . . . . 8 6. The Direction of Sunrise and Sunset . . 10 7. Telling Time by the Sun . . . . 12 8. Other Ways of Telling Time ... 13 9. The Height of the Sun at Noon . . .15 10. The Light We Receive from the Sun . . 19 11. The Sunlight Makes Plants Green . . .20 12. Other Changes of Color which are Caused by Sunlight '. ... . . . . . 22 13. The Sunlight Good for Plants and Animals 25 14. Light Travels in Straight Lines . . .26 15. The Reflection of Light . . . . 29 16. Light from Sources Other Than the Sun . 33 17. The Heat we Receive from the Sun . . 39 18. Expansion Due to Heat ' .. . . . 44 19. The Thermometer an Application of Expansion 48 20. Heat Produces Light . .... . . . 53 21. Heat from Friction . . . . . . 54 22. Heat from Combustion . . . . 58 23. Combustibles and Fuels . . . 60 24. Flames . ... . . . 62 25. First Aid to the Burned . . . . 64 26. Conduction of Heat 66 X CONTENTS 27. Air a Necessity of Life . * . . . .71 28. Air in the Soil and in Water- .... 72 29. The Composition of the Atmophere . . 75 30. Oxygen and its Uses . ... . - :' 78 31. Nitrogen and its Uses '.' .-/:..: Op;. ^ . 80 32. Carbon Dioxide .. . . . "".^ .--> . 81 33. Respiration. The Necessity for Pure Air .85 34. Water is a Liquid . ' . . . . .. . 89 35. Water can Pass into Some Things . '. r ' -91 36. Solution and its Oddities . .- "-'.- . 95 37. Crystals ', . . . . . ."..' . 98 38. Water for Drinking . : . . . . 100 39. Water for Cleansing . . . " . ' -. 102 40. Plants Need Water . . .. . : . 105 41. Capillarity . . . . . ... 106 42. The Beginning of Plant Life . : > - ' .113 4(3. The Testing of Seeds . . .: ^-. . 114 44. The Proper Planting of Seeds ~ . '% ' '. 116 45. The Needs of the Plant i| '. / , - ' ., : -'. 118 46. Birds . . . ' / .i . ; . ' '.. ; 'J'. 120 47. Wild and Garden Flowers . . . ' \ 122 48. Trees . . ' .' V ' ". ,'. : \'\ ''^. 123 49. A Queer Plant Yeast . . \\& "\ 127 50. Another Queer Kind of Plant The Bacteria 129 51. Souring and Decay . V . - . | . ". 130 52. Disease and Sanitation ^' , . . '/.f .'. 133 53. The Source of All Food - .-^ . ... ' ; . :. 137 54. The Farm a Workshop .1 ; " ,.:;: I; , . 140 55. Tilling the Soil . . . . ' ^ .141 56. Irrigation and Drainage of Farms , . '. . 144 57. Gardening . .-* '.'... : ?-*!. 1 .- '1 .*.'. 145 CONTENTS XI 58. Simple Measurement .'' V. . . 151 59. Everything Has Weight. The Balance . 154 60. Everything Occupies Space . . . .159 61. Density . . . . . . . .160 62. Drawings './.... V ".:.c>; .. . -. . . 162 63. Forces . ..- * ' '-. ... 164 64. The Plumb-bob and the Pendulum . . . 167 65. The Lever . . . : ... . . 168 66. The Inclined Plane . .' . . .170 67. The Lodestone . . . . . .174 68. Steel Magnets . .' , -, . . . 175 69. Weather Observations . . . . . 182 70. How to Make Blue-print Paper . . 183 71. Solar Heaters . . . .. . . . 184 72. Hot-Air Engines . . . " .- . . 185 73. Fireproofing . .. . .. - . . . 185 74. Waterproofing . ._ : .. ;* * . . . 186 75. Flavoring Extracts and Perfumes .. . . 187 76. To Remove Grease Spots and Stains . . 188 77. How to Make Soap ,.-..... . . 188 78. Bread Making . 1 . . . . 189 79. Alcohol for Industrial Purposes .. . . 19C 80. The Pantagraph . . .. " . . . 191 81. Levelling ' ,\. .. ' '. ; .' .. , . 192 APPENDIX. Reference Books on Birds . . .; '. , 195 Reference Books on Flowers . ^. ... 195 Reference Books on Trees ' . . . .. . 195 List of Apparatus and Materials . . . . . 196 LIST OF EXPERIMENTS. Section Page 3. Expt. 1. To Locate the North by the North . Star 3 Expt. 2. The Movement of the Great Dipper 4 Expt. 3. To Locate the North by Means of Shadows 5 5. Expt. 4. To Locate the South by Means of a Watch ..... 8 6. Expt. 5. The Direction of Sunrise and Sunset 10 Expt. 6. To Record the Direction of Sunset 11 7. Expt. 7. The Sundial 12 8. Expt. 8. The Sand-glass .... 14 9. Expt. 9. The Height of the Sun at Noon by by Shadows . . . . 15 Expt. 10. The Height of the Sun at Noon in Degrees ..... 16 10. Expt. 11. The Appearance of the Sun through Smoked Glass . . 19 11. Expt. 12. The Effect of Sunlight upon Grow- ing Plants . . . .20 12. Expt. 13. Fading and Bleaching ... 22 Expt. 14. Blue Prints of Leaves and other Articles ... . . .23 14. Expt. 15. The Way Light Travels . . 26 Expt. 16. How to Make and Use a Pin-hole Camera . . . . ' . . 27 15. Expt. 17. Reflection from Mirrors . .29 Expt. 18. Diffused Reflection of Light . , 31 LIST OF EXPERIMENTS XIII 16. Expt. 19. Ordinary Sources of Light . .33 Expt. 20. Cold Light : .. ' . . . . 36 17. Expt. 21. The Varying Heat from the Sun . 40 Expt. 22. The Amount of Heat Received by Different Colors .... 42 Expt. 23. The "Burning Glass" ... 43 18. Expt. 24. Heat Causes Expansion . . 44 Expt. 25. The Result of Unequal Expansion 46 19. Expt. 26. How to Read a Thermometer . 50 Expt. 27. Hot or Cold? .;' ... 52 21. Expt. 28. Primitive Fire-making ... 55 Expt. 29. The Flint and Steel Gaslighter . 56 22. Expt. 30. Complete and Incomplete Combus- tion ... . . .59 23. Expt. 31. The Combustion of Different Mate- rials . . . . . . 61 24. Expt. 32. The Cause of Flames . . . 62 25. Expt. 33. Drill for Extinguishing.. Burning Clothing . . . . . . .64 26. Expt. 34. Good and Poor Conductors of Heat 67 27. Expt. 35. Holding the Breath and Deep Breathing / . . . . 71 Expt. 36. The Effect of Depriving a Plant of Air . ... . . 71 28. Expt. 37. To Show the Presence of Air in Soil and Water . . . ." 73 29. Expt. 38. The Amount of Oxygen in the Air 76 Expt. 39. The Amount of Carbon Dioxide In the Air . . . .- 77 30. Expt. 40. To Prepare and Use Oxygen . 78 32. Expt. 41. Carbon Dioxide from Combustion and the Breath 82 XIV LIST OF EXPERIMENTS 33. Expt. 42. The Gapacity of the Lungs . . 86 34. Expt. 43. The Level . .. . ."'. . 89 Expt. 44. Water Seeks its own Level. Size of Drops . . . . . 90 35. Expt. 45. Porous Bodies Absorb Water . 92 Expt. 46. To Make Porous Bodies Waterproof 93 Expt. 47. Filtration . . . . . 93 36. Expt. 48. Solution and its Oddities ., : v 95 Expt. 49. The Use of Gasolene and Alcohol as Solvents . . . . 97 37. Expt. 50. Crystallization . . ., . 98 39. Expt. 51. Hard and Soft Water. Soap . 103 40. Expt. 52. The Effect of Water upon Seeds and Plants . . . .106 41. Expt. 53. Examples of Capillarity . .. 107 Expt. 54. How Water is Held in the Soil . 108 Expt. 55. Capillarity in Plants . /.. . . 110 42. Expt. 56. The "Pocket Garden" .-; . . 113 43. Expt. 57. Germination Tests . . . 114 44. Expt. 58. The Proper Depth of Planting . 116 47. Expt. 59. A Flower Collection . . .122 48. Expt. 60. A "Tree" Collection . ,. . . 125 Expt. 61. Planting Tree Seeds . . .126 49. Expt. 62. Fermentation . . . 128 51. Expt. 63. How to Preserve Milk . . . 131 58. Expt. 64. Measurement . . . ,. 153 59. Expt. 65. Making a Balance and Weighing 156 60. Expt. 66. Displacement of Water by Solids and Air . 159 61. Expt. 67. Density - 161 62. Expt. 68. Blue Prints from Tracings . * 163 LIST OF EXPERIMENTS XV 63. Expt. 69. Weighing by Elasticity . . 165 64. Expt. 70. The Pendulum ... . . 168 65. Expt. 71. The Use of the Lever . . .169 66. Expt. 72. The Use of the Inclined Plane . 170 68. Expt. 73. Magnetic Materials . . . 175 68. Expt. 74. To Draw a Magnetic Field . . 176 68. Expt. 75. Blue Prints of Magnetic Fields . 177 68. Expt. 76. Attraction and Repulsion . .178 74. Expt. 77. Waterproofing . . . .186 77. Expt. 78. Soap Making . " :. . . . 189 79. Expt. 79. Making and Distilling Alcohol . 191 THE GUIDE SCIENCE FOR THE FIFTH GRADE THE SUN, STARS, AND PLANETS. 1. Time of Sunrise and Sunset. Did you see the sun rise this morning? Was it too early for you? Does the sun always rise before you do? What time did the sun set last night? Does the sun always set at that time? Watch the time of sunrise and sunset for several days and keep a record of your results. The days are longer in summer than in winter be- cause the sun rises earlier and sets later than in winter. The longest day of the year is June 21 and the shortest day is December 21. On two days of the year the sun rises at six o'clock in the morning and sets at six o'clock in the evening. These two days are half way between June 21 and December 21. Count the days on a calendar and tell what are the dates of these two days. These days are called the Equinoxes, meaning equal nights. You will discover, if you keep a record of the time of sunrise and sunset, that the sun always rises as much before noontime as it sets after noontime. See Experi- ment 3. Thus the forenoon and the afternoon are of the same length. What can you say of the number of hours between sunset and midnight and the number of hours between midnight and sunrise? 2. Experiments. We can learn from teachers and from books or we Elem. Sci. 1 THE SUN, STARS, AND PLANETS carl le^rn from the things themselves. All of our knowl- edge comes from experience with the actual things which have been studied in the past by those who have written books about them. The use of books, then, saves time for we can read in a few minutes the results of years of study. Our teachers also can help us very much because they have learned from other books, from other teachers, and from things. Wherever it is possible we should study things. We may forget what the books say and what the teacher has said, but we can easily remember what we ourselves have done. Whenever we try to dis- cover from the thing itself how it acts, we are perform- ing an experiment. The best way in which to learn science is by means of experiments, because science is a study of how every- thing acts and why it acts as it does. We may not have our books with us always, and if we can discover from the things themselves what we want to know we shall become independent, and learn without help from books or from teachers. There are many studies which must be learned from books but science is an exception. The record which you are keeping of the time of sunrise and sunset is an experiment. The value of experiments, then, is that we can learn from the very thing what we want to know. 3. Direction. The North. Sometimes it is important to know in what direction you should go in order to arrive at a certain place. In cities and towns the direction can be easily learned from the streets. We are directed to go a certain number of blocks one wav and then a certain number of blocks an- DIRECTION. THE NORTH 3 other way. On the ocean and in the open country, how- ever, where there are no roads, we must depend upon some other method of rinding our way. One method is by means of a star which is so nearly in the north that it is called the North Star. Among all the stars which brighten the sky at night, it would be very hard to find the North Star if there were not a huge sign in the sky which always points to it, ; 'This sign is called the Great Dipper. The two stars which are the farthest from the handle are called the "pointers" because they point to the North Star. Let us try to locate the north by the North Star. To do this we shall perform an experiment. Experiment 1. To Locate the North by Means of the North Star. Materials: Two straight sticks, string. a. Look in the sky until you find the Great Dipper Then glance from one "pointer" past the other "pointer" until your glance has gone beyond it five times the dis- tance between the two pointers. There you will see the North Star. When you look at this star you are looking almost exactly north. b. If we did not make some record of the direction of the North Star we should be unable next day to tell exactly where the north is. To make a record we need two sticks. Drive one stick into the ground in a place from which the North Star is visible. Then go south from this stick about five feet and drive the second stick into the ground in such a position that by looking just past its edge, you can see the North Star just past the edge of the first stick. The two sticks are said to be in 4 THE SUN, STARS, AND PLANETS line with the North Star, because if a line were drawn from one stick to the other, and then extended far enough it would pass to the North Star. A string stretched be- tween the two sticks forms a line which points north. Review Questions, 1. 1. When did the sun rise this morning? 2. How can you tell the time of sunrise by the time of sunset? 3. Why are books valuable? 4. What is an experiment? 5. What are some of the advantages of performing experiments? 6. When should we use books and when should we experiment? 7. How do those who write books learn what to write? 8. How do we direct persons from one place to an- other, in a city? 9. What must we do in the open country, or on the ocean, to know in what direction we are going? 10. Why did you drive two sticks in the ground to make a line pointing north? Could you have done it with one stick? Experiment 2. *The Movement of the Great Dip- per. Apparatus: Rule, scissors, dividers. Materials: Cardboard 6"xl2", paper fastener, or pin and piece of cork. * See Section 62 before performing this experiment THE MOVEMENT OF THE GREAT DIPPER 5 a. Cut the cardboard into two squares 6"x6" and find the center of each piece. To do this lay the rule upon the cardboard so that it crosses it and touches two corners. Make a short line near the center and repeat for the other two corners. Where the two lines meet is the center. Open your dividers so that the points are two and one-half inches apart; place one point upon the center of one piece of cardboard and draw a circle. Upon 6 THE SUN, STARS, AND PLANETS this circle draw the Great Dipper and Cassiopek,. as shown in the illustration, and fasten it by means of a paper fastener, or a pin pushed through the centers into a piece of cork. b. Hold the apparatus so that you must look toward the north in order to see it. Turn the circular piece so that the Great Dipper is in the position in which you saw those stars at eight o'clock last night, and mark with the date the square piece of cardboard where the line comes which passes through the "pointers." c. Look at the Great Dipper at seven o'clock and at nine o'clock. Does it move in the same direction as the hands of a clock or in the other direction ? d. Look at the Great Dipper once a week for a few weeks, and then once a month, always at eight o'clock, and mark the square piece with the date. See how much of the way around the North Star the Great Dipper goes in one month and then tell where you think the Great Dipper will be in six months. Experiment 3. To Locate the North by Means of Shadows. Apparatus: Long nail, board. a. Drive the nail into a level board placed where the sun will shine upon it all day. Mark along the shadow of the nail at nine, ten, and eleven o'clock, in the morn- ing, and at one, two, and three o'clock in the afternoon. Half-way between the shadows which were cast at nine o'clock and three o'clock is north. Half-way between the shadows cast at ten o'clock and two o'clock also is north. The same is true of the other two shadows. Can you discover some rule in regard to the directions of CIRCULAR MEASUREMENT 7 shadows in the forenoon and in the afternoon? Why do you think so many shadows were marked? What would you do if part of the day were cloudy? The north side of trees has the most moss, as a rule, because that side receives the least sunshine and is the wettest. Since moss requires a large amount of moisture it cannot live on the sunny side of trees, unless there is a great deal of rain. 4. Circular Measurement. If you stand in one place and turn around until you face the same way as you did before you began to move, you have made one revolution, or a complete circle. If someone told you to turn one-half or one-quarter the way around you would know how far to turn. Perhaps you could turn one-eighth the way around. If someone wanted you to turn one-sixteenth the way around you probably would not know how far to turn. In order to 8 THE SUN, STARS, AND PLANETS measure any part of a revolution, or a circle, it has been divided into 360 parts called degrees. A degree means a step. The number 360 was chosen because it can be divided evenly by so many numbers. See if it can be divided by 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12. Try divid- ing 360 by other numbers. A semi-circle divided into 180 degrees is called a protractor. It is used to measure the part of a revolution, or circle, which one direction turns from another direction. The short and proper way of writing "degrees" is to use a little circle after the num- ber. For example, 75 degrees may be written 75. This means 75 parts of a circle. 5. Other Directions. If you face the north, the south is behind you ; the east is at your right and the west is at your left. These four points of direction are each a quarter of a revolution, or a quarter of a circle, from the next one. How many degrees between any two of them? How many degrees between the north and the south. If one direction is 183 dgrees from another direction the two directions are said to be opposite each other. Is the east opposite to the west? Why? Experiment 4. To Locate the South by Means of a Watch. a. Hold the watch so that the hour hand points toward the sun. The south direction will then be just half way between the hour hand and the figure XII on the watch. Do this both in the morning and afternoon and see if the result is the same. Can you tell where the north is from this experiment? OTHER DIRECTIONS These four directions, north, south, east, and west are not enough for even ordinary use, so the half- way points are named according to the directions between which they come. The directions north and south are named first, thus : North-east, north- west, south-east, and south - west How many degrees are there between north-east and east? Between north-east and north-west? Between south-east and south-west? Review Questions, 2. 1. Make a drawing of the Great Dipper as it was the last time you saw it, and write the date and hour when you saw it. 2. How often does the Great Dipper seem to go around the North Star? 3. Which side of the house is the driest, the north side or the south side? Why? 4. Is it better to answer the last question after noticing the rooms of a house, or to find the answer in some book? 5. How many degrees are there in half a circle? In a quarter of a circle? If you are walking along a 10 THE SUN, STARS, AND PLANETS street and turn into a side street, how many degrees da you turn? 6. What is a protractor? For what is it used? 7. If you face the south, where is the east? The west? 8. If you are facing east, how much must you turn in order to face north? Would you turn towar.d the left or toward the right? 