,transcriber's ,note3 ,minor inconsistencies in spelling1 punctuation and formatting are retained as in the original4 ,where detailed corrections have been made on the text these are listed at the end of this document4 ,disclaimer3 ,this is a work of historical interest only and much of the scientific content has been superseded4 ,there are numerous experiments described in this book which are hazardous and should not be attempted4 ,advice given on handling toxic substances1 electrical apparatus etc4 should not be followed4 ,do not try this at home6 99 99 99 99 99 ,,common ,,science ,,new-,,world ,,science ,,series ,edited by ,john ,w4 ,ritchie 99 99 99 99 99 ,,science ,,for ,,beginners ,by ,delos ,fall ,,trees1 ,,stars1 ,,and ,,birds ,by ,edwin ,lincoln ,moseley ,,common ,,science ,by ,carleton ,w4 ,washburne ,,human ,,physiology ,by ,john ,w4 ,ritchie ,,sanitation ,,and ,,physiology ,by ,john ,w4 ,ritchie ,,laboratory ,,manual ,,for ,,use ,,with ,,human ,,physiology ,by ,carl ,hartman 99 99 99 99 99 ,,exercise ,,and ,,review ,,book ,,in ,,biology ,by ,j4 ,g4 ,blaisdell ,,personal ,,hygiene ,,and ,,home ,,nursing ,by ,louisa ,c4 ,lippitt ,,science ,,of ,,plant ,,life ,by ,edgar ,nelson ,transeau 99 99 99 99 99 ,,zo,,logy ,by ,t4 ,d4 ,a4 ,cockerell ,,experimental ,,organic ,,chemistry ,by ,augustus ,p4 ,west 99 99 99 99 99 ,,new-,,world ,,science ,,series ,edited by ,john ,w4 ,ritchie ,,common ,,science by ,carleton ,w4 ,washburne ,superintendent of ,schools1 ,winnetka1 ,illinois ,formerly ,supervisor in ,physical ,sciences and ,instructor in ,educational ,psychology ,state ,normal ,school ,san ,francisco1 ,california ,,illustrated ,,with ,,photographs ,,and ,,drawings ,yonkers-on-,hudson1 ,new ,york ,,world ,,book ,,company #aiba ,,world ,,book ,,company ,,the ,,house ,,of ,,applied ,,knowledge ,established1 #aije1 by ,caspar ,w4 ,hodgson ,,yonkers-,,on-,,hudson1 ,,new ,,york #babf ,,prairie ,,avenue1 ,,chicago ,one of the results of the ,world ,war has been a widespread desire to see the forces of science which proved so mighty in destruction employed generally and systematically for the promotion of human welfare4 ,world ,book ,company1 whose motto is ,the ,application of the ,world's ,knowledge to the ,world's ,needs1 has been much in sympathy with the movement to make science an integral part of our elementary education1 so that all our people from the highest to the lowest will be able to use it for themselves and to appreciate the possibilities of ameliorating the conditions of human life by its application to the problems that confront us4 ,we count it our good fortune1 therefore1 that we are able at this time to offer ,common ,science to the schools4 ,it is one of the new type of texts that are built on educational research and not by guess1 and we believe it to be a substantial contribution to the teaching of the subject ,,nwss3,,wcs-#b ,copyright1 #aibj1 by ,world ,book ,company ,copyright in ,great ,britain ,all rights reserved ,,preface ,a collection of about #bjjj questions asked by children forms the foundation on which this book is built4 ,rather than decide what it is that children ought to know1 or what knowledge could best be fitted into some educational theory1 an attempt was made to find out what children want to know4 ,the obvious way to discover this was to let them ask questions4 ,the questions collected were asked by several hundred children in the upper elementary grades1 over a period of a year and a half4 ,they were then sorted and classified according to the scientific principles needed in order to answer them4 ,these principles constitute the skeleton of this course4 ,the questions gave a very fair indication of the parts of science in which children are most interested4 ,physics1 in simple1 qualitative form1--not mathematical physics1 of course1--comes first2 astronomy next2 chemistry1 geology1 and certain forms of physical geography 7weather1 volcanoes1 earthquakes1 etc47 come third2 biology1 with physiology and hygiene1 is a close fourth2 and nature study1 in the ordinary school sense of the term1 comes in hardly at all4 ,the chapter headings of this book might indicate that the course has to do with physics and chemistry only4 ,this is because general physical and chemical principles form a unifying and inclusive matrix for the mass of applications4 ,but the examples and descriptions throughout the book include physical geography and the life sciences4 ,descriptive astronomy and geology have1 however1 been omitted4 ,these two subjects can be best grasped in a reading course and field trips1 and they have been incorporated in separate books4 ,the best method of presenting the principles to the children was the next problem4 ,the study of the questions asked had shown that the children's interests were centered in the explanation of a wide variety of familiar facts in the world about them4 ,it seemed evident1 therefore1 that a presentation of the principles that would answer the questions asked would be most interesting to the child4 ,experience with many different classes had shown that it is not necessary to subordinate these explanations of what children really wish to know to other methods of instruction of doubtful interest value4 ,obviously the quantitative methods of the high school and college were unsuitable for pupils of this age4 ,we want children to be attracted to science1 not repelled by it4 ,the assumption that scientific method can be taught to children by making them perform uninteresting1 quantitative experiments in an effort to get a result that will tally with that given in the textbook is so palpably unfounded that it is scarcely necessary to prove its failure by pointing to the very unscientific product of most of our high school science laboratories4 ,after a good deal of experimenting with children in a number of science classes1 the method followed in this book was developed4 ,briefly1 it is as follows3 ,at the head of each section are several of the questions which1 in part1 prompted the writing of the section4 ,the purpose of these is to let the children know definitely what their goal is when they begin a section4 ,the fact that the questions had their origin in the minds of children gives reasonable assurance that they will to some extent appeal to children4 ,these questions in effect state the problems which the section helps to solve4 ,following the questions are some introductory paragraphs for arousing interest in the problem at hand1--for motivating the child further4 ,these paragraphs are frequently a narrative description containing a good many dramatic elements1 and are written in conversational style4 ,the purpose is to awaken the child's imagination and to make clear the intimate part which the principle under consideration plays in his own life4 ,when a principle is universal1 like gravity1 it is best brought out by imagining what would happen if it ceased to exist4 ,if a principle is particular to certain substances1 like elasticity1 it sometimes can be brought out vividly by imagining what would happen if it were universal4 ,contrast is essential to consciousness4 ,to contrast a condition that is very common with an imagined condition that is different brings the former into vivid consciousness4 ,incidentally1 it arouses real interest4 ,the story-like introduction to many sections is not a sugar coating to make the child swallow a bitter pill4 ,it is a psychologically sound method of bringing out the essential and dramatic features of a principle which is in itself interesting1 once the child has grasped it4 ,another means for motivating the work in certain cases consists in first doing a dramatic experiment that will arouse the pupil's interest and curiosity4 ,still another consists in merely calling the child's attention to the practical value of the principle4 ,following these various means for getting the pupil's interest1 there are usually some experiments designed to help him solve his problem4 ,the experiments are made as simple and interesting as possible4 ,they usually require very inexpensive apparatus and are chosen or invented both for their interest value and their content value4 ,with an explanation of the experiments and the questions that arise1 a principle is made clear4 ,then the pupil is given an opportunity to apply the principle in making intelligible some common fact1 if the principle has only intelligence value2 or he is asked to apply the principle to the solution of a practical problem where the principle also has utility value4 ,the inference exercises which follow each section after the first two consist of statements of well-known facts explainable in terms of some of the principles which precede them4 ,they involve a constant review of the work which has gone before1 a review which nevertheless is new work--they review the principles by giving them new applications4 ,furthermore1 they give the pupil very definite training in explaining the common things around him4 ,for four years a mimeographed edition of this book has been used in the elementary department of the ,san ,francisco ,state ,normal ,school4 ,during that time various normal students have tried it in public school classes in and around ,san ,francisco and ,oakland1 and it has recently been used in ,winnetka1 ,illinois4 ,it has been twice revised throughout in response to needs shown by this use4 ,the book has proved itself adaptable to either an individual system of instruction or the usual class methods4 ,,to ,,the ,,teacher ,do not test the children on the narrative description which introduces most sections1 nor require them to recite on it4 ,it is there merely to arouse their interest1 and that is likely to be checked if they think it is a lesson to be learned4 ,it is not at all necessary for them to know everything in the introductory parts of each section4 ,if the children are interested1 they will remember what is valuable to them2 if they are not1 do not prolong the agony4 ,the questions which accompany and follow the experiments1 the applications or required explanations at the ends of the sections1 and the extensive inference exercises1 form an ample test of the child's grasp of the principles under discussion4 ,it is not necessary to have the children write up their experiments4 ,the experiments are a means to an end4 ,the end is the application of the principles to everyday facts4 ,if the children can make these applications1 it does not matter how much of the actual experiments they remember4 ,if possible1 the experiments should be done by the pupils individually or in couples1 in a school laboratory4 ,where this cannot be done1 almost all the experiments can be demonstrated from the teacher's desk if electricity1 water1 and gas are to be had4 ,alcohol lamps can be substituted for gas1 but they are less satisfactory4 ,it is a good plan to have pupils report additional exemplifications of each principle from their home or play life1 and in a quick oral review to let the rest of the class name the principles back of each example4 ,this course is so arranged that it can be used according to the regular class system of instruction1 or according to the individual system where each child does his own work at his natural rate of progress4 ,the children can carry on the work with almost no assistance from the teacher1 if provision is made for their doing the experiments themselves and for their writing the answers to the inference exercises4 ,when the individual system is used1 the children may write the inference exercises1 or they may use them as a basis for study and recite only a few to the teacher by way of test4 ,in the elementary department of the ,san ,francisco ,state ,normal ,school1 where the individual system is used1 the latter method is in operation4 ,the teacher has a card for each pupil1 each card containing a mimeographed list of the principles1 with a blank after each4 ,whenever a pupil correctly explains an example1 a figure #a is placed in the blank following that principle2 when he misapplies a principle1 or fails to apply it1 an x is placed after it4 ,when there are four successive #a's after any principle1 the teacher no longer includes that principle in testing that child4 ,in this way the number of inference exercises on which she hears any one individual recite is greatly reduced4 ,this plan would probably have to be altered in order to adapt it to particular conditions4 ,the ,socratic method can be employed to great advantage in handling difficult inferences4 ,the children discuss in class the principle under which an inference comes1 and the teacher guides the discussion1 when necessary1 by skillfully placed questions designed to bring the essential problems into relief4#a ,footnote #a3 ,at the ,california ,state ,normal ,school in ,san ,francisco1 this course in general science is usually preceded by one in introductory science4 ,the chapters and sections in this book are not of even length4 ,in order to preserve the unity of subject matter1 it was felt desirable to divide the book according to subjects rather than according to daily lessons4 ,the varying lengths of recitation periods in different schools1 and the adaptation of the course to individual instruction as well as to class work1 also made a division into lessons impracticable4 ,each teacher will soon discover about how much matter her class1 if she uses the class method1 can take each day4 ,probably the average section will require about #b days to cover2 the longest sections1 #e days4 ,the entire course should easily be covered in one year with recitations of about #be minutes daily4 ,two #ej-minute periods a week give a better division of time and also ought to finish the course in a year4 ,under the individual system1 the slowest diligent children finish in #g or #h school months1 working #d half-hours weekly4 ,the fastest do it in about one third that time4 ,upon receipt of #bj cents1 the publishers will send a manual prepared by the author1 containing full instructions as to the organization and equipment of the laboratory or demonstration desk1 complete lists of apparatus and material needed1 and directions for the construction of a chemical laboratory4 ,the latter is a laboratory course in which the children are turned loose among all sorts of interesting materials and apparatus1--kaleidoscope1 microscope1 electric bell1 toy motor1 chemicals that effervesce or change color when put together1 soft glass tubing to mold and blow1 etc4 ,the teacher demonstrates various experiments from time to time to show the children what can be done with these things1 but the children are left free to investigate to their heart's content4 ,there is no teaching in this introductory course other than brief answers to questions4 ,the astronomy and geology reading usually accompany the work in introductory science4 ,,acknowledgments ,to ,frederic ,burk1 president of the ,san ,francisco ,state ,normal ,school1 ,i am most under obligation in connection with the preparation of this book4 ,his ideas inspired it1 and his dynamic criticism did much toward shaping it4 ,my wife1 ,heluiz ,chandler ,washburne1 gave invaluable help throughout the work1 especially in the present revision of the course4 ,one of my co-workers on the ,normal ,school faculty1 ,miss ,louise ,mohr1 rendered much assistance in the classification and selection of inferences4 ,miss ,beatrice ,harper assisted in the preparation of the tables of supplies and apparatus1 published in the manual to accompany this book4 ,and ,i wish to thank the children of the ,normal ,school for their patience and cooperation in posing for the photographs4 ,the photographs are by ,joseph ,marron4 ,,contents ,,chapter ,,page #a4 ,,gravitation #a #a4 ,a real place where things weigh nothing and where there is no up or down #a #b4 ,water seeks its own level #f #c4 ,the sea of compressed air in which we live3 ,air pressure #aj #d4 ,sinking and floating3 ,displacement #bc #e4 ,how things are kept from toppling over3 ,stability #bi #b4 ,,molecular ,,attraction #cf #f4 ,how liquids are absorbed3 ,capillary attraction #cf #g4 ,how things stick to one another3 ,adhesion #da #h4 ,the force that makes a thing hold together3 ,cohesion #dd #i4 ,friction #di #c4 ,,conservation ,,of ,,energy #eg #aj4 ,levers #eg #aa4 ,inertia #ff #ab4 ,centrifugal force #gb #ac4 ,action and reaction #gg #ad4 ,elasticity #hb #d4 ,,heat #hh #ae4 ,heat makes things expand #hh #af4 ,cooling from expansion #id #ag4 ,freezing and melting #if #ah4 ,evaporation #ajj #ai4 ,boiling and condensing #ajg #bj4 ,conduction of heat and convection #aaf #e4 ,,radiant ,,heat ,,and ,,light #abb #ba4 ,how heat gets here from the sun2 why things glow when they become very hot #abb #bb4 ,reflection #abi #bc4 ,the bending of light3 ,refraction #acf #bd4 ,focus #adb #be4 ,magnification #aej #bf4 ,scattering of light3 ,diffusion of light #aeh #bg4 ,color #afa #f4 ,,sound #agd #bh4 ,what sound is #agd #bi4 ,echoes #ahc #cj4 ,pitch #ahe #g4 ,,magnetism ,,and ,,electricity #aij #ca4 ,magnets2 the compass #aij #cb4 ,static electricity #aif #h4 ,,electricity #bjc #cc4 ,making electricity flow #bjc #cd4 ,conduction of electricity #bac #ce4 ,complete circuits #bai #cf4 ,grounded circuits #bbe #cg4 ,resistance #bbi #ch4 ,the electric arc #bcc #ci4 ,short circuits and fuses #bdj #dj4 ,electromagnets #bdg #i4 ,,mingling ,,of ,,molecules #bei #da4 ,solutions and emulsions #bei #db4 ,crystals #bfe #dc4 ,diffusion #bfh #dd4 ,clouds1 rain1 and dew3 ,humidity #bgd #de4 ,softening due to oil or water #bij #aj4 ,,chemical ,,change ,,and ,,energy #bic #df4 ,what things are made of3 ,elements #bic #dg4 ,burning3 ,oxidation #cab #dh4 ,chemical change caused by heat #cbc #di4 ,chemical change caused by light #cbf #ej4 ,chemical change caused by electricity #cce #ea4 ,chemical change releases energy #cdj #eb4 ,explosions #cdb #aa4 ,,solution ,,and ,,chemical ,,action #cdi #ec4 ,chemical change helped by solution #cdi #ed4 ,acids #cea #ee4 ,bases #cee #ef4 ,neutralization #cfj #eg4 ,effervescence #cfe #ab4 ,,analysis #cgj #eh4 ,analysis #cgj ,,appendixes3 ,a4 ,the ,electrical ,apparatus #cgi ,b4 ,construction of the ,cigar-box ,telegraph #cha ,,index #chc ,,common ,,science ,,chapter ,,one ,,gravitation ,,section #a4 ,a real place where things weigh nothing and where there is no up or down4 ,why is it that the oceans do not flow off the earth8 ,what is gravity8 ,what is down1 and what is up8 ,there is a place where nothing has weight2 where there is no up or down2 where nothing ever falls2 and where1 if people were there1 they would float about with their heads pointing in all directions4 ,this is not a fairy tale2 every word of it is scientifically true4 ,if we had some way of flying straight toward the sun about #afj1jjj miles1 we should really reach this strange place4 ,let us pretend that we can do it4 ,suppose we have built a machine that can fly far out from the earth through space 7of course no one has really ever invented such a machine74 ,and since the place is far beyond the air that surrounds the earth1 let us imagine that we have fitted out the air-tight cabin of our machine with plenty of air to breathe1 and with food and everything we need for living4 ,we shall picture it something like the cabin of an ocean steamer4 ,and let us pretend that we have just arrived at the place where things weigh nothing3 ,when you try to walk1 you glide toward the ceiling of the cabin and do not stop before your head bumps against it4 ,if you push on the ceiling1 you float back toward the floor4 ,but you cannot tell whether the floor is above or below1 because you have no idea as to which way is up and which way is down4 ,as a matter of fact there is no up or down4 ,you discover this quickly enough when you try to pour a glass of water4 ,you do not know where to hold the glass or where to hold the pitcher4 ,no matter how you hold them1 the water will not pour--point the top of the pitcher toward the ceiling1 or the floor1 or the wall1 it makes no difference4 ,finally you have to put your hand into the pitcher and pull the water out4 ,it comes4 ,not a drop runs between your fingers--which way can it run1 since there is no down8 ,the big lump of water stays right on your hand4 ,this surprises you so much that you let go of the pitcher4 ,never mind2 the pitcher stays poised in mid-air4 ,but how are you going to get a drink8 ,it does not seem reasonable to try to drink a large lump of water4 ,yet when you hold the lump to your lips and suck it you can draw the water into your mouth1 and it is as wet as ever2 then you can force it on down to 7or rather toward7 your throat with your tongue4 ,still you have left in your hand a big piece of water that will not flow off4 ,you throw it away1 and it sails through the air of the cabin in a straight line until it splashes against the wall4 ,it wets the wall as much as water on the earth would1 but it does not run off4 ,it sticks there1 like a splash-shaped piece of clear1 colorless gelatin4 ,suppose that for the sake of experimenting you have brought an elephant along on this trip4 ,you can move under him 7or over him--anyway between him and the floor71 brace your feet on the floor1 and give him a push4 7,if he happens to step on your toes while you are doing this1 you do not mind in the least1 because he does not weigh anything1 you know47 ,if you push hard enough to get the elephant started1 he rises slowly toward the ceiling4 ,when he objects on the way1 and struggles and kicks and tries to get back to the floor1 it does not help him at all4 ,his bulky1 kicking body floats steadily on till it crashes into the ceiling4 ,no chairs or beds are needed in this place4 ,you can lie or sit in mid-air1 or cling to a fixture on a wall1 resting as gently there as a feather might4 ,there is no need to set the table for meals--just lay the dishes with the food on them in space and they stay there4 ,if the top of your cup of chocolate is toward the ceiling1 and your plate of food is turned the other way1 no harm is done4 ,your feet may happen to point toward the ceiling1 while some one else's point toward the floor1 as you sit in mid-air1 eating4 ,there is some difficulty in getting the food on the dishes1 so probably you do not wish to bother with dishes1 after all4 ,do you want some mashed potatoes8 ,all right1 here it is--and the cook jerks the spoon away from the potatoes1 leaving them floating before you1 ready to eat4 ,it is literally a topsy-turvy place4 ,do you want to know why all this would happen8 ,here is the reason3 ,there is a great force known as gravitation4 ,it is the pull that everything in the universe has on everything else4 ,the more massive a thing is1 the more gravitational pull it has on other objects2 but the farther apart things are1 the less pull they have on each other4 ,the earth is very massive1 and we live right on its surface2 so it pulls us strongly toward it4 ,therefore we say that we weigh something4 ,and since every time we roll off a bed1 for instance1 or jump off a chair1 the earth pulls us swiftly toward it1 we say that the earth is down4 ,down simply means toward the thing that is pulling us4 ,if we were on the surface of the moon1 the moon would pull us4 ,down would then be under our feet or toward the center of the moon1 and the earth would be seen floating up in the sky4 ,for up means away from the thing which is pulling us4 ,,why ,,water ,,does ,,not ,,flow ,,off ,,the ,,earth4 ,it was because people did not know about gravitation that they laughed at ,columbus when he said the earth was round4 ,why1 if the earth were round1 they argued1 the water would all flow off on the other side4 ,they did not know that water flows downhill because the earth is pulling it toward its center by gravitation1 and that it does not make the slightest difference on which side of the earth water is1 since it is still pulled toward the center4 ,,why ,,the ,,world ,,does ,,not ,,fall ,,down4 ,and people used to wonder what held the earth up4 ,the answer1 as you can see1 is easy4 ,there simply is no up or down in space4 ,the earth cannot fall down1 because there is no down to fall to4 ,down merely means toward the earth1 and the earth cannot very well fall toward itself1 can it8 ,the sun is pulling on it1 though2 so the earth could fall into the sun1 and it would do so1 if it were not swinging around the sun so fast4 ,you will see how this keeps it from falling into the sun when you come to the section on centrifugal force4 ,,why ,,there ,,is ,a ,,place ,,where ,,things ,,weigh ,,nothing4 ,now about the place where gravitation has no effect4 ,since an object near the sun is pulled more by the sun than it is by the earth1 and since down here near the earth an object is pulled harder by the earth than by the sun1 it is clear that there must be a place between the sun and the earth where their pulls just balance2 and where the sun pulls just as hard one way as the earth pulls the other way1 things will not fall either way1 but will float4 ,the place where the pulls of the sun and the earth are equal is not halfway between the earth and the sun1 because the sun is so much larger and pulls so much more powerfully than the earth1 that the place where their pulls balance is much nearer the earth than it is to the sun4 ,as a matter of fact1 it can be easily calculated that this spot is somewhere near #afj1jjj miles from the earth4 ,there are other spots like it between every two stars1 and in the center of the earth1 and in the center of every other body4 ,you see1 in the center of the earth there is just as much of the earth pulling one way as there is pulling the other1 so again there is no up or down4 ,,application #a4 ,explain why the people on the other side of the earth do not fall off2 why you have weight2 why rivers run downhill2 why the world does not fall down4 ,,section #b4 ,water seeks its own level4 ,why does a spring bubble up from the ground8 ,what makes the water come up through the pipe into your house8 ,why is a fire engine needed to pump water up high8 ,you remember that up where the pull of the earth and the sun balance each other1 water could not flow or flatten out4 ,let us try to imagine that water1 here on the earth1 has lost its habit of flattening out whenever possible--that1 like clay1 it keeps whatever shape it is given4 ,first you notice that the water fails to run out of the faucets4 7,for in most places in the world as it really is1 the water that comes through faucets is simply flowing down from some high reservoir47 ,people all begin to search for water to drink4 ,they rush to the rivers and begin to dig the water out of them4 ,it looks queer to see a hole left in the water wherever a person has scooped up a pailful4 ,if some one slips into the river while getting water1 he does not drown1 because the water cannot close in over his head2 there is just a deep hole where he has fallen through1 and he breathes the air that comes down to him at the bottom of the hole4 ,if you try to row on the water1 each stroke of the oars piles up the water1 and the boat makes a deep furrow wherever it goes so that the whole river begins to look like a rough1 plowed field4 ,when the rivers are used up1 people search in vain for springs4 7,no springs could flow in our everyday world if water did not seek its own level2 for the waters of the springs come from hills or mountains1 and the higher water1 in trying to flatten out1 forces the lower water up through the ground on the hillsides or in the valleys47 ,so people have to get their water from underground or go to lakes for it4 ,and these lakes are strange sights4 ,storms toss up huge waves1 which remain as ridges and furrows until another storm tears them down and throws up new ones4 ,but with no rivers flowing into them1 the lakes also are used up in time4 ,the only fresh water to be had is what is caught from the rain4 ,even wells soon become useless2 because as soon as you pump up the water surrounding the pump1 no more water flows in around it2 and if you use a bucket to raise the water1 the well goes dry as soon as the supply of water