6. The Direction of Sunrise and Sunset Where did the sun rise this morning"? Where dicf it set last night? Does the sun always rise in the same place? Does it always set in the same place? Where would the shadow of a stick point at sunrise? Where at noon? Where at sunset? An experiment is the best way of answering these questions. Experiment 5. *The Direction of Sunrise and Sun- set by Shadows. Apparatus : Hatpin, protractor. a. Stick a hatpin into the North- South line which you determined in Experiment 1, or in Experiment 3. Mark its shadow at sunrise and at sunset. Place the straight side of the protractor along the North-South line, with its center mark at the hatpin, and tell how many degrees the direction of sunrise is from the North- South line. Repeat for the direction of sunset. The direction of sunset is as much away from the south direc- tion as is the direction of sunrise. See if this is the same after a few days. If this is true we can learn the di- rection of sunrise by knowing the direction of sunset. * This experiment can be performed only at home. THE DIRECTION OF SUNRISE 11 Tile position of the sun varies from day to day, the sun being farther to the south in winter than in sum- mer. The sun rises in the east and sets in the west on two (Jays only. What are those days? How can you find out? Experiment 6. *To Record the Direction of Sunset. a. Use the apparatus of Experiment 5. and arrange your results in the form of a table. Direction should al- ways be measured from the North-South line whenever we wish to be exact. If the direction is just east or just west, we say so. All other directions are given as the number of degrees they are from the north toward the east or west, and from the south toward the east or west. If the direction of sunset is 80 degrees from the north, the record should be : N. 80 W. If it is 70 degrees from the South, the record should be : S. 70 W. What is the difference between N. 90* W. and S.90 W? b. The table for the record should be as follows : Date Direction Once a week is often enough to take the observations. Try it at home and see how your results compare with those of the other pupils. Review Questions. 3. 1. Begin with the direction north, and name the four principal directions, and the half-way directions, all the way around the circle, starting toward the east Now repeat starting toward the west. 2. Where did the sun rise this morning? * This experiment e'art be performed only at home. 12 THE SUN, STARS, AND PLANKTS 3. How can you tell the direction of sunrise by knowing the direction of sunset? 4. On what days does the sun rise at six o'clock and set at six o'clock? 5. How can you tell when it is noon by a shadow? 6. How can you tell where the north is by a shadow? 7. If the sun sets S. 85 W. where does it rise? Make a drawing of this, using the protractor, and obtain your answer from the drawing. 8. If the sun sets N. 80 W. where does it rise? Make a drawing as in the previous question. 7. Telling Time by the Sun. In olden times, before clocks were made, people used to tell time by the sun. Even now there are many persons who can judge the time very nearly, by the posi- tion of the sun in the sky. Yet it is impossible to learn the time from the sun, with exactness, unless we make use of a simple piece of apparatus. Just a stick driven into the ground is all that is necessary. When the shadow points north it is noon. See Experiment 3. When the shadows cast at sunrise and sunset are oppo- site each other the time of each is six o'clock. If the semi-circle on the north side of the stick is divided into twelve equal parts, the shadow will take one hour to pass over each part. These divisions may be marked with the hours between six in the morning and six at night. Over how many degrees does the shadow move in one hour? Experiment 7. The Sundial. Apparatus: Board, protractor, nail. TELLING TIME BY THE SUN 13 a. Draw a circle on a board using the protractor, and divide it into 24 equal parts. How many de- grees are there in each part? Drive a nail into its center so that it makes an angle of 90 with the board, in all directions. You can do this by hold- ing your protractor against the nail as you drive it. Draw a line from the nail lengthwise of the board and place the board so that this line runs north and south. How can you do this? Mark this line 12, where it crosses the circle on the north side, and then mark the other divisions properly Is there any need to mark all of the divisions? Why? What time does the shadow tell in the illustration? 8. Other Ways of Telling Time. The sundial is a good way of telling time on sunny days, but if we want to know the time when the sun is not shining we must use other methods. Long ago the sand-glass, or hour-glass was invented to tell the length of an hour. This was made by connecting two bulbs or globes by means of a small tube and having one glob^ filled with sand. The filled globe was placed on top and the sand slipped slowly through the small hole into the lower globe. When all the sand had left the upper globe an hour had passed. Then the hour-glass was turned up- side down and a record was kept of the number of hours. Why was the name hour-glass given? 14 THE SUN, STARS, AND PLANETS An ingenious scheme of telling time was by means of water. Water was placed in a tank and allowed to flow out through a small hole into a little tank where there was a float made of wood. As the water rose the float rose and indicated the hours by marks on the side of the little tank. Nowadays clocks are used in which wheels are allowed to turn slowly by means of a pen- dulum. See Section 64. Next year we shall study more about clocks. Experiment 8. The Sand-glass, Apparatus: Two small bottles, two stop- pers, a piece of glass tubing J/" diameter, small triangular file, fine sand. a. Bore a hole in the two stoppers for the glass tube and insert the tube in the stoppers with their tops together. The tube should not extend beyond the stoppers. Fill ono. bottle with fine, dry sand, insert the stoppers into the bottles and the sand-glass is finished. b. How long does it take for the sand to run through? Keep changing the amount of sand until it takes exactly one minute, or exactly two minutes for the sand to run through. Is this an hour-glass? A sand- glass made like this and which would run for three and a half or four minutes would be useful for timing the boiling of eggs. THE HEIGHT OF THE SUN AT NOON 15 9. The Height of the Sun at Noon. When is the sun highest in the sky? If the sun is in line with the surface of the earth at sunrise, and grad- ually becomes higher then gradually becomes lower un- til at sunset it is again in line with the surface of the earth, the highest point must have been reached half- way between sunrise and sunset. What time is this? What can you say about the length of shadows at sunrise and at noon? At sunset and at noon? When is the shortest shadow? Is the length of a shadow at noon al- ways the same? If you do not know, how are you going to find out? The varying length of a shadow shows the height of the sun. Experiment 9. The Height of the Sun at Noon by Means of a Shadow. a. Measure the length of the shadow of a window- sill at noon today. b. One week later measure it again. Is it the same? Continue to measure the shadow once a week, keeping a record of the lengths similar to the record used in Experiment 6. Later you will have some ques- tions about this experiment to answer. See Section 69 We can measure the height of trees and buildings and mountains in feet and inches but we cannot measure the height of the sun in this manner. We always meas- ure the height of the sun and stars by the number of de- grees which we have to look upward from the surface of the ocean, or a lake. We call looking along the surface of THE SUN, STARS, AND PLANETS a body of water zero degrees high, overhead ninety degrees high. We call directly Experiment 10. The Height of the Sun at Noon Measured in Degrees. Apparatus: Chalk box, protractor, nail, two tacks. a. Take an empty chalk box and with the open side toward you tack the protractor so that its straight side crosses the short end of the box half-way and is parallel with the long side. Drive a brad at the center point of the protractor. With your rule held against the brad and over the 85 division, mark the edge of the box with pen- cil. Repeat for each 5. The marks on the edge of the chalk box are not the same distance apart, but a shadow of the nail falls on each mark in succession for each 5. See if this is not true. The apparatus should appear like the illustration. b. Place the box so that the shadow of the nail at noon falls across the protractor and on the edge of the THE HEIGHT OF THE SUN IN DEGREES 17 box. What is the number of degrees that the sun is high at noon? Repeat once a week and keep a record as in the last experiment. Do you think that the sun is ever over- head? Can you find out? Review Questions, 4. 1. Name four ways of telling time. 2. When did the sun set last night? Then when did the sun rise yesterday? 3. If the hole in the tube of the hour-glass were smaller would it make any difference in the time which it would take for the sand to run through? 4. When is the sun the highest in the sky? How can you tell? 5. What are the two ways of stating how high the sun is? Next year you will learn more concerning the sun, stars, and planets. Now we are going to study about what we receive from the sun. Elem. Sci. 2 THE GUIDE LIGHT 10. The Light We Receive from the Sun. Just after sunrise and just before sunset we may look at the sun without hurting our eyes. The sun looks large and red. The reason it looks large is because we can compare its size with the size of other objects, and when we notice that it appears larger than a distant house or tree we realize that it is very large. The sun appears red because the light in coming along the surface of the earth has passed through a large amount of dust and fine drops of water, which have sifted the light until most of its strength has been taken out. /s the sun mounts higher and higher in the sky, the light passes through less and less of the fine particles, and we say the light becomes brighter. On hazy days, or when there is smoke in the air, the sun looks red even at noontime. To show that the reason why the sun ap- pears red is because the light is sifted, we can perform the following experiment. Experiment 11. The Appearance of the Sun through Smoked Glass. Apparatus: Glass, candle. a. Hold a piece of ordinary window glass in the flame of a candle or the flame of a kerosene lamp, moving the glass around in order to distribute the smok. Tf the glass is held still in the flame it will break. Smoke one side only. The material on the glass is soot. b. Hold the smoked glass between the sun and one of your eyes, closing the other one. How does the sun appear? Move the glass so that you look through more 20 LIGHT or less soot. How does the color of the sun appear to change? 11. The Sunlight Makes Plants Green. If a board or plank is laid on the grass for several days, so that the sunlight cannot reach it, the grass will be light yellow, and even white, when the board is first removed. In a few days, however, the grass will regain its usual green color. What caused the change? Pota- toes and onions which sprout in the dark have very light green or light yellow stalks and leaves. If these are brought into the sunlight they become green. Although plants may grow in the dim light they need the sunlight in order to grow well and to bear fruit. Experiment 12. The Effect of Sunlight upon Grow- ing Plants. a. Cut a thin slice of cork from a stopper and trim it into some shape, such as a heart, or a cross, or a clover leaf, and pin it upon a growing leaf which must be left upon the tree. The best way to fasten the piece upon the leaf is to push two pins through it, through the leaf, and into another piece of cork, which is held on the under side of the leaf. Do not touch it for one week. At the end EFFECT OF SUNLIGHT ON PLANTS 21 of a week remove the pieces of cork and report how the leaf appears. Let the leaf remain upon the tree and ex- amine it at the end of another week. What has happened ? b. Try other designs and remove the leaves from the tree when the cork covers are removed. See who can make the best design, Review Questions, 5. 1. Which way does the Great Dipper move around the North Star, clock-wise or the other way around? 2. Look at the Great Dipper as early as you can see it and as late as you can stay up, and see if you can tell how many degrees it moves in one hour. 3. If the sun rises exactly in the east and sets ex- actly in the west, through how many degrees does it move? How many hours does it take? 4. At what hour does the sun rise when it rises ex- actly in the east? Through how many degrees does the sun move in one hour? 5. Why does the sun appear larger at sunrise and sunset than it does at noontime? 6. Why does the sun appear red at sunrise and sunset? 7. Is it ever red at any other time? Why? 8. What makes plants green? How can you show this? 9. When do plants grow best? Why? 10. Did you obtain your answers to these questions from books? What is the best way of obtaining these answers? 22 LIGHT 12. Other Changes of Color which are Caused by the Sunlight. If we are out in the sunlight a great deal our skin becomes brown and we say that we are tanned. This change of color is due to the sun and it takes place in order to protect the body from the effects of too much sunlight. Some persons do not tan very easily, but be- come red and often blisters are caused where the skin has been exposed very long to the sunshine. Even persons who do tan easily are sunburned if they try to become tanned in a few days, while if they are not too long in the sunlight at one time, the skin will protect itself by putting a shield between the sun and the tender inner skin. Just as smoked glass shut out so much sunlight that we could look at the bright noonday sun without hurting our eyes, so the tanned skin keeps out the strong sunlight and we can expose it to the sun's glare without harm. If the coloring material is not distributed evenly throughout the skin little patches come which are called freckles. When we speak of the sun as causing plants to be green and the skin to tan, we must remember that the plants and the skin are alive. If the sun shines upon things which are without life it can affect the color which the things have, causing it to become lighter, and in some cases, even making the material white or nearly white. The change in color is called fading, while the removal of the color from an object is called bleaching. Experiment 13: Fading and Bleaching, a. Obtain several pieces of differently-colored cot- ton cloth and cut each piece into halves. Keep one of FADING AND BLEACHING 23 the halves of each piece in the dark, so that the color will not change. Wet the other halves with water and ex- pose them to the bright sunlight until there is a change in color. The pieces should be kept wet and it may take a few days before there is much change. Make a list of the colors and tell how soon they changed and what each color became. b. Wet and expose a piece of unbleached white cot- ton cloth to the bright sunlight. Compare the result with another piece which has not been exposed. This is the oM-fashioned way of bleaching and is the best method, although it is slow. Bleaching may be ac- complished much more quickly by the use of chemicals, but the cloth is weakened and wears, out more quickly. The sunlight changes the color of certain chemicals in a strange way. We can make use of this knowledge and cause the sun to print designs for us on paper. The simplest paper for this purpose is called blue-print paper. It may be purchased cheaply or may be made very cheap- ly. See Section 70. Experiment 14. Blue Prints of Leaves and other Articles. Apparatus: Piece of window glass, leaves, lace, any thin article, blue-print paper at least 4"x5". a. Lay a piece of blue-print paper face up upon a 24 LIGHT book. Place upon this a leaf, a piece of lace, or any thin ar- ticle, and cover with the piece of glass. Expose to the bright sunlight until the color of the paper is a bronze. This color must be learned by experience. When you think that the color is right, re- move the paper and wash it for five min- utes in running wa- ter, or move it about in a basin of water. The exposed part of the paper should be a dark blue, while the rest should be a pure white. If the blue color is not dark, it means that you did not leave the paper in the sunlight long enough. If the light part is not white, but is somewhat blue, it is because you exposed the paper too long. You should repeat this ex- periment at home until you can obtain clear white prints upon a dark blue surface. Blue-print paper will also be used in Experiments 68 and 75. Review Questions, 6. 1. If the sun should rise exactly in the south-east, tell exactly where it would set. Why? SUNLIGHT GOOD FOR PLANTS AND ANIMALS 25 2. If the sun rises at six o'clock where do shadows point at that time? Can you devise some method of telling the exact east? Can you do this by means of the sunset? 3. Is the sun ever exactly overhead? If it should be exactly overhead what would the length of shadows be then? 4. What is the best way of measuring the height of the sun? 5. How could you make a yellow figure upon a red apple? 6. What does the sun do to your skin? Why does this happen ? 7. What does the sunlight do to color? 13. The Sunlight Good for Plants and Animals. Although plants cannot move about the same as animals, they do turn their leaves toward the sun and even grow in the direction of the sunlight. Look at the plants which are near the window in the room, and notice how they lean toward the sunlight. This shows that the sunlight is good for plants. If there were no sunlight most of the plants would soon die. The sunlight is also good for animals and man. If a person stays indoors too much he will becorrre sickly. We should be out in the sunlight as much as possible, and our buildings and houses should have many win- dows so that the sunlight can enter freely. The sun has a stimulating effect upon the body, and often persons take sunbaths to improve their general health. Taking a sunbath usually means sitting in the sunshine, but in hospitals they are given by having the patients lie on cots, being covered only by a sheet. 26 LIGHT There is another way in which sunlight helps us and that is by killing disease germs. Much of our sickness is caused by little plants, called bacteria, which are so small that they cannot be seen. These plants grow best in dark and damp places and for that reason we should live in dry and sunny houses. If the sunlight which comes in through many windows is too much for our comfort we can shut it out, but if the windows are too few in number there is no way of obtaining enough sun- light. Windows are as cheap as the wall they take the place of, and to have few windows is no economy. 14. Light Travels in Straight Lines. What is meant by a straight line? When we say "As straight as a string," do we mean a tightly pulled string or a loose string? If carpenters wish to mark a straight line on a building they rub some chalk upon a string, stretch it tightly where they desire the line, and then pulling the middle out a little, let it snap back upon the wall. Some of the chalk leaves the string and makes a straight line. Why is the line straight? Try making straight lines with a chalk-line. Now that you know just what is meant by the word "straight" you can see that light travels in straight lines. If there is a .candle or a lamp in a room, can you go any- where in the room so that you cannot see the light? How does the light come to you from the candle or lamp, straight or curved? Experiment 15. The Way Light Travels. Apparatus: Slim stick three or four feet long, string, two pieces of cardboard, candle. THE PINHOLE CAMERA 27 a. Make a bow of the stick by means of the string, having the string come over the ends of the stick. Sight along the tight string at a candle. Does the light come to your eye in a straight line? b. Make a hole with your pencil point through the center of one piece of cardboard, and hold it three or four inches from the lighted candle. Hold the other piece of cardboard near the first piece, on the side away from the candle. What do you see? A darkened room is best for this experiment. If you do not see anything distinctly it may be because the hole is either too large or too small. What you see is an image. Explain why the image has the position in which you see it? If light started from the top of the candle and passed through the hole, in a straight line, would it strike the top or the bottom of the second piece of cardboard? Experiment 16. How to Make and Use a Pin-hole Camera. Materials: Chalk box, piece of ground glass to fit as cover to chalk box, tinfoil, cardboard box, waxed or greased paper to cover one end of cardboard box. a. Cut a hole in the center of the bottom of the chalk box about one-quarter of an inch across. Cover this hole with a piece of tinfoil and make a pin-hole in it. Slide the ground glass into the chalk box as a cover, with the ground side out. The camera is finished. b. Second method. Break one end out of a card- board box, paste the cover on, and cover the open end 28 LIGHT with waxed paper, or paper with grease on it. Make a hole with a pencil point in the end of the box which is opposite the paper. Both cameras may be used in the same way, but the first one will give better images. c. Turn the pin-hole end of your camera toward the objects you wish to see in the camera. Bright ob- jects are the best for this purpose. Cover the head and the other end of the box with a cloth, or a jacket, and yon will see an image in all its natural colors. Where is the top of the image? Where is the right side of the image? How do you explain this result? Review Questions, 7. 1. If you look along the surface of a body of water and then look exactly overhead, through how many de- grees have you tipped your head? 2. If plants die, will the sun make the leaves green? What besides the sunlight is necessary in order that the plants be green? 3. What is the use of tan upon the skin? What is the harm of using chemicals to bleach 4. cloth? 5. them? How do plants show that sunlight is good for THE REFLECTION OF LIGHT 29 6. If you were choosing a house in which to live, what would you notice especially? 7. Give two proofs that light travels in straight lines. 8. Why is the image in the pin-hole camera upside down? 15. The Reflection of Light. Light travels in straight lines until it strikes against something. Then it is turned back, and, although it still travels in straight lines, the direction of the light has been changed. This turning, or bending, of light is called reflection. When the object which causes the reflec- tion is smooth and shiny we seem to see the light in the object. If you look at the reflection of any object in a mirror, it seems to be back of the mirror. This is called regular reflection, because what we see appears just like the object. The appearance of an object in a mirror is called an image. Can you imagine why it is called an image? Experiment 17. Reflection from Mirrors. Apparatus: Mirror at least 2"x4", block of wood 2"x2"x4", two rubber bands, foot rule, pin. a. Turn the mirror toward the sun but tip it down- ward so that the reflected light is on the wall about as high as your head. Now turn the mirror about 45 de- grees to the right. Through how many degrees does the spot of light move? Repeat, turning the mirror to the left. What result do you obtain? In turning the mirror from the right position to the left position you moved it 30 LIGHT through 90 degrees. Through how many degrees did the spot of light move? Make a drawing to show how the light came from the sun and was reflected from the mirror. b. Fasten the mirror to the block of wood by means of the rubber bands, and place it on a board. Stick a pin two inches in front of the mirror and place the rule so that its end touches the mirror and the pin comes at the two inch mark. Look in the mirror and tell how far back of the mirror the image of the pin is. Place the pin at different distances and repeat. Having made several trials, and having obtained the same results in each trial, you can now draw your conclusions. How far back of the mirror is the image compared with the distance the object is in front of the mirror? DIFFUSED REFLECTION OF LIGHT 31 If the object upon which the light falls is rough some of the light is reflected, but, since the rough surface is made of tiny surfaces which face in all directions, the light is scattered in all directions. In the case of this experi- ment we cannot see the sun in the object if it is shining upon it, but we see that the object is brighter. We call this scattering of light, diffused reflection. All objects which give light are seen by the light which they pro- duce; all other objects are seen by the light which they reflect. Light is diffused by particles of dust and tiny drops of water in the air which are too small to be seen. The light which we receive from the sky and from clouds is due to diffused reflection. Diffused light is best for the eyes. Experiment 18. Diffused Reflection of Light. Apparatus: Two blackboard erasers, glass. Materials: Little milk, sheet of white paper. a. Darken the room except for one window through which the sunshine is coming. Notice the particles of dust which are shining by reflected light. Stand across the room and look for the particles in the sunbeam. Can you see them? Why? The sky is bright for the same reason that the sunbeam appears to be bright. If there were no dust in the air you could not see a sunbeam. Knock two blackboard erasers together in the sunbeam and tell what happens. Look at your companions' faces as you do this and see if they become brighter. b. Put a glass of water in the sunbeam and notice how it appears. Now add a drop or two of milk. What color does the water become? Could you see a glass of water across the room better if there were a few drops LIGHT of milk in it? Why? Add some more milk and tell what color the water becomes. When only a little light is reflected what color is reflected? Why is the sky blue? If all the light is reflected what color is it? c. Notice the amount of light upon the ceiling. Now hold a sheet of white paper in the sunbeam and tell what change there is in the amount of light. The moon shines by light reflected from the sun, so moonlight is only sun- light which has gone to the moon before coming to us. Review Questions, 8. 1. Face the north. After turning 135 to the right, in what direction are you facing? If you had turned to the left, in what direction would you be facing? 2. If the sun is in the south direction every day in the year, at noon, how can the sun be farther south in winter than in summer? 3. If the sun sets at quarter before seven o'clock, at what time will it rise next day? 4. What is the best manner of finding the line which is half-way between the shadows in Experiment 3? 5. What is the cause of freckles? Why do not all persons become freckled? 6. If you looked at a very large and very bright mirror would you see the mirror? Explain. 7. How do you see other persons? Do they give light? 8. If you are five feet in front of a mirror and then move three feet nearer, how much nearer are you to your image? 9. Why are shades used over lamps and other lights? SOURCES OF LIGHT 33 10. Why is the sky blue? You have seen the sky when it is nearly white; what might cause a clear black sky? 16. Light from Sources Other Than the Sun. The sun is by far the best source of light. There is no light so powerful, and none so beneficial to plants and animals. Most animals, except those that prowl at night, go to sleep soon after sunset; but man has long been accustomed to staying awake much later. The need of light was first met by the use of campfires. If a per- son wished to leave the campfire he would remove a burn- ing stick or fire-brand, and carry it with him. Thus the torch was a natural outgrowth from the campfire. Later, man learned that some kinds of wood, or wood which had been soaked in grease, made better torches than a fire- brand taken from the campfire. Still later, man made lamps in which wicks burned in grease or oil. The flame was uncovered and was smoky and dim. The candle was a much more modern invention and, as you know, is still used. The modern oil lamp, having the flame covered with a chimney was a vast improvement over the ancient oil or grease lamp. The burning of illuminating gas was the next advance in lighting and was soon followed by the electric light. In all of the methods of producing light, except by electricity, we obtain more heat than light in all cases where light is obtained from burning a material. Even the electric light produces more heat than light. Experiment 19. Ordinary Sources of Light. Apparatus: Oil lamp, Bunsen burner, gasoline Elem. Sci. 3 34 LIGHT lamp, or alcohol lamp, test tubes, test-tube holder. Materials: Pieces of wood, candle, iron wire No. 28, soft coal. a. Darken the room as much as possible. Bijrn pieces of wood (matches will do) and describe the light which is obtained. Light the candle. Is the light steady? Why? Light the kerosene lamp but do not put on the chimney. Describe the flame and light obtained. Would you like to be in a room for a long time with this kind of a light? Put the chimney on and state what difference you note. b. If there is gas in the school, light a Bunsen burner and describe the light when the dampers at the bottom are closed. Open the dampers. What is the difference in the light? Hold a piece of No. 28 iron wire, colled into a spiral, in the flame. Where does the light come from? Light the alcohol lamp. What kind of light does burn- ing alcohol give? Could you read by it. Hold the iron Cut supplied through United State Department of Agriculture COLD LIGHT 35 spiral in the flame. Could you read by this light? This kind of light is called secondary, because it is caused by the heat of the flame, although the flame gives very little light. First the heat comes from the flame, and second the light comes from the wire. c. Put a few pieces of wood, or soft coal, in a test tube and hold it, by means of the test- tube holder, in the alcohol or gas flame. Tell what happens. See if you can light what is coming out of the tube. It is gas. A large amount of gas is made by heating coal. While the heat from our sources of light is very acceptable during cold weather, it becomes decidedly un- pleasant on the hot nights when we must use lights. For this reason scientists are trying to obtain some source of light which will produce less heat than any we now use. The whiter the light the less heat is produced com- pared with the intensity of the light. Thus reddish or yellowish lights produce much more heat than light, while white light, although it produces a large amount of heat, yields more light in proportion. Name some yellow lights and some white lights. Nature supplies a yellowish light which is practically cold. Fireflies and glowworms are examples of this sort of light. Try to catch some glowworms and examine them. Decaying fishbones sometimes give a faint light, but, like the light obtained from fireflies and glowworms, is of no practical 36 LIGHT value. This kind of light is called phosphorescence. So far, man has not produced any really cold light which is sufficiently strong for practical purposes. The experi- ment shows one form of cold light which is used to a slight extent on match-boxes, clock faces, and around door bells so that they may be seen in the dark. Experiment 20. Cold Light. Apparatus: A matchbox with the word "matches'" made of luminous paint. a. Place the matchbox so that the direct sunlight will fall upon it for at least ten minutes, and then exam- ine it in a dark room. It may be necessary to remain in the dark room for a few minutes before your eyes will become accustomed to the darkness. What do you see? b. Keep the matchbox in a perfectly dark place for two or three days and then examine it without removing" it from the dark. Can you see anything? c. Place the matchbox in the sunlight for ten min- utes and again examine in a dark room. What do you conclude is the real source of light in the case of lumi- nous paints? Review Questions, 9. 1. What side of trees has the most moss? Why? 2. How can you locate the south by means of a watch? 3. If the sun rises exactly in the east, what is the time of sunset? 4. Could you tell time by the Great Dipper? REVIEW QUESTIONS 37 5. What are some of the advantages of sunlight? 6. What are the two kinds of reflection, and what is the chief difference between them? 7. If you move a mirror 10, how much will a re- flected beam of sunlight move? 8. What are some of the sources of light? 9. Why does most light give heat? THE GUIDE HEAT. 17. The Heat we Receive from the Sun. The heat which we receive from the sun is necessary for animal life and for plant life. As you know, it is useless to plant seeds in very cold weather, and animals often die when they do not have a warm place in which to live. (Later we shall learn more about the effect of heat upon plants.) Just as the amount of light which we receive from the sun varies with the different seasons, so the amount of heat which we also receive from the sun changes from hour to hour and from season to season. When is the warmest part of the day? When is the coolest part? Look back at Section 10 and try to explain why this is so. When is the warmest part of the year? When is the coldest part? Perhaps you may obtain a suggestion from Section 9. The next experiment will show why the heat from the sun varies as it does. Experiment 21. *The Varying Heat from the Sun. Apparatus: Scissors, protractor. Materials: Cardboard 12"x8", paper staple. a. Make the apparatus as shown in the illustration. The radius of the quarter circle should be five inches. The divisions numbered 1 to 44 should be one-fourth inch, and the movable strip should be one inch wide. One inch of the end of the strip should be bent up and a quar- * See Section 62 before performing this experiment. 40 HEAT ter inch hole made in the center. The line of divisions represents the surface of a small part of the earth ; the movable piece represents a sunbeam one inch wide. When this "sunbeam" is perpendicular to the ''surface of the earth" it covers one inch. How many degrees are needed between two lines to make them perpendicular to each other? If the "sunbeam" is at any other angle it covers more than one inch of the "surface of the earth." Now if you had just enough butter to cover one slice of bread but had to cover two slices with it, how thick would the butter be? Suppose that you were so un- fortunate as to be obliged to cover three slices with the same amount of butter, how thick would the butter be? In a manner similar to this the sunshine is spread "thick or thin" upon the surface of the earth, as the height of the sun varies with the time of day and with the changes of season. b. Place your apparatus in the sunshine early in the morning, or late in the afternoon, in suc;h a manner that the movable arm "sunbeam" may be aimed at the AMOUNT OF HEAT FROM THE SUN 41 sun, while the "surface of the earth" is parallel with the real surface of the earth. The best way to do this is to place the arm in such a position that the sun shines through the hole in the bent end. and falls lengthwise along the middle of the strip. Read the angle on the protractor. This is the elevation of the sun. Count the number of spaces covere'd by the ''sunbeam." How strong is the sunlight compared with what it would be if it were perpendicular to the "surface of the earth?" Remember your buttered bread ! c. Repeat (b.) at noon. What is the elevation of the sun? How many spaces are covered by the "sun- beam"? How strong is the sunlight compared with what it was early in the day? d. Take a reading once a week, of the sun at noon and the number of spaces covered by the "sunbeam." Continue this experiment the rest of the year. Keep a record and compare it with the record which you are keeping of Experiment 10 The amount of heat which is taken up by different objects is very different, although all of the objects may be near one another in the sunshine. Shiny objects do not become very warm in the sunshine. What is the effect of shiny objects upon light? They do the same thing to heat and therefore they do not become warm. White objects and those having light colors also are quite cool in the sunshine, but are warmer than the shiny objects because they do not reflect so much heat. Dark colored and rough objects reflect very little heat 42 HEAT and thus become very warm. What color of clothing should be worn in hot weather? Why? Experiment 22. The Amount of Heat Received by Different Colors. Apparatus: Two spice cans of the same size, kero- sene lamp, pieces of paper, white, red, yellow, and black. a. Polish one spice can and smoke the other in the flame of a kerosene lamp. Fill each with the same amount of water and expose both in the bright sunshine. At the end of twenty minutes dip a ringer into each and tell what the difference is between them. See Section 71. b. While waiting for the water to become warm expose the pieces of paper to the bright sunshine and arrange them in the order of their warmth, putting the hottest one first and the coldest one last. We have seen that the amount of heat from sunshine varies with the altitude of the sun, because when the sun is low a given amount of sunshine is spread over a much greater surface than when the sun is higher. Do you think that if we could cause more sunshine to fall upon a certain surface it would become warmer? See Experi- ment 17. There is another means by which light and heat may be gathered together so that what falls upon a large surface is caused to cover only a very small surface. This is accomplished by the use of a circular shaped piece of glass, thicker at the center than at the edges, called a lens, or "burning glass." THE "BURNING GLASS" 43 Experiment 23. "The Burning Glass." Apparatus: A lens at least 3" in diameter. Materials : Bits of paper, cloth, wood and leather. a. Hold the lens flat to the light as it comes from the sun and catch the light, after it has passed through the lens, upon a piece of paper. Move the lens toward or away from the paper until the spot of light is as small as possible. Tell what happens. Why is it best to have the spot of light as small as possible? Repeat, using cloth, wood, and leather in the place of paper. Which do you think would become hot quicker, black or white paper? Try it. Notice the dark ring around the bright spot. Where has the light gone? Review Questions, 10. 