standing in it has been drawn4 ,you will understand more about water seeking its own level if you do this experiment3 ,,experiment #a4 ,put one end of a rubber tube over the narrow neck of a funnel 7a glass funnel is best71 and put the other end of the tube over a piece of glass tubing not less than #e or #f inches long4 ,hold up the glass tube and the funnel1 letting the rubber tube sag down between them as in ,figure #a4 ,now fill the funnel three fourths full of water4 ,raise the glass tube higher if the water starts to flow out of it4 ,if no water shows in the glass tube1 lower it until it does4 ,gradually raise and lower the tube1 and notice how high the water goes in it whenever it is held still4 ,this same thing would happen with any shape of tube or funnel4 ,you have another example of it when you fill a teakettle3 the water rises in the spout just as high as it does in the kettle4 ,illustration3 ,,fig4 #a4 ,the water in the tube rises to the level of the water in the funnel4 ,,why ,,water ,,flows ,,up ,,into ,,your ,,house4 ,it is because water seeks its own level that it comes up through the pipes in your house4 ,usually the water for a city is pumped into a reservoir that is as high as the highest house in the city4 ,when it flows down from the reservoir1 it tends to rise in any pipe through which it flows1 to the height at which the water in the reservoir stands4 ,if a house is higher than the surface of the water in the reservoir1 of course that house will get no running water4 ,,why ,,fire ,,engines ,,are ,,needed ,,to ,,force ,,water ,,high4 ,in putting out a fire1 the firemen often want to throw the water with a good deal of force4 ,the tendency of the water to seek its own level does not always give a high enough or powerful enough stream from the fire hose2 so a fire engine is used to pump the water through the hose1 and the stream flows with much more force than if it were not pumped4 ,,application #b4 ,a4 ,c4 ,wheeler of ,chicago bought a little farm in ,indiana1 and had a windmill put up to supply the place with water4 ,but at first he was not sure where he should put the tank into which the windmill was to pump the water and from which the water should flow into the kitchen1 bathroom1 and barn4 ,the barn was on a knoll1 so that its floor was almost as high as the roof of the house4 ,which would have been the best place for the tank3 high up on the windmill 7which stood on the knoll by the barn71 or the basement of the house1 or the attic of the house8 ,illustration3 ,,fig4 #b4 ,where is the best location for the tank8 ,,application #c4 ,a man was about to open a garage in ,san ,francisco4 ,he had a large oil tank and wanted a simple way of telling at a glance how full it was4 ,one of his workmen suggested that he attach a long piece of glass tubing to the side of the tank1 connecting it with an extra faucet near the bottom of the tank4 ,a second workman said1 ,no1 that won't do4 ,your tank holds ever so much more than the tube would hold1 so the oil in the tank would force the oil up over the top of the tube1 even when the tank was not full4 ,who was right8 ,illustration3 ,,fig4 #c4 ,when the tank is full1 will the oil overflow the top of the tube8 ,,section #c4 ,the sea of compressed air in which we live3 ,air pressure4 ,does a balloon explode if it goes high in the air8 ,what is suction8 ,why does soda water run up a straw when you draw on the straw8 ,why will evaporated milk not flow freely out of a can in which there is only one hole8 ,why does water gurgle when you pour it out of a bottle8 ,we are living in a sea of compressed air4 ,every square inch of our bodies has about #ae pounds of pressure against it4 ,the only reason we are not crushed is that there is as strong pressure inside of our bodies pushing out as there is outside pushing in4 ,there is compressed air in the blood and all through the body4 ,if you were to lie down on the ground and have all the air pumped out from under you1 the air above would crush you as flat as a pancake4 ,you might as well let a dozen big farm horses trample on you1 or let a huge elephant roll over you1 as let the air press down on you if there were no air underneath and inside your body to resist the pressure from above4 ,it is hard to believe that the air and liquids in our bodies are pressing out with a force great enough to resist this crushing weight of air4 ,but if you were suddenly to go up above the earth's atmosphere1 or if you were to stay down here and go into a room from which the air were to be pumped all at once1 your body would explode like a torpedo4 ,when you suck the air out of a bottle1 the surrounding air pressure forces the bottle against your tongue2 if the bottle is a small one1 it will stick there4 ,and the pressure of the air and blood in your tongue will force your tongue down into the neck of the bottle from which part of the air has been taken4 ,in the same way1 when you force the air out of a rubber suction cap1 such as is used to fasten reading lamps to the head of a bed1 the air pressure outside holds the suction cap tightly to the object against which you first pressed it1 making it stick there4 ,we can easily experiment with air pressure because we can get almost entirely rid of it in places and can then watch what happens4 ,a place from which the air is practically all pumped out is called a vacuum4 ,here are some interesting experiments that will show what air pressure does3 ,illustration3 ,,fig4 #d4 ,when the point is knocked off the electric lamp1 the water is forced into the vacuum4 ,,experiment #b4 ,hold a burned-out electric lamp in a basin of water1 break its point off1 and see what happens4 ,all the common electric lamps 7less than #gj watts7 are made with vacuums inside4 ,the reason for this is that the fine wire would burn up if there were any air in the lamps4 ,when you knock the point off the globe1 it leaves a space into which the water can be pushed4 ,since the air is pressing hard on the surface of the water except in the one place where the vacuum in the lamp globe is1 the water is forced violently into this empty space4 ,it really is a good deal like the way mud comes up between your toes when you are barefoot4 ,your foot is pressing on the mud all around except in the spaces between your toes1 and so the mud is forced up into these spaces4 ,the air pressure on the water is like your foot on the mud1 and the space in the lamp globe is like the space between your toes4 ,since wherever there is air it is pressing hard1 the only space into which it can force water or anything else is into a place from which all the air has been removed1 like the inside of the lamp globe4 ,the reason that the water does not run out of the globe is this3 the hole is too small to let the air squeeze up past the water1 and therefore no air can take the place of the water that might otherwise run out4 ,in order to flow out1 then1 the water would have to leave an empty space or vacuum behind it1 and the air pressure would not allow this4 ,,why ,,water ,,gurgles ,,when ,,it ,,pours ,,out ,,of ,a ,,bottle4 ,you have often noticed that when you pour water out of a bottle it gurgles and gulps instead of flowing out evenly4 ,the reason for this is that when a little water gets out and leaves an empty space behind1 the air pushing against the water starts to force it back up2 but since the mouth of the bottle is fairly wide1 the air itself squeezes past the water and bubbles up to the top4 ,,experiment #c4 ,put a straw or a piece of glass tube down into a glass of water4 ,hold your finger tightly over the upper end1 and lift the tube out of the water4 ,notice how the water stays in the tube4 ,now remove your finger from the upper end4 ,the air holds the water up in the tube because there is no room for it to bubble up into the tube to take the place of the water2 and the water1 to flow out of the tube1 would have to leave a vacuum1 which the air outside does not allow4 ,but when you take your finger off the top of the straw or tube1 the air from above takes the place of the water as rapidly as it flows out2 so there is no tendency to form a vacuum1 and the water leaves the tube4 ,now do you see why you make two holes in the top of a can of evaporated milk when you wish to pour the milk out evenly8 ,illustration3 ,,fig4 #e4 ,the water is held in the tube by air pressure4 ,,experiment #d4 ,push a rubber suction cap firmly against the inside of the bell jar of an air pump4 ,try to pull the suction cap off4 ,if it comes off1 press it on again2 place the bell jar on the plate of the air pump1 and pump the air out of the jar4 ,what must have been holding the suction cap against the inside of the jar8 ,does air press up and sidewise as well as down8 ,test this further in the following experiment3 ,illustration3 ,,fig4 #f4 ,an air pump4 ,,experiment #e4 ,put a cork into an empty bottle4 ,do not use a new cork1 but one that has been fitted into the bottle many times and has become shaped to the neck4 ,press the cork in rather firmly1 so that it is air-tight1 but do not jam it in4 ,set the bottle on the plate of the air pump1 put the bell jar over it1 and pump the air out of the jar4 ,what makes the cork fly out of the bottle8 ,what was really in the empty bottle8 ,why could it not push the cork out until you had pumped the air out of the jar8 ,,experiment #f4 ,wax the rims of the two ,magdeburg hemispheres 7see ,fig4 #g74 ,screw the lower section into the hole in the plate of the air pump4 ,be sure that the stop valve in the neck of the hemisphere is open4 7,the little handle should be vertical47 ,fit the other section on to the first1 and pump out as much air as you can4 ,close the stop valve4 ,unscrew the hemispheres from the air pump4 ,try to pull them apart--pull straight out1 taking care not to slide the parts4 ,if you wish1 let some one else take one handle1 and see if the two of you can pull it apart4 ,illustration3 ,,fig4 #g4 ,the experiment with the ,magdeburg hemispheres4 ,before you pumped the air out of the hemisphere1 the compressed air inside of them 7you remember all the air down here is compressed7 was pushing them apart just as hard as the air outside of them was pushing them together4 ,when you pumped the air out1 however1 there was hardly any air left inside of them to push outward4 ,so the strong pressure of the outside air against the hemispheres had nothing to oppose it4 ,it therefore pressed them very tightly together and held them that way4 ,this experiment was first tried by a man living in ,magdeburg1 ,germany4 ,the first set of hemispheres he used proved too weak1 and when the air in them was partly pumped out1 the pressure of the outside air crushed them like an egg shell4 ,the second set was over a foot in diameter and much stronger4 ,after he had pumped the air out1 it took sixteen horses1 eight pulling one way and eight the opposite way1 to pull the hemispheres apart4 ,,experiment #g4 ,fill a bottle 7or flask7 half full of water4 ,through a one-hole stopper that will fit the bottle1 put a bent piece of glass tubing that will reach down to the bottom of the bottle4 ,set the bottle1 thus stoppered1 on the plate of the air pump1 with a beaker or tumbler under the outer end of the glass tube4 ,put the bell jar over the bottle and glass1 and pump the air out of the jar4 ,what is it that forces the water up and out of the bottle8 ,why could it do this when the air was pumped out of the bell jar and not before8 ,,how ,a ,,seltzer ,,siphon ,,works4 ,a seltzer siphon works on the same principle4 ,but instead of the ordinary compressed air that is all around us1 there is in the seltzer siphon a gas 7carbon dioxid7 which has been much more compressed than ordinary air4 ,this strongly compressed gas forces the seltzer water out into the less compressed air1 exactly as the compressed air in the upper part of the bottle forced the water out into the comparative vacuum of the bell jar in ,experiment #g4 ,,experiment #h4 ,fill a toy balloon partly full of air by blowing into it1 and close the neck with a rubber band so that no air can escape4 ,lay a saucer over the hole in the plate of the air pump1 so that the rubber of the balloon cannot be sucked down the hole4 ,lay the balloon on top of this saucer1 put the bell jar over it1 and pump the air out of the jar4 ,what makes the balloon expand8 ,what is in it8 ,why could it not expand before you pumped the air out from around it8 ,a toy balloon expands for the same reason when it goes high in the air4 ,up there the air pressure is not so strong outside the balloon1 and so the gas inside makes the balloon expand until it bursts4 ,illustration3 ,,fig4 #h4 ,a siphon4 ,the air pushes the water over the side of the pan4 ,,experiment #i4 ,lay a rubber tube flat in the bottom of a pan of water1 so that the tube will be filled with water4 ,let one end stay under water1 but pinch the other end tightly shut with your thumb and finger and lift it out of the pan4 ,lower this closed end into a sink or empty pan that is lower than the pan of water4 ,now stop pinching the tube shut4 ,this device is called a siphon 7,fig4 #h74 ,,experiment #aj4 ,put the mouth of a small syringe1 or better1 of a glass model lift pump1 under water4 ,draw the handle up4 ,does the water follow the plunger up1 stand still1 or go down in the pump8 ,when you pull up the plunger1 you leave an empty space2 you shove the air out of the pump or syringe ahead of the plunger4 ,the air outside1 pressing on the water1 forces it up into this empty space from which the air has been pushed4 ,but air pressure cannot force water up even into a perfect vacuum farther than about #cc feet4 ,if your glass pump were1 say1 #dj feet long1 the water would follow the plunger up for a little over #cj feet1 but nothing could suck it higher2 for by the time it reaches that height it is pushing down with its own weight as hard as the air is pressing on the water below4 ,no suction pump1 or siphon1 however perfect1 will ever lift water more than about #cc feet1 and it will do well if it draws water up #bh or #cj feet4 ,this is because a perfect vacuum cannot be made4 ,there is always some water vapor formed by the water evaporating a little1 and there is always a small amount of air that has been dissolved in water1 both of which partly fill the space above the water and press down a little on the water within the pump4 ,illustration3 ,,fig4 #i4 ,a glass model suction pump4 ,if you had a straw over #cc feet long1 and if some one held a glass of lemonade for you down near the sidewalk while you leaned over from the roof of a three-story building with your long straw1 you could not possibly drink the lemonade4 ,the air pressure would not be great enough to lift it so high1 no matter how hard you sucked1--that is1 no matter how perfect a vacuum you made in the upper part of the straw4 ,the lemonade would rise part way1 and then your straw would be flattened by the pressure outside4 ,some days the air can force water up farther in a tube than it can on other days4 ,if it can force the water up #cc feet today1 it will perhaps be able to force it up only #cj feet immediately before a storm4 ,and if it forces water up #cc feet at sea level1 it may force it up only #ae or #bj feet on a high mountain1 for on a mountain there is much less air above to make pressure4 ,the pressure of the air is different in different places2 where the air is heavy and pressing hard1 we say the pressure is high2 where the air is light and not pressing so hard1 we call the pressure low4 ,a place where the air is heavy is called an area of high pressure2 where it is light1 an area of low pressure4 7,see ,section #dd47 ,,what ,,makes ,,winds8 ,it is because the air does not press equally all the time and everywhere that we have winds4 ,naturally1 if the air is pressing harder in one place than in another1 the lower air will be pushed sidewise in the areas of high pressure and will rush to the areas where there is less pressure4 ,and air rushing from one place to another is called wind4 ,illustration3 ,,fig4 #aj4 ,,application #d4 ,a man had two water reservoirs1 which stood at the same level1 one on each side of a hill4 ,the hill between them was about #ej feet high4 ,one reservoir was full1 and the other was empty4 ,he wanted to get some of the water from the full reservoir into the empty one4 ,he did not have a pump to force the water from one to the other1 but he did have a long hose1 and could have bought more4 ,his hose was long enough to reach over the top of the hill1 but not long enough to go around it4 ,could he have siphoned the water from one reservoir to the other8 ,would he have had to buy more hose8 ,,application #e4 ,two boys were out hiking and were very thirsty4 ,they came to a deserted farm and found a deep well2 it was about #dj feet down to the water4 ,they had no pump1 but there was a piece of hose about #ej feet long4 ,one boy suggested that they drop one end of the hose down to the water and suck the water up1 but the other said that that would not work--the only way would be to lower the hose into the water1 close the upper end1 pull the hose out and let the water pour out of the lower end of the hose into their mouths4 ,a stranger came past while the boys were arguing1 and said that neither way would work2 that although the hose was long enough1 the water was too far down to be raised in either way4 ,he advised the boys to find a bucket and to use the hose as a rope for lowering it4 ,who was right8 ,,inference ,,exercise ,,explanatory ,,note4 ,in the inference exercises in this book1 there is a group of facts for you to explain4 ,they can always be explained by one or more of the principles studied1 like gravitation1 water seeking its own level1 or air pressure4 ,if asked to explain why sucking through a straw makes soda water come up into your mouth1 for instance1 you should not merely say air pressure1 but should tell why you think it is air pressure that causes the liquid to rise through the straw4 ,the answer should be something like this3 ,the soda water comes up into your mouth because the sucking takes the air pressure away from the top of the soda water that is in the straw4 ,this leaves the air pressing down only on the surface of the soda water in the glass4 ,therefore1 the air pressure pushes the soda water up into the straw and into your mouth where the pressure has been removed by sucking4 ,sometimes1 when you have shown that you understand the principles very well1 the teacher may let you take a short cut and just name the principle1 but this will be done only after you have proved by a number of full answers that you thoroughly understand each principle named4 ,some of the following facts are accounted for by air pressure2 some by water seeking its own level2 others by gravitation4 ,see if you can tell which of the three principles explains each fact3 #a4 ,rain falls from the clouds4 #b4 ,after rain has soaked into the sides of mountains it runs underground and rises1 at lower levels1 in springs4 #c4 ,when there are no springs near1 people raise the water from underground with suction pumps4 #d4 ,as fast as the water is pumped away from around the bottom of a pump1 more water flows in to replace it4 #e4 ,after you pump water up1 it flows down into your pail from the spout of the pump4 #f4 ,you can drink lemonade through a straw4 #g4 ,if a lemon seed sticks to the bottom of your straw1 the straw flattens out when you suck4 #h4 ,when you pull your straw out to remove the seed1 there is no hole left in the lemonade2 it closes right in after the straw4 #i4 ,if you drop the seed1 it falls to the floor4 #aj4 ,if you tip the glass to drink the lemonade1 the surface of the lemonade does not tip with the glass1 but remains horizontal4 ,,section #d4 ,sinking and floating3 ,displacement4 ,what keeps a balloon up8 ,what makes an iceberg float8 ,why does cork float on the water and why do heavier substances sink8 ,if iron sinks1 why do iron ships not sink8 ,again let us imagine ourselves up in the place where gravitation has no effect4 ,suppose we lay a nail on the surface of a bowl of water4 ,it stays there and does not sink4 ,this does not seem at all surprising1 of course1 since the nail no longer has weight4 ,but when we put a cork in the midst of the water1 it stays there instead of floating to the surface4 ,this seems peculiar1 because the less a thing weighs the more easily it floats4 ,so when the cork weighs nothing at all1 it seems that it should float better than ever4 ,of course there is some difficulty in deciding whether it ought to float toward the part of the water nearest the floor or toward the part nearest the ceiling1 since there is no up or down2 but one would think that it ought somehow to get to the outside of the water and not stay exactly in the middle4 ,if put on the outside1 however1 it stays there as well4 ,a toy balloon1 in the same way1 will not go toward either the ceiling or the floor1 but just stays where it is put1 no matter how light a gas it is filled with4 ,the explanation is as follows3 ,for an object to float on the water or in the air1 the water or air must be heavier than the object4 ,it is the water or air being pulled under the object by gravity1 that pushes it up4 ,therefore1 if the air and water themselves weighed nothing1 of course they would be no heavier than the balloon or the cork2 the air or water would then not be pulled in under the balloon or cork by gravity1 and so would not push them up1 or aside4 ,illustration3 ,,fig4 #aa4 ,the battleship is made of steel1 yet it does not sink4 ,,why ,,iron ,,ships ,,float4 ,when people first talked about building iron ships1 others laughed at them4 ,iron sinks1 they said1 and your boats will go to the bottom of the sea4 ,if the boats were solid iron this would be true1 for iron is certainly much heavier than water4 ,but if the iron is bent up at the edges1--as it is in a dish pan1--it has to push much more water aside before it goes under than it would if it were flattened out4 ,the water displaced1 or pushed aside1 would have to take up as much room as was taken up by the pan and all the empty space inside of it1 before the edge would go under4 ,naturally this amount of water would weigh a great deal more than the empty pan4 ,but suppose you should fill the dish pan with water1 or suppose it leaked full4 ,then you would have the weight of all the water in it added to the weight of the pan1 and that would be heavy enough to push aside the water in which it was floating and let the pan sink4 ,this is why a ship sometimes sinks when it springs a leak4 ,you may be able to see more clearly why an iron ship floats by this example3 ,suppose your iron ship weighs #fjjj tons and that the cargo and crew weigh another #ajjj tons4 ,the whole thing1 then1 weighs #gjjj tons4 ,now that ship is a big1 bulky affair and takes up more space than #gjjj tons of water does4 ,as it settles into the water it pushes a great deal of water out of the way1 and after it sinks a certain distance it has pushed #gjjj tons of water out of the way4 ,since the ship weighs only #gjjj tons1 it evidently cannot push aside more than that weight of water2 so part of the ship stays above the water1 and all there is left for it to do is to float4 ,if the ship should freeze solid in the water where it floated and then could be lifted out of the ice by a huge derrick1 you would find that you could pour exactly #gjjj tons of water into the hole where the ship had been4 ,but if you built your ship with so little air space in it that it took less room than #gjjj tons of water takes1 it could go clear under the water without pushing #gjjj tons of water aside4 ,therefore a ship of this kind would sink4 ,the earth's gravity is pulling on the ship and on the water4 ,if the ship has displaced 7pushed aside7 its own weight of water1 gravity is pulling down on the water as hard as it is on the ship2 so the ship cannot push any more water aside1 and if there is enough air space in it1 the ship floats4 ,perhaps the easiest way to say it is like this3 ,anything that is lighter than the same volume of water will float2 since a cubic foot of wood weighs less than a cubic foot of water1 the wood will float2 since a quart of oil is lighter than a quart of water1 the oil will float2 since a pint of cream is lighter than a pint of milk1 the cream will rise4 ,in the same way1 anything that is lighter than the same volume of air will be pushed up by the air4 ,when a balloon with its passengers weighs less than the amount of air that it takes the place of at any one time1 it will go up4 ,since a quart of warm air weighs less than a quart of cold air1 the warm air will rise4 ,you can see how a heavy substance like water pushes a lighter one1 like oil1 up out of its way1 in the following experiment3 ,,experiment #aa4 ,fill one test tube to the brim with kerosene slightly colored with a little iodine4 ,fill another test tube to the brim with water1 colored with a little blueing4 ,put a small square of cardboard over the test tube of water1 hold it in place1 and turn the test tube upside down4 ,you can let go of the cardboard now1 as the air pressure will hold it up4 ,put the mouth of the test tube of water exactly over the mouth of the test tube of kerosene4 ,pull the cardboard out from between the two tubes1 or have some one else do this while you hold the two tubes mouth to mouth4 ,if you are careful1 you will not spill a drop4 ,if nothing happens when the cardboard is pulled away1 gently rock the two tubes1 holding their mouths tightly together4 ,illustration3 ,,fig4 #ab4 ,the upper tube is filled with water and the lower with oil4 ,what will happen when she pulls the cardboard out8 ,oil is lighter than water1 as you know1 because you have seen a film of oil floating on water4 ,when you have the two test tubes in such a position that the oil and water can change1 the water is pulled down under the kerosene because gravity is pulling harder on the water than it is pulling on the kerosene4 ,the water1 therefore1 goes to the bottom and this forces the kerosene up4 ,,application #f4 ,three men were making a raft4 ,for floats they meant to use some air-tight galvanized iron cylinders4 ,one of them wanted to fill the cylinders with cork1 because1 he said1 cork is what you put in life preservers and it floats better than anything ,i know of4 ,they'd be better with nothing in them at all1 said a second4 ,pump all the air out and leave vacuums4 ,they're air-tight and they are strong enough to resist the air pressure4 ,but the third man said1 ,why1 you've got to have some air in them to buoy them up4 ,cork would be all right1 but it isn't as light as air2 so air would be the best thing to fill them with4 ,which way would the floats have worked best8 ,,application #g4 ,a little girl was telling her class about icebergs4 ,they are very dangerous1 she said1 and ships are often wrecked by running into them4 ,you see1 the sun melts the top off them so that all there is left is under water4 ,the sailors can't see the ice under water1 and so their ships run into it and are sunk4 ,another girl objected to this2 she said1 ,that couldn't be2 the ice would bob up as fast as the top melted4 ,no1 it wouldn't1 said a boy4 ,if that lower part wasn't heavier than water1 it never would have stayed under at all4 ,and if it was heavier at the beginning1 it would still be heavier after the top melted off4 ,who was right8 ,,inference ,,exercise ,explain the following3 #aa4 ,when you wash dishes1 a cup often floats on top of the water1 while a plate made of the same sort of china sinks to the bottom of the pan4 #ab4 ,if you put the cup in sidewise1 it sinks4 #ac4 ,the water in the cup1 when lying on its side1 is exactly as high as the water in the dish pan4 #ad4 ,if you put a glass into the water1 mouth first1 the water cannot get up into the glass2 if you tip it a little1 there are bubbles in the water and some water enters the glass4 #ae4 ,if you let a dish slip while you are wiping it1 it crashes to the floor4 #af4 ,it is much harder to hold a large platter while you are wiping it than