1. What is the difference between fading and bleaching? 2. What is a sunbath? How are they taken? 3. What is diffused light? How can it be produced? 4. Whicli is hotter, red light or white light? 5. Give some examples of cold light. 6. What part of the day is hottest? Why? 7. What material becomes the hottest in the sun- shine? 8. How may we obtain a large amount of the sun's heat in a very small space? 44 HEAT 9. Write to pupils in schools four or five hundred miles to the east or west of you, and ask them to tell you the position of the Great Dipper at eight o'clock. 18. Expansion Due to Heat. Whenever anything is heated it becomes larger. This increase in size is called expansion. It is an in- crease in length, breadth, and thickness. In liquids, such as water, we notice the increase in volume. The increase of volume is also evident in the case of gases, of which air is an example. In solids, however, it is the increase in length only, which causes us to be watchful. The next time you are near a railroad track look for the spaces between the ends of the rails. Are the spaces large or small? Is the day hot or cold? If these spaces were not left when the rails were laid in cold weather, they would expand in hot weather and having no space in which to expand, would bend sidewise, al- lowing the car wheels to leave them. If you were lay- ing rails on a very hot day would you put the ends close together, or would you leave a space between them? A practical use of expansion due to heat is made in putting iron tires upon wheels. The tires are quite hot when they are placed around the wheel and, as they cool off they contract; that is, become smaller and thus grip the wheel very tightly. See Section 72. Experiment 24. Heat Causes Expansion. Apparatus: Lamp chimney, candle, two small blocks of wood, iron wire No. 18, rule, 4-ounce bottle, cork to fit bottle, glass tube one foot long, tumbler, alcohol lamp or Bunsen burner. HEAT CAUSES EXPANSION 45 a. Arrange appara- tus as shown. Light the candle and immediate- ly mark the position of the end of the wire. Watch it and tell what happens. What causes the change? Blow out the candle and explain what happens. b. Bore a hole in the cork stopper so that the glass tube will fit it snugly. Push the tube into the hole so that the end is even with the inner side of the stopper, and insert the stopper tightly into the bottle. Place the other end in a tumbler of water. Warm the bottle with the hands, while watching the end of the tube which is under water. What happens? Why? Now warm the bottle gently with a flame? What occurs? Allow the bottle to cool. What do you see ? Why? As the air cooled it contracted thus occupying less room, or space. The surface of the water in the tube merely fits against the air. 46 HEAT c. Fill the bottle with cold water and in- sert the stopper. The water should run up the tube not more th^n two^ inches. Mark the surface of the water with a piece of string tied tightly around the^tube. Heat the bottle gently and tell what happens. Explain. Let the water cool and explain what happens. Some materials expand more than, others when they are heated. Thus tin expands twice as much as does steel, while lead and zinc expand still more. Steel expands the least and zinc the most. This difference of expan- sion leads to results which appear strange until we think about what is occurring. A common example is the loosening of preserve jar covers when the jars are turned upside down and the covers placed in hot water. The metal cover expands more than the glass does ami becomes loose. Experiment 25. The Result of Unequal Expansion. Apparatus: Apparatus as shown in cut, consisting of a bar of brass and a bar of iron fastened together, alcohol or gas lamp, bottle to hold apparatus. Materials: Ice, salt. a. Notice that the bars are straight. Heat very hot by holding the bars in the flame. Which way do they bend, with the brass or the iron outside? Which UNEQUAL EXPANSION 47 expands the more, brass or iron? Let the bars cool and see if they are straight, as at first. b. Put the bars in salt and ice and let them become cool. Which way do they bend? A metal which, when heated, expands faster than another metal, also contracts faster when cooled. The unequal expansion of metals is made use of for practical purposes. The illustration shows a strip of two metals which are joined together their entire length, and then bent into the shape of a shepherd's crook. As the metals become warmer, due to the increased warmth of a room, the metal on the right expands more than the other metal and causes them both to bend to the left. This bending brings together the double metal and a screw which act like an electric push button. Instead of ringing a bell, however, the electricity changes the dampers of the furnace so that the air of the room will not be so warm. When the room cools off, the metals bend the other way and cause the electric- ity to open the dampers again. The machine is called a heat regulator because it regulates the amount of heat which a room receives. Cut supplied by the Jewell Heat Regulator Co. 48 HEAT Review Questions, 11. 1. What are the advantages of a sunny house? 2. How does heat come to us from the sun, in curves or in straight lines? What makes you think so? 3. Why do you cover your head when you look at the image in a pin-hole camera? 4. When you are reading at night should you have the light shining directly into your eyes? How should you light your books? 5. Can you really see a sunbeam ?What do you see? 6. What color of clothes should we wear in sum- mer? Why? 7. What is expansion and what causes it? 8. Do all things expand the same amount? 19. The Thermometer an Application of Expansion. It is warm today? How do you judge? If you have been running it may seem warmer to you than to some- one who has been sitting quietly. The best way to learn about the warmth is by means of a thermometer. This is merely a tube with a large end called a bulb, and is much like the bottle and tube which was used in Experi- ment 24, c. In fact, we can use that apparatus in the place of a thermometer, but the change in the height of the water would be too little to measure easily for ordi- nary changes of warmth. We saw, however, that as th? water became warmer it expanded and ran up the tube. When anything is hot we say that it has a high temper- ature, and when it is cold we call the temperature low. Thus we can make this statement: When the temper- THE THERMOMETER ature rose the water rose in the tube, and when the temperature went down the water also went down. Temperature then, is the condition of warmth, high temperature being very warm and low temperature very cold. The usual thermometer is a very thin tube closed at one end and with a bulb at the other end. This bulb may contain mercury, sometimes called quicksilver, or it may contain colored alcohol. It is the mercury or alcohol in the bulb which expands and pushes a tiny thread of liquid up the tube. The ther- mometer is marked either on the glass or on the back, into divisions called degrees, and these degrees are numbered from zero up and down. There are two kinds of markings on thermometers. The ther- mometer which is used ordinarily is called by the inventor's name, Fahrenheit, and has the temperature of freezing water marked 32 degrees, and the temperature of boiling water marked 212 degrees. The illustration shows a Fahrenheit thermom- eter. The other thermometer is used by scientists everywhere, and in many foreign countries by everyone. This is called the Centigrade thermometer and has the freezing temperature of water marked degrees and the boiling temperature of water marked 100 degrees. Of course the temperature of freezing water is really just the same no matter what it is called, just as you are the same person whether you are called bv Elem. Sci. 4 50 HEAT your real name or yonr nickname ; that is, 32 degrees Fahrenheit and degrees Centigrade are the same tem- perature. The temperature of boiling water is also the same although it is called 212 degrees Fahrenheit and 100 degrees Centigrade. If you do not state whether the tem- perature is according to the Fahrenheit thermometer or the Centigrade thermometer, it is understood to be the Fahrenheit. Degrees are marked the same as the degrees of a circle, that is, in the place of writing 60 degrees Fah- renheit we may put 60 F. Experiment 26. How to Read a Thermometer. Apparatus: Cheap thermometer. a. Count the number of divisions between the fig- ures 40 and 50. How many spaces are there? What is the difference between 40 and 50? Then how many degrees does each space mark? All thermometers are not marked the same and you should find out every time you use a thermometer just how many degrees are covered by each space. b. Obtain the temperature of the room. To do this the thermometer should come to rest, that is, there should be no difference between two readings taken two or three minutes apart. The temperature of a room should be 65 to 68 degrees Fahrenheit at the same height as the heads of those sitting. If the temperature out- doors is more than 68 degrees the temperature indoors may be uncomfortably high, but we should try to keep the temperature at 68 degrees. c. Take the outdoor temperature in the morning just before school begins, at noon, and at the close of TEMPERATURE SENSATIONS 51 school. Keep a record of the temperature and you can tell the hot days and the cold days, without trusting to your memory. A record is to be trusted. See Section 69. Another practical application of the unequal expan- sion of metals is the dial thermometer. You have all seen thermometers which have a hand moving over what appears very much like the face of a clock. In the place of the hours, however, the face is marked into divisions which are numbered usually from zero to a- hundred or more. The word "Fah- renheit" generally i s printed upon the face of the instrument. The movement of the hand is caused by the winding up, or the unwinding, of a spiral, due to the un- equal expansion of the two metals of which it is composed. The illustra- tion shows the spiral but does not show the two metals. Both metals are quite thin and are fas f - ened together their entire length just as we learned the heat regulator was made. We should not depend upon our feelings in regard to temperature. If we have been exercising we are warm Cut supplied by the Standard Thermometer Co. 52 HEAT and may endanger our health by remaining in a room which seems comfortable, when really it is too cold. The thermometer is the only true guide to be followed if we wish to know the real temperature. Of course, if we are exercising, the temperature may be much below 68 degrees and do us no harm. The temperature of 68 degrees is proper for persons who are sitting still, or moving about only a little. Is your room at the right temperature? The following experiment will show you how little it is possible to trust our feelings or sensations. Experiment 27. Hot or Cold? Apparatus : Three cups or other similar dishes, sauce pan, alcohol or gas lamp, ring stand, wire gauze. Materials: Ice. a. Fill one cup with water which is as hot as you can bear putting your hand into ; fill the second cup with water at the temper- ature of the room ; the third cup should be rilled with ice cold water. Place the fingers of one hand in the hot water and those of the other hand in the very cold water and let them remain for one full minute. Then place the fingers of both hands in the cup containing the water ar the temperature of the room. How do the fingers feel? Is the last water hot or cold? Can you trust your sensations? Review Questions, 12. 1. If the sun rises at seven o'clock, at what time will it set? HEAT PRODUCES LIGHT 53 2. On which side of a street is it better to live, the north side or the south side? Before answering think where the sun is at noon and the direction from which the sunshine comes. 3. What is one thing we can do in order to keep well? 4. How may we obtain light from a flame which gives a large amount of heat but gives no light of itself? 5. If a person could be dressed in very shiny cloth- ing, just like a mirror, would he be warm or cold in the sunshine? Explain. 6. What use is made of the expansion of metals? 7. What use is made of the expansion of liquids? 8. How do you read a thermometer? 9. If the temperature in the morning is 48 F. and at noon it is 65F., what has been the change in temper- ature? 10. Why should we not depend upon, our feelings concerning the temperature of a room? 20. Heat Produces Light. In Section 16 we learned that heat is one of the sources of light and that it is impossible, as far as we know at the present time, to produce cold light which is strong enough for ordinary use. The light which we obtain from heat, however, is not always the. same, for we have a dull red light, a yellow light and a dazzling white light. What causes the difference? Did you ever see a blacksmith working at his anvil? Sometimes the iron is red-hot when he removes it from the forge, and sometimes it is white-hot. Now you know the difference, and if you are nearby you can feel the difference. 54 HEAT We have learned that water boils at 212 Fahren- heit, and we have always thought of "boiling hot" as being very hot. Of course we have known that the fire is much hotter but we have never thought much about it. Ice water (32F.) is changed to boiling water (212F.) by an increase of 180, yet the lowest temperature at which there is a dull red light is about 950 Fahrenheit. The temperature of bright red light is much higher, yellow light is caused by a still higher temperature, while daz- zling white light is caused by the extremely high tem- perature of 2200 F. The electric light which we have in our houses is a good example of light from heat. 21. Heat from Friction. When two objects are rubbed together we say there is friction between the objects. This friction makes it hard for the objects to move past each other and it re- quires more strength where there is much friction than where the friction is less. Oil has the power to reduce the friction between two objects and for that reason we oil the bearings of machinery, also the curves of railroad tracks, or we grease the places where we want one part to slip easily over another part. Another name for oiling is lubricating. Try rubbing your hands together, pressing them firmly against each other and moving them rapidly. How do they feel? Why do persons rub their hands together in cold weather? Rub a coin on your coat sleeve or on the carpet and tell what happens. Feel of a gimlet after boring a hole, and explain the results. Sometimes the bearings of railroad car wheels become so hot, even if FIRE-MAKING 55 they are well lubricated, that they set the oil on fire, and it is said there is a "hot box," The old way of making fire depended upon friction. So great heat can be produced by rapidly rubbing two sticks together that they may be caused to glow, and even burst into flame. Indians used this method for making fire but it is hard to do, and requires skill and patience. There is an easier way to accomplish the same result, which we will now try. Experiment 28. Primitive Fire-making. Materials: Two blocks of wood 2"x4"x6", circular wooden rod 7"long and pointed at both ends, a bow and string, similar to the one used in Experiment 15, lubricat- ing oil or grease. a. Bore a hole part way through the blocks at their center points, and arrange the apparatus as shown in the illustration. Lubricate the hole in the top block but put nothing in the hole in the lower block. Why is this done? Bear down hard on the top block and move the bow back- ward and forward very rapidly. You may not be able to make the lower block burn but you should be able to make it smoke. Does the hole in the upper block become equally hot? Why? This apparatus is called a fire drill ; and this method of obtaining fire also was used in olden times. Another method of making fire was by means of the flint and steel. Flint is a very hard stone and when it is 56 HEAT struck against iron or steel it removes little pieces, and the friction is so great that they become almost white hot. These tiny particles used to be caught upon shred- ded linen, called tinder, which caught fire and burned. As soon as the fire was obtained the tinder was covered up and kept for next time. Flint was also used for discharging guns. The hammer of the gun carried a piece of flint, and as it fell, it touched a piece of steel sending a shower of sparks down into the powder. These guns were called flint- locks. Experiment 29. The Flint and Steel Gaslighter. Apparatus: A friction gaslighter. Materials: Alcohol, piece of cloth. a. Examine the lighter, noticing the steel file and Cut supplied by the Safety Gas Lighter Co. MATCHES 57 the material which rubs against it. This is not flint, but the action of the lighter is very much like the old flint and steel. b. Make sparks with the lighter. To do so, quickly rub the parts together. Feel of the sparks. Are they hot? Make the sparks in illuminating gas. Does the gas light? If there is no gas try lighting a piece of cloth which is very wet with alcohol. Do gas and alcohol have to be very warm in order to begin to burn? The modern way of obtaining fire is by means of matches. How do you light a match? What causes the match to light? So the modern way is much like the ancient way, after all. The only difference is that the materials on the head of the match begin to burn at a very low temperature, just as gas and alcohol were set on fire by sparks which were not noticeably hot. As soon as the match begins to burn its temperature rises to more than 1000F. Since matches are so easily set on fire, or ignited, as it is called, they should be kept where there can be no friction. It is not safe to keep them in the cardboard box in which they are sold, for sometimes mice gnaw through these boxes and ignite the matches by biting them. The best way in which to keep matches is in a tin pail, or box, having a tightly fitting cover. Not only is that the safest way but the covered matches will also be kept dry and good. 58 HEAT Review Questions, 13. 