it is to hold a small butter plate4 #ag4 ,if you set a hot glass upside down on the oilcloth table cover1 the oilcloth bulges up into it when the hot air and steam shrink and leave a partial vacuum within the glass4 #ah4 ,if you spill any of the dishwater on the floor1 it flattens out4 #ai4 ,you may use a kind of soap that is full of invisible little air bubbles2 if you do1 the soap will float on top of the water4 #bj4 ,when you drop a dry dishcloth into water1 it floats until all the pores are filled with water2 then it sinks4 ,,section #e4 ,how things are kept from toppling over3 ,stability4 ,why is it harder to keep your balance on stilts than on your feet8 ,why does a rowboat tip over more easily if you stand up in it8 ,in ,pisa1 ,italy1 there is a beautiful marble bell tower which leans over as if it were just about to fall to the ground4 ,yet it has stood in this position for hundreds of years and has never given a sign of toppling4 ,the foundations on which it rested sank down into the ground on one side while the tower was being built 7it took over #bjj years to build it71 and this made it tip4 ,but the men who were building it evidently felt sure that it would not fall over in spite of its tipping4 ,they knew the law of stability4 ,illustration3 ,,fig4 #ac4 ,the ,leaning ,tower of ,pisa4 ,all architects and engineers and builders have to take this law into consideration or the structures they put up would topple over4 ,and your body learned the law when you were a little over a year old1 or you never could have walked4 ,it is worth while for your brain to know it1 too1 because it is a very practical law that you can use in your everyday life4 ,if you wish to understand why the ,leaning ,tower of ,pisa does not fall over1 why it is hard to walk on stilts1 why a boat tips when a person stands up in it1 why blocks fall when you build too high with them1 and how to keep things from tipping over1 do the following experiment and read the explanation that follows it3 ,,experiment #ab4b ,unscrew the bell from a doorbell or a telephone4 ,you will not harm it at all1 and you can put it back after the experiment4 ,cut a sheet of heavy wrapping paper or light-weight cardboard about #e #i inches4 ,roll this so as to make a cylinder about #e inches high and as big around as the bell4 ,hold it in shape by pasting it or putting a couple of rubber bands around it4 ,cut two strips of paper about an inch wide and #h inches long2 lay these crosswise2 lay the bell1 round side down1 on the center of the cross4 ,push a paper fastener through the hole in the bell 7the kind shown in ,figure #ad7 and through the crossed pieces of paper1 spreading the fastener out so as to fasten the paper cross to the rounded side of the bell4 ,bend the arms of the cross up around the bell and paste them to the sides of the paper cylinder so that the bell makes a curved bottom to the cylinder1 as shown in ,figure #ae4 ,illustration3 ,,fig4 #ad4 ,footnote #b3 ,,to ,,the ,,teacher4 ,if you have a laboratory1 it is well to have this cylinder already made for the use of all classes4 ,illustration3 ,,fig4 #ae4 ,in this cylinder the center of weight is so high that it is not over the bottom if the cylinder is tipped to any extent4 ,so the cylinder falls over easily and lies quietly on its side4 ,illustration3 ,,fig4 #af4 ,but in this one the center of weight is so low that it is over the base1 no matter what position the cylinder is in4 ,illustration3 ,,fig4 #ag4 ,so even if the cylinder is laid on its side it immediately comes to an upright position again4 ,try to tip the cylinder over4 ,now stuff some crumpled paper loosely into the cylinder1 filling it to the top4 ,tip the cylinder again4 ,will it stay on its side now8 ,force all the crumpled paper to the bottom of the cylinder4 ,now will it stay on its side8 ,take out the crumpled paper and lay a flat stone in the bottom of the bell1 holding it in place by stuffing some crumpled paper in on top of it4 ,will the cylinder tip over now8 ,take the stone out1 put the crumpled paper in the bottom of the cylinder1 put the stone on top of the paper1 and again try to tip the cylinder over4 ,will it fall8 99 99 99 99 99 ,the center of the cylinder was always in one place1 of course4 ,but the center of the weight in that cylinder was usually near the bottom1 because the bell weighed so much more than the paper4 ,when you raised the center of weight by putting the stone up high or filling the cylinder with crumpled paper1 just a little tipping moved the center of weight so that it was not directly over the bell on which the cylinder was resting4 ,whenever the center of weight is not over the base of support 7the bottom on which the thing is standing71 an object will topple over4 ,moving the center of weight up 7,figs4 #ae and #af7 makes an object less stable4 ,the two main points to remember about stability are these3 the wider the base of an object1 the harder it is to tip over2 and the lower the center of the weight is1 the harder it is to tip over4 ,if you were out in a rowboat in a storm1 would it be better to sit up straight in the seat or to lie in the bottom of the boat8 ,why is a flat-bottomed boat safer than a canoe8 ,illustration3 ,,fig4 #ah4 ,which vase would be the hardest to upset8 ,where do you suppose the center of weight of the ,leaning ,tower of ,pisa is1--near the bottom or near the top8 ,,application #h4 ,if you had a large flower to put into a vase and you did not want it to tip over easily1 which of the three vases shown in ,figure #ah would you choose8 ,,application #i4 ,some boys made themselves a little sail-boat and went sailing in it4 ,a storm came up4 ,the boat rocked badly and was in danger of tipping over4 ,throw out all the heavy things1 quick6 shouted one4 ,no1 no1 don't for the life of you do it6 called another4 ,chop down the mast--here1 give me the hatchet6 another one said4 ,crouch way down--lie on the bottom4 ,no1 keep moving over to the side that is tipped up6 ,hold the things in the bottom of the boat still1 so they'll not keep rolling from side to side4 ,jump out and swim6 ,every one was shouting at once4 ,which parts of the advice should you have followed if you had been on board8 ,,inference ,,exercise ,explain the following3 #ba4 ,a ship when it goes to sea always carries ballast 7weight7 in its bottom4 #bb4 ,if the ship springs a leak below the water line1 the water rushes in4 #bc4 ,the ship's pumps suck the water up out of the bottom of the ship4 #bd4 ,the water pours back into the sea from the mouths of the pumps4 #be4 ,as the sailors move back and forth on the ship during a storm1 they walk with their legs spread far apart4 #bf4 ,although the ship tips far from side to side1 it rights itself4 #bg4 ,however far the ship tips1 the surface of the water in the bottom stays almost horizontal4 #bh4 ,while the ship is in danger1 the people put on life preservers1 which are filled with cork4 #bi4 ,when the ship rocks violently1 people who are standing up are thrown to the floor1 but those who are sitting down do not fall over4 #cj4 ,if the ship fills with water faster than the engines can pump it out1 the ship sinks4 ,,chapter ,,two ,,molecular ,,attraction ,,section #f4 ,how liquids are absorbed3 ,capillary attraction4 ,why do blotters pull water into themselves when a flat piece of glass will not8 ,how does a towel dry your face8 ,suppose you could turn off nature's laws in the way that you can turn off electric lights4 ,and suppose you stood in front of a switchboard with each switch labeled with the name of the law it would shut off4 ,of course1 there is no such switchboard1 but we know pretty well what would happen if we could shut off various laws4 ,one of the least dangerous-looking switches would be one labeled ,,capillary ,,attraction4 ,and now1 just for fun1 suppose that you have turned that switch off in order to see the effect4 ,at first you do not notice any change2 but after a while you begin to feel perspiration collecting all over your body as if your clothes were made of rubber sheeting4 ,soon this becomes so uncomfortable that you decide to take a bath4 ,but when you put your wash cloth into the water you find that it will not absorb any water at all2 it gets a little wet on the outside1 but remains stiff and is not easy or pleasant to use4 ,you reach for a sponge or a bath brush1 but you are no better off4 ,only the outside of the sponge and brush becomes wet1 and they remain for the most part harsh and dry4 ,then perhaps you try to dry yourself with a towel4 ,but that does not work2 not a drop of water will the towel absorb4 ,you might as well try to dry yourself on the glossy side of a piece of oilcloth4 ,by this time you are shivering2 so you probably decide to light the oil stove and get warm and dry over that4 ,but the oil will not come up the wick6 ,as a last resort you throw a dressing gown around you 7it does not get wet7 and start a fire in the fireplace4 ,this at last warms and dries you2 but as soon as you are dressed the clammy feeling comes again--your clothes will not absorb any perspiration4 ,while the capillary attraction switch is turned off you will simply have to get used to this4 ,then suppose you start to write your experience4 ,your fountain pen will not work4 ,even an ordinary pen does not work as well as it ought to4 ,it makes a blot on your paper4 ,if you use the blotter you are dismayed to find that the blot spreads out as flat as if you were pressing a piece of glass against it4 ,you take your eraser and try to remove the blot4 ,to your delight you find that it rubs out as easily as a pencil mark4 ,the ink has not soaked into the paper at all4 ,you begin to see some of the advantages in shutting off capillary attraction4 ,perhaps you are writing at the dining-room table1 and you overturn the inkwell on the tablecloth4 ,never mind1 it is no trouble to brush the ink off4 ,not a sign of stain is left behind4 ,by and by you look outdoors at the garden4 ,everything is withering4 ,the moisture does not move through the earth to where the roots of the plants can reach it4 ,before everything withers completely1 you rush to the switchboard and turn on the capillary attraction again4 ,you can understand this force of capillary attraction better if you perform the following experiments3 ,,experiment #ac4 ,fill a glass with water and color it with a little blueing or red ink4 ,into the glass put two or three glass tubes1 open at both ends1 and with bores of different sizes4 7,one of these tubes should be so-called thermometer tubing1 with about #a mm4 bore47 ,watch the colored water and see in which of the tubes it is pulled highest4 ,,experiment #ad4 ,put a clean washed lamp wick into the glass of colored water and watch to see if the water is pulled up the wick4 ,now let the upper end of the wick hang over the side of the glass all night4 ,put an empty glass under the end that is hanging out4 ,the next morning see what has happened4 ,illustration3 ,,fig4 #ai4 ,will the water be drawn up higher in the fine glass tube or in a tube with a larger opening8 ,illustration3 ,,fig4 #bj4 ,the water rises through the lamp wick by capillary attraction4 ,the space between the threads of the wick1 and especially the still finer spaces between the fibers that make up the threads1 act like fine tubes and the liquid rises in them just as it did in the fine glass tube4 ,wherever there are fine spaces between the particles of anything1 as there are in a lump of sugar1 a towel1 a blotter1 a wick1 and hundreds of other things1 these spaces act like fine tubes and the liquid goes into them4 ,the force that causes the liquid to move along fine tubes or openings is called capillary attraction4 ,capillary attraction--this tendency of liquids to go into fine tubes--is caused by the same force that makes things cling to each other 7adhesion71 and that makes things hold together 7cohesion74 ,the next two sections tell about these two forces2 so you will understand the cause of capillary attraction more thoroughly after reading them4 ,but you should know capillary attraction when you see it now1 and know how to use it4 ,the following questions will show whether or not you do3 ,,application #aj4 ,suppose you have spilled some milk on a carpet1 and that you have at hand wet tea leaves1 dry corn meal1 some torn bits of a glossy magazine cover1 and a piece of new cloth the pores of which are stopped up with starch4 ,which would be the best to use in taking up the milk8 ,,application #aa4 ,a boy spattered some candle grease on his coat4 ,his aunt told him to lay a blotter on the candle grease and to press a hot iron on the blotter1 or to put the blotter under his coat and the iron on top of the candle grease1--he was not quite sure which4 ,while he was trying to recall his aunt's directions1 his sister said that he could use soap and water to take the grease out2 then his brother told him to scrape the spot with a knife4 ,which would have been the right thing for him to do8 ,,inference ,,exercise ,explain the following3 #ca4 ,a pen has a slit running down to the point4 #cb4 ,when a man smokes1 the smoke goes from the cigar into his mouth4 #cc4 ,a blotter which has one end in water soon becomes wet all over4 #cd4 ,cream comes to the top of milk4 #ce4 ,it is much harder to stand on stilts than on your feet4 #cf4 ,oiled shoes are almost waterproof4 #cg4 ,city water reservoirs are located on the highest possible places in or near cities4 #ch4 ,you can fill a self-filling fountain pen by squeezing the bulb1 then letting go4 #ci4 ,the oceans do not flow off the world4 #dj4 ,when you turn a bottle of water upside down the water gurgles out instead of coming out in a smooth1 steady stream4 ,,section #g4 ,how things stick to one another3 ,adhesion4 ,why is it that when a thing is broken it will not stay together without glue8 ,why does chalk stay on the blackboard8 ,now that you have found out something about capillary attraction1 suppose that you should go to the imaginary switchboard again and tamper with some other law of nature4 ,an innocent-looking switch1 right above the capillary attraction switch1 would be labeled ,,adhesion4 ,suppose you have turned it off3 ,in an instant the wall paper slips down from the walls and crumples to a heap on the floor4 ,the paint and varnish drop from the woodwork like so much sand4 ,every cobweb and speck of dust rolls off and falls in a little black heap below4 ,when you try to wash1 you cannot wet your hands4 ,but they do not need washing1 as the dirt tumbles off1 leaving them cleaner than they ever were before4 ,you can jump into a tank of water with all your clothes on and come out as dry as you went in4 ,you discover by the dryness of your clothes that capillary attraction stopped when the adhesion was turned off1 for capillary attraction is just a part of adhesion4 ,but you are not troubled now with the clamminess of unabsorbed perspiration4 ,the perspiration rolls off in little drops1 not wetting anything but running to the ground like so much quicksilver4 ,your hair is fluffier than after the most vigorous shampoo4 ,your skin smarts with dryness4 ,your eyes are almost blinded by their lack of tears4 ,even when you cry1 the tears roll from your eyeballs and eyelids like water from a duck's back4 ,your mouth is too dry to talk2 all the saliva rolls down your throat1 leaving your tongue and cheeks as dry as cornstarch4 ,i think you would soon turn on the adhesion switch again4 ,,experiment #ae4 ,touch the surface of a glass of water1 and then raise your finger slightly4 ,notice whether the water tends to follow or to keep away from your finger as you raise it4 ,now dip your whole finger into the water and draw it out4 ,notice how the water clings1 and watch the drops form and fall off4 ,notice the film of water that stays on1 wetting your finger1 after all dropping stops4 ,illustration3 ,,fig4 #ba4 ,as the finger is raised the water is drawn up after it4 ,which do you think is the stronger1 the pull of gravity which makes some of the water drip off1 or the pull of adhesion which makes some of the water cling to your finger8 ,if the pull of gravity is stronger1 would not all the water drop off1 leaving your finger dry8 ,if the pull of adhesion is the stronger1 would not all the water stay on your finger1 none dropping off8 ,the truth of the matter is that gravity is stronger than adhesion unless things are very close together2 then adhesion is stronger4 ,the part of the water that is very close to your finger clings to it in spite of gravity2 the part that is farther away forms drops and falls down because of the pull of gravity4 ,adhesion1 then1 is the force that makes things cling to each other when they are very close together4 ,,why ,,it ,,is ,,easier ,,to ,,turn ,a ,,page ,,if ,,you ,,wet ,,your ,,finger4 ,water spreads out on things so that it gets very close to them4 ,the thin film of water on your finger is close enough to your finger and to the page which you are turning to cling to both2 so when you move your finger1 the page moves along with it4 ,,why ,,dust ,,clings ,,to ,,the ,,ceiling ,,and ,,walls4 ,the fine particles of dust are wafted up against the ceiling and walls by the moving air in the room4 ,they are so small that they can fit into the small dents that are in plaster and paper and can get very close to the wall4 ,once they get close enough1 the force of adhesion holds them with a pull stronger than that of gravity4 ,oily and wet surfaces catch dust much more readily than clean1 dry ones1 simply because the dust can get so much closer to the oil or water film and because this film flows partly around each dust particle and holds it by the force of adhesion4 ,this is why your face gets much dirtier when it is perspiring than when it is dry4 ,,application #ab4 ,explain why cobwebs do not fall from the ceiling2 why dust clings to a wet broom2 why a postage stamp does not fall off an envelope4 ,,inference ,,exercise ,explain the following3 #da4 ,there are no springs on the tops of high mountains4 #db4 ,people used to shake sand over their letters after writing them in ink4 #dc4 ,people used to make night lights for bedrooms by pouring some oil into a cup of water and floating a piece of wick on the oil4 ,the oil always stayed on top of the water1 and went up through the wick fast enough to keep the light burning4 #dd4 ,your face becomes much dirtier when you are perspiring4 #de4 ,ink bottles are usually made with wide bases4 #df4 ,when you spill water on the floor1 you cannot wipe it up with wrapping paper1 but you can dry it easily with a cloth4 #dg4 ,oiled mops are used in taking up dust4 #dh4 ,cake will stick to a pan unless the pan is greased4 #di4 ,although the earth turns completely over every day1 we never fall off it4 #ej4 ,signs are fastened sometimes to windows or to the wind shields of automobiles by little rubber suction caps4 ,,section #h4 ,the force that makes a thing hold together3 ,cohesion4 ,what makes rain fall in drops8 ,why are diamonds hard8 ,you have not yet touched any of the most dangerous switches on the imaginary switchboard of universal laws4 ,but if your experience in turning off the capillary attraction and adhesion switches did not discourage you1 you might try turning off the one beside them labeled ,,cohesion3 ,illustration3 ,,fig4 #bb4 ,el ,capitan1 ,yosemite ,valley1 ,california4 ,if the force of cohesion were suspended1 a mountain like this would immediately become the finest dust4 ,things happen too swiftly for you to know much about them4 ,the house you are in falls to dust instantly4 ,you fall through the place where the floor has been2 but you do not bump on the cement basement floor below1 partly because there is no such thing as a hard floor or even hard ground anywhere1 and partly because you disintegrate--fall to pieces--so completely that there is nothing left of you but a grayish film of fine dust and a haze of warm water4 ,with a deafening roar1 rocks1 skyscrapers1 and even mountains tumble down1 fall to pieces1 and sink into an inconceivably fine dust4 ,nothing stands up in the world--not a tree1 not an animal1 not an island4 ,with a wild rush the oceans flood in over the dust that has been nations and continents1 and then this dust turns to a fine muddy ooze in the bottom of a worldwide sea4 ,but it is an ocean utterly different from what we have in the real world4 ,there are no waves4 ,neither are there any reflections of clouds in its surface1--first because the clouds would fly to pieces and turn to invisible vapor1 and second1 because the ocean has no surface--it simply melts away into the air and no one can tell where the water stops and where the air begins4 ,then the earth grows larger and larger4 ,the ocean turns to a heavy1 dense1 transparent steam4 ,the fine mud that used to be rocks and mountains and living things turns to a heavy1 dense gas4 ,our once beautiful1 solid1 warm1 living earth now whirls on through space1 a swollen1 gaseous globe1 utterly dead4 ,and the only thing that prevents all this from actually happening right now is that there is a force called cohesion that holds things together4 ,it is the pull which one particle of anything has on another particle of the same material4 ,the paper in this book1 the chair on which you are sitting1 and you yourself are all made of a vast number of unthinkably small particles called molecules1 each of which is pulling on its neighbor with such force that all stay in their places4 ,substances in which they pull the hardest1 like steel1 are very hard to break in two2 that is1 it is difficult to pull the molecules of these substances apart4 ,in liquids1 such as water1 the molecules do not pull nearly so hard on each other4 ,in a gas1 such as air1 they are so far apart that they have practically no pull on each other at all4 ,that is why everything would turn to a gas if the force of cohesion stopped4 ,why things would turn cold will be explained in ,chapter #d4 ,cohesion1 adhesion1 and capillary attraction1 all are the result of the pull of molecules on each other4 ,the difference is that capillary attraction is the pulling of particles of liquids up into fine spaces1 as when a lamp wick draws up oil2 adhesion is the pull of the particles of one substance or thing on the particles of another when they are very close together1 as when water clings to your hand or when dust sticks to the ceiling2 while cohesion is the clinging together of the particles of the same substance1 like the holding together of the particles of your chair or of this paper4 ,when you put your hand into water it gets wet because the adhesion of the water to your hand is stronger than the cohesion of the water itself4 ,the particles of the water are drawn to your hand more powerfully than they are drawn to each other4 ,but in the following experiment1 you have an example of cases where cohesion is stronger than adhesion3 ,,experiment #af4 ,pour some mercury 7quicksilver7 into a small dish and dip your finger into it4 ,as you raise your finger1 see if the mercury follows it up as the water did in ,experiment #ad4 ,when you pull your finger all the way out1 has the mercury wet it at all8 ,put a lamp wick or a part of your handkerchief into the mercury4 ,does it draw the mercury up as it would draw up water8 ,illustration3 ,,fig4 #bc4 ,the mercury does not wet the finger1 and as the finger is lifted the mercury does not follow it4 ,the reason for this peculiarity of mercury is that the pull between the particles of mercury themselves is stronger than the pull between them and your finger or handkerchief4 ,in scientific language1 the cohesion of the mercury is stronger than its adhesion to your finger or handkerchief4 ,although this seems unusual for a liquid1 it is what we naturally expect of solid things2 you would be amazed if part of the wood of your school seat stuck to you when you got up1 for you expect the particles in solid things to cohere--to have cohesion--much more strongly than they adhere to something else4 ,it is because solids have such strong cohesion that they are solids4 ,,application #ac4 ,explain why mercury cannot wet your fingers2 why rain falls in drops2 why it is harder to drive a nail into wood than into soap2 why steel is hard4 ,,inference ,,exercise ,explain the following3 #ea4 ,ink spilled on a plain board soaks in1 but on a varnished desk it can be easily wiped off4 #eb4 ,when a window is soiled you can write on it with your finger2 then your finger becomes soiled4 #ec4 ,a starched apron or shirt stays clean longer than an unstarched one4 #ed4 ,when you hold a lump of sugar with one edge just touching the surface of a cup of coffee1 the coffee runs up the lump4 #ee4 ,a drop of water on a dry plate is not flat but rounded4 #ef4 ,it is hard to write on cloth because the ink spreads out and blurs4 #eg4 ,if you roughen your finger nails by cleaning them with a knife1 they will get soiled much more quickly than if you keep them smooth by using an orange stick4 #eh4 ,when you dip your pen in the ink and then move it across the paper1 it makes ink marks on the paper4 #ei4 ,if you suck the air out of a bottle1 the bottle will stick to your tongue4 #fj4 ,you cannot break a thick piece of iron with your hands4 ,,section #i4 ,friction4 ,what makes ice slippery8 ,how does a brake stop a car8 ,why do things wear out8 ,it would not be such a calamity if we were to turn off friction from the world4 ,still1 ,i doubt whether we should want to leave it off much longer than was necessary for us to see what would happen4 ,suppose we imagine the world with all friction removed3 ,a man on a bicycle can coast forever along level ground4 ,ships at sea can shut off steam and coast clear across the ocean4 ,no machinery needs oiling4 ,the clothes on your body feel smoother and softer than the finest silk4 ,perpetual motion is an established fact instead of an absolute impossibility2 everything that is not going against gravity will keep right on moving forever or until it bumps into something else4 ,but1 if there is no friction and you want to stop1 you cannot4 ,suppose you are in an automobile when all friction stops4 ,you speed along helplessly in the direction you are going4 ,you cannot steer the machine--your hands would slip right around on the steering wheel1 and even if you turn it by grasping the spoke1 your machine still skids straight forward4 ,if you start to go up a hill1 you slow down1 stop1 and then before you can get out of the machine you start backward down the hill again and keep on going backward until you smash into something4 ,a person on foot does not fare much better4 ,if he is walking at the time friction ceases1 the ground is suddenly so slippery that he falls down and slides along on his back or stomach in the same direction he was walking1 until he bumps into something big or starts to slip up a slope4 ,if he reaches a slope1 he1 like the automobile1 stops an instant a little way up1 then starts sliding helplessly backward4 ,another man is standing still when the friction is turned off4 ,he cannot get anywhere4 ,as soon as he starts to walk forward1 his feet slip out from under him and he falls on his face4 ,he lies in the same spot no matter how he wriggles and squirms4 ,if he tries to push with his hands1 they slip over the rough ground more easily than they now slip through air4 ,he cannot push sideways enough even to turn over4 ,if there happens to be a rope within reach and one end is tied to a tree1 he might try to take hold of the rope to pull himself along4 ,but no matter how tightly he squeezes1 the rope slips right through his hands when he starts to pull4 ,if1 however1 there is a loop in the rope1 he can slip his hand through the loop and try to pull4 ,but the knots with which the rope is tied immediately come untied and he is as helpless as ever4 ,even if he takes hold of a board fence he is no more successful4 ,the nails in the board slip out of their holes and he is left with a perfectly slippery and useless board on the ground beside him for a companion4 ,as it grows cold toward evening he may take some matches out of his pocket and try to start a fire4 ,aside from the difficulty of his being unable to hold them except by the most careful balancing or by shutting them up within his slippery hands1 he is entirely incapable of lighting them2 they slip over the cement beneath him or over the sole of his shoe without the least rubbing4 ,in the real world1 however1 it is fortunately as impossible to get away from friction as it is to get away from the other laws we have tried to imagine as being turned off4 ,there is always some friction1 or rubbing1 whenever anything moves4 ,a bird rubs against the air1 the point of a spinning top rubs against the sidewalk on which it is spinning4 ,your shoes rub against the ground as you walk and so make it possible for you to push yourself forward4 ,the drive wheels of machinery rub against the belts and pull them along4 ,there is friction between the wheels of a car and the track they are pushing against1 or the wheels would whirl around and around uselessly4 ,illustration3 ,,fig4 #bd4 ,hockey is a fast game because there is little friction between the skates and the ice4 ,but we can increase or decrease friction a great deal4 ,if we make things rough1 there is more friction between them than if they are smooth4 ,if we press things tightly together1 there is more friction than if they touch lightly4 ,a nail in a loose hole comes out easily1 but in a tight hole it sticks2 the pressure has increased the friction4 ,a motorman in starting a trolley car sometimes finds the track so smooth that the wheels whirl around without pushing the car forward2 he pours some sand on the track to make it rougher1 and the car starts4 ,when you put on new shoes1 they are so smooth on the bottom that they slip over the ground because of the lack of friction4 ,if you scratch the soles1 they are rougher and you no longer slip4 ,if you try to pull a stake out of the ground1 you have to squeeze it harder than the ground does or it will slip out of your hands instead of slipping out of the ground4 ,when you apply a brake to an automobile1 the brake must press tightly against the axle or wheel to cause enough friction to stop the automobile4 ,there are always two results of friction3 heat and wear4 ,sometimes these effects of friction are helpful to us1 and sometimes they are quite the opposite4 ,the heat from friction is helpful when it makes it possible for us to light a fire1 but it is far from helpful when it causes a hot box because of an ungreased wheel on a train or wagon1 or burns your hands when you slide down a rope4 ,the wear from friction is helpful when it makes it possible to sandpaper a table1 scour a pan1 scrub a floor1 or erase a pencil mark2 but we don't like it when it wears out automobile tires1 all the parts of machinery1 and our clothes4 ,,experiment #ag4 ,hold a nail against a grindstone while you turn the stone4 ,notice both the wear and heat4 ,let the nail rest lightly on the stone part of the time and press hard part of the time4 ,which way does the nail get hotter8 ,which way does it wear off more quickly8 ,run it over a pane of glass and see if it gets as hot as it does on the grindstone2 if it wears down as quickly4 ,,why ,,we ,,oil ,,machinery4 ,we can decrease friction by keeping objects from pressing tightly against each other1 and by making their surfaces smooth4 ,the most common way of making surfaces smooth is by oiling or greasing them4 ,a film of oil or grease makes things so smooth and slippery that there is very little friction4 ,that is why all kinds of machinery will run so smoothly if they are kept oiled4 ,and since the oil decreases friction1 it decreases the wear caused by friction4 ,so well-oiled machines last much longer than machines that are not sufficiently oiled4 ,illustration3 ,,fig4 #be4 ,the friction of the stone heats the nail and wears it away4 ,,why ,,ball ,,bearings ,,are ,,used4 ,there is much less friction when a round object rolls over a surface than when two surfaces slide over one another1 unless the sliding surfaces are very smooth2 think how much easier it is to pull a wagon forward than it would be to take hold of the wheels and pull the wagon sidewise4 ,so when you want the least possible friction in a machine you use ball bearings4 ,the bearings are located in the hub of a wheel4 ,then1 instead of the axle rubbing against the hub1 the bearings roll inside of the hub4 ,this causes very little friction2 and the friction is made still less by keeping the bearings oiled4 ,,application #ad4 ,suppose you were making a bicycle1--in which of the following places would you want to increase the friction1 and in which would you want to decrease it8 ,handle grips1 axles1 pedals1 tires1 pedal cranks1 the sockets in which the handle bar turns1 the nuts that hold the parts together4 ,,application #ae4 ,a small boy decided to surprise his mother by oiling her sewing-machine4 ,he put oil in the following places3 ,on the treadle1 on the large wheel over which the belt runs1 on the axle of the same wheel1 on the groove in the little wheel up above where the belt runs1 on the joint where the needle runs up and down1 on the little rough place under the needle that pushes the cloth forward4 ,which of these did he do well to oil and which should he have let alone8 ,,inference ,,exercise ,explain the following3 #fa4 ,rivers flow north as well as south1 although we usually speak of north as up north4 #fb4 ,tartar and bits of food stick to your teeth4 #fc4 ,brushing your teeth with tooth powder cleans them4 #fd4 ,when a chair has gliders 7smooth metal caps7 on its feet1 it slides easily across the floor4 #fe4 ,when you wet your finger1 you can turn a page more easily4 #ff4 ,a lamp wick draws oil up from the lower part of a lamp to the burner4 #fg4 ,the sidewalks on steep hills are made of rough cement4 #fh4 ,certain fish can rise in the water by expanding their air bladders1 although this does not make them weigh any less4 #fi4 ,when your hands are cold1 you rub them together to warm them4 #gj4 ,it is dangerous to stand up in a rowboat or canoe4 ,,chapter ,,three ,,conservation ,,of ,,energy ,,section #aj4 ,levers4 ,how a big weight can be lifted with a little force2 how one thing moving slowly a short distance can make another move swiftly a long distance4 ,why can you go so much faster on a bicycle than on foot8 ,how can a man lift up a heavy automobile by using a jack8 ,why can you crack a hard nut with a nutcracker when you cannot crack it by squeezing it between two pieces of iron8 ,give me a lever1 long enough and strong enough1 and something to rest it on1 and ,i can lift the whole world1 said an old ,greek philosopher4 ,and as a philosopher he was right2 theoretically it would be possible4 ,but since he needed a lever that would have been as long as from here to the farthest star whose distance has ever been measured1 and since he would have had to push his end of the lever something like a quintillion 7#a1jjj1jjj1jjj1jjj1jjj1jjj7 miles to lift the earth one inch1 his proposition was hardly a practical one4 ,but levers are practical4 ,without them there would be none of our modern machines4 ,no locomotives could speed across the continents2 no derricks could lift great weights2 no automobiles or bicycles would quicken our travel2 our very bodies would be completely paralyzed4 ,yet the law back of all these things is really simple4 ,you have often noticed on the see-saw that a small child at one end can be balanced by a larger child at the other end1 provided that the larger child sits nearer the middle4 ,why should it matter where the larger child sits8 ,he is always heavier--why doesn't he overbalance the small child8 ,it is because when the small child moves up and down he goes a longer distance than the large child does4 ,in ,figure #bf the large boy moves up and down only half as far as the little girl does4 ,she weighs only half as much as he1 yet she balances him4 ,illustration3 ,,fig4 #bf4 ,the little girl raises the big boy1 but in doing it she moves twice as far as he does4 ,you will begin to get a general understanding of levers and how they work by doing the following experiment3 ,,experiment #ah4 ,for this experiment there will be needed a small pail filled with something heavy 7sand or stones will do71 a yardstick with a hole through the middle and another hole near one end and with notches cut here and there along the edge1 and a post or table corner with a heavy nail driven into it to within an inch of the head4 ,the holes in the yardstick must be large enough to let the head of this nail through4 ,put the middle hole of the yardstick over the nail1 as is shown in ,figure #bg4 ,the nail is the fulcrum of your lever4 ,now hang the pail on one of the notches about halfway between the fulcrum and the end of the stick and put your hand on the opposite side of the yardstick at about the same distance as the pail is from the fulcrum4 ,raise and lower the pail several times by moving the opposite end of the lever up and down4 ,see how much force it takes to move the pail4 ,now slide your hand toward the fulcrum and lower and raise the pail from that position4 ,is it harder or easier to lift the pail from here than from the first position8 ,which moves farther up and down1 your hand or the pail8 ,next1 slide your hand all the way out to the end of the yardstick and raise and lower the pail from there4 ,is the pail harder or easier to lift8 ,does the pail move a longer or a shorter distance up and down than your hand8 ,if you wanted to move the pail a long way without moving your hand as far1 would you put your hand nearer to the fulcrum or farther from it than the pail is8 ,illustration3 ,,fig4 #bg4 ,the yardstick is a lever by which he lifts the pail4 ,illustration3 ,,fig4 #bh4 ,a lever with the weight between the fulcrum and the force4 ,suppose you wanted to lift the pail with the least possible effort1 where would you put your hand8 ,notice another fact3 when your hand is at the end of the yardstick1 it takes the same length of time to move a long way as the pail takes to move a short way4 ,then which is moving faster1 your hand or the pail8 ,,experiment #ai4 ,put the end hole of the yardstick on the nail1 as shown in ,figure #bh4 ,the nail is still the fulcrum of your lever4 ,put the pail about halfway between the fulcrum and the other end of the stick1 and hold the end of the stick in your hands4 ,raise and lower your hand to see how hard or how easy it is to lift the pail from this position4 ,which is moving farther1 your hand or the pail8 ,which is moving faster8 ,now put your hand about halfway between the fulcrum and the pail and raise and lower it4 ,is it harder or easier to raise than before8 ,which moves farther this time1 your hand or the pail8 ,which moves faster8 ,if you wanted to make the pail move farther and faster than your hand1 would you put your hand nearer to the fulcrum than the pail is1 or farther from the fulcrum than the pail8 ,if you wanted to move the pail with the least effort1 where would you put your hand8 ,,experiment #bj4 ,use a pair of long-bladed shears and fold a piece of cardboard once to lie astride your own or some one else's finger4 ,put the finger1 protected by the cardboard1 between the two points of the shears4 ,then squeeze the handles of the shears together4 ,see if you can bring the handles together hard enough to hurt the finger between the points4 ,now watch the shears as you open and close the blades4 ,which move farther1 the points of the shears or the handles8 ,which move faster8 ,next1 put the finger1 still protected by the cardboard1 between the handles of the shears and press the points together4 ,can you pinch the finger this way harder or less hard than in the way you first tried8 ,do the points or handles move farther as you close the shears8 ,which part closes with the greater force8 ,illustration3 ,,fig4 #bi4 ,you cannot pinch hard enough this way to hurt4 ,illustration3 ,,fig4 #cj4 ,but this is quite different4 ,,experiment #ba4 ,use a ,dover egg beater4 ,fasten a small piece of string to one of the blades1 so that you can tell how many times it goes around4 ,turn the handle of the beater around once slowly and count how many times the blade goes around4 ,which moves faster1 the handle or the blade8 ,where would you expect to find more force1 in the cogs or in the blades8 ,test your conclusion this way3 ,put your finger between the blades and try to pinch it by turning the handle2 then place your finger so that the skin is caught between the cogs and try to pinch the finger by turning the blades4 ,where is there more force8 ,where is there more motion8 ,,experiment #bb4 ,put a spool over the nail which was your fulcrum in the first two experiments4 7,take the stick off the nail first1 of course47 ,use this spool as a pulley4 ,put a string over it and fasten one end of your string to the pail 7,fig4 #cb74 ,lift the pail by pulling down on the other end of the string4 ,notice that it is not harder or easier to move the pail when it is near the nail than when it is near the floor4 ,when your hand moves down from the nail to the floor1 how far up does the pail move8 ,does the pail move a greater or less distance than your hand1 or does it move the same distance8 ,next fasten one end of the string to the nail4 ,set the pail on the floor4 ,pass the string through the handle of the pail and up over the spool 7,fig4 #cc74 ,pull down on the loose end of the string4 ,is the pail easier to lift in this way or in the way you first tried8 ,as you pull down with your hand1 notice whether your hand moves farther than the pail1 not so far as the pail1 or the same distance4 ,is the greater amount of motion in your hand or in the pail8 ,then where would you expect the greater amount of force8 ,illustration3 ,,fig4 #ca4 ,when the handle is turned the blades of the egg beater move much more rapidly than the hand4 ,will they pinch hard enough to hurt8 ,the whole idea of the lever can be summed up like this3 one end of the contrivance moves more than the other4 ,but energy cannot be lost2 so to make up for this extra motion at one end more force is always exerted at the other4 ,this rule is true for all kinds of levers1 blocks and tackles or pulley systems1 automobile and bicycle gears1 belt systems1 cog systems1 derricks1 crowbars1 and every kind of machine4 ,in most machines you either put in more force than you get out and gain motion1 or you put in more motion than you get out and gain force4 ,in the following examples of the lever see if you can tell whether you are applying more force and obtaining more motion1 or whether you are putting in more motion and obtaining more force3 ,cracking nuts with a nut cracker4 ,beating eggs with a ,dover egg beater4 ,going up a hill in an automobile on low gear4 ,speeding on high gear4 ,cutting cloth with the points of shears4 ,cutting near the angle of the shears4 ,turning a door knob4 ,picking up sugar with sugar tongs4 ,pinching your finger in the crack of a door on the hinge side4 ,illustration3 ,,fig4 #cb4 ,his hand goes down as far as the pail goes up4 ,,application #af4 ,suppose you wanted to lift a heavy frying pan off the stove4 ,you have a cloth to keep it from burning your hand4 ,would it be easier to lift it by the end of the handle or by the part of the handle nearest the pan8 ,,application #ag4 ,a boy was going to wheel his little sister in a wheelbarrow4 ,she wanted to sit in the middle of the wheelbarrow2 her brother thought she should sit as near the handles as possible so that she would be nearer his hands4 ,another boy thought she should sit as near the wheel as possible4 ,who was right8 ,,application #ah4 ,james ,mc,dougal lived in a hilly place4 ,he was going to buy a bicycle4 ,i want one that will take the hills easily1 he said4 ,the dealer showed him two bicycles4 ,on one the back wheel went around three times while the pedals went around once2 on the other the back wheel went around four and a half times while the pedals went around once4 ,which bicycle should ,james have chosen8 ,if he had wanted the bicycle for racing1 which should he have chosen8 ,,application #ai4 ,a wagon stuck in the mud4 ,the driver got out and tried to help the horse by grasping the spokes and turning the wheel4 ,should he have grasped the spokes near the hub1 near the rim1 or in the middle8 ,illustration3 ,,fig4 #cc4 ,with this arrangement the pail travels more slowly than the hand4 ,will it seem heavier or lighter than with the arrangement shown in ,figure #cb8 ,,inference ,,exercise ,explain the following3 #ga4 ,when you turn on the faucet of a distilled-water bottle1 bubbles go up through the water as the water pours out4 #gb4 ,a clothes wringer has a long handle4 ,it wrings the clothes drier than you can wring them by hand4 #gc4 ,you use a crowbar when you want to raise a heavy object such as a rock4 #gd4 ,sometimes it is almost impossible to get the top from a jar of canned fruit unless you let a little air under the edge of the lid4 #ge4 ,it is much easier to carry a carpet sweeper if you take hold near the sweeper part than it is if you take hold at the end of the handle4 #gf4 ,you can make marks on a paper by rubbing a pencil across it4 #gg4 ,a motorman sands the track when he wishes to stop the car on a hill4 #gh4 ,on a faucet there is a handle with which to turn it4 #gi4 ,before we pull candy we butter our fingers4 #hj4 ,you can scratch glass with very hard steel but not with wood4 ,,section #aa4 ,inertia4 ,why is it that if you push a miniature auto rapidly1 it will go straight8 ,why does the earth never stop moving8 ,when you jerk a piece of paper from under an inkwell1 why does the inkwell stay still8 ,when you are riding in a car and the car stops suddenly1 you are thrown forward2 your body tends to keep moving in the direction in which the car was going4 ,when a car starts suddenly1 you are thrown backward2 your body tends to stay where it was before the car started4 ,when an automobile bumps into anything1 the people in the front seat are often thrown forward through the wind shield and are badly cut2 their bodies keep on going in the direction in which the automobile was going4 ,when you jump off a moving street car1 you have to run along in the direction the car was going or you fall down2 your body tries to keep going in the same direction it was moving1 and if your feet do not keep up1 you topple forward4 ,generally we think that it takes force to start things to move1 but that they will stop of their own accord4 ,this is not true4 ,it takes just as much force to stop a thing as it does to start it1 and what usually does the stopping is friction4 ,when you shoot a stone in a sling shot1 the contracting rubber pulls the stone forward very rapidly4 ,the stone has been started and it would go on and never stop if nothing interfered with it4 ,for instance1 if you should go away off in space--say halfway between here and a star--and shoot a stone from a sling shot1 that stone would keep on going as fast as it was going when it left your sling shot1 forever and ever1 without stopping1 unless it bumped into a star or something4 ,on earth the reason it stops after a while is that it is bumping into something all the time--into the particles of air while it is in the air1 and finally against the earth when it is pulled to the ground by gravity4 ,if you threw a ball on the moon1 the person who caught it would have to have a very thick mitt to protect his hand1 and it would never be safe to catch a batted fly4 ,for there is no air on the moon1 and therefore nothing would slow the ball down until it hit something2 and it would be going as hard and fast when it struck the hand of the one who caught it as when it left your hand or the bat4 ,illustration3 ,,fig4 #cd4 ,when the paper is jerked out1 the glass of water does not move4 ,,try ,,these ,,experiments3 ,,experiment #bc4 ,fill a glass almost to the brim with water4 ,lay a smooth piece of writing paper #aj or #aa inches long on a smooth table1 placing it near the edge of the table4 ,set the glass of water on the paper near its inner edge 7,fig4 #cd74 ,take hold of the edge of the paper that is near the edge of the table4 ,move your hand a little toward the glass so that the paper is somewhat bent4 ,then1 keeping your hand near the level of the table1 suddenly jerk the paper out from under the glass4 ,if you give a quick enough jerk and keep your hand near the level of the table1 not a drop of water will spill and the glass will stay almost exactly where it was4 ,this is because the glass of water has inertia4 ,it was standing still1 and so it tends to remain standing still4 ,your jerk was so sudden that there was not time to overcome the inertia of the glass of water2 so it stayed where it was4 ,,experiment #bd4 ,have a boy on roller skates skate down the hall or sidewalk toward you and have him begin to coast as he comes near4 ,when he reaches you1 put out your arm and try to stop him4 ,notice how much force it takes to stop him in spite of the fact that he is no longer pushing himself along4 ,now let the boy skate toward you again1 coasting as before2 but this time have him swing himself around a corner by taking hold of you as he passes4 ,notice how much force it takes just to change the direction in which he is moving4 ,illustration3 ,,fig4 #ce4 ,when a boy is moving rapidly1 it takes force to change the direction of his motion4 ,you see the boy's inertia makes him tend to keep going straight ahead at the same speed2 it resists any change either in the speed or the direction of his motion4 ,so it takes a good deal of force either to stop him or to turn him4 ,if1 on the other hand1 you had no inertia1 you could neither have stopped him nor turned him2 he would have swept you right along with him4 ,it was because inertia made you tend to remain still1 that you could overcome part of his inertia4 ,at the same time he overcame part of your inertia1 for he made you move a little4 ,inertia is the tendency of a thing to keep on going forever in the same direction if once it is started1 or to stand still forever unless something starts it4 ,if moving things did not have inertia 7if they did not tend to keep right on moving in the same direction forever or until something changed their motion71 you could not throw a ball2 the second you let go of it1 it would stop and fall to the ground4 ,you could not shoot a bullet any distance2 as soon as the gases of the gunpowder had stopped pushing against it1 it would stop dead and fall4 ,there would be no need of brakes on trains or automobiles2 the instant the steam or gasoline was shut off1 the train or auto would come to a dead stop4 ,but you would not be jerked in the least by the stopping1 because as soon as the automobile or train stopped1 your body too would stop moving forward4 ,your automobile could even crash into a building without your being jarred4 ,for when the machine came to a sudden stop1 you would not be thrown forward at all1 but would sit calmly in the undamaged automobile4 ,if you sat in a swing and some one ran under you1 you would keep going up till he let go1 and then you would be pulled down by gravity just as you now are4 ,but just as soon as the swing was straight up and down you would stop2 there would be no inertia to make you keep on swinging back and up4 ,if the inertia of moving things stopped1 the clocks would no longer run1 the pendulums would no longer swing1 nor the balance wheels turn2 nothing could be thrown2 it would be impossible to jump2 there would cease to be waves on the ocean2 and the moon would come tumbling to the earth4 ,the earth would stop spinning2 so there would be no change from day to night2 and it would stop swinging about in its orbit and start on a rush toward the sun4 ,but there is always inertia4 ,and all things everywhere and all the time tend to remain stock still if they are still1 until some force makes them move2 and all things that are moving tend to keep on moving at the same speed and in the same direction1 until something stops them or turns them in another direction4 ,,application #bj4 ,explain why you should face forward when alighting from a street car2 why a croquet ball keeps rolling after you hit it2 why you feel a jolt when you jump down from a high place4 ,,inference ,,exercise ,explain the following3 #ha4 ,it is much easier to erase charcoal drawings than water-color paintings4 #hb4 ,when an elevator starts down suddenly you feel lighter for a moment1 while if it starts up quickly you feel heavier4 #hc4 ,you can draw a nail with a claw hammer when you could not possibly pull it with your hand even if you could get hold of it4 #hd4 ,when an automobile bumps into anything1 the people in the front seat are often thrown forward through the wind shield4 #he4 ,certain weighted dolls will rise and stand upright1 no matter in what position you lay them down4 #hf4 ,some automobile tires have little rubber cups all over them which are supposed to make the tires cling to the pavement and thus prevent skidding4 #hg4 ,it is hard to move beds and bureaus which have no castors or gliders4 #hh4 ,when you jump off a moving street car1 you lean back4 #hi4 ,all water flows toward the oceans sooner or later4 #ij4 ,you can skate on ice1 but not on a sidewalk1 with ice skates4 ,,section #ab4 ,centrifugal force4 ,why does not the moon fall down to the earth8 ,why will a lasso go so far after it is whirled8 ,why does a top stand on its point while it is spinning8 ,if centrifugal force suddenly stopped acting1 you would at first not notice any change4 ,but if you happened to get into an automobile and rode down a muddy street1 you would be delighted to find that the mud did not fly up from the wheels as you sped along4 ,and when you went around a slippery corner1 your automobile would not skid in the least4 ,if a dog came out of a pool of water and shook himself while centrifugal force was not acting1 the water1 instead of flying off in every direction1 would merely drip down to the ground as if the dog were not shaking himself at all4 ,a cowboy would find that he could no longer throw his lasso by whirling it around his head4 ,a boy trying to spin his top would discover that the top would not stand on its point while spinning1 any better than when it was not spinning4 ,these are little things1 however4 ,most people would be quite unconscious of any change for some time4 ,then1 as night came on and the full moon rose1 it would look as if it were growing larger and larger4 ,it would seem slowly to swell and swell until it filled the whole sky4 ,then with a stupendous crash the moon would collide with the earth4 ,every one would be instantly killed4 ,and it would be lucky for them that they were2 for if any people survived the shock of the awful collision1 they would be roasted to death by the heat produced by the striking together of the earth and the moon4 ,moreover1 the earth would be whirled swiftly toward the sun1 and a little later the charred earth would be swept into the sun's vast1 tempestuous flames4 ,when we were talking about inertia1 we said that if there were no inertia1 the moon would tumble down to the earth and the earth1 too1 would fall into the sun4 ,that was because if there were no inertia there would be no centrifugal force4 ,for centrifugal force is not really a force at all1 but it is one form of inertia--the inertia of whirling things4 ,do this experiment3 ,,experiment #be4 ,hold a pail half full of water in one hand4 ,swing it back and forth a couple of times2 then swing it swiftly forward1 up1 and on around1 bringing it down back of you 7,fig4 #cf74 ,swing it around this way swiftly and evenly several times1 finally stopping at the beginning of the up swing4 ,it is centrifugal force that keeps the water in the pail4 ,it depends entirely on inertia4 ,you see1 while the pail is swinging upward rapidly1 the water is moving up and tends by its inertia to keep right on moving in the same upward direction4 ,before you get it over your head1 the tendency of the water to keep on going up is so strong that it pulls on your arm and hand and presses against the bottom of the