1. What is the color of the sun at sunrise and sun- set? Why is it this color? 2. Which is hotter, red-hot or white-hot? 3. Why does the sun appear red when you look at it through a piece of smoked glass? 4. In what direction do plants grow if they are placed near a window? Why? 5. What is a straight line? How can you make a straight line? 6. Why do we receive more heat from the sun in summer than in winter? 7. What are the three sources of heat which we have studied? 8. What would be the result if you did not lubricate the hole in the upper block in Experiment 28? 9. What are the sparks when flint and steel are struck together? 10. What is the difference between the modern way of making fire and the olden way? 22. Heat from Combustion. By far the greatest amount of the heat which we enjoy comes from the sun. We have seen, however, that as winter draws near we receive less and less heat from the sun, so that it becomes necessary for us to obtain heat from some other source. Our usual source of heat is from the burning of something. Combustion is another name for burning. There are two kinds of combustion, complete and HEAT FROM COMBUSTION 59 incomplete. By complete combustion is meant that all of the material has been burned and none wasted. This can be accomplished by giving the fire a proper amount of air. Did you ever see heavy, black smoke coming out a chimney? That smoke was part of the material which should have been burned in the fire, and it meant a loss to the one who was running the fire. The smoke showed that there was incomplete combustion. If the com- bustion had been complete there would have been no visible smoke. There are other reasons, besides economy, why fires should not be allowed to send off vast amounts of smoke. The particles of smoke, called soot, slowly settle and spoil the appearance of buildings, soil our linen, and affect our health. It is very bad for us to breathe in smoke and soot. In many cities it is against the law to allow chim- neys to smoke to any unnecessary amount. Experiment 30. Complete and Incomplete Com- bustion. Apparatus : Alcohol lamp filled with alcohol, alcohol lamp filled with turpentine, Bunsen burner. Materials: Piece of broken chinaware, piece of iron wire No. 28. a. Light the alcohol lamp. Is there any smoke? Is the flame hot? Hold a piece of fine iron wire in the flame and notice how hot it becomes. Hold a piece of chinaware in the flame. Does any- thing collect upon it? b. Light the turpentine lamp. Is there any smoke? 60 HEAT Is the flame as hot as the flame of the alcohol? Why? Which combustion is best? c. Hold a piece of chinaware in the flame of the turpentine lamp. What collects upon it? What is its color? d. Hold the piece of china- ware, with its coating, in the flame of the alcohol lamp for sev- eral minutes. What does this prove about the wastefulness of smoky combustion? e. Light the Bunsen burner and note the difference in the flame when the air vents are closed and when they are open. When is combustion more nearly perfect? Ai? 23. Combustibles and Fuels. Anything which burns is a combustible. Fuels arc only those combustibles which we ordinarily burn to produce heat. You are familiar with the common fuels which are coal, coke, wood, charcoal, oil and gas. What do you notice when you burn them? Do they all burn with a flame? In any combustion it is necessary to have air. In our stoves the amount of air is regulated by dampers. Do you open or close the dampers when you want a hot fire? If there is not enough air the fire will smoke, and finally go out. What causes incomplete combustion? COMBUSTIBLES 61 There is always a waste in the burning of fuels, even when the combustion is complete, for all fuels, except oil and gas, contain substances which do not burn. These substances produce the ashes which we always find under our fires. These ashes often contain particles of fuel which would have burned if the fire had been hotter, so it is seen that there are two losses from incomplete com- bustion. What are they? All combustibles, except some oils and some gases, come directly from plants or animals. The following experiment will show the difference between the two kinds of combustion. Experiment 31. The Combustion of Different Ma- terials. Apparatus: Alcohol lamp or Bunsen burner. Materials : Wood, charcoal, coal, coke, paper, straw, feathers, piece of wool, piece of silk, piece of cotton, piece of linen, whalebone, piece of leather. a. Hold a piece of each material in the flame and note how it burns. Arrange all of those materials which burn easily in one list and those that burn slowly in another list. Which ones come from animals and which from plants? Which is the safest clothing to wear when near flames, cotton or woolen? Goods may be prepared so that they will not burn readily. This is called fireproofing. See Section 73. 62 HEAT 24. Flames. In our experiments with combustibles we found that, while some of them burned with a flame, others only glowed. The difference is caused by a gas, as only gases burn with a flame. But, you will say, you saw wood burn with a flame, and wood is not a gas. That is true, but when the wood is heated so that it ignites, part of it is changed into a gas and it is the burning of this gas which causes the flame. It is just the same with a candle. The wax, when it is heated, changes into a gas and the burning gas causes the flame. Whenever you see a flame you may be sure that a gas is burning. There are two kinds of flames, those which give a large amount of light and those which give only a very little light. Those flames which give light are called luminous. Can you name some luminous flames? Name one flame which is not luminous. How can you obtain light from a flame which is not luminous? Luminous flames show that the combustion is not complete, the light being due to little particles which are not hot enough to burn. A flame which can hardly be seen is the result of very nearly complete combustion, and these flames are much hotter than the luminous flames. Experiment 32. The Cause of Flames. Apparatus: Test tube, test-tube holder, alcohol lamp, piece of glass tubing y" thick, 4" long. Materials: Bits of wood, candle. a. Put some bits of wood in a test tube and heat them in the flame of an alcohol lamp. What do you see THE CAUSE OF FLAMES collecting on the inside of the test tube? Continue to heat the wood until smoke comes out of the open end. Try lighting this with a match. How does it burn, with a flame or a glow? What must it be? Where did it come from? b. Continue to heat the bits of wood until the smoke ceases to come off, then remove from the flame. After the tube has cooled a little pour out what remains from the wood. What does it look like? How does it burn? Why does it burn this way? c. Light a candle, let it burn for a short time, and then blow it out. Have a burning match all ready to hold over the candle. It should ignite. What burns? d. Light a candle and hold a glass tube in the flame as shown in the illustration. A gas will pass up the tube and may be ignited at the top. Where does the gas come from? e. If there is gas, try the experiment as shown in the illustration. Review Questions, 14. 1. What is our guide from which we may learn direction in the open country? How can you find the guide? 2. What direction is 45 to the east of north? What direction is S. 45 W?. 64 HEAT 3. Can you see a light in the dark. Can you see a person in the dark? Explain. 4. What kind of light is best for the eyes? 5. What are the sources of heat? 6. When you see smoke coming from a chimney in large quantities what do you know about the fire which causes it? 7. What is the difference between combustibles and fuels? 8. Why do some things burn with a flame while others only glow when they are burning? 9. What are the best combustibles, those from plants or those from animals? 10. What makes a flame invisible? 25. First Aid to the Burned. If the clothing is on fire the flames may be slapped out, unless a large amount of the clothing is burning. Tn this case the person should roll, or be rolled, upon the floor. This crushes out the flames. Where possible the person should be wrapped in any heavy material, such as a mat or a rug, or even a coat. The wrapping should be very tight. The person should not be allowed to stand, as the flames will rush upward, setting more of the cloth- ing on fire, and perhaps causing the person to breathe the flame, which is very dangerous. Under no circum- stance should the person be allowed to run about. If persons would act quickly, harmful and even many a dangerous burning accident could be avoided. Be quick ! Experiment 33. Drill for Extinguishing Burning Clothing. THE TREATMENT OF BURNS 65 Apparatus: Children. Materials: Rug or coat. a. Let one child be supposed to have burning cloth- ing and let two or three other children slap out the imag- inary flames, and wrap the burning child in a rug or coat, and roll him upon the floor. The pupils who do this should be those who are best fitted to illustrate the method for the class. As other pupils improve they should be allowed to show the class this drill, perhaps at the end of each month. The treatment of burns which are not severe is very simple. Just moisten the burnt part with warm or cold water and put on all the baking soda which will stick. If the burn is quite bad, but has not blistered, the baking soda may be bandaged on the burn with clean cloth which has been torn into strips three-fourth of an inch wide. If the burns are serious the water blisters should be pricked with a needle, which has been heated ret-hot and used as soon as cool, to allow the water to run out, and then anply a mixture of equal parts limewater and olive qil. Cover the burn with absorbent cotton which has been soaked in the same mixture, and bandage snugly, but not tightly. If the burns are very serious it is best to call a physician. Limewater may be prepared by putting one ounce of fresh unslaked lime into a pint of cold water, shaking until the lime breaks up, and allowing to settle. The clear liquid should be poured off the top and kept in well- stoppered bottles. A bottle containing equal parts of Elem. Sci. 5 66 HEAT lime-water and olive oil should be kept in every kitchen. If limewater is not at hand, use baking soda and olive oil. Any of the following materials may be used for burns: baking soda, olive oil, limewater, white lead and linseed oil, powdered chalk, cornstarch, laundry starch, flour of any kind, mucilage or dissolved gelatine covered with any of the powders mentioned above. Since quick- ness means much to the patient, ease in obtaining the remedy should have first consideration. There is another danger which is connected with burns because the skin is usually destroyed. This gives the bacteria a chance to enter and produce trouble for us. To overcome these little plants we must bathe the affected parts with some material which is an antiseptic, that is, something which is against the poisoning. We should do this whenever we break our skin by any means. There are many antiseptic washes to be obtained in drug stores and the proper kind can always be obtained. Heat is harmful to bacteria If the temperature Is 212 F. Where articles are known to contain bacteria they may be killed by keeping them at the boiling point of water for twenty minutes, or a shorter time at a higher temnerature. 26. Conduction of Heat. When we use a stove-poker for a few minutes, the part which we are holding becomes uncomfortably hot. We call this travelling of heat along an object, conduction. If the heat reaches the cold end quickly, we say that the material is a good conductor. If we put a wooden handle on our poker, we may CONDUCTION OF HEAT 67 poke as long as we wish and our hands will not be burned. That is because wood is a poor conductor. Most metals are good conductors of heat, although some metals do not conduct heat as well as others. Water is a poor con- ductor of heat. Experiment 34. Good and Poor Conductors of Heat. Apparatus: Alcohol or gas lamp, pieces of copper and iron wires No. 12, 6"long, test tube. a. Hold the end of the copper wire in one hand and the end of the iron wire in the other hand, and put the free ends into the flame of a burner. Which one be- came warm first? Which is the better conductor? Hold the poor conductor in the flame and notice that it takes a long time to become hot at the hand. b. Fill the test tube nearly full of water and place as shown in the flame of a burner, so that the top of the water is heated. Do not let the flame touch the glass where there is no water, as it will break. When the water boils at the top how it the bottom? Is water a good or a poor conductor of heat? If you wanted to heat water where would you heat it, at the bottom or top? How does the ocean become heated, at the top or the bottom? THE GUIDE AIR, 27. Air a Necessity of Life. There can be no life of any sort without air. Ani- mals breathe it and plants need it, in order to live. There is air even in water and fishes could not live without this air. We live In an ocean of air which surrounds the whole earth and this ocean is called the atmosphere. The meaning of the word "atmosphere" is breath-sphere. Do you think that the atmosphere Is well named? Experiment 35. Holding- the Breath and Deep Breathing. a. See how many seconds you can hold your breath. You should be able to hold it one minute, with practice. b. Stand erect with the chest up, without having any of your muscles hard and take just as long- a breath as you can, breathing through the nose. When you think that you cannot draw in, or inhale, any more air, contract all the muscles of the body, and hold the breath for a few seconds. Slowly let the air come out. Letting the air out is called exhaling. Repeat several times and then see how long you can hold your breath. Always take this exercise before holding your breath. Why can you hold it longer than you did at first? Experiment 36. *The Effect of Depriving a Plant of Air. * Adapted from Farmers' Bulletin 408, U. S. Dept. of Agriculture. THE GUIDE AIR, 27. Air a Necessity of Life. There can be no life of any sort without air. Ani- mals breathe it and plants need it, in order to live. There is air even in water and fishes could not live without this air. We live in an ocean of air which surrounds the whole earth and this ocean is called the atmosphere. The meaning of the word "atmosphere" is breath-sphere. Do you think that the atmosphere is well named? Experiment 35. Holding the Breath and Deep Breathing. a. See how many seconds you can hold your breath. You should be able to hold it one minute, with practice. b. Stand erect with the chest up, without having any of your muscles hard and take just as long a breath as you can, breathing through the nose. When you think that you cannot draw in, or inhale, any more air, contract all the muscles of the body, and hold the breath for a few seconds. Slowly let the air come out. Letting the air out is called exhaling. Repeat several times and then see how long you can hold your breath. Always take this exercise before holding your breath. Why can you hold it longer than you did at first? Experiment 36. *The Effect of Depriving a Plant of Air. * Adapted from Farmers' Bulletin 408, U. S. Dept. of Agriculture. 