pail above it4 ,its tendency to go on up is stronger than the downward pull of gravity4 ,as you swing the pail on backward1 the water of course has to move backward1 too2 so now it tends to keep on moving backward2 and when the pail is starting down behind you1 the water is tending to fly out in the backward direction in which it has just been going4 ,therefore it still pushes against the bottom of the pail and pulls away from your shoulder1 which is in the center of the circle about which the pail is moving4 ,by the time you have swung the pail on down1 the water in it tends to keep going down1 and it is still pulling away from your shoulder and pressing against the bottom of the pail4 ,illustration3 ,,fig4 #cf4 ,why doesn't the water spill out8 ,in this way1 during every instant the water tends to keep going in the direction in which it was going just the instant before4 ,the result is that the water keeps pulling away from your shoulder as long as you keep swinging it around4 ,all whirling things tend to fly away from the center about which they are turning4 ,this is the law of centrifugal force4 ,the earth1 for example1 as it swings around the sun1 tends to fly away from the center of its orbit4 ,this tendency of the earth--its centrifugal force--keeps it from being drawn into the sun by the powerful pull of the sun's gravitation4 ,at the same time it is this gravitation of the sun that keeps the earth from flying off into space1 where we should all be frozen to icicles and lost in everlasting night4 ,for if the sun's pull stopped1 the earth would fly off as does a stone whirled from the end of a string1 when you let go of the string4 ,the moon1 in like manner1 would fly away from the earth and sun if gravitation stopped pulling it1 but it would crash into us if its centrifugal force did not keep it at a safe distance4 ,have you ever sat on a spinning platform1 sometimes called the social whirl1 in an amusement park1 and tried to stay on as it spun faster and faster8 ,it is centrifugal force that makes you slide away from the center and off at the edge4 ,illustration3 ,,fig4 #cg4 ,an automobile race4 ,notice how the track is banked to keep the cars from overturning on the curves4 ,,how ,,cream ,,is ,,separated ,,from ,,milk ,,by ,,centrifugal ,,force4 ,the heavier things are1 the harder they are thrown out by centrifugal force4 ,milk is heavier than cream1 as you know from the fact that cream rises and floats on top of the milk4 ,so when milk is put into a centrifugal separator1 a machine that whirls it around very rapidly1 the milk is thrown to the outside harder than the cream1 and the cream therefore stays nearer the middle4 ,as the bowl of the machine whirls faster1 the milk is thrown so hard against the outside that it flattens out and rises up the sides of the bowl4 ,thus you have a large hollow cylinder of milk on the outside against the wall of the bowl1 while the whirling cream forms a smaller cylinder inside the cylinder of milk4 ,by putting a spout on the machine so that it reaches the inner cylinder1 the cream can be drawn off1 while a spout not put in so far will draw off the milk4 ,,why ,a ,,spinning ,,top ,,stands ,,on ,,its ,,point4 ,when a top spins1 all the particles of wood of which the top is made are thrown out and away from the center of the top1 or rather they tend to go out and away4 ,and the pull of these particles out from the center is stronger than the pull of gravitation on the edges of the top to make it tip over2 so it stands upright while it spins4 ,spin a top and see how this is4 ,,application #ba4 ,explain how a motor cyclist can ride on an almost perpendicular wall in a circular race track4 ,explain how the earth keeps away from the sun1 which is always powerfully pulling the earth toward it4 ,,inference ,,exercise ,explain the following3 #ia4 ,as you tighten a screw it becomes harder to turn4 #ib4 ,there is a process for partly drying food by whirling it rapidly in a perforated cylinder4 #ic4 ,it is easier to climb mountains in hobnailed shoes than in smooth-soled ones4 #id4 ,when you bore a hole with a brace and bit1 the hand that turns the brace goes around a circle many times as large as the hole that is being bored4 #ie4 ,the hands of some persons become red and slightly swollen if they swing them while taking a long walk4 #if4 ,a flywheel keeps an engine going between the strokes of the piston4 #ig4 ,in dry parts of the country farmers break up the surface of the soil frequently1 as less water comes up to the surface through pulverized soil than would come through the fine pores of caked earth4 #ih4 ,after you have apparently cleaned a grease spot out of a suit it often reappears when you have worn the suit a few days4 #ii4 ,mud flies up from the back wheel of a boy's bicycle when he rides along a wet street4 #ajj4 ,a typewriter key goes down less than an inch1 yet the type bar goes up nearly #e inches4 ,,section #ac4 ,action and reaction4 ,how can a bird fly8 ,what makes it stay up in the air8 ,what makes a gun kick8 ,why do you sink when you stop swimming8 ,whenever anything moves1 it pushes something else in an opposite direction4 ,when you row a boat you can notice this2 you see the oars pushing the water backward to push the boat forward4 ,also1 when you shoot a bullet forward you can feel the gun kick backward2 or when you pull down hard enough on a bar1 your body rises up and you chin yourself4 ,but the law is just as true for things which are not noticeable4 ,when you walk1 your feet push back against the earth2 and if the earth were not so enormous and you so small1 and if no one else were pushing in the opposite direction1 you would see the earth spin back a little for each step you took forward1 just as the big ball that a performing bear stands on turns backward as the bear tries to walk forward4 ,illustration3 ,,fig4 #ch4 ,the horse goes forward by pushing backward on the earth with his feet4 ,the usual way of saying this is1 ,action and reaction are equal and opposite4 ,if you climb a rope1 the upward movement of your body is the action2 but you have to pull down on the rope to lift your body up4 ,this is the reaction4 ,without this law of action and reaction no fish could swim1 no steamboat could push its way across the water1 no bird could fly1 no train or machine of any kind could move forward or backward1 no man or animal could walk or crawl4 ,the whole world of living things would be utterly paralyzed4 ,illustration3 ,,fig4 #ci4 ,as he starts to toss the ball up1 will he weigh more or less8 ,when anything starts to move1 it does so by pushing on something else4 ,when your arms start to move up1 they do so by pushing your body down a little4 ,when you swim1 you push the water back and down with your arms and legs1 and this pushes your body forward and up4 ,when a bird flies up into the air1 it pushes its body up by beating the air down with its wings4 ,when an airplane whirs along1 its propeller fans the air backward all the time4 ,street-car tracks are kept shiny by the wheels1 which slip a little as they tend to shove the track backward in making the car move forward4 ,automobile tires wear out in much the same way1--they slip and are worn by friction as they move the earth back in pushing the automobile forward4 ,in fact1 if there are loose pebbles or mud on the road1 you can see the pebbles or mud fly back1 as the wheels of the automobile begin to turn rapidly and give their backward push to the earth beneath4 ,illustration3 ,,fig4 #dj4 ,action and reaction are equal2 when he pushes forward on the ropes1 he pushes backward with equal force on the seat4 ,here are a couple of experiments that will show you action and reaction more clearly3 ,,experiment #bf4 ,stand on a platform scale and weigh yourself4 ,when the beam is exactly balanced1 move your hands upward and notice whether you weigh more or less when they start up4 ,now move them downward2 when they start down1 do you weigh more or less8 ,toss a ball into the air1 and watch your weight while you are tossing it4 ,does your body tend to go up or down while you are making the ball go up8 ,,experiment #bg4 ,go out into the yard and sit in a rope swing4 ,stop the swing entirely4 ,keep your feet off the ground all through the experiment4 ,now try to work yourself up in the swing2 that is1 make it swing by moving your legs and body and arms1 but not by touching the ground4 7,try to make it swing forward and backward only2 when you try to swing sidewise1 the distance between the ropes spoils the experiment47 ,see if you can figure out why the swing will not move back and forth4 ,notice your bodily motions2 notice that when half of your body goes forward1 half goes back2 when you pull back with your hands1 you push your body forward4 ,if you watch yourself closely1 you will see that every backward motion is exactly balanced by a forward motion of some part of your body4 ,,application #bb4 ,explain why you push forward against the table to shove your chair back from it2 why a bird beats down with its wings against the air to force itself up2 why you push back on the water with your oars to make a rowboat go forward4 ,,inference ,,exercise ,explain the following3 #aja4 ,water comes up city pipes into your kitchen4 #ajb4 ,when you try to push a heavy trunk1 your feet slip out from under you and slide in the opposite direction4 #ajc4 ,when you turn a bottle of water upside down with a small piece of cardboard laid over its mouth1 the water stays in the bottle4 #ajd4 ,you can squeeze a thing very tightly in a vise4 #aje4 ,there is a water game called log rolling2 two men stand on a log floating in the water and roll the log around with their feet1 each one trying to make the other lose his balance4 ,explain why the log rolls backward when the man apparently runs forward4 #ajf4 ,the oil which fills up the spaces between the parts of a duck's feathers keeps the duck from getting wet when a hen would be soaked4 #ajg4 ,sleds run on snow more easily than wagons do4 #ajh4 ,in coasting down a hill1 it is difficult to stop at the bottom4 #aji4 ,when you light a pinwheel1 the wheel whirls around as the powder burns1 and the sparks fly off in all directions4 #aaj4 ,you cannot lift yourself by your own boot straps4 ,,section #ad4 ,elasticity4 ,what makes a ball bounce8 ,how does a springboard help you dive8 ,why are automobile and bicycle tires filled with air8 ,suppose there were a man who was perfectly elastic1 and who made everything he touched perfectly elastic4 ,fortunately there is no such person1 but suppose an elastic man did exist3 ,he walks with a spring and a bound2 his feet bounce up like rubber balls each time they strike the earth2 his legs snap back into place after each step as if pulled by a spring4 ,if he stumbles and falls to the ground1 he bounces back up into the air without a scar4 7,you see1 his skin springs back into shape even if it is scratched1 so that a scratch instantly heals47 ,and he bounces on and on forever without stopping4 ,suppose you1 seeing his plight1 try to stop him4 ,since we are pretending that he makes everything he touches elastic1 the instant you touch him you bounce helplessly away in the opposite direction4 ,you may think your clothes will be wrinkled by all this bouncing about1 but since we are imagining that you have caught the elastic touch from the elastic man1 your clothes which touch you likewise become perfectly elastic4 ,so no matter how mussed they get1 they promptly straighten out again to the condition they were in when you touched the elastic man4 ,if you notice that your shoe lace was untied just before you became elastic1 and you now try to tie it and tuck it in1 you find it most unmanageable4 ,it insists upon flying out of your shoe and springing untied again4 ,perhaps your hair was mussed before you became elastic4 ,now it is impossible to comb it straight2 each hair springs back like a fine steel wire4 ,if you take a handkerchief from your pocket to wipe your perspiring brow1 you find that it does not stay unfolded4 ,as soon as it is spread out on your hand1 it snaps back to the shape and the folds it had while in your pocket4 ,suppose you bounce up into an automobile for a ride4 ,the automobile1 now being made elastic by your magic touch1 bounds up into the air at the first bump it strikes1 and thereafter it goes hopping down the street in a most distressing manner1 bouncing off the ground like a rubber ball each time it comes down4 ,and each time it bumps you are thrown off the seat into the air4 ,you find it hard to stay in any new position4 ,your body always tends to snap back to the position you were in when you first became elastic4 ,if you touch a trotting horse and it becomes elastic1 the poor animal finds that his legs always straighten out to their trotting position1 whether he wants to walk or stand still or lie down4 ,imagine the plight of a boy pitching a ball1 or some one yawning and stretching1 or a clown turning a somersault1 if you touch each of these just in the act and make him elastic4 ,their bodies always tend to snap back to these positions4 ,whenever the clown wants to rest1 he has to get in the somersault position4 ,the boy pitcher sleeps in the position of winding up to throw the ball4 ,the one who was yawning and stretching has to be always on the alert1 because the instant he stops holding himself in some other position1 his mouth flies open1 his arms fly out1 and every one thinks he is bored to death4 ,you might touch the clay that a sculptor is molding and make it elastic4 ,the sculptor can mold all he pleases1 but the clay is like rubber and always returns at once to its original shape4 ,if you make a tree elastic when a man is chopping it down1 his ax bounces back from the tree with such force as nearly to knock him over1 and no amount of chopping makes so much as a lasting dent in the tree4 ,suppose you step in some mud4 ,the mud does not stick to your shoes4 ,it bends down under your weight1 but springs back to form again as soon as your weight is removed4 ,and if you try to spread some elastic butter on bread1 nothing will make the butter stay spread4 ,the instant you remove your knife1 the butter rolls up again into the same kind of lump it was in before4 ,as for chewing your bread1 you might as well try to chew a rubber band4 ,you force your jaws open1 and they snap back on the bread all right2 then they spring open again1 and snap back and keep this up automatically until you make them stop4 ,but for all this vigorous chewing your bread looks as if it had never been touched by a tooth4 ,sewing is about as difficult4 ,the thread springs into a coil in the shape of the spool4 ,no hem stays turned2 the cloth you try to sew springs into its original folds in a most exasperating manner4 ,on the whole1 a perfectly elastic world would be a hopeless one to live in4 ,elasticity is the tendency of a thing to go back to its original shape or size whenever it is forced into a different shape or size4 ,a thing does not have to be soft to be elastic4 ,steel is very elastic2 that is why good springs are almost always made of steel4 ,glass is elastic2 you know how you can bounce a glass marble4 ,rubber is elastic1 too4 ,air is elastic in a different way2 it does not go back to its original shape1 since it has no shape1 but if it has been compressed and the pressure is removed it immediately expands again2 so a football or any such thing filled with air is decidedly elastic4 ,that is why automobile and bicycle tires are filled with air2 it makes the best possible springs4 ,balls bounce because they are elastic4 ,when a ball strikes the ground1 it is pushed out of shape4 ,since it is elastic it tries immediately to come back to its former shape1 and so pushes out against the ground4 ,this gives it such a push upward that it flies back to your hand4 ,sometimes people confuse elasticity with action and reaction4 ,but the differences between them are very clear4 ,action and reaction happen at the same time2 your body goes up at the same time that you pull down on a bar to chin yourself2 while in elasticity a thing moves first one way1 then the other2 you throw a ball down1 then it comes back up to you4 ,another difference is that in action and reaction one thing moves one way and another thing is pushed the other way2 while in elasticity the same thing moves first one way1 then the other4 ,if you press down on a spring scale with your hand1 you are lifting up your body a little to do it2 that is action and reaction4 ,but after you take your hand off the scale the pan springs back up3 first it was pushed down1 then it springs back to its original position2 it does this because of the elasticity of its spring4 ,,application #bc4 ,explain why basket balls are filled with air2 why springs are usually made of steel2 why we use rubber bands to hold papers together2 why a toy balloon becomes small again when you let the air out4 ,,inference ,,exercise ,explain the following1 being especially careful not to confuse action and reaction with elasticity3 #aaa4 ,when you want to push your chair back from a table1 you push forward against the table4 #aab4 ,the pans in which candy is cooled must be greased4 #aac4 ,good springs make a bed comfortable4 #aad4 ,paper clips are made of steel or spring brass4 #aae4 ,a spring door latch acts by itself if you close the door tightly4 #aaf4 ,on a cold morning1 you rub your hands together to warm them4 #aag4 ,if an electric fan is not fastened in place and has not a heavy base1 it will move backward while it is going4 #aah4 ,doors with springs on them will close after you4 #aai4 ,when you jump down on the end of a springboard1 it throws you into the air4 #abj4 ,you move your hands backward to swim forward4 ,,note4 ,there are really two kinds of elasticity1 which have nothing to do with each other4 ,elasticity of form is the tendency of a thing to go back to its original shape1 as rubber does4 ,if you make a dent in rubber1 it springs right back to the shape it had before4 ,elasticity of volume is the tendency of a substance to go back to its original size1 as lead does4 ,if you manage to squeeze lead into a smaller space1 it will spring right back to the same size as soon as you stop pressing it on all sides4 ,but a dent in lead will stay there2 it has little elasticity of form4 ,air and water--all liquids1 in fact--have a great deal of elasticity of volume1 but practically no elasticity of form4 ,they do not tend to keep their shape1 but they do tend to fill the same amount of space4 ,putty and clay likewise have very little elasticity of form2 when you change their shape1 they stay changed4 ,jelly and steel and glass have a great deal of elasticity of form4 ,when you dent them or twist them or in any way change their shape1 they go right back to their first shape as soon as they can4 ,when we imagined a man with an elastic touch1 we were imagining a man who gave everything he touched perfect elasticity of form4 ,it is elasticity of form that most people mean when they talk about elasticity4 ,,chapter ,,four ,,heat ,,section #ae4 ,heat makes things expand4 ,how does a thermometer work8 ,what makes the mercury rise in it8 ,why does heat make things get larger8 ,when we look at objects through a microscope1 they appear much larger and in many cases we are able to see the smaller parts of which they are made4 ,if we had a microscope so powerful that it made a tiny speck of dust look as big as a mountain 7of course no such microscope exists71 and if we looked through this imaginary microscope at a piece of iron1 we should find to our surprise that the particles were not standing still4 ,the iron would probably look as if it were fairly alive with millions of tiny specks moving back and forth1 back and forth1 faster than the flutter of an insect's wings4 ,these tiny moving things are molecules4 ,everything in the world is made of them4 ,it seems strange that we should know this1 since there really are no microscopes nearly powerful enough to show the molecules to us4 ,yet scientists know a great deal about them4 ,they have devised all sorts of elaborate experiments--very accurate ones--and have tested the theories about molecules in many ways4 ,they have said1 for instance1 ,now1 if this thing is made of molecules1 then it will grow larger when we make the molecules move faster by heating it4 ,then they heated it--in your next experiment you will see what happened4 ,this is only one of thousands of experiments they have performed1 measuring over and over again1 with the greatest care1 exactly how much an object expanded when it was heated a certain amount2 exactly how much heat was needed to change water to steam2 exactly how far a piece of steel of a certain size and shape could bend without breaking2 exactly how crystals form--and so on and so on4 ,and they have always found that everything acts as if it were made of moving molecules4 ,their experiments have been so careful and scientists have found out so much about what seem to be molecules1--how large they are1 what they probably weigh1 how fast they move1 and even what they are made of1--that almost no one has any doubt left that fast-moving molecules make up everything in the world4 ,illustration3 ,,fig4 #da4 ,a thermometer4 ,to go back1 then3 if we looked at a piece of iron under a microscope that would show us the molecules1--and remember1 no such powerful microscope could exist1--we should see these quivering particles1 and nothing more4 ,then if some one heated the iron while we watched the molecules1 or if the sun shone on it1 we should see the molecules move faster and faster and separate farther and farther4 ,that is why heat expands things4 ,when the molecules in an object move farther apart1 naturally the object expands4 ,heat is the motion of the molecules4 ,when the molecules move faster 7that is1 when the iron grows hotter71 they separate farther and the iron swells4 ,illustration3 ,,fig4 #db4 ,a thermometer made of a flask of water4 ,it does not show the exact degree of heat of the water1 but it does show whether the water is hot or cold4 ,,how ,,we ,,can ,,tell ,,the ,,temperature ,,by ,,reading ,a ,,thermometer4 ,the mercury 7quicksilver7 in the bulb of the thermometer like everything else expands 7swells7 when it becomes warm4 ,it is shut in tightly on all sides by the glass1 except for the little opening into the tube above4 ,when it expands it must have more room1 and the only space into which it can move is up in the tube4 ,so it rises in the tube4 ,illustration3 ,,fig4 #dc4 ,will the hot ball go through the ring8 ,water will do the same thing4 ,you can make a sort of thermometer1 using water instead of mercury1 and watch the water expand when you heat it4 ,here are the directions for doing this3 ,illustration3 ,,fig4 #dd4 ,when the wire is cold1 it is fairly tight4 ,,experiment #bh4 ,fill a flask to the top with water4 ,put a piece of glass tubing through a stopper1 letting the tube stick #h or #aj inches above the top of the stopper4 ,put the stopper into the flask1 keeping out all air2 the water may rise #b or #c inches in the glass tube4 ,dry the flask on the outside and put it on a screen on the stove or ring stand1 and heat it4 ,watch the water in the tube4 ,what effect does heat have on the water8 ,here are two interesting experiments that show how solid things expand when they are heated3 ,,experiment #bi4 ,the brass ball and brass ring shown in ,figure #dc are called the expansion ball and ring4 ,try pushing the ball through the ring4 ,now heat the ball over the flame for a minute or two--it should not be red hot--and try again to pass it through the ring4 ,heat both ball and ring for a short time4 ,does heating expand the ring8 ,,experiment #cj4 ,go to the electric apparatus 7described on page #cgi7 and turn on the switch that lets the electricity flow through the long resistance wire4 ,watch the wire as it becomes hot4 ,,application #bd4 ,a woman brought me a glass-stoppered bottle of smelling salts and asked me if ,i could open it4 ,the stopper was in so tightly that ,i could not pull it out4 ,i might have done any of the following things3 ,tried to pull the stopper out with a pair of pliers2 plunged the bottle up to the neck in hot water2 plunged it in ice-cold water2 tried to loosen the stopper by tapping it all around4 ,which would have been the best way or ways8 ,illustration3 ,,fig4 #de4 ,but notice how it sags when it is hot4 ,,application #be4 ,i used to buy a quart of milk each evening from a farmer just after he had milked4 ,he cooled most of the milk as soon as it was strained1 to make it keep better4 ,he asked me if ,i wanted my quart before or after it was cooled4 ,either way he would fill his quart measure brim full4 ,which way would ,i have received more milk for my money8 ,,inference ,,exercise ,explain the following3 #aba4 ,billiard balls will rebound from each other and from the edges of the table again and again and finally stop4 #abb4 ,in washing a tumbler in hot water it is necessary to lay it in sidewise and wet it all over1 inside and out1 to keep it from cracking2 if it is thick in some parts and thin in others1 like a cut-glass tumbler1 it is not safe to wash it in hot water at all4 #abc4 ,the swinging of the moon around the earth keeps the moon from falling to the earth4 #abd4 ,a fire in a grate creates a draft up the chimney4 #abe4 ,telegraph wires and wire fences put up in the summer must not be strung too tightly4 #abf4 ,candy usually draws in somewhat from the edge of the pan as it hardens4 #abg4 ,a meat chopper can be screwed to a table more tightly than you can possibly push it on4 #abh4 ,a floor covered with linoleum is more easily kept clean than a plain wood floor4 #abi4 ,rough seams on the inside of clothes chafe your skin4 #acj4 ,you can take the top off a bottle of soda pop with an opener that will pry it up1 but you cannot pull it off with your fingers4 ,,section #af4 ,cooling from expansion4 ,we get our heat from the sun2 then why is it so cold up on the mountain tops8 ,what is coldness8 ,here is an interesting and rather strange thing about heat and expansion4 ,although heat expands things1 yet expansion does not heat them4 ,on the contrary1 if a thing expands without being heated from an outside source1 it actually gets cold6 ,you see1 in order to expand1 it has to push the air or something else aside1 and it actually uses up the energy of its own heat to do this4 ,you will understand this better after you do the next experiment4 ,,experiment #ca4 ,wet the inside of a test tube4 ,hold the mouth of the test tube against the opening of a carbon dioxid tank4 ,open the valve of the tank with the wrench and let the compressed gas rush out into the test tube until the mouth of the test tube is white4 ,shut off the valve4 ,feel your test tube4 ,what has happened is this3 ,the gas was tightly compressed in the tank4 ,it was not cold2 that is1 it had some heat in it1 as everything has4 ,when you let it loose1 it used up much of its heat in pushing the air in the test tube and all around it out of the way4 ,in this way it lost its heat1 and then it became cold4 ,cold means absence of heat1 as dark means absence of light4 ,so when the compressed gas used up its heat in pushing the air out of its way1 it became so cold that it froze the water in your test tube4 ,illustration3 ,,fig4 #df4 ,the expansion of the compressed gas freezes the moisture on the tube4 ,,one ,,reason ,,why ,,it ,,is ,,always ,,cold ,,high ,,up ,,in ,,the ,,air4 ,even on hot summer days aviators who fly high suffer from the cold4 ,you might think that they would get warmer as they went up nearer the sun2 one reason that they get colder instead is this3 ,as you saw in the last experiment1 a gas that expands gets very cold4 ,air is a kind of gas4 ,and whenever air rises to where there is not so much air crowding down on it from above1 it expands4 ,so the air that rises high and expands gets very cold4 ,consequently mountains which reach up into this high1 cold air are snow covered all the year round2 and aviators who fly high suffer keenly from the cold4 ,there are