72 AIR Apparatus: Two glasses or bottles, burner, stand, dish for heating. Materials: Geranium cuttings, olive oil, cardboard. a. Heat the water slowly. What comes out of the water long before it boils? Boil the water for two or three minutes and allow it to cool. b. Fill one of the glasses two-thirds full of water which has not been boiled, and fill the other glass two- third full of the boiled water, after it has become cold. Pre- pare two cardboard covers, as shown in the illustration, and put a geranium cutting in each. Pour olive oil on the surface of the boiled water to a depth of a quarter of an inch, being careful 'not to get the oil upon the cut end of the geranium slip. Watch the cuttings for a week or ten days and note the difference between the growth of roots upon the two cuttings. Do plants need air in order that their roots may grow? 28. Air in the Soil and in Water. If we take a handful of soil and examine it we will notice that it is made up of many fine particles of irregu- lar shape and size, which do not fit tightly together. Thus there are left a large number of tiny holes between the little particles, which all added make a large space. These spaces are all filled with air. When the sun is shining upon the soil it becomes warm and the air in it expands, and some of it comes out of the soil. As the ground cools off at night, the air within AIR IN SOIL AND WATER 73 the soil contracts again and more air enters to take the place left by the contraction. Since plant roots need air, can you see the advantage of cool nights during the sum- mer? Water also contains air, as was learned from the last experiment. In the next experiment we will see just how much air is held in water when it is cold. if! Experiment 37. To Show the Presence of Air in Soil and Water. Apparatus: Tin can, glass, two test tubes, one-hole stopper, glass tube two feet long, burner. Materials: Soil, water. a. Fill the tin can nearly full of dry soil, loosely packed, and quickly pour a glassful of water upon it. What do you notice? What can you say about the presence of air in soil? b. Throw away the wet soil and fill again with loosely packed, dry soil. Fill the glass even full of water and pour it slowly upon the soil, not allowing the top of the soil to be covered|p|r with water at any time. Continue to add water until the soil will take no more and the water surface comes up to the surface of the soil. How much water have you added? How much air was there in the soil? c. Arrange the apparatus as shown in the illustration. To bend glass tubing it should be held in the flame of an ordinary gas burner, or an alcohol lamp, or in the flame produced by an attachment for the Bunsen burner, as shown in the illustration, called a 74 AIR wing top burner. At least two inches of the tube should be heated, and it should be turned slowly so that all sides may receive the same amount of heat. When the glass has become soft, it should be re- moved from the flame and quickly bent at right angles and held in this position until it has hardened. If the bend is not well rounded it shows that the glass was not evenly heated. The second bend is to be made in the same way. Fill the test tube full of cold water and after properly arranging the apparatus, gently heat it. The outlet tube should dip into a little water. As the water is heated it expands and passes over into the other test tube. Do you see any air collecting in the heated tube? Where does it come from? If the water is heated too much it will begin to boil and may force most of itself over into the other tube. It is not necessary to heat it until it boils. Allow the water to cool and notice what part of the tube is occupied by air. This is the air which fishes use, and they could not live in water which had been boiled and then cooled. Review Questions, 16. 1. Which kind of soil will become the warmer in the sunshine, dark colored or light colored? Which is best for early planting? 2. When is the sunshine warmer, when the sun appears red or when it appears white? 3. How many degrees away from the direction of THE COMPOSITION OF THE ATMOSPHERE 75 a shadow is the direction of the light? How do you define these two directions? 4. How can you tell the time of sunrise if you know the time of sunset? 5. What is the proper temperature for the school- room and the home? 6. Why does the ground become warm faster than a pond? 7. Which will burn us the more, a piece of wood or a piece of copper, if both are at the same temper- ature? Explain. 8. Where do we live in our ocean of air, at the bot- tom or the top? Could we live anywhere else than where we do? 9. Would it do any harm to water plants so much that the ground would be covered with water? 10. What collects on the inside of a glass of cold water if left in a warm room? 29. The Composition of the Atmosphere. Some mornings when you come to school it is fogg\ and you think how damp the air is. Even if it is not foggy you have often noticed that the air is damp and you have heard persons say, "Clothes will not dry today." On other days, however, it has been brisk and bracing and the air has been called dry. Though the air has seemed dry it still contained water in an invisible form. It is from the invisible form of water that dew, fog, and clouds are formed. The amount of water in the air varies from day to day and even from hour to hour. The air near large bodies of water usually contains more moisture than 76 AIR does the air in other places. Why? If you leave a glass of cold water in a warm room, what collects on the outside? There is another part of the atmosphere called carbon dioxide, which also varies according to the local- ity. In the open country there is very little of this gas, but in cities, and in rooms where there are a large num- ber of persons, it may increase so as to harm us, for it is not a good gas to breathe. Although the amount of water and carbon dioxide in the atmosphere varies greatly, the largest portion of the air is composed of two gases which do not vary About one-fifth of the air is oxygen, and about four- fifths is nitrogen. These gases are so important that we will study them one at a time. Thus you see that the air which you thought was just one thing is really composed chiefly of four substances: nitrogen, oxygen, carbon dioxide, and water. Besides these, there are argon, dust, and bacteria. Experiment 38. The Amount of Oxygen in the Air. Apparatus: Saucer, glass, candle, flat cork stopper, a. Cut the can- dle so that it is not more than one inch long and make a "life pre- server" for it from the stopper. To do this, cut a round hole in the stop- per, in which the candle will fit tightly. The cork CARBON DIOXIDE 77 need be only one-fourth of an inch thick, but it should be placed near the wick end of the candle. Fill the saucer with water, place the candle upon the water, light it, and cover with the glass. Tell what happens. b. How high did the water rise? The candle has used all of the oxygen and left the nitrogen. How much of the air is nitrogen and how much is oxygen, according to your experiment? Why did not the candle go out at once? Why did not the water begin to rise when the candle was covered? Before answering this question you must think of the effect of heat upon a gas. See Experiment 24. Why did the water continue to rise after the candle went out? Note : The same experiment may be repeated with a large bottle, having straight sides, and a cake pan, or bread pan, to see if the same results will be re- peated. The following experiment is for the teacher : \ j Experiment 39. The Amount of Carbon Diox- j| ide in the Air. Apparatus: A twenty-ounce glass-stoppered bottle, glass measure graduated in cubic centi- meters, medicine dropper graduated to hold one- third of a cubic centimeter. Materials: Limewater solution (pure water left in contact with slaked lime until the water will not take up any more lime. Dilute the clear decanted liquid with 99 times its own volume), phenolphthalein solution (dissolve one part of phenolphthalein in 500 times its own weight of 50 per cent alcohol.) AIR a. Fill bottle with pure water, and empty it in the place where the air is to be tested. This will insure the bottle being filled entirely with the air of the room. Add 10 c. c. of limewater solution and one-third c. c. of phenolphthalein solution, stopper, and shake. If the red color disappears in three minutes or less, the air is unfit to breathe. 30. Oxygen and its Uses. We have learned that air is necessary for life of any kind and that it is composed of nitrogen, oxygen, carbon dioxide and water. We have also learned that it is the oxygen which caused the candle to burn since it stopped burning- when all the oxygen had been used. Therefore we call oxygen the supporter of combustion. Just as the candle needs oxygen in order to burn, so we need oxygen in order to live. It it only the oxygen of the air which the body uses ; the nitrogen is exhaled unchanged. If there are many persons in a close room most of the oxy- gen will soon be used and the air will become unfit for breathing. Headaches and drowziness are more often produced by bad air than by hard lessons. Yawning is caused by a desire to obtain more oxygen. Since it is the oxygen of the air which supports com- bustion and air is composed of only one-fifth oxygen, we might suspect that combustibles would burn much more vigorously in oxygen than air. Let us see if this is true. Experiment 40. To Prepare and Use Oxygen. Apparatus: Test tube, test-tube holder, burner. THE PREPARATION OF OXYGEN 79 Materials: Potassium chlorate (powdered), manga- nese dioxide, splinters of wood. a. Mix equal parts of potassium chlorate and man- ganese dioxide on a piece of paper, and pour into a test tube. Hold the test tube in the flame of the burner, by means of the test-tube holder, until it becomes very hot. Then light a splinter of wood, let burn for a while, blow out the flame, and insert the glowing end into the tube, continuing to heat the tube. What happens? There is oxy- gen coming from the mixture in the tube. Does wood burn better in oxygen than in air? Is oxygen invisible or visible? Colored or colorless? Review Question, 17. 1. Why does the skin become tanned? 2. If you run toward your image in a mirror going ten feet a second, how fast will you approach your image? 3. How should the lights of a house be arranged to give the best light for the eyes? 4. Why are woolen underclothes better protection from cold than cotton garments? 5. Should the thermometer hane near the floor, on the level of your head, or near the ceiling of a room to be of use to us? 6. How can you show that there is air in water? 7. Give all the reasons which mike you think that there is water in the air. 8. How can you show that about four-fifths of the air is nitrogen ? 9. Why does pure oxygen support combustion better than air? 10. What is one cause of headaches? 80 AIR 31. Nitrogen and its Uses. As we have learned, about four-fifth of the air is nitrogen. We saw that it was oxygen which supported combustion and that pure oxygen supported combustion much more vigorously than air, because air is only one- fifth oxygen. What do you 'think the effect would be upon fires if all of the air were oxygen? One of the uses of nitrogen, then, is to lessen the effect of oxygen. Where the amount of one substance is reduced by the addition of another we say that the first substance is diluted, and call the process dilution. Nitrogen dilutes the oxygen. Pure oxygen is sometimes inhaled, under the advice of a doctor, by those who have weak lungs. For a long time it was thought that nitrogen had no other use than to dilute the oxygen. Now it is known that tiny plants, so small that they are invisible, called bacteria, live upon the roots of some of the larger plants and absorb the nitrogen from the air. This they change into material which is needed by the larger plants. This is one example of the good which bacteria do for us. Later we shall learn that they help us in many ways. CARBON DIOXIDE 81 The larger plants cannot take in the nitrogen until it has been changed by the bacteria, and many of the plants could not live if it were not for the bacteria. The little lumps upon the roots of the plant in the illustration are called nodules. Each nodule is the home of bacteria. The illustration is the root of the garden-pea, but there are nodules upon the roots of many other plants and trees. Whenever you see these nodules you will know that there are many helpful bacteria within them. The kind of food v r hich the plants form from the material supplied by the bacteria is the source of our strength. When we study plants and food we shall learn more about these bacteria and their work. 32. Carbon Dioxide. The amount of carbon dioxide in the air varies according to the location. Near factories there is a larger amount than in the open country, or on the ocean, while in a room where there are many persons the amount may become very great. This shows that fires produce it and animals exhale it. In the open country, air contains only three or four parts of carbon dioxide in ten thousand parts. The gas is a combination of oxygen and carbon. Coal, coke, and charcoal, all of which are fuels, are chiefly carbon. If the air of the room contains eight to ten parts of carbon dioxide in ten thousand parts of air it is unfit for us to breathe. Since exhaled air contains four hun- dred parts in ten thousand, it can easily be seen that there should be, not only a supply of fresh air, but the stale air should be removed continually. In addition to carbon Cut supplied through United States Department of Agriculture. Elem. Sci. 6 82, AIR dioxide we exhale small, invisible particles of decayed animal matter which also are poisonous unless diluted with plenty of fresh air. You all know the story of the Black Hole of Calcutta, and the fatal results from the lack of .fresh air. > ," Carbon dioxide has its use and it is a most important one. Plants absorb it and break it up into its parts, car- bon and oxygen. The plants keep the carbon, making wood of it, and give out the oxygen to the air again. Thus plants purify the air. For that reason we should have plants in our -school rooms and houses. Plants owe their ability to take in carbon dioxide to the green color- ing matter in their leaves and stalks. We have learned that the sunlight causes plants to be green, and so you see that it is the sun which causes plants to grow. That is why plants grow in the direction of the sun. Experiment 41. Carbon Dioxide from Combustion and from the Breath. Apparatus: Candle, funnel, syringe bulb, glass tube, 1,0" long, test tube. << Materials: Limewater (all the slaked lime that will dissolve in water; use the clear liquid only.) a. Arrange' apparatus as shown in the illustration, light candle, and force the gases which come from the candle into the limewater. What happens? What caused the change? b. Blow out candle and repeat. In this case it is the air of the room which is being forced into the lime- water. Does the change take place? SOURCES OF CARBON DIOXIDE c. Take the apparatus out of doors and repeat. Do you finally see any change? d. Now repeat (b.) and (c.), counting the number of times it is necessary to squeeze the bulb in order to obtain the same result. Divide the number of times it takes indoors by the number of times required out of doors. The result will show about how much more car- bon dioxide there is indoors than out of doors. If the room is properly ventilated there should be little differ- ence. Is the schoolroom properly ventilated? 84 AIR e. Blow through the glass tube into some limewater. Do you think that you exhale the same gas as a candle produces? The illustration shows a method of collecting the oxygen which is given off by a plant. In this case it must be a water plant, but oxygen is given off by all vegetation. If you wish to perform this experiment you must collect some water plants and place them in the bottom of a large dish. Cover them with a funnel, which may be made of tin, and fill the dish until the top of the funnel is covered with water to a depth of one inch. Take a test tube, fill it with water, cover the end with your thumb, and invert it in the dish, not letting any water escape. Slide the test tube over the end of the funnel and set the whole apparatus in the bright sun- shine. In a few minutes you will see bubbles forming, and in a day or two, the test tube will contain enough oxygen for a test. To remove the test tube lift it from the funnel, putting your thumb asfain over its mouth, while it is under the water, and re- move from the water. Turn the test tube right side up, RESPIRATION 85 keeping the thumb tightly in place. Test for oxygen. How will you do it? Is it oxygen? How do you know? 33. Respiration. The Necessity for Pure Air. Breathing consists of inhaling and exhaling. Breath- ing is also called respiration. Do you know how many breaths you take in a minute? How can you find out? Do you always take the same number of breaths in a minute? What makes you breathe faster sometimes? Your heart beats faster when you breathe faster. A grown person, or adult, breathes 18 times a minute, not exercising, and his heart beats 72 times a minute, or four times the number of breaths. Young persons breathe faster and their hearts beat faster. Usually the heart beats four times for each breath. We should breathe through our nose because it is a sort of sieve which keeps the dust from passing on to the lungs, and it also warms the air a little before it reaches our lungs. If persons find trouble in breathing through the nose they should consult a doctor. The amount of air which we ordinarily inhale and exhale at each breath is 30 cubic inches. When we draw a long breath, or "heave a sigh," the quantity of air which we inhale or exhale is about 130 cubic inches. By trying, we can exhale about 100 cubic inches more. Even then there remains about 100 cubic inches which cannot be exhaled. The amount of air which the lungs hold is called their capacity. All persons do not have the same lung capacity, but where the capacity is less than it should be, it may be increased by breathing exercises and the right kind of physical exercise. 86 AIR Experiment 42. The Capacity of the Lung's. Apparatus: Large bottle, holding at least a gallon, cork stopper to fit, large pan, holding at least two gallons, piece of rubber tubing- three feet long, piece of glass tubing which has had its rough edges rounded off in a flame. a. Fill the bottle full of water, insert the stopper and invert in a pan in which there is about two quarts of water. Remove the stopper and slip one end of the rubber tubing up into the bottle, which should be tipped a little to one side, and held there, in order not to jam the tubing. The glass tubing should be inserted in the other end of the rubber tubing to serve for a mouthpiece, which may be washed before each pupil uses it. Take several long breaths before measuring your lung capacity. Then take the longest breath possible, place the tube in the mouth, and blow hard. Keep on blowing until you can- not exhale a bubble more. Immediately remove the rubber tube from the bottle and estimate your lunsf capacity. There are 231 cubic inches in a gallon. Tf 100 cubic inches of air still remained in your lungs, what is the capacity of your lungs? The amount of air which is needed per minute, in a room in which there are several persons, cannot be found out by multiplying the number of cubic inches used in each breath by the number of breaths per minute, and by the number of persons in the room. We must remem- ber that the air which we exhale contains four hundred parts of carbon dioxide in ten thousand, while the proper THE NECESSITY FOR PURE AIR 87 amount of carbon dioxide is no more than eight or ten parts in ten thousand. Now 400 is 50 times 8. This means that one breath spoils 50 times that amount of air, not only for others but even for ourselves. For this reason it is very necssary to have a large supply of fresh air. If there are lights burning in the room, such as kerosene lamps or gas, much more air is needed. An ordinary light spoils as much air as four persons in the same time. Electric light does not affect the air. Review Questions, 18. 1. Why does pouring hot water into a glass dish break it? Would there be any difference if the glass were thin? 2. What is the result of incomplete combustion? Why is it not wise to allow incomplete combustion? 3. Why should a person not run if his clothing is on fire? What should he do if he is alone? 4. What kind of clothing is most liable to burn? 5. What is the composition of the air? 6. What would happen if there were no nitrogen? 7. How does carbon dioxide get into the air? 8. At the ordinary rate of breathing, how much air will twenty pupils breathe in half an hour? How much air will they spoil in the same time? 9. Find the number of cubic inches of air in your schoolroom and tell how many times it must be changed in every half hour in order to give you enough fresh air, if you were the only person in the room. 10. Solve Problem 9 for the number of persons in your room. THE GUIDE WATER. 34. Water is a Liquid. A block of wood, or a stone, has a shape which does not change. What is the shape of a quart of water? Water will fit any dish that you put it into, and thus has no shape of its own. Anything which has a shape which does not change is called a solid. If the material fits the dish into which it is put and leaves no empty spaces, it is a liquid. While water is a liquid and fits perfectly every dish into which it may be put, there is one part which is always the same. This is the top of the water, called its surface. The surface of water is always flat, or hori- zontal. Another name for horizontal, is level. All parts of a horizontal, or a level line are the same distance from the center of the earth. If we want to make the floor of a house level we can do so by means of a hori- zontal surface of water. Experiment 43. The Level. Apparatus: Pie tin, small round bottle and stopple. a. Half fill the pie tin with water and place it upon the board which you are to make level. If the water does not come up the same distance all around the tin, when it is on the board, the board is not level, or hori- zontal. Put little pieces of wood or stones, under the. low sides of the board until the water is at the same height all around the tin. Can a board be horizontal in one direction, say north and south, and not horizontal in 90 WATER the east and west directions? Is there any difference between being level and being horizontal? b. Half fill the little bottle with water and lay it upon its side on a board. When the surface of the water is the same distance. up from the side of the bottle, all along, the board is horizontal in the direction of the length of the bottle. How can you make a board level by . means of the bottle? The bottle is called a level. A simple level is shown in the illustra- tion. In this level the tube is curved so that the air bubble is always at the highest part. A block of wood, or a stone, will stay where you put it; water will run off. All liquids act in the same manner and are said to flow. If the water faucet is gradually shut so that the flow of water becomes less and less, the stream will suddenly break into drops. How would a rainstorm be if water did not break into drops? Water- drops are all the same size unless the drops come together. Do raindrops ever come together? On account of the flowing of water there is a saying, "Water always seeks its own level." This means that the surface of water is at the same level everywhere if the water can flow freely between all parts. Experiment 44. *Water Seeks its own Level. Size- of Drops. * It is desirable to take Sec. 58 before performing this experiment. WATER SEEKS ITS OWN LEVEL 91 Apparatus: Funnel, rubber tubing, glass tube to make apparatus as shown in the illustration, medicine dropper, graduate (50 c. c.), small dish. a. Fill the funnel and tube with water and hold the funnel and tube in various positions. What do you notice in regard to the level of the water in the funnel and the level of the water in the tube? b. Fill the medicine dropper and carefully count the drops which are needed to make 5 cubic centimeters. In reading the graduate it must be placed on a level table and the reading must be taken with the eye on a level with the surface of the water. Read the lower surface of the water. How many drops in one cubic centimeter? If there are 946 cubic centimeters in a quart, how many drops of water are there in a quart? 35. Water can Pass into Some Things. If we put a sponge into water some of the water goes into the sponge. The same thing is true of clothing. WATER We know that if we step into water it soaks into and through our shoes. All bodies which allow water to pass into them or through them are called porous, on account of many little holes in them which are called pores. When porous bodies take in water we say that they absorb water. There are other bodies which are porous although they do not seem to be so unless we experiment with them. A brick is very porous, and so are many rocks. As you know, the ground is porous, or the rain would not sink into it. Experiment 45. * Porous Bodies Absorb Water. Apparatus: Balance, weights, cake pan. Materials: Sponge, cloth, brick, porous stone. a. Weigh the sponge dry, let it soak in water and weigh again. What is the gain in weight? How much water could a pound of sponge take in? b. Repeat with the brick. The brick should remain -in the water for a full day. c. Repeat with the cloth and .porous stone. The only reason that some bodies are porous is because they contain little holes, or pores. If we wish to keep the water out of a body we must close the holes, just as we close the gate to keep out the dogs or other animals. Preparing material so that it will not permit water to enter is called waterproofing. See Section 74. Experiment 46. To Make Porous Bodies Water- proof. * Section 59 should precede this experiment. WATERPROOFING 93 Apparatus: Burner, ring stand, wire gauze, tin dish. Materials: Piece of cloth, 4"x5", paraffin. a. Melt the paraffin by gentle heat and dip the cloth into it. While the paraffin on the cloth is still warm, shape the cloth into a four-sided box. When cold it should hold water. What keeps the water from going through the cloth? Rubber is the material which is commonly used to fill the pores of porous material, in order to make it waterproof, as rubber is not altered by ordinary changes in temperature. Do you think that your box would hold hot water? While it is not pleasant to have water come through our clothing or even our houses, the porosity of materials has its use. Water which passes through the small pores has lost a large amount of its dirt. The separation of dirt from water, by means of porous bodies, is called filtration, and the porous body is called a filter. All water which comes from the earth in springs and wells has been filtered by passing through the porous ground. We can filter water, where necessary, by means of porous dishes or porous paper. Experiment 47. Filtration. Apparatus: Funnel, funnel-holder (cut a hole in the small end of a chalk box), test tubes. 94 WATER Materials: Sawdust, sand, filter paper. a. To use filter paper, fold it in halves and then again in quar- ters, as shown in the illustration. Separate one thickness from the other three and place in funnel. Mix some sawdust, sand and water. Then filter. Does the water pass through clear? Review Questions, 19. 1. What are two causes of the variation in the heat which we receive from the sun? 2. What causes contraction ? 3. What part of the room is the warmest, near the ceiling, on the level of your head, or near the floor? 4. What are the advantages of deep breathing? How can you prove your answer by figures? 5. Name the parts of the air that are used by plants, stating how they are used, and the parts of the air which are taken in by animals, giving the use of each part. 6. If you were given a long rubber tube, which would reach across the room, and two glass tubes to fit the ends of the rubber tube, tell how you could put two shelves on the opposite sides of the room at exactly the same level. 7. How could you find out whether a body is porous? 8. Name all of the porous bodies you can think of and state the advantages or disadvantages which are due to their porosity. 9. What is meant by waterproofing. Give some examples of waterproofing. SOLUTION 95 10. Why is water from springs usually clear, while water in rivers is dirty? 36. Solution. When we put sand or sawdust into water we could still see it. Can you see sugar when you have put a little into water and have stirred it well? If a solid disappears, when put into a liquid, we say that the solid dissolves, and we call the result a solution. Not only does water dissolve solids but it can also hold gases in solution. Any liquid which can dissolve solids or gases is called a solvent. In Section 28 we saw that water can hold con- siderable air in solution if the water were cold. The best way to learn more about solution is by experimenting. Experiment 48. Solution and its Oddities. Apparatus: Two glasses, tin spoon, burner, tin cans, thermometer, funnel, filter paper, glass rod. Materials: Sugar, salt, baking soda, cream of tar- tar, ammonium chloride (commonly called sal ammoniac). a Fill a glass full of water. Very slowly add some sugar while carefully stir- ring. Note that it is possible to add considerable sugar without making the water overflow. Now add some salt in the same way to the same water. Can you do it without making the water overflow? What is one of the oddities of solution? Try filter- ing the solution. Do the sugar and the salt pass through? The method of pouring liquids from a glass is shown in the illustration. 96 WATER b. Put a little cold water in one glass and the same amount of hot water in another glass. Now see how much sugar will dissolve in the cold water and how much in the hot water. When a solvent holds all of a solid it can, the solution is said to be saturated for that temper- ature. Which solution becomes saturated first, the hot one or the cold one? Which is better for dissolving solids, cold water or hot water? c. Fill a glass one-fourth full of cold water, take its temperature, and then add half as much sal ammoniac as there is water. Stir rapidly and immediately take its temperature. W r hat is another oddity of solution? Can you explain (b.) above, now that you have done (c.) ? Do you think that the solution is saturated? Why? d. Put a little dry baking soda and a little dry cream of tartar into a dry glass. Nothing will happen. Now add some water. What happens? Solution per- mits the action of one material upon the other. The gas is carbon dioxide and it is this gas which makes soda biscuits rise- Water owes its power of removing dirt to the fact that it can dissolve so many substances, but there are many kinds of material which water cannot dissolve. Fortunately for us there are other solvents which can dissolve some of these. Two common examples of spe- cial solvents are alcohol and gasolene. We should be very careful when we are using either of these solvents. OTHER SOLVENTS 97 not to be near a fire, or even be in the same room with a fire or a burning lamp, for both are very easily set on fire. Gasolene produces a gas which may be set on fire by a flame although several feet away. Experiment 49. *The Use of Gasolene and Alcohol as Solvents. Apparatus: Two small bottles with stoppers. Materials: Gasolene, alcohol, kerosene, pieces of cloth, grease (lard), rosin, pitch. a. Shake a little grease with water in a bottle. Does the grease dissolve in the water? Pour off the water, add gasolene and shake again. What is the result? b. Put a very little grease on a piece of cloth. This will make a grease spot. To remove the grease spot the space all around the spot should be wet with gasolene before putting the gasolene upon the spot itself. If gasolene is put upon the grease first the grease will spread and leave a ring after the spot has been removed. Try putting the gasolene upon a grease spot on a s'econd piece of cloth and notice the familiar ring when the gasolene has evaporated. Shake a little powdered rosin with water in a bottle. Does the water dissolve the rosin? Pour off the water, add some alcohol, and shake again. What is the effect of alcohol upon the rosin? Pour the result upon a smooth piece of wood and allow the alcohol to evaporate undis- turbed. How does the wood appear? Rosin is used in cheap varnishes. Do the cheap varnishes scratch easily? Put some pitch upon a piece of cloth and remove it with kerosene. It may be necessary to allow the cloth * Thil~experiment may be omitted or performed only by the teacher. Elem. Sci. 7 98 WATER to soak in the kerosene for some time. Pitch may be removed from the hands with kerosene. The kerosene may then be removed with soap and water. 37. Crystals. We have seen that some solids can disappear in solution. Do you think that they can come out of solu- tion and appear again? The only way in which we can get a solid out of solution is to drive off the water by means of heat, called boiling, or we can let the water pass off slowly and without bubbling. This last method is called evaporation. Let us learn about this by some experi- ments. Experiment 50. Crystallization. Apparatus: Burner, ring stand, wire gauze, two beakers, three glasses, stirring rod, deep dish. Materials: Alum (powdered), copper sulphate, common salt, string. a. To a little water add one half as much powdered alum and stir for a few minutes. Does it all dissolve? Now put it on the ring stand, resting it upon the wire gauze, and heat it until it boils. Does heat aid solution? Place the beaker containing the solution, in a dish of cold water and stir it constantly until cold. What happens? Heat the beaker again until all of the alum has dis- solved and then place it again in the dish of cold water, but do not stir it or touch it until it is cold. What is the result? What you see are crystals. Which method produces the larger crystals, rapid cooling or slow cool- ing? Keep the crystals. CRYSTALLIZATION 99 b. Repeat (a.), using the same amount of water but using three-fourth as much copper sulphate as water, in the place of alum. What are your results? Note the shape of the crystals. Are they the same as the alum crystals? A micro- scope, such as is shown in the illus-' tration will help you, although it is not a necessity. c. Make a saturated solution of common salt, one of alum, and one of copper sulphate. Place in separate glasses and in each solution hang a piece of string from a little stick placed across the top of the glasses. Set aside for a few days. The water will evaporate and leave the solids. Are all the crystals the same shape? The crystals of any one substance are always the same where they have formed slowly and have had plenty of room in which to form. Can you tell the difference between a salt crystal and an alum crystal? There are many crystals in nature although there are but six different kinds. We m?.v imitate a few of the- crystals by cutting out the shades, as shown in the illus- 100 WATER trations, from thick paper, folding: on the dotted lines, and pasting their edges together by means of strips of paper. 38. Water for Drinking. There is hardly any pure water as it occurs in nature. On account of the great power which water has to dis- solve so many substances, there is usually some material held in solution. Fortunately for us, many of the sub- stances found in water are not harmful to man, while some of them are very helpful. The harmful substances which are dissolved in water are usually so bad tasting that there is little danger from them, for no one will drink the water. While the dissolved material is usually harmless, there is great danger in drinking impure water. This is due to a kind of plant life we have already become acquainted with in Sections 13 and 25. Some of these, which we learned were called bacteria, may cause typhoid fever. Although the water is clear and seems pure, the bacteria may be present. On the other hand, dirty water may be free from bacteria and be harmless. Wells should be so located that drainage cannot possibly reach them, for decayed animal matter is what these bacteria live upon. Since water can pass through the porous rocks, wells must be far away from open drains and stables. The body requires a large amount of water and most grown persons do not drink enough. The more water we drink the better are the wastes carried from the body. We have learned that while water can dissolve many DRINKING Y\ >''/''>: 101 things, a limited amount of water can dissolve only a limited amount of any one solid. Thus, unless we drink a sufficient amount of water, the impurities which are produced in our bodies by the wear and tear of living, or those which are taken in with food, will not be carried off rapidly enough. Unless we are warm we should drink all the water we desire. It is best to drink slowly and often, rather than rapidly and in large quantities. While the drinking of a large amount of water is very desirable, and even necessary, yet there are other common drinks which are harmful. Any drink which contains alcohol, such as beer, wines, whiskey, brandy, and many others, cannot fail to harm a person to some extent. Alcohol is a poison, and even a small amount of a poison will have some harmful effect. Some persons who use drinks which contain alcohol may seem to be unaffected, but they do not know how much greater progress they might have made if they had left alcohol alone. Alcohol should always be considered as a drug. Compared with alcohol, coffee and tea are not very harmful to grown persons unless used to excess. Young persons should not drink either coffee or tea until they have completed their growth. Even grown persons should be careful not to drink too much of either coffee or tea. A person who uses too much of these drinks becomes nervous and irritable, and his eyes are often affected. Review Questions, 20. 1. Why is it warmer in summer than in winter? Why is it warmer near noon than at sunrise or sunset? 1G2; ; WATER 2. If your clothing should be set on fire, what would you do. 4 What would you do if you saw the clothing of another person burning? 3. Why are you sure that there must be air. in water? 4. How much air does a person spoil by breathing for one hour? 5. What is the best kind of light to use in our Houses? Why? 6. Why are brick houses sometimes damp? Could the dampness have been prevented? 7. Why do we stir or beat frosting for cake for a long time? If we did not beat fudge what would be the result? 8. What is meant by evaporation? W r hat causes evaporation to be more rapid? 