several reasons for this coldness of the high air4 ,this is just one of them4 ,,application #bf4 ,explain why air usually cools when it rises2 why high mountain tops are always covered with snow4 ,,inference ,,exercise ,explain the following3 #aca4 ,you should not fill a teakettle brim full of cold water when you are going to put it on the stove4 #acb4 ,it is harder to erase an ink mark than a pencil mark4 #acc4 ,bearings of good watches1 where there is constant rubbing on the parts1 are made of very hard jewels4 #acd4 ,you feel lighter for an instant when you are in an elevator which starts down suddenly4 #ace4 ,when men lay cement sidewalks1 they almost always make cracks across them every few feet4 #acf4 ,to cool hot coffee one sometimes blows on it4 #acg4 ,it is much easier to turn the latch of a door with the knob than with the spindle when the knob is off4 #ach4 ,patent-leather shoes do not soil as easily as plain leather shoes4 #aci4 ,we use rubber bands to hold things together tightly4 #adj4 ,as air goes up it usually cools4 ,,section #ag4 ,freezing and melting4 ,when water freezes in a pipe1 why does the pipe burst8 ,what is liquid air8 ,why does not the wire in an electric lamp melt when it is red hot8 ,suppose we looked at a piece of ice through the imaginary microscope that shows us the molecules4 ,the ice molecules would be different from the iron molecules in size1 but they would be vibrating back and forth in exactly the same way1 only with less motion4 ,it is because they have less motion that we say the ice is colder than the iron4 ,then let us suppose that the sun was shining on the ice while we watched the ice molecules4 ,first we should see movements of the ice molecules become gradually more rapid1 just as the iron molecules did when the iron was warmed4 ,then1 as they moved faster and faster1 they would begin to bump into each other and go around every which way1 each molecule bumping first into one neighbor1 then into another1 and bouncing back in a new direction after each collision4 ,this is what causes the ice to melt4 ,when its molecules no longer go back and forth in the same path all the time1 the ice no longer keeps its shape1 and we call it water--a liquid4 ,almost all solid substances will melt when they are heated4 ,or1 to put it the other way around1 every liquid will freeze solid if it gets cold enough4 ,even liquid air 7which is ordinary air cooled and compressed until it runs like water7 can be frozen into a solid chunk4 ,some things will melt while they are still very cold2 solid air1 for instance1 melts at a temperature that would freeze you into an icicle before you could count ten4 ,other things1 such as stones1 are melted only by terrific heat4 ,when the little particles of water that make up the clouds become very cold1 they freeze as they gather and so make snowflakes4 ,when the little particles of water in the air1 that usually make dew1 freeze while they are gathering on a blade of grass1 we call it frost4 ,when raindrops are carried up into colder1 higher air while they are forming1 they freeze and turn to hail4 ,when snow or frost or hail or ice is heated1 it melts and turns back to water4 ,illustration3 ,,fig4 #dg4 ,why did the bottle break when the water in it turned to ice8 ,but here is a strange fact3 although heat usually expands things1 water expands when it freezes4 ,like everything else1 however1 water also expands when it becomes hot1 as you found when you made a kind of thermometer1 using a flask of water and a glass tube4 ,but if you should put that flask into a freezing mixture of ice and salt1 you would find that when the water became very cold it would begin to expand a little immediately before it froze4 ,and it is very lucky for us that water does expand when it freezes1 because if it did not1 ice would be heavier than water is4 ,but since the water expands as it freezes1 ice weighs less than water and floats4 ,and that is why lakes and oceans and rivers freeze over the top and do not freeze at the bottom4 ,if they froze from the bottom up1 as they would if the ice sank as it formed1 every river and lake would be solid ice in the winter4 ,all the harbors outside the tropics would probably be ice-bound all winter long4 ,and the ice in the bottom of the lakes and rivers and in the ocean would probably never melt4 ,so in the case of freezing water1 and in the case of a couple of metals1 there is a point where coldness1 not heat1 makes things expand4 ,,experiment #cb4 ,take a ketchup bottle with a screw cap and a cork that fits tightly4 ,fill it to the top with water2 put a long pin beside the cork while you insert it1 so that the water can be crowded out as the cork goes down2 then when you have pushed the cork in tightly1 pull out the pin4 ,screw the cap on the bottle so as to hold the cork fast4 ,put the bottle in a pail or box1 and pack ice and salt around it4 ,within an hour you should be able to see what the freezing water does to the bottle4 ,,application #bg4 ,explain why ice is lighter than water2 why we have no snow in summer4 ,,inference ,,exercise ,explain the following3 #ada4 ,sealing wax is held over a candle flame before it is applied to a letter4 #adb4 ,automobile tires tighten upon a sudden change from cold weather to hot4 #adc4 ,when paper has been rolled1 it tends to curl up again after being unrolled4 #add4 ,seats running across a car are much more comfortable when a car starts and stops1 than are seats running along the sides4 #ade4 ,you cannot siphon water from a low place to a higher one4 #adf4 ,candles get soft in hot weather4 #adg4 ,meteorites fall to the earth from the sky4 #adh4 ,when you preserve fruit and pour the hot fruit into the jars1 you fill the jars brim full and screw on the cap air-tight2 yet a few hours later the fruit does not fill the jars2 there is some empty space between the top of the fruit and the cover4 #adi4 ,water pipes burst in the winter when it is very cold4 #aej4 ,when people want to make iron castings1 they first melt the iron1 then pour it into molds4 ,they leave it in the molds until cold4 ,after that the iron holds the shape of the molds4 ,explain why the iron changes from a liquid to a solid4 ,,section #ah4 ,evaporation4 ,why is it that when ink is spilled it dries up1 but when it is in the bottle it does not dry up8 ,what put the salt into the ocean8 ,why do you feel cold when you get out of the bathtub8 ,wet clothes get dry when they are hung on the clothes-line4 ,the water in them evaporates4 ,it turns to invisible vapor and disappears into the air4 ,water and all liquids evaporate when they are long exposed to the air4 ,if they didn't--well1 let us imagine what the world would be like if all evaporation should suddenly stop3 ,you find that your face is perspiring and your hands as well4 ,you wipe them on your handkerchief1 but soon they are moist again1 no matter how cool the weather4 ,after wiping them a few more times your handkerchief becomes soaking wet1 and you hang it up to dry4 ,there may be a good breeze stirring1 yet your handkerchief does not get dry4 ,by this time the perspiration is running off your face and hands1 and your underclothes are getting drenched with perspiration4 ,illustration3 ,,fig4 #dh4 ,an evaporating dish4 ,you hurry into the house1 change your clothes1 bathe and wipe yourself dry with a towel4 ,when you find that your wet things are not drying1 and that your dry ones are rapidly becoming moist1 you hastily build a fire and hang your clothes beside it4 ,no use1 your clothes remain as wet as ever4 ,if you get them very hot the moisture in them will boil and turn to steam1 of course1 but the steam will all turn back to water as soon as it cools a little and the drops will cling to your clothes and to everything around the room4 ,you will have to get used to living in wet clothes4 ,you won't catch cold1 though1 since there is no evaporation to use up your heat4 ,but the water problem outside is not one of mere inconvenience4 ,it never rains4 ,how can it when the water from the oceans cannot evaporate to form clouds8 ,little by little the rivers begin to run dry--there is no rain to feed them4 ,no fog blows in from the sea2 no clouds cool the sun's glare2 no dew moistens the grass at night2 no frost shows the coming of cold weather2 no snow comes to cover the mountains4 ,in time there is no water left in the rivers2 every lake with an outlet runs dry4 ,there are no springs1 and1 after a while1 no wells4 ,people have to live on juicy plants4 ,the crops fortunately require very little moisture1 since none evaporates from them or from the ground in which they grow4 ,and the people do not need nearly as much water to drink4 ,little by little1 however1 the water all soaks too deep into the ground for the plants to get it4 ,gradually the continents become great deserts1 and all life perishes from the land4 ,all these things would really happen1 and many more changes besides1 if water did not evaporate4 ,yet the evaporation of water is a very simple occurrence4 ,as the molecules of any liquid bounce around1 some get hit harder than others4 ,these are shot off from the rest up into the air1 and get too far away to be drawn back by the pull of the molecules behind4 ,this shooting away of some of the molecules is evaporation4 ,and since it takes heat to send these molecules flying off1 the liquid that is left behind is colder because of the evaporation4 ,that is why you are always cold after you leave the bathtub until you are dry4 ,the water that evaporates from your body uses up a good deal of your heat4 ,illustration3 ,,fig4 #di4 ,diagram illustrating how in the evaporation of water some of the molecules shoot off into the air4 ,gasoline evaporates more quickly than water4 ,that is why your hands become so cold when you get them wet with gasoline4 ,since heat is required to evaporate a liquid1 the quickest way to dry anything is to warm it4 ,that is why you hang clothes in the sun or by the stove to dry4 ,try these experiments3 ,,experiment #cc4 ,read a thermometer that has been exposed to the room air4 ,now dip it in water that is warmer than the air1 taking it out again at once4 ,watch the mercury4 ,does the thermometer register a higher or a lower temperature than it did at the beginning8 ,what is taking up the heat from the mercury8 ,,experiment #cd4 ,put a few drops of water in each of two evaporating dishes4 ,leave one cold2 warm the other over the burner1 but do not heat it to boiling4 ,which evaporates more quickly8 ,,why ,,the ,,sea ,,is ,,salt4 ,you remember various fairy stories about why the sea is salt4 ,for a long time the saltness of the sea puzzled people4 ,but the explanation is simple4 ,as the water from the rains seeps through the soil and rocks1 it dissolves the salt in them and continually carries some of it into the rivers4 ,so the waters of the rivers always carry a very little salt with them out to sea4 ,the water in the ocean evaporates and leaves the salt behind4 ,for millions of years this has been going on4 ,so the rivers and lakes1 which have only a little salt in them1 keep adding their small amounts to the sea1 and once in the sea the salt never can get out4 ,the oceans never get any fuller of water1 because water only flows into the ocean as fast as it evaporates from the ocean4 ,yet more salt goes into the ocean all the time1 washed down by thousands of streams and rivers4 ,so little by little the ocean has been growing more and more salty since the world began4 ,illustration3 ,,fig4 #ej4 ,a view of the ,dead ,sea4 ,great ,salt ,lake and the ,dead ,sea1 unlike most lakes1 have no rivers flowing out of them to carry the salt and water away1 but rivers flow into them and bring along small amounts of salt all the time4 ,then the water evaporates from ,great ,salt ,lake and the ,dead ,sea1 leaving the salt behind2 and that is why they are so very salty4 ,when people want to get the salt out of sea water1 they put the sea water in shallow open tanks and let the water evaporate4 ,the salt is left behind4 ,,experiment #ce4 ,dissolve some salt in warm water until no more will dissolve4 ,pour the clear liquid off into an evaporating dish1 being careful not to let any solid particles of the salt go over4 ,either set the dish aside uncovered1 for several days1 or heat it almost to boiling and let it evaporate to dryness4 ,what is left in the dish8 ,,application #bh4 ,some girls were heating water for tea1 and were in a hurry4 ,they had only an open stew pan to heat the water in4 ,cover the pan with something2 you'll let all the heat out6 ,helen said4 ,no1 you want as much heat to go through the water as possible4 ,leave the lid off so that the heat can flow through easily1 said ,rose4 ,the water will evaporate too fast if the lid is off1 and all the heat will be used up in making it evaporate2 it will take it much longer to get hot without the lid1 ,louise argued4 ,that's not right1 ,rose answered4 ,boiling water evaporates fastest of all4 ,we want this to boil1 so let it evaporate2 leave the lid off4 ,what should they have done8 ,,application #bi4 ,two men were about to cross a desert4 ,they had their supply of water in canvas water bags that leaked just enough to keep the outside of the bags wet4 ,naturally they wanted to keep the water as cold as possible4 ,i'm going to wrap my rubber poncho around my water bag and keep the hot desert air away from the water1 said one4 ,i'm not4 ,i'm going to leave mine open to the air1 the other said4 ,which man was right8 ,why8 ,,inference ,,exercise ,explain the following3 #aea4 ,when you go up high in an elevator1 you feel the pressure of the air in your ears4 #aeb4 ,water is always flowing into ,great ,salt ,lake2 it has no outlet2 yet it is getting more nearly empty all the time4 #aec4 ,a nail sinks while a cork floats in water4 #aed4 ,steep hillsides are paved with cobblestones instead of asphalt4 #aee4 ,if you place one wet glass tumbler inside another you can pull them apart only with difficulty1 and frequently you break the outer one in the attempt4 #aef4 ,sausages often break their skins when they are being cooked4 #aeg4 ,a drop of water splashed against a hot lamp chimney cracks it4 #aeh4 ,when you shoot an air gun1 the air is compressed at first2 then when it is released it springs out to its original volume and throws the bullet ahead of it4 #aei4 ,leather soles get wet through in rainy weather1 while rubbers remain perfectly dry on the inside4 #afj4 ,when you want to clean a wooden floor1 you scrub it with a brush4 ,,section #ai4 ,boiling and condensing4 ,what makes a geyser spout8 ,how does a steam engine go8 ,once more let us imagine we are looking at molecules of water through our magical microscope4 ,but this time suppose that the water has been made very hot4 ,if we could watch the molecules smash into each other and bound about more and more madly1 suddenly we should see large numbers of them go shooting off from the rest like rifle bullets1 and they would fly out through the seemingly great spaces between the slower molecules of air4 ,this would mean that the water was boiling and turning to steam4 ,here are a couple of experiments that will show you how much more room water takes when it turns to steam than while it remains just water3 ,,experiment #cf4 ,pour a half inch of water into the bottom of a test tube4 ,put a cork in the test tube so tightly that it will not let any steam pass it1 but not too tightly4 ,hold the test tube with a test-tube clamp at arm's length over a flame1 pointing the cork away from you4 ,wait for results4 ,the reason the cork flew out of the test tube is this3 ,steam takes a great deal more room than water does1--many times as much room2 so when the water in the test tube turned to steam1 the steam had to get out and pushed the cork out ahead of it4 ,illustration3 ,,fig4 #ea4 ,in a minute the cork will fly out4 ,,experiment #cg4 ,pour about half an inch of water into the bottom of a flask4 ,bring it to a vigorous boil over the burner and let it boil half a minute4 ,now take the flask off the flame and quickly slip the mouth of a toy balloon over the mouth of the flask4 ,watch what happens4 ,if things go too slowly1 you can speed them up by stroking the outside of the flask with a cold1 wet cloth4 ,when the balloon has been drawn into the flask as far as it will go1 you can put the flask back on the burner and heat the water till it boils4 ,when the balloon has been forced out of the flask again and begins to grow large1 take the flask off the burner4 ,do this before the balloon explodes4 ,the reason the balloon was drawn into the flask was that the steam in the flask turned back to water as it cooled1 and took very much less space4 ,this left a vacuum or empty space in the flask4 ,what pushed the balloon into the empty space8 ,illustration3 ,,fig4 #eb4 ,a toy balloon has been slipped over the mouth of a flask that is filled with steam4 ,illustration3 ,,fig4 #ec4 ,as the steam condenses and leaves a vacuum1 the air pressure forces the balloon into the flask4 ,,how ,,steam ,,makes ,,an ,,engine ,,go4 ,the force of steam is entirely due to the fact that steam takes so much more room than the water from which it is made4 ,a locomotive pulls trains across continents by using this force1 and by the same force a ship carries thousands of tons of freight across the ocean4 ,the engines of the locomotive and the ship are worked by the push of steam4 ,a fire is built under a boiler4 ,the water is boiled2 the steam is shut in2 the only way the steam can get out is by pushing the piston ahead of it2 the piston is attached to machinery that makes the locomotive or ship move4 ,,one ,,theory ,,about ,,the ,,cause ,,of ,,volcanoes4 ,the water that sinks deep down into some of the hot parts of the earth turns to steam1 takes up more room1 and forces the water above it out as a geyser4 ,it is thought by some scientists that volcanoes may be started by the water in the ocean seeping down through cracks to hot interior parts of the world where even the stone is melted2 then the water1 turning to steam1 pushes its way up to the surface1 forcing dust and stone ahead of it1 and making a passage up for the melted stone1 or lava4 ,the persons who hold this view call attention to the fact that volcanoes are always in or near the sea4 ,if this is the true explanation of volcanoes1 then we should have no volcanoes if steam did not take more room than does the water from which it comes4 ,here is a very practical fact about boiling water that many people do not know2 and their gas bills would be much smaller if they knew it4 ,try this experiment3 ,illustration3 ,,fig4 #ed4 ,will boiling water get hotter if you make it boil harder8 ,,experiment #ch4 ,heat some water to boiling4 ,put the boiling-point thermometer into the water 7the thermometer graduated to #aaj ,centigrade and #bbj ,fahrenheit71 and note the temperature of the boiling water4 ,turn up the gas and make the water boil as violently as possible4 ,read the thermometer4 ,does the water become appreciably hotter over the very hot fire than it does over the low fire1 if it is boiling in both cases8 ,but in which case is more steam given off8 ,will a very hot fire make the water boil away more rapidly than a low fire8 ,when you are cooking potatoes1 are you trying to keep them very hot or are you trying to boil the water away from them8 ,which are you trying to do in making candy1 to keep the sugar very hot or to boil the water away from it8 ,all the extra heat you put into boiling water goes toward changing the water into steam2 it cannot raise the water's temperature1 because at the moment when water gets above the boiling point it ceases to be water and becomes steam4 ,this steam takes up much more room than the water did1 so it passes off into the air4 ,you can tell when a teakettle boils by watching the spout to see when the steam#c pours forth from it in a strong1 steady stream4 ,if the steam took no more room than the water1 it could stay in the kettle as easily as the water4 ,footnote #c3 ,what you see is really not the steam1 but the vapor formed as the steam condenses in the cool room4 ,the steam itself is invisible1 as you can tell by looking at the mouth of the spout of a kettle of boiling water4 ,you will see a clear space before the white vapor begins4 ,the clear space is steam4 ,,distilling4 ,when liquids are mixed together and dissolved in each other1 it looks as if it would be impossible to take them apart4 ,but it isn't4 ,they can usually be separated almost perfectly by simply boiling them and collecting their vapor4 ,for different substances boil at different temperatures just as they melt at different temperatures4 ,liquid air will boil on a cake of ice2 it takes the intense heat of the electric furnace to boil melted iron4 ,alcohol boils at a lower temperature than water2 gasoline boils at a lower temperature than kerosene4 ,and people make a great deal of practical use of these facts when they wish to separate substances which have different boiling temperatures4 ,they call this distilling4 ,you can do some distilling yourself and separate a mixture of alcohol and water in the following manner3 ,,experiment #ci4 ,first1 pour a little alcohol into a cup--a few drops is enough--and touch a lighted match to it4 ,will it burn8 ,now mix two teaspoonfuls of alcohol with about half a cup of water and enough blueing to color the mixture4 ,pour a few drops of this mixture into the cup and try to light it4 ,will it burn8 ,now pour this mixture into a flask4 ,pass the end of the long bent glass rod 7the worm7 through a one-hole rubber stopper that will fit the flask 7,fig4 #ee74 ,put the flask on a ring stand and1 holding it steady1 fasten the neck of the flask with a clamp that is attached to the stand4 ,put the stopper with the worm attached into the flask1 and support the worm with another clamp4 ,put a dry cup or beaker under the lower end of the worm4 ,set a lighted burner under the flask4 ,when the mixture in the flask begins to boil1 turn the flame down so that the liquid will just barely boil2 if it boils violently1 part of the liquid splashes up into the lower end of the worm4 ,as the vapor rises from the mixture and goes into the worm1 it cools and condenses4 ,when several drops have gone down into the cup1 try lighting them4 ,what is it that has boiled and then condensed3 the water1 the alcohol1 or the blueing8 ,or is it a mixture of them8 ,illustration3 ,,fig4 #ee4 ,by distillation clear alcohol can be separated from the water and red ink with which it was mixed4 ,alcohol is really made in this way1 only it is already mixed in the water in which the grains fermented and from which people then distil it4 ,gasoline and kerosene are distilled from petroleum2 there is a whole series of substances that come from the crude oil1 one after the other1 according to their boiling points1 and what is left is the foundation for a number of products1 including paraffine and vaseline4 ,,experiment #dj4 ,put some dry1 fused calcium chlorid on a saucer and set it on the plate of the air pump4 ,this is to absorb the moisture when you do the experiment4 7,this calcium chlorid is not the same as the chlorid of lime which you buy for bleaching or disinfecting47 ,fill a flask or beaker half full of water and bring it to a boil over a ,bunsen burner4 ,quickly set the flask on the plate of the air pump4 ,the water will stop boiling1 of course4 ,cover the flask and the saucer of calcium chlorid with the bell jar immediately1 and pump the air out of the jar4 ,watch the water4 ,the water begins to boil again because water will boil at a lower temperature when there is less air pressure on its surface4 ,so although the water is too cool to boil in the open air1 it is still hot enough to boil when the air pressure is partially removed4 ,it is because of this that milk is evaporated in a vacuum for canning2 it is not necessary to make it so hot that it will be greatly changed by the heat1 if the boiling is done in a vacuum4 ,on a high mountain the slight air pressure lets the water boil at so low a temperature that it never becomes hot enough to cook food4 ,,application #cj4 ,two college students were short of money and had to economize greatly4 ,they got an alcohol lamp to use in cooking their own breakfasts4 ,they planned to boil their eggs4 ,let's boil the water gently1 using a low flame1 one said2 we'll save alcohol4 ,it would be better to boil the eggs fast and get them done quickly1 so that we could put the stove out altogether1 the other replied4 ,which was right8 ,,application #ca4 ,two girls were making candy4 ,they put a little too much water into it4 ,let us boil the candy hard so that it will candy more quickly1 said one4 ,why1 you wasteful girl1 said the other4 ,it cannot get any hotter than the boiling point anyhow1 so you can't cook it any faster4 ,why waste gas8 ,which girl was right8 ,,inference ,,exercise ,explain the following3 #afa4 ,warm air rises4 #afb4 ,the lid of a teakettle rattles4 #afc4 ,heating water makes a steam engine go4 #afd4 ,when an automobile with good springs and without shock absorbers goes over a rut1 the passengers do not get a jolt1 but immediately afterward bounce up into the air4 #afe4 ,comets swing around close to the sun1 then off again into space2 how do they get away from the sun8 #aff4 ,when you wish to pour canned milk out1 you need two holes in the can to make it flow evenly4 #afg4 ,liquid air changes to ordinary air when it becomes even as warm as a cake of ice4 #afh4 ,skid chains tend to keep automobiles from skidding on wet pavement4 #afi4 ,a warm iron and a blotter will take candle grease out of your clothes4 #agj4 ,candies like fudge and nougat become hard and dry when left standing several days open to the air4 ,,section #bj4 ,conduction of heat and convection4 ,why does a feather comforter keep you so warm8 ,when you heat one end of a nail1 how does the heat get through to the other end8 ,how does a stove make the whole room warm8 ,here is a way to make heat run a race4 ,see whether the heat that goes through an iron rod will beat the heat that goes through a glass rod1 or the other way round3 ,illustration3 ,,fig4 #ef4 ,the metal balls are fastened to the iron and glass rods with drops of wax4 ,,experiment #da4 ,take a solid glass rod and a solid iron rod1 each about a quarter inch in diameter and about #f inches long4 ,with sealing wax or candle grease stick three ball bearings or pieces of lead1 all the same size1 to each rod1 about an inch apart1 beginning #b inches from the end4 ,hold the rods side by side with their ends in a flame1 and watch the balls fall off as the heat comes along through the rods4 ,the heat that first melts off the balls beats4 ,illustration3 ,,fig4 #eg4 ,does the heat travel faster through the iron or through the glass8 ,what really happens down among the molecules when the heat travels along the rods is that the molecules near the flame are made to move more quickly2 they joggle their neighbors and make them move faster2 these joggle the ones next to them1 and so on down the line4 ,heat that travels through things in this way is called conducted heat4 ,anything like iron1 that lets the heat travel through it quickly1 is called a good conductor of heat4 ,anything like glass1 that allows the heat to travel through it only with difficulty1 is called a poor conductor of heat1 or an insulator of heat4 ,a silver spoon used for stirring anything that is cooking gets so hot all the way up the handle that you can hardly hold it1 while the handle of a wooden spoon never gets hot4 ,pancake turners usually have wooden handles4 ,metals are good conductors of heat2 wood is a poor conductor4 ,an even more obvious example of the conducting of heat is seen in a stove lid2 your fire is under it1 yet the top gets so hot that you can cook on it4 ,when anything feels hot to the touch1 it is because heat is being conducted to and through your skin to the sensitive little nerve ends just inside4 ,but when anything feels cold1 it is because heat is being conducted away from your skin into the cold object4 ,,air ,,carries ,,heat ,,by ,,convection4 ,one of the poorest conductors of heat is air2 that is1 one particle of air can hardly give any of its heat to the next particle4 ,but particles of air move around very easily and carry their heat with them2 and they can give the heat they carry with them to any solid thing they bump into4 ,so when air can move around1 the part that is next to the stove1 for instance1 becomes hot2 this hot air is pushed up and away by cold air1 and carries its heat with it4 ,when it comes over to you in another part of the room1 some of its heat is conducted to your body4 ,when air currents--or water currents1 which work the same way--carry heat from one place to another like this1 we say that the heat has traveled by convection4 ,illustration3 ,,fig4 #eh4 ,convection currents carrying the heat of the stove about the room4 ,since heat is so often carried to us by convection1--by warm winds1 warm air from the stove1 warm ocean currents1 etc41--it seems as if air must be a good conductor of heat4 ,but if you shut the air up into many tiny compartments1 as a bird's feathers do1 or as the hair on an animal's back does1 so that it cannot circulate1 the passage of heat is almost completely stopped4 ,when you use a towel or napkin to lift something hot1 it is not so much the fibers of cotton which keep the heat from your hand2 it is principally the very small pockets of air between the threads and even between the fibers of the threads4 ,,cold ,,the ,,absence ,,of ,,heat4 ,cold is merely the absence of heat2 so if you keep the heat from escaping from anything warm1 it cannot become cold2 while if you keep the heat from reaching a cold thing it cannot become warm4 ,a blanket is just as good for keeping ice from melting1 by shutting the heat out1 as it is for keeping you warm1 by holding heat in4 ,,application #cb4 ,explain why ice is packed in straw or sawdust2 why a sweater keeps you warm4 ,select from the following list the good conductors of heat from the poor conductors 7insulators73 glass1 silver1 iron1 wood1 straw1 excelsior1 copper1 asbestos1 steel1 nickel1 cloth1 leather4 ,illustration3 ,,fig4 #ei4 ,diagram of a hot-water heater4 ,what makes the water circulate8 ,,inference ,,exercise ,explain the following3 #aga4 ,if the axle of a wheel is not greased1 it swells until it sticks fast in the hub2 this is a hot box4 #agb4 ,when you have put liquid shoe polish on your shoes1 your feet become cold as it dries4 #agc4 ,the part of an ice-cream freezer which holds the cream is usually made of metal1 while that which goes outside and contains the ice and salt is usually made of wood4 #agd4 ,the steam in a steam radiator rises from a boiler in the basement to the upper floors4 #age4 ,when you throw a ball1 it keeps going for a while after it leaves your hand4 #agf4 ,clothes keep you warm1 especially woolen clothes4 #agg4 ,the ,leaning ,tower of ,pisa does not fall over4 #agh4 ,it is almost impossible to climb a greased pole4 #agi4 ,heat goes up a poker that is held in a fire4 #ahj4 ,a child can make a bicycle go rapidly without making his feet go any faster than if he were walking4 ,,chapter ,,five ,,radiant ,,heat ,,and ,,light ,,section #ba4 ,how heat gets here from the sun2 why things glow when they become very hot4 ,if we were to go back to our imaginary switchboard we should find a switch1 between the heat and the light switches1 labeled ,,radiation4 ,suppose we turn it off3 ,instantly the whole world becomes pitch dark2 so does the sky4 ,we cannot see the sun or a star2 no electric lights shine2 and although we can light a match1 it gives no light4 ,the air above the burning match is hot1 and we can burn our fingers in the invisible flame1 but we can see nothing whatever4 ,yet the world does not get cold4 ,if we leave the switch off for years1 while the earth remains in darkness and we all live like blind people1 it never gets cold4 ,winter and summer are alike1 day and night are just the same4 ,gradually1 after many ages1 the ice and snow in the north and in the far south begin to melt as the warmth from the rest of the world is conducted to the polar regions4 ,and the heat from the interior of the earth makes all the parts of the earth's surface warmer4 ,winds almost stop blowing4 ,ocean currents stop flowing4 ,the land receives less rainfall1 until finally everything turns to a desert2 almost the only rain is on the ocean4 ,animals die even before the rivers dry up1 for the flesh eaters are not able to see their prey1 and since1 without light1 all green things die1 the animals that live on plants soon starve4 ,men have to learn to live on mushrooms1 which grow in the dark4 ,the world is plunged into an eternal warm1 pitch-black night4 ,illustration3 ,,fig4 #fj4 ,it is by radiation that we get all our heat and light from the sun4 ,turning off the radiation would cause all these things to happen1 because it is by radiation that we get all our heat from the sun and all our light from any source4 ,and it is by radiation that the earth loses heat into space in the night and loses still more heat into space during the winter4 ,we do not get our heat from the sun by conduction2 we cannot1 because there is nothing between us and the sun to conduct it4 ,the earth's air1 in amounts thick enough to count1 goes up only a hundred miles or so4 ,it is really just a thin sort of blanket surrounding the earth4 ,the sun is #ic1jjj1jjj miles away4 ,between us and the sun there is empty space4 ,there are no molecules to speak of in that whole vast distance4 ,so if heat traveled only by conduction1--that is1 if radiation stopped1--we should be so completely shut off from the sun that we should not know there was such a thing4 ,but even if we filled the space between us and the sun with copper or silver1 which are about the best conductors of heat in the world1 it would take the heat from the sun years and years to be conducted down to us4 ,yet we know that the sun's heat really gets to us in a few minutes4 ,this is because heat can travel in a very much quicker way than by conduction4 ,it radiates through space1 just as light does4 ,and it can come the whole #ic1jjj1jjj miles from the sun in about #h minutes4 ,this is so fast that if it were going around the world instead of coming from the sun1 it would go around #g-a_/b times before you could say ,jack ,robinson1--really1 because it takes you at least one second to say ,jack ,robinson4 ,we are not absolutely sure how heat gets here so fast4 ,but what most scientists think nowadays is that there is a sort of invisible rigid stuff1 not made of molecules or of anything but just itself1 called ether4 7,this ether1 if there really is such a thing1 is not related at all to the ether that doctors use in putting people to sleep4 ,it just happens to have the same name47 ,the ether is supposed to fill all space1 even the tiny spaces between molecules4 ,the fast moving particles of the sun joggle the ether up there1 and make ripples that spread out swiftly all through space4 ,when those ripples strike our earth1 they make the molecules of earth joggle1 and that is heat4 ,the ripples that spread out from the sun are called ether waves4 ,but the important and practical fact to know is that there is a kind of heat1 called radiant heat1 that can pass through empty space with lightning-like quickness4 ,and when this radiant heat strikes things1 it is partly absorbed and changed to the usual kind of heat4 ,this radiant heat is closely related to light4 ,as a matter of fact1 light is only the special kind of ether waves that affect our eyes4 ,radiant heat is invisible4 ,the ether waves that are visible we call light4 ,in terms of ether waves1 the only difference between light and radiant heat is that the ripples in light are shorter4 ,so it is no wonder that when we get a piece of iron hot enough1 it begins to give off light2 and we say it is red hot4 ,what happens to the ether is this3 ,as the molecules of iron go faster and faster 7that is1 as the iron gets hotter and hotter71 they make the ripples in the ether move more frequently until they get short enough to be light instead of radiant heat4 ,objects give off radiant heat without showing it at all2 the warmth that you feel just below a hot flatiron is mainly radiant heat4 ,when anything becomes hot enough to glow1 we say it is incandescent4 ,that is why electric lamps are called incandescent lamps4 ,the fine wires--called the filament--in the lamp get so hot when the electricity flows through them that they glow or become incandescent1 throwing off light and radiant heat4 ,it is the absorbing of the radiant heat by your hand that makes you feel the heat the instant you turn an electric lamp on4 ,try this experiment3 ,,experiment #db4 ,turn on an incandescent lamp that is cold4 ,feel it with your hand a second1 then turn it off at once4 ,is the glass hot8 7,the lamp you use should be an ordinary #be1 #dj1 or #fj watt vacuum lamp47 ,the radiant heat from the incandescent filament in the lamp passed right out through the vacuum of the lamp1 and much of it went on through the glass to your hand4 ,you already know what a poor conductor of heat glass is2 yet it lets a great deal of radiant heat pass through it1 just as it does light4 ,as soon as the lamp stops glowing1 the heat stops coming2 the glass is not made hot and you no longer feel any heat4 ,in one way the electric filament shining through a vacuum is exactly like the sun shining through empty space3 the heat from both comes to us by radiation4 ,if a lamp glows for a long time1 however1 the glass really does become hot4 ,that is partly because there is not a perfect vacuum within it 7there is a little gas inside that carries the heat to the glass by convection71 and it is partly because the glass does not let quite all of the radiant heat and light go through it1 but absorbs some and changes it to the regular conducted heat4 ,one practical use that is made of a knowledge of the difference between radiant and conducted heat is in the manufacture of thermos bottles4 ,,experiment #dc4 ,take a thermos bottle apart4 ,examine it carefully4 ,if it is the standard thermos bottle1 with the name thermos on it1 you will find that it is made of two layers of glass with a vacuum between them4 ,the vacuum keeps any conducted heat from getting out of the bottle or into it4 ,but1 as you know1 radiant heat can flash right through a vacuum4 ,so to keep it from doing this the glass is silvered1 making a mirror out of it4 ,just as a mirror sends light back to where it comes from1 it sends practically all radiant heat back to where it comes from4 ,heat1 therefore1 cannot get into the thermos bottle or out of it either by radiation or conduction4 ,and that is why thermos bottles will keep things very hot or ice-cold for such a long time4 ,fill the thermos bottle with boiling water1 stopper it1 and put it aside till the next day4 ,see whether the water is still hot4 ,illustration3 ,,fig4 #fa4 ,how a thermos bottle is made4 ,notice the double layer of glass in the broken one4 ,if we could make the vacuum perfect1 and surround all parts of the bottle1 even the mouth1 with the perfect vacuum1 and if the mirror were perfect1 things put into a thermos bottle would stay boiling hot or icy cold forever and ever4 ,,why ,,it ,,is ,,cool ,,at ,,night ,,and ,,cold ,,in ,,winter4 ,it is the radiation of heat from the earth into space that makes the earth cooler at night and cold in winter4 ,much of the heat that the earth absorbs from the sun in the daytime radiates away at night4 ,and since it keeps on radiating away until the sun brings us more heat the next day1 it is colder just before dawn than at midnight1 more heat having radiated into space4 ,for the same reason it is colder in ,january and ,february than in ,december4 ,it is in ,december that the days are shortest and the sun shines on us at the greatest slant1 so that we get the least heat from it2 but we still have left some of the heat that was absorbed in the summer4 ,and we keep losing this heat by radiation faster than we get heat from the sun1 until almost spring4 ,,application #cc4 ,distinguish between radiant and conducted heat in each of the following examples3 7a7 ,the sun warms a room through the window4 7b7 ,a room is cooler with the shades down than up1 when the sun shines on the window4 7c7 ,but even with the shades down a room on the sunny side of the house is warmer than a room on the shady side4 7d7 ,when a mirror is facing the sun1 the back gets hot4 7e7 ,if you put your hand in front of a mirror held in the sun1 the mirror reflects heat to your hand4 7f7 ,if you put a plate on a steam radiator1 the top of the plate gradually becomes hot4 7g7 ,if anything very hot or cold touches a gold or amalgam filling of a sensitive tooth1 you feel it decidedly4 7h7 ,the handle of your soup spoon becomes hot when the bowl of it is in the hot soup4 7i7 ,the moon is now very cold1 although it probably was once very hot4 ,,inference ,,exercise ,explain the following3 #aha4 ,trees bend in the wind1 then straighten up again4 ,why do they straighten up8 #ahb4 ,a cloth saturated with kerosene and placed in the bottom of a clock will oil the clockworks above it4 #ahc4 ,in cold weather the doorknob inside the front door is cold4 #ahd4 ,it is cool in the shade4 #ahe4 ,clothes get hot when you iron them4 #ahf4 ,potatoes fried in deep fat cook more quickly than those boiled in water4 #ahg4 ,if you hold your hand near a vacuum electric lamp globe that is glowing1 some of the heat will go out to your hand at once4 #ahh4 ,rubbing silver with fine powder polishes it4 #ahi4 ,a mosquito can suck your blood4 #aij4 ,a hot-water tank becomes hot at the top first1 then gradually heats downward4 ,when you light the gas under an ordinary hot-water heater1 the hot water circulates to the top of the boiler1 while the cold water from the boiler pushes into the bottom part of the heater1 as shown in ,figure #ei4 ,what causes this circulation8 ,,section #bb4 ,reflection4 ,how is it that you can see yourself in a mirror8 ,what makes a ring around the moon8 ,why can we see clouds and not the air8 ,why is a pair of new shoes or anything smooth usually shiny8 ,if we turn off a switch labeled ,,reflection ,,of ,,light on our imaginary switchboard1 we think at first that we have accidentally turned off ,,radiation again1 for once more everything instantly becomes dark around us4 ,we cannot see our hands in front of our faces4 ,although it is the middle of the day1 the sky is jet black4 ,but this time we see bright stars shining in it4 ,and among them is the sun1 shining as brightly as ever and dazzling our eyes when we look at it4 ,but its light does no good4 ,when we look down from the sky toward the earth1 everything is so black that we should think we were blind if we had not just seen the stars and sun4 ,groping our way along to an electric lamp1 we turn it on4 ,it shines brightly1 but it does not make anything around it light2 everything stays absolutely invisible4 ,it is as if all things in the world except the lights had put on some sort of magic invisible caps4 ,we can strike a match and see its flame4 ,we can see a fire on the hearth4 ,we may feel around for the invisible poker1 and when we find it1 we may put it in the fire4 ,when it becomes hot enough1 it will glow red and become visible4 ,we can make a match head glow by rubbing it on a wet finger4 ,we can even see a firefly1 if one comes around4 ,but only those things which are glowing of themselves1 like flames1 and red-hot pokers1 and fireflies1 will be visible4 ,the reason why practically everything would be invisible if there were no reflection of light is this3 ,when you look at anything1 as a man1 for instance1 what you really see is the light that hits him and bounces back 7reflects7 into your eyes4 ,suppose you go into a dark room and turn on an electric light4 ,instantly ripples of light flash out from the lamp in every direction4 ,as soon as they strike the object you are looking at1 they reflect 7bounce back7 from it to your eyes4 ,when light strikes your eyes1 you see4 ,of course1 when you look at an electric lamp1 or a star1 or the sun1 or anything that is incandescent 7so hot that it shines by its own light71 you can see it1 whether reflection exists or not4 ,but most things you look at do not shine by their own light4 ,this book that you are reading simply reflects the light in the room to your eyes2 it would not give any light in a dark room4 ,the paper reflects a good deal of light that strikes it1 so it looks very light2 the print reflects practically none of the light that strikes it1 so it looks dark1 or black1 just as a keyhole looks black because it does not reflect any light to your eyes4 ,but without reflection1 the book would be entirely invisible4 ,the only kind of print you could read if there were no reflection would be the electric signs made out of incandescent lamps arranged to form letters4 ,,what ,,the ,,ring ,,around ,,the ,,moon ,,is2 ,,what ,,sunbeams ,,are4 ,the reason you sometimes see a ring around the moon is that some of the moonlight reflects from tiny droplets of water in the air1 making them visible4 ,in the same way1 the dust in the air of a room becomes visible when the sun shines through it and is reflected by each speck of dust2 we call it a sunbeam4 ,but we are not really looking directly at the sunlight2 we are seeing the part of the sunlight that is reflected by the dust specks4 ,have you ever noticed that when you stand a little to one side of a mirror where you cannot see your own image in it1 you can sometimes see that of another person clearly1 while he cannot see his own image but can see yours8 ,it is easy to understand this by comparing the reflection of the light from your face to his eye and from his face to your eye1 to the bouncing of a ball from one person to another4 ,suppose you and a friend are standing a little way apart on sandy ground where you cannot bounce a ball1 but that between you there is a plank4 ,if each of you is standing well away from the plank1 neither one of you can possibly bounce the ball on it in such a way that he can catch it himself4 ,yet you can easily bounce it to your friend and he can bounce it to you4 ,illustration3 ,,fig4 #fb4 ,the ball bounces from one boy to the other1 but it does not return to the one who threw it4 ,the mirror is like that plank2 it is something that will reflect 7bounce7 the light directly4 ,the light from your face goes into the mirror1 just as you may throw the ball against the plank1 and the light is reflected to your friend just as the ball is bounced to him2 so he sees your image in the mirror4 ,if he can see you1 you can see him1 just as when you bounce the ball to him he can bounce it to you4 ,but you may be unable to see yourself1 just as you may be unable to bounce the ball on the plank so that you yourself can catch it4 ,in other words1 when light strikes against something it bounces away1 just as a rubber ball bounces from a smooth surface4 ,if you throw a ball straight down1 it comes straight up2 if light shines straight down on a flat1 smooth surface1 it reflects straight up4 ,if you throw a ball down at a slant1 it bounces up at the same slant in the opposite direction2 if light strikes a smooth surface at a slant1 it reflects at the same slant in the opposite direction4 ,illustration3 ,,fig4 #fc4 ,in the same way1 the light bounces 7reflects7 from one boy to the other4 ,it does not return to the point from which it started and neither boy can see himself4 ,but to reflect light directly and to give a clear image1 the surface the light strikes must be extremely smooth1 just as a tennis court must be fairly smooth to make a tennis ball rebound accurately4 ,any surface that is smooth enough will act like a mirror1 although naturally1 if it lets most of the light go through1 it will not reflect as well as if it sends all the light back4 ,a pane of glass is very smooth1 and you can see yourself in it1 especially if there is not much light coming through the glass from the other side to mix up with your reflection4 ,but if the pane of glass is silvered so that no light can get through1 you have a real mirror2 most of the light that leaves your face is reflected to your eyes again4 ,,why ,,smooth ,,or ,,wet ,,things ,,are ,,shiny4 ,when a surface is very smooth1 we say it is shiny or glossy4 ,even black shoes1 if they are polished1 become smooth enough to reflect much of the light that strikes them2 of course the parts where the light is being reflected do not look black but white1 as any one who has tried to paint or draw a picture of polished shoes knows4 ,anything wet is likely to be shiny1 because the surface of water is usually smooth enough to reflect light rather directly4 ,if a surface is uneven1 like a pool with ripples on it1 the light reflects unevenly1 and you see a distorted image2 your face seems to be rippling and moving in the water4 ,illustration3 ,,fig4 #fd4 ,how should the mirror be placed8 ,,application #cd4 ,some boys were playing war and were in a ditch that they called a trench4 ,they wanted to make a simple periscope so that they could look out of the ditch at the enemy without being in danger4 ,they had an old stovepipe and a mirror4 ,practically all of them agreed that if the mirror were fixed in the top of the stovepipe and if they looked up through the bottom1 they would be able to see over the side of the ditch4 ,but they had an argument as to how the mirror should be placed4 ,each drew a diagram to show how he thought the mirror should be arranged1 using dotted lines to show how the light would come from the enemy to their eyes4 ,three of the diagrams are shown in ,figure #fd4 ,the boy who drew the first said3 ,if you want to see the enemy1 the mirror's got to face him4 ,then it will reflect the light down to your eyes4 ,the boy who drew the second said3 ,no1 the light would just go back to him again4 ,the mirror must slant so that the light that strikes it at a slant will be reflected to your eye at the same slant4 ,how could it get to your eye at all1 the third boy said1 if the mirror didn't face you8 ,you've got to have the mirror reflect right down toward your face4 ,then all the light that strikes it will come down to you4 ,which arrangement would work8 ,,inference ,,exercise ,explain the following3 #aia4 ,your hands do not get wet when you put them into mercury4 #aib4 ,when beating hot candy1 we sometimes put it in a pan of water4 #aic4 ,electric stoves frequently have bright reflectors4 #aid4 ,we put ice in the top of a refrigerator4 #aie4 ,you can jack up the back part of an automobile when you could not possibly lift it up4 #aif4 ,the sun shines up into your face and sunburns you when you are on the water4 #aig4 ,people in the tropics dress largely in white4 #aih4 ,menthol rubbed into your skin makes it feel very cold afterward4 #aii4 ,we feel the heat of the sun almost as soon as the sun rises4 #bjj4 ,you can shoot a stone far and hard with a sling shot4 ,,section #bc4 ,the bending of light3 ,refraction4 ,how do glasses help your eyes8 ,on a hot day1 how is it that you see heat waves rising from the street8 ,what makes the stars twinkle8 ,light usually travels in straight lines4 ,if the light from an object comes from straight in front of you1 you know that the object is straight in front of you4 ,but you can bend light so that it seems to come from a different place1 thus making things seem to be where they are not4 ,,experiment #dd4 ,hold a triangular glass prism vertically 7straight up and down7 in front of one eye1 closing the other eye4 ,look through the prism1 turning it or your head around until you see a chair through it4 ,watch only the chair through the prism4 ,when you are sure you know just where it is1 try to sit down in it4 ,now look for a pencil or a piece of chalk through the prism1 in the same way4 ,when you think you know where it is1 try to pick it up4 ,the reason the chalk and chair seem to be where they are not is that the prism bends the light that comes from them and makes the light seem to come from somewhere else4 ,as you already know1 when you look at a chair you see the light that reflects from it4 ,you judge where the chair is by the direction from which the light is coming when it reaches your eye4 ,but if the light is bent on its way1 so that it comes to your eye as it ordinarily comes from an object off to one side1 naturally you think the thing you are looking at is off to one side4 ,maybe the diagram 7,fig4 #fe7 will make this clearer4 ,illustration3 ,,fig4 #fe4 ,in passing through the prism the light is bent so that an object at b appears to be at c4 ,here in a is an object the same height as the eye4 ,the light comes straight to the eye1 and one knows that the object is level with the eye4 ,in b the object is in the same position as in a1 but the prism bends the light so that it strikes the eye with an upward slant4 ,so the person thinks the object is below the eye at c4 ,here is another experiment with bending light3 ,,experiment #de4 ,fill a china cup with water4 ,put a pencil in it1 letting the pencil rest at a slant from left to right4 ,lower your head until it is almost level with the surface of the water4 ,how does the pencil look8 ,illustration3 ,,fig4 #ff4 ,the pencil is not bent1 but the light that comes from it is4 ,the reason the pencil looks bent is because the light from the part of it under the water is bent when it passes from the water into the air on its way to your eye2 so the slant at which it comes to your eye is the same slant at which it ordinarily would come from a bent pencil4 ,,experiment #df4 ,fill a glass with water4 ,put the pencil into it in the same way you put it in the cup in the previous experiment1 letting the pencil slant from left to right4 ,lower your head this time until it is on a level with the water in the glass1 and look through the glass and water at the pencil4 ,notice what happens where the pencil goes into the water4 ,what you see is explained in the same way as are the things that took place in the other experiments in refraction1 or bending of light4 ,the light from the part of the pencil above the water comes straight to your eye1 of course2 so you see it just as it is4 ,but the light from the part of the pencil in the water is bent when it comes out of the water into the air on its way to your eye4 ,this makes it come to your eye from a different direction and makes the lower part of the pencil seem to be in a place to one side of the place where it really is4 ,the pencil1 therefore1 looks broken4 ,illustration3 ,,fig4 #fg4 ,the bending of the light by the water in the glass causes the pencil to look broken4 ,whenever light passes first through something dense like water or glass1 and then through something rare or thin like air1 it is bent one way2 whenever it passes from a rare medium into a dense one1 it is bent the other way4 ,light passing from a fish to your eye is bent one way2 light passing from you to the fish's eye is bent the other way1 but the main point is that it is bent4 ,and when light is bent before reaching your eyes it usually makes things seem to be where they are not4 ,if light goes through a perfectly smooth1 flat pane of glass1 it is bent one way when it goes into the glass and back the other way when it comes out2 so it seems to be perfectly straight and we see things practically as they are through a good window4 ,but if the window glass has flaws in it1 so that some parts are a little thicker than others1 the uneven parts act like prisms and bend the light to one side4 ,this makes anything we look at through a poor window seem bent out of shape4 ,of course the things are not bent any more than your pencil in the water was bent1 but they look misshapen because the light from them is bent2 the reflected light is all we see of things anyway4 ,illustration3 ,,fig4 #fh4 ,the light is bent when it enters a window pane and is bent again in the opposite direction when it leaves it4 ,the air itself is uneven in a way4 ,the parts of the air that are warm1 as you already know1 are thinner and