9. When do we need the more water for drinking, when we have been perspiring a great deal, or hardly perspiring at all? 10. Explain how harmful drinks may harm us although we may not notice the harm. 39. Water for Cleansing. The most important use for water is for drinking. We shall see in the next section that plants, as well as animals, require a large amount of water in order to live. The use for water which is next in importance to its. use for drinking and for plants, is its use for cleansing. Water owes its power of cleansing to its ability to dissolve so many substances. We know that if water has some dissolved substance HARD AND SOFT WATER 103 already in solution it will not dissolve other substances as readily as will pure water. If water has very little dissolved material in it, it will cleanse easily. We call such water soft. Rain water which has fallen after it has been raining for some time, is very soft. Why? Water obtains its dissolved material from the ground. Water which contains dissolved substances is called hard. Soft water makes suds with soap very easily while hard water does not. Since soap has the power of acting with the water to dissolve or loosen dirt, if it does not dissolve in the water and form suds, the water is hard to use for washing. Cleansing Is much easier with soft water than with hard water. Experiment 51. *Hard and Soft Water. Soap. Apparatus: Burner, ring stand, tin cup, pint bottle with stopper. Materials: Distilled water, powdered or shaved soap. a. Measure the smallest amount of soap which will just begin to make suds when shaken with a half pint of distilled water in a pint bottle. This will give you a standard, for distilled water is absolutely pure and will make suds with the least amount of soap. Any other water will use more soap. b. See how much soap is necessary to produce suds with a half pint of ordinary water. Take another half pint of the same kind of water which has been boiled for at least five minutes. Does it take more or less soap to make suds with the boiled water than with the unboiled water? Hard water which can be made soft by boiling * See Experiment 79. Distillation. 104 WATER is called temporarily hard. If the water is not rendered soft by boiling it is called permanently hard. Was the water you used temporarily or permanently hard, or was it soft? Since hard water requires more soap than soft water, in order to produce suds, the use of hard water for cleans- ing is more expensive than the use of soft water. Water which is tem- porarily hard contains carbon diox- ide, as well as a solid. When we boil it the heat drives off the gas and the solid collects on the side's and bottom' of the dish ; thus both are removed on account of the heat and the water becomes soft. How could you show that carbon diox- ide is driven off from temporarily hard water? We wash our clothing to remove the visible dirt so that the clothing will be neat and clean. At the same time we remove the invisible dirt which is usually more harmful than the visible. The invisible dirt is composed chiefly of material which has been left by the perspira- tion when it evaporated, particles of dead skin and bacteria. ' Since the perspiration comes from our bodies it is of great importance that we keep our skin clean not alone visibly clean but really free from anything which can be washed off. The mouths of the tubes through which the perspiration comes, called pores. PLANTS NEED WATER 105 ''""should be kept clean and open by frequent baths which Bought to be taken daily, if possible. Dirt cannot be removed completely without the use "of soap. ' There are two kinds of soap laundry soap and " toilet soap. Soap which is suitable for washing clothes and for general housecleaning is usually unfit to be used "on the skm. ' On the other hand, toilet soap, which is intended for tender skin, would have little cleaning ;; power if used "on clothes. See Section 77. -40. Plants Need Water. We all know" that plants need water, for if we forget "to water them they quickly wilt, and, if they go too long without water they die. If the plants have only wilted they soon take up the water and become stiff and vigor- " ous again. In the next section we will learn the reason 'for this change. The amount of water which plants "need is very great. The water is carried away from the leaves by evaporationjust as it is -carried from wet clothes "which are hung 'to dry. When we think of the very large surface of the leaves of a tree we wi 1 ! realize that the amount of water which can be given off is enormous. We call the giving off of water from the leaves of a plant transpiration. Transpiration ^takes place only on ' "' the under si'de of ' leaves. Seeds will not begin to open unless' they are supplied with water. Then they swell' Trn'fil they 'burst, and the "young plant comes forth. The ^amotint'th'at'seeds swell 'is always a surprise, as you know 'if you 'have ever "put beans to soak'." 106 WATER Experiment 52. The Effect of Water upon Seeds and Plants. Apparatus: Two glasses large enough to cover a small plant. Materials: Beans, a plant in a can or pot, two pieces of cardboard 6"x6". a. Fill a glass one-half full of beans and then com- pletely fill the glass with water. Set aside for twenty-four hours and tell what happened. The beans may. be dried by putting them in the sun. b. Cut a slit in each piece of cardboard from the middle t)f one side to the center, Slip the pieces around the stem of the plant from opposite sides and press them down upon the top of the flower-pot Cover the plant with the glass and set it in the sun. The experiment should ap- pear like the illustration. What collects on the glass after an hour or so? Where does it come from ? Why were the pieces of cardboard used? 41. Capillarity. The word "capillary" means "like a hair," that is, Very fine. Capillarity is the strange action of liquids in Cut supplied through Uhited States Department of Agriculture. CAPILLARITY 107 tubes which are as fine as a hair, or even finer. Let US perform some experiments which show capillarity and talk about it afterwards. Experiment 53. Examples of Capillarity. Apparatus: Several 6" pieces of glass tubing of different diameters, two glasses, lamp wick, block of wood. Materials: Cube .sugar, red ink, a. Fill one of the glasses with water and place the tubes in it. Describe how the water goes up the tubes. A little red ink, added to the water, will make it easier to see the water in the tubes. In which tube does the water go the highest? You can make a very fine glass tube by heating a short piece of ordinary glass tubing in the flame of a wing burner, and then suddenly pulling the two ends as far apart as you can reach. Water will go six or eight inches up such a tube. Try it. b. Fill one glass with water and place it upon the block of wood. Now wet the lamp wick thoroughly, wring it as dry as possible and bend it over the edge of the glass so that it reaches the bot- tom of the glass* while the other end falls into the other p"lass placed near the block. The lower glass should be empty. Tell what happens in a few min- utes. What is this an example of? The oil in a lamp reaches the flame in the same way. c. Dip one corner of a lump of sugar in some colored 108 WATER water and see how quickly the water passes through the whole lump. Capillarity acts in all directions. Thus if we lay a lamp wick flat upon a table with one of its ends in a little pool of water the other end will soon be wet. Capillar- ity acts faster downward than in any other direction. Can you explain why this is so? When you put a drop of ink upon a blotter, how does it act? What causes it to act in this manner? Think of all the examples of capillarity you can. Bodies must be porous in order that there may be the little holes in which capillarity may act. If we wish to stop capillarity we must close the holes. We have learned that water is necessary for plants and that the 'soil must be kept damp if we expect the plants to grow well. How do you suppose that the soil holds the water? Did you ever see water put into a saucer which was placed under a flower pot? How did the plant obtain the water? All soils are not the same in their ability to hold, or take up, water and the follow- ing experiment will show the right kind of soil to use for flowers. Experiment 54. How Water is Held in the Soil. Apparatus: Chalk box, or other small box, with four or five holes in one side large enough to hold stu- dent lamp chimneys, four or five student lamp chimneys, .with. cheese cloth tied over their smaller ends, pan. CAPILLARITY IN SOILS 109 Materials: Gravel, sand, coarse soil, fine soil, vege- table mold. a. Arrange the apparatus as shown in the illustra- tion and have the water cover the ends of the chimneys. Fill each chimney with a different kind of material. In which d o e s!f the water rise :pl the highest? In which does the water rise the fastest? Which soil would you prefer to have on your farm, if you were a farmer? The farmer is very much concerned with capillarity and we will study it some more when we come to Section 54, in which we shall learn that the farm is just like a workshop. Capillarity, besides bringing the water to the roots of plants, is one of the causes of the rise of sap in the stalks of plants and trunks of trees. The evapo- ration of water from the leaves aids the rise of sap, just as the burning of the oil in lamps aids the capillarity in the wicks in bringing the oil to the flame. The next Cut supplied through United States Department of Agriculture. 110 WATER experiment will prove that capillarity acts in plants, as well as showing where the sap rises. Experiment 55. Capillarity in Plants. Apparatus : Glass, knife. Materials: Red ink, twigs of any tree having flat leaves. a. Cut a few twigs and put them immediately into some water which is strongly colored with red ink. Place the glass in the sun and in a draft of air, if possible. At the end of ten minutes remove one twig and split it lengthwise. Where did the colored water go? Remove another twig at the end of half an hour and examine in the same way. Leave another twig for a full day. How do the leaves appear? How did the colored water get through the stem? Make a drawing of the twig, split lengthwise, showing just where the colored water passed through it. If the stalks of plants are not woody, they receive their stiffness from the capillary tubes in them being full of water. If the plants do not receive enough water the tubes become empty and the stalks flabby. We say that the plants wilt. When is a garden hose stiffer, full of water or empty? Review Questions, 21. 1. What was the position of the Great Dipper last night at eight o'clock? 2. What are the uses of nitrogen? REVIEW QUESTIONS 111 3. How is carbon dioxide harmful and in what way is it helpful? 4. What are some of the oddities of solution? 5. Name all the uses of water. Which one is the most important? 6. Why is soft water cheaper to use than hard water although the same price is paid for each? 7. How can you prove that plants obtain water from below the surface of the ground? How do they do it? 8. Why is wet earth heavier than dry earth? Which kind of earth would be heavier when wet, a fine earth or a coarse earth? Explain. 9. Why do farmers break up the soil so that it is fine, before they plant? 10. Why do our feet become wet when we walk on the wet sidewalk? THE GUIDE PLANTS AND ANIMALS. 42. The Beginning of Plant Life. The beginning of all plant life is in the seed. As long as the seed remains dry the little plant rests, but as soon as water is absorbed by the seed it cracks open and the tiny plant begins to grow. Let us examine some seeds and learn how the plant gets its first start. Experiment 56. The "Pocket Garden." Apparatus : A plate and a saucer. Materials: Blotting paper, seeds of beet, bean, corn, pea, radish, squash. a. Lay a square of blotting paper upon the plate and upon it place the seeds. Cover the seeds with an- other square of blotting paper and moisten both with water. Now cover all with the saucer. Keep the blotting paper moist but do not have the seeds under water. Cut supplied through United States Department of Agriculture. Elam. Sci. 8 114 PLANTS AND ANIMALS Keep in a warm place and examine once a day, noting the order in which the seeds sprout. b. Make several drawings of each seed, showing the method by which the baby plant comes out of the seed. c. Write a description of the roots, stem, and leaves of each plant.* Note to teachers: This work may be extended over con- siderable time and many other seeds may be sprouted. The drawings and descriptions would make a good supplement to the English and art work. 43. The Testing of Seeds. All seeds do not sprout because all of them are not perfect seeds, or have been harmed in some manner. It is of very great importance to the farmer that he obtain good seed, for otherwise he might plant many seeds which would not grow. Tm*is the crop would be less than it should be and the farm would not be as productive as it might otherwise be. Most farmers now test their seeds because they have learned that a little trouble in the beginning will save them much money in the end. The testing of seeds to see if they will all sprout is called the germination test. Experiment 57. * Germination Tests. Apparatus: Shallow wooden tray, tacks, string. Materials: Sand, seeds of various kinds from va- rious stores. a. Mark off the sides of the box into two-inch spaces and drive a tack at each mark. Now lace the piece of string backward and forward so as to divide the open end of the tray into squares, two inches on each side. * Adapted from Farmers' Bulletin 409, U. S. Dept. of Agriculture. TESTING SEEDS 115 Mark tire sides of the tray as shown in the illustration sm;d Sll ibe tex with dry sand, heaping it a little. After scraping ? 1 9 Brass . ? ? R4 Cork ? ? 24 Glass ? ? 25 Iron ? ? 7 7 Lead . ? ' ? 11 3 Pine . . ? ? 55 Stone ? ? 26 Zinc . ? ? 7. 62. Drawings. In all science work it is very desirable to illustrate the experiments, which you write up, by means of draw- ings. Drawing is like writing, since we use both to express on paper the ideas which we wish to keep in good form, but drawing is often a better means of expres- sion than writing as it sometimes is impossible to write r or even explain by speech, some idea which we have. There are two kinds of drawing; that made without instruments, called freehand drawing, add that made with instruments called mechanical drawing. In science work mechanical drawing is used more than freehand drawing. DRAWINGS 163 - The chief instruments for mechanical drawing are the rule, square, triangle, and compass. A cheap kind of compass is shown in the illustration. The rule is used for making straight lines, the square for forming right angles, triangle for obtaining different slants or angles, and the compass for drawing circles or parts of a circle. All that you need in your science work is a rule and a compass. The longest distance across a circle is its diameter and the distance from the cen- ter of the circle to the outside of the circle is called the radius. If you wish to make copies of your drawings the following experiment shows one method. Experiment 68. Blue Prints from Tracings. Apparatus: Piece of window glass a little larger than the drawing which is to be copied, thumb tacks. Materials: Tracing paper, blue-print paper. a. Make the drawing upon any kind of paper and then cover it with a piece of tracing paper, fastening it with thumb tacks. Trace the drawing with a very soft pencil so that the line will be very dark. Use the rule and compass when tracing just as you would in the first drawing. After the tracing is made, place a piece of blue-print paper upon a board or book and lay the trac- ing upon it, right side up. Cover both with the piece of window glass and expose to the sun until the blue- print paper has become a bronze color. See Experiment 164 MECHANICS 14 for full directions for the use of blue - print paper. Section 70 tells how to make blue-print paper. Review Questions, 26. L How many hours of sunlight were there yester- day? How many hours, without sunlight were there last night? 2. What is the direction of sunset now? How can you tell the direction of sunrise without seeing the sun rise? 3. What is a flame? Prove your answer. Why does charcoal burn without a flame? 4. What are some of the ways of keeping food from spoiling? Which is the worst method? Why? 5. Why is the farmer's occupation the most im- portant? Explain. 6. What are some of the advantages of the French system of measurement? 7. Explain why it is better to use the larger weights before using the smaller ones in weighing. S. When you blow through a tube into a liquid what is inside the bubbles? What does this show? 9. What is meant when it is said that the density of one body is greater than that of another body? 10. Besides talking and writing,, how else can you express an idea? 63, Forces. Any push or pull is called a force. Weight is a pull between the object and the earth and, as we have learned, is called the force of gravity. When we say that a body weighs five pounds we mean that the pull between the FORCES 165 body and the earth is five pounds* It would be neces- sary to pull the body, from on top, with a force of five pounds, to keep it from falling, or we could accomplish the same result by pushing the body from underneath. We have used a balance to find out the weights of bod- ies. In that case we compared the weight of an object with the weight of some standard. That is we com- pared pulls. Some bodies move as a whole, that is, if one part is pushed or pulled so that It moves the whole of the mass moves* Other bodies, such as rubber and thin pieces of many kinds of material, may be moved in one part while the rest remains motionless. H we fasten a rubber band at one end we may move the other end a considerable distance without causing the fastened end to move. When the 75 cents ' cloth by the Macmillan Company - net > Outline of Science for the Fifth Grade. Published by Percy E. Rowell, Berkeley, California Outline of Science for the Sixth Grade. Published by Percy E. Rowell, Berkeley, California Outline of Science for the Fifth and Sixth Grades. Published by- Percy E. Rowell, Berkeley, Cali- fornia Outline of Science for the Seventh Grade. Published by Percy E. Rowell, Berkeley, California Outline .of Science for the Eighth Grade. Published by Percy E. Rowell, Berkeley, California Outlines of Science for the Seventh and Eighth Grades. Published by Percy E. 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