more expanded than are the cold parts4 ,so light going from cold air into warm or from warm air into cold1 will be bent4 ,and this is why you see what are called heat waves above a stove or rising from a hot beach or sidewalk4 ,really these are just waves of hot air rising1 and they bend the light that comes through them so as to give everything behind them a wavy appearance4 ,stars twinkle for much the same reason4 ,as the starlight comes down through the cold air and then through the warm air it is bent1 and the star seems to be to one side of where it really is2 but the air does not stand still1--sometimes it bends the light more and sometimes less4 ,so the star seems to move a little back and forth4 ,and this is what we call twinkling4 ,really it is the bending of light4 ,,application #ce4 ,explain why an unevenness in your eye will keep you from seeing clearly2 how glasses can help this2 why good mirrors are made from plate glass1 which is very smooth1 instead of from the cheaper and more uneven window glass2 why fishes in a glass tank appear to be where they are not4 ,,inference ,,exercise ,explain the following3 #bja4 ,the fire in the open fireplace ventilates a room well by making air go up the chimney4 #bjb4 ,a drop of water glistens in the sun4 #bjc4 ,dust goes up to the ceiling and clings there4 #bjd4 ,when you look at a person under moving water1 his face seems distorted4 #bje4 ,you sit in the sun to dry your hair4 #bjf4 ,paste becomes hard and unfit for use when left open to the air4 #bjg4 ,in laundries clothes are partly dried by whirling them in perforated cylinders4 #bjh4 ,circus balloons are filled by building a big fire under them4 #bji4 ,unevenness in a window pane makes telephone wires seen through it look crooked and bent4 #baj4 ,you can see the image of a star even in a shallow puddle4 ,illustration3 ,,fig4 #fi4 ,when the light from one point goes through the lens1 it is bent and comes together at another point called the focus4 ,,section #bd4 ,focus4 ,how can you take pictures with a camera8 ,what causes the picture in the camera to be inverted8 ,why is a magnifying glass able to set things on fire when you let the sun shine through it8 ,in your eye1 right back of the pupil1 there is a flattened ball1 as clear as glass1 called the lens4 ,if the lens were left out of your eye1 you never could see anything except blurs of light and shadow4 ,if you looked at the sun it would dazzle you practically as much as it does now4 ,however1 you would not see a round sun1 but only a blaze of light4 ,you could tell night from day as well as any one1 and you could tell when you stepped into the shade4 ,if some one stepped between you and the light1 you would know that some one was between you and the light or that a cloud had passed over the sun1--you could not be quite sure which4 ,in short1 you could tell all degrees of light and dark apart nearly as well as you can now1 but you could not see the form of anything4 ,in the front of a camera there is a flattened glass ball called the lens4 ,if you were to remove it1 the camera would not take any pictures2 it would take a blur of light and shade and nothing more4 ,illustration3 ,,fig4 #gj4 ,the light from each point of the candle flame goes out in all directions4 ,in front of a moving-picture machine there is a large lens1 a piece of glass rounded out toward the middle and thinner toward the edges4 ,if you were to take that lens off while the machine was throwing the motion pictures on the screen1 you would have a flicker of light and shade1 but no picture4 ,it is the lens that forms the pictures in your eye1 on a photographic plate or film1 and on a moving-picture screen4 ,and a lens is usually just a piece of glass or something glassy1 rounded out in such a way as to make all the spreading light that reaches it from one point come together in another point1 as shown in ,figure #fi4 ,as you know1 when light goes out from anything1 as from a candle flame or an incandescent lamp1 or from the sun1 it goes in all directions4 ,if the light from the point of a candle flame goes in all directions1 and if the light from the base of the flame also goes in all directions1 the light from the point will get all mixed up with the light from the base1 as shown in ,figure #gj4 ,naturally1 if the light from the point of the candle flame is mixed up with the light from the base and the beams are all crisscross1 you will not get a clear picture of the flame4 ,illustration3 ,,fig4 #ga4 ,the reading glass is a lens which focuses the light from the candle flame and forms an image4 ,,experiment #dg4 ,fasten a piece of paper against a wall and place a lighted candle about #d feet in front of it4 ,look at the paper4 ,is there any picture of the candle flame on it8 ,now hold a magnifying glass 7reading glass7 near the candle1 between the candle and the paper1 so that the light will shine through the lens on to the paper4 7,the magnifying glass is a lens47 ,move the lens slowly toward the paper until you get a clear picture of the candle flame4 ,is it right side up or upside down8 ,the lens has brought the light from the candle flame to a focus2 all the light that goes through the lens from one point of the flame has been brought together at another point 7,fig4 #gb74 ,in the diagram you see all the light from the point of the candle flame spreading out in every direction4 ,but the part that goes through the lens is brought together at one point1 called the focus4 ,of course the same thing happens to the light from the base of the candle flame 7,fig4 #gc74 ,just as before1 all the light from the base of the flame is brought to a focus4 ,the light spreads out until it reaches the lens4 ,then the lens bends it together again until it comes to a point4 ,illustration3 ,,fig4 #gb4 ,the light from the tip of the candle flame is focused at one point4 ,illustration3 ,,fig4 #gc4 ,and the light from the base of the flame is focused at another point4 ,illustration3 ,,fig4 #gd4 ,the light from the tip and base 7and from every other point7 of the flame is1 of course1 focused at the same time4 ,in this way an image of the flame is formed4 ,but of course the light from the base of the flame is focused at the same time as the light from the point2 so what really happens is that which is illustrated in ,figure #gd4 ,in this diagram1 we have drawn unbroken lines to show the light from the point of the candle flame and dotted lines to show the light from the base of the flame4 ,this is so that you can follow the light from each part and see where it goes4 ,compare this diagram with the one where the light is shown all crisscrossed 7,fig4 #gj71 and you will see why the lens makes an image1 while you have no image without it4 ,by looking at the last diagram 7,fig4 #gd7 you can also see how the image happens to be upside down4 ,,experiment #dh4 ,set up the candle and piece of paper as you did for the last experiment1 but move the magnifying glass back and forth between the paper and the candle4 ,notice that there is one place where the image of the candle is very clear4 ,does the image become clearer or less clear if you move the lens closer to the candle8 if you move it farther from the candle8 ,the explanation is this3 ,after the light comes together into a point1 it spreads out again beyond the point1 as shown in ,figure #ge4 ,so if you hold the lens in such a way that the light comes to a focus before it reaches the paper1 the paper will catch the spreading light and you will get a blur instead of a sharp image4 ,it is as shown in ,figure #gf4 ,illustration3 ,,fig4 #ge4 ,the light spreads out again beyond the focus4 ,illustration3 ,,fig4 #gf4 ,so if the light comes to a focus before it reaches the paper1 the image will be blurred4 ,on the other hand1 if you hold your lens in such a way that the light has not yet come to a focus when it reaches the paper1 naturally you again have a blur of light instead of a point1 and the image is not sharp and definite 7,fig4 #gg74 ,illustration3 ,,fig4 #gg4 ,or if the light reaches the paper before it comes to a focus1 the image will be blurred4 ,and that is why good cameras have the front part1 in which the lens is set1 adjustable2 you can move the lens back and forth until a sharp image is formed on the plate4 ,motion-picture machines and stereopticons likewise have lenses that can be moved forward and back until they form a sharp focus on the screen4 ,even the lens in your eye has muscles that make it flatter and rounder1 so that it can make a clear image on the sensitive retina in the back of your eye4 ,the lens in the eyes of elderly people often becomes too hard to be regulated in this way1 and so they have to wear one kind of glasses to see things near them clearly and another kind to see things far away4 ,the kind of lens we have been talking about is the convex lens4 ,convex means bulging out in the middle4 ,there are other kinds of lenses1 some flat on one side and bulging out on the other1 some hollowed out toward the middle instead of bulging1 and so on4 ,but the only lens that most people make much use of 7except opticians7 is the convex lens that bulges out toward the center4 ,the convex lens makes a clear image and it is the only kind of lens that will do this4 ,illustration3 ,,fig4 #gh4 ,lenses of different kinds4 ,,why ,,you ,,can ,,set ,,fire ,,to ,,paper ,,with ,a ,,magnifying ,,glass4 ,a convex lens brings light to a focus1 and it also brings radiant heat to a focus4 ,and that is why you can set fire to things by holding a convex lens in the sunlight so that the light and heat are focused on something that will burn4 ,all the sun's radiant heat that strikes the lens is brought practically to one point1 and all the light which is absorbed at this point is changed to heat4 ,when so much heat is concentrated at one point1 that point becomes hot enough to catch fire4 ,,application #cf4 ,explain why there is a lens in a moving-picture machine2 why a convex lens will burn your hand if you hold it between your hand and the sun2 why the front of a good camera is made so that it can be moved closer to the plate or farther away from it1 according to the distance of the object you are photographing2 why there is a lens in your eye4 ,,inference ,,exercise ,explain the following3 #baa4 ,cut glass ware sparkles4 #bab4 ,an unpainted floor becomes much dirtier and is harder to clean than a painted one4 #bac4 ,if you sprinkle wet tea leaves on a rug before sweeping it1 not so much dust will be raised4 #bad4 ,food leaves a spoon when the spoon is struck sharply upon the edge of a stewpan4 #bae4 ,an image is formed on the photographic plate of a camera4 #baf4 ,ripples in a pool distort the image seen in it4 #bag4 ,cream rises to the top of a bottle of milk4 #bah4 ,your eyes have to adjust themselves differently to see things near by and to see things at a distance4 #bai4 ,a vacuum cleaner does not wear out a carpet nearly as quickly as a broom or a carpet sweeper does4 #bbj4 ,you can see a sunbeam in a dusty room4 ,,section #be4 ,magnification4 ,why is it that things look bigger under a magnifying glass than under other kinds of glass8 ,how does a telescope show you the moon1 stars1 and planets8 ,how does a microscope make things look larger8 ,everybody knows1 of course1 that a convex lens in the right position makes things look larger4 ,people use convex lenses to make print look larger when they read1 and for that reason such lenses are often called reading glasses4 ,for practical purposes it is not necessary to understand how a convex lens magnifies2 the important thing is the fact that it does magnify4 ,but you may be curious to know just how a magnifying glass works4 ,first1 you should realize that the image formed by a convex lens is not always larger than the object4 ,repeat ,experiment #da1 but this time move the lens from near the candle toward the paper1 past the point where it makes its first clear image4 ,keep moving the lens slowly toward the paper until a second image is formed4 ,which image is larger than the flame8 ,which is smaller8 ,illustration3 ,,fig4 #gi4 ,a section of the eye4 ,the important point in this experiment is for you to see that if the lens is nearer to the image on the paper than it is to the candle1 the image is smaller than the candle4 ,that is why a photograph is usually smaller than the thing photographed2 it would be impossible to take a picture of a house or a mountain if the lens in the camera gave a magnified image4 #d,your eye is a small camera4 ,it has a lens in the front2 it is lined with black2 and at the back there is a sensitive part on which the picture is formed4 ,this sensitive part of the eye is called the retina4 ,it is in the back part of your eyeball and is made of many very sensitive nerve endings4 ,when the light strikes these nerve endings1 it sends an impulse through the nerves to the back part of the brain2 then you know that the image is formed4 ,and1 of course1 since your eyeball is small and many of the things you see are large1 the image on the retina must be much smaller than the object itself1 and this is because the lens is so much nearer to the retina than it is to the object4 ,footnote #d3 ,the following explanation may be omitted by any children who are not interested in it4 ,let such children skip to the foot of page #aef4 ,illustration3 ,,fig4 #hj4 ,how an image is formed on the retina of the eye4 ,illustration3 ,,fig4 #ha4 ,a simpler diagram showing how an image is formed in the eye4 ,illustration3 ,,fig4 #hb4 ,a diagram showing how a reading glass causes things to look larger by making the image on the retina larger4 ,illustration3 ,,fig4 #hc4 ,diagram showing how a reading glass enlarges the image on the retina4 ,more lines are drawn in than in ,figure #hb4 ,you can understand magnification best by looking at ,figures #hj1 #ha1 #hb1 and #hc4 ,in ,figure #hj there are a candle flame1 the lens of an eye1 and the retina on which the image is being formed4 ,figure #ha is the same as ,figure #hj1 with all the lines left out except the outside ones that go to the lens4 ,it is shown in this way merely for the sake of simplicity4 ,all the lines really belong in this diagram as in the first4 ,in both diagrams the size of the image on the retina is the distance between the point where the top line touches it and the point where the bottom line touches it4 ,in order to make anything look larger1 we must make the image on the retina larger4 ,a magnifying glass1 or convex lens1 if put in the right place1 will do this4 ,in the next diagram1 ,figure #hb1 we shall include the magnifying glass1 leaving out all lines except the two outside ones shown in ,figure #ha4 ,you will notice that the magnifying glass starts to bend the lines together1 and that the lens in the eye bends them farther together2 so they cross sooner1 and the image is larger4 ,figure #hc shows more of the lines drawn in4 ,illustration3 ,,fig4 #hd4 ,diagram of a microscope4 ,the two important points to notice are these3 ,first1 the magnifying glass is too close to the eye for the light to be brought to a focus before it reaches the eye2 the light is bent toward a focus1 but it reaches the eye before the focus is formed4 ,the focus is formed for the first time on the retina itself4 ,second1 the magnifying glass bends the light on its way to your eye so that the light crosses sooner in your eye and spreads out farther before it comes to a focus4 ,this forms the larger image1 as you see in the simple diagram1 ,figure #hb4 ,illustration3 ,,fig4 #he4 ,this is the way a concave mirror forms a magnified image4 ,illustration3 ,,fig4 #hf4 ,the concave mirror forms an image of the burning candle4 ,,how ,,the ,,microscope ,,works4 ,but the microscope is different4 ,it works like this3 ,the first lens is put very near the object which you are examining4 ,this lens brings the light from the object to a focus and forms an image1 much larger than the object itself1 high up in the tube4 ,if you held a piece of paper there you would see the image4 ,but since there is nothing there to stop the light1 it goes on up the tube1 spreading as it goes4 ,then there is another lens which catches this light and bends it inward on its way to your eye1 just as any magnifying glass does4 ,next the lens in the eye forms an image on the retina4 ,the diagram 7,fig4 #hd7 will make this clearer4 7,a real microscope is not so simple1 of course1 and usually has two lenses wherever the diagram shows one47 ,what actually happens is that the first lens makes an image many times as big as the object2 then you look at this image through a magnifying glass1 so that the object is made to look very much larger than it really is4 ,that is why you can see blood corpuscles and germs and cells through a microscope1 when you cannot see them at all with your naked eye4 ,illustration3 ,,fig4 #hg4 ,the great telescope of the ,yerkes ,observatory at ,lake ,geneva1 ,wisconsin4 ,a ,,mirror ,,that ,,magnifies4 ,a convex lens is not the only thing that can magnify4 ,a concave mirror1 which is one that is hollowed out toward the middle1 does the same thing4 ,when light is reflected by such a mirror1 it acts exactly as if it had gone through a convex lens 7,fig4 #he74 ,,experiment #di4 ,place the lighted candle and the paper about #d feet apart1 as you did in ,experiment #dg4 ,hold a concave mirror back of the candle 7so that the candle is between the mirror and the paper72 then move the mirror back1 the mirror casting the reflection of the candle light on the paper1 until a clear image of the candle is formed4 ,look at your image in the concave mirror4 ,does it look larger or smaller than you8 ,,how ,,telescopes ,,are ,,made4 ,astronomers use convex lenses in some of their telescopes2 in others1 called reflecting telescopes1 they use concave mirrors4 ,both do the same work1 making the moon1 the planets1 and the sun look much larger than they otherwise would4 ,,application #cg4 ,explain how a reading glass makes print look larger2 how you can see germs through a microscope2 what kind of mirror will magnify2 what kind of lens will magnify4 ,,inference ,,exercise ,explain the following3 #bba4 ,the water that forms rain comes from the ocean1 yet the rain is not salty4 #bbb4 ,iron glows when it is very hot4 #bbc4 ,you can start a fire with sunlight by holding a reading glass at the right distance above the fuel4 #bbd4 ,big telescopes make it possible for us to see in detail the surface structure of the moon4 #bbe4 ,a room is lighter if it has white walls than if it has dark walls4 #bbf4 ,iron is heated by a blacksmith before he shapes it4 #bbg4 ,a dentist's mirror is concave2 he sees your teeth enlarged in it4 #bbh4 ,good penholders usually have cork or rubber tips4 #bbi4 ,a man's suit becomes shiny when it gets old4 #bcj4 ,when you look at a window from the sidewalk1 you frequently see images of the houses across the street4 ,,section #bf4 ,scattering of light3 ,diffusion4 ,why is it that on a dark day the sun cannot be seen through light clouds8 ,why do not the stars come out in the daytime8 ,if you were on the moon1 you could see the stars in the daytime4 ,the sun would be shining even more brightly than it does here1 but the sky around the sun would be pitch black1 except for the stars shining out of its blackness4 ,the reason is that there is no air on the moon to scatter the light4 ,,why ,,we ,,cannot ,,see ,,the ,,stars ,,in ,,the ,,daytime4 ,most of the sun's light that comes to the earth reaches us rather directly2 that is why we can see the image of the sun4 ,but part of the sunlight is scattered by particles of air1 and that is why the whole sky is bright in the daytime4 ,you know1 of course1 that the blue sky is only the air that surrounds the earth4 ,enough of the light is scattered around to make the sky as bright as the stars look from here2 so we cannot see the stars through the sky in the daytime4 ,,how ,a ,,cloud ,,can ,,hide ,,the ,,sun ,,without ,,cutting ,,off ,,all ,,its ,,light4 ,when a cloud drifts between us and the sun1 we no longer see the sun2 yet the earth does not become dark4 ,the sun's light is evidently still reaching us4 ,the cloud is made of millions of very tiny droplets of water4 ,when the sunlight strikes the curved sides of these droplets1 it is reflected at all angles according to the way it strikes1 as shown in ,figure #hi4 ,illustration3 ,,fig4 #hh4 ,the sunlight is scattered 7diffused7 by the clouds4 ,the photograph shows in the foreground the ,parliament ,buildings1 ,london1 ,england4 ,some of the light is reflected back into the sky2 that is why everything becomes darker when the sun goes behind a cloud2 but much of the light comes through to us1 at all sorts of slants4 ,when it comes all higgledy-piggledy and crisscross like this1 no lens can put it together again2 it is as hopelessly broken up as ,humpty-,dumpty was4 ,but much of the light gets here just the same2 so we see it without seeing the form of the sun4 ,light that cannot be brought to a focus is called scattered or diffused light4 ,when you look through a ground-glass electric lamp1 you cannot see the filament2 the light passing through all the rough parts of the glass gets so scattered that you cannot bring it to a focus4 ,therefore1 no image of the filament in the incandescent lamp can be formed on the retina of your eye4 ,illustration3 ,,fig4 #hi4 ,how the droplets in a cloud scatter the rays of light4 ,a piece of white paper reflects practically all the light that strikes it4 ,yet you cannot see yourself in a piece of ordinary white paper4 ,the trouble is that the paper is too rough2 there are too many little uneven places that reflect the light at all sorts of angles2 the light is scattered and the lens in your eye cannot bring it to a focus4 ,,application #ch4 ,explain why a scrim curtain will keep people from seeing into a room1 but will not shut the light out2 why curtains soften the light of a room2 why indirect lighting 7i4e4 light thrown up against the ceiling and then reflected down into the room by the rough ceiling7 is better for your eyes than is the old-time direct lighting4 ,,inference ,,exercise ,explain the following3 #bca4 ,the alcohol formed by the yeast in making bread light is practically all gone by the time the bread is baked4 #bcb4 ,the oceans do not flow off the earth at the south pole4 #bcc4 ,lamp globes often have frosted bottoms4 #bcd4 ,a damp dust cloth will take up the dust1 without making it fly4 #bce4 ,the stars twinkle when their light passes through the moving air currents that surround the earth4 #bcf4 ,shears for cutting tin and metal have long handles and short blades4 #bcg4 ,a coin at the bottom of a glass of water seems raised when you look at it a little from one side4 #bch4 ,you have to brace your feet to row well4 #bci4 ,light from the northern part of the sky1 where the sun is not1 does not make sharp shadows4 #bdj4 ,pokers and lifters for stove lids often have open spiral handles4 ,,section #bg4 ,color4 ,what makes the ocean look green in some places and blue in others8 ,what makes the sky blue8 ,what causes material to be colored8 ,what makes a rainbow8 ,what is color8 ,illustration3 ,,fig4 #ij4 ,making a rainbow on the wall4 ,color is merely a kind of light4 ,we say that a sweater is red2 really the sweater is not red1 but the light that it reflects to our eyes is red4 ,we speak of a piece of red glass1 but the glass is not red2 it is the light that it lets pass through it that is red4 ,white is not really a color2 all colors put together make white4 ,experiments #ej and #ea will prove this4 ,illustration3 ,,fig4 #ia4 ,the prism separates the white light into the rainbow colors4 ,,experiment #ej4 ,hold a prism in the sunlight by the window and make a rainbow on the wall4 ,the diagram here shown illustrates how the prism breaks up the single beam of white light into different-colored beams of light4 ,illustration3 ,,fig4 #ib4 ,when the wheel is rapidly whirled the colors blend to make white4 ,,experiment #ea4 ,rotate the color disk on the rotator and watch it4 ,make it go faster and faster until all the colors are perfectly merged4 ,what color do you get by combining all the colors of the rainbow8 ,if the colors on the disk were perfectly clear rainbow colors1 in exactly the same proportion as in the rainbow1 the whirling would give a white of dazzling purity4 ,since you can break up pure white light into all the colors1 and since you can combine all the colors and get pure white light1 it is clear that white light is made up of all the colors4 99 99 99 99 99 ,as we have already said1 light is probably vibrations or waves of ether4 ,light made of the longest waves that we can see is red4 ,if the waves are a little shorter1 the light is orange2 if they are shorter yet1 it is yellow2 still shorter1 green2 shorter still1 blue2 while the shortest waves that we can see are those of violet light4 ,black is not a color at all2 it is the absence of light4 ,we say the night is black when we cannot see anything4 ,a deep hole looks black because practically no light is reflected up from its depths4 ,when you see anything black1 you really see the things around it and the parts of it that are not perfectly black4 ,a pair of shoes1 for instance1 has particles of gray dust on them2 or if they are very shiny they reflect part of the light that strikes them as a white high-light4 ,but the really black part of your shoes would be invisible against an equally black background4 ,a black thing absorbs the light that strikes it and turns it to heat4 ,here is an experiment that will prove this to you3 ,,experiment #eb4 7a7 ,on a sunny day1 take three bottles1 all of the same size and shape1 and pour water out of a pitcher or pan into each bottle4 ,do not run the water directly from the faucet into the bottle1 because sometimes that which comes out of the faucet first is warmer or colder than that which follows2 in the pitcher or pan it will all be mixed together1 and so you can be sure that the water in all three bottles is of the same temperature to begin with4 ,wrap a piece of white cotton cloth twice around one bottle2 a piece of red or green cotton cloth of the same weight twice around the second bottle1 and a piece of black cotton cloth of the same weight twice around the third bottle1 fastening each with a rubber band4 ,set all three bottles side by side in the sunlight1 with #b or #c inches of space between them4 ,leave them for about an hour4 ,now put a thermometer into each to see which is warmest and which is least warm4 ,from which bottle has most of the light been reflected back into the air by the cloth around it8 ,which cloth absorbed most of the light and changed it into heat8 ,does the colored cloth absorb more or less light than the white one8 than the black one8 ,illustration3 ,,fig4 #ic4 ,which color is warmest in the sunlight8 7b7 ,on a sunny day when there is snow on the ground1 spread three pieces of cotton cloth1 all of the same size and thickness1 one white1 one red or green1 and one black1 on top of the snow1 where the sun shines on them4 ,watch them for a time4 ,under which does the snow melt first8 ,the white cloth is white because it reflects all colors back at once4 ,it therefore absorbs practically no light4 ,but the reason the black cloth looks black is that it reflects almost none of the colors--it absorbs them all and changes them to heat4 ,the colored cloth reflects just the red or the green light and absorbs the rest4 ,maybe you will understand color better if it is explained in another way4 ,suppose ,i throw balls of all colors to you1 having trained you to keep all the balls except the red ones4 ,i throw you a blue ball2 you keep it4 ,i throw a red ball2 you throw it back4 ,i throw a green ball2 you keep it4 ,i throw a yellow ball2 you keep it4 ,i throw two balls at once1 yellow and red2 you keep the yellow and throw back the red4 ,i throw a blue and yellow ball at the same time2 you keep both balls4 ,now suppose ,i change this a little4 ,instead of throwing balls1 ,i shall throw lights to you4 ,you are trained always to throw red light back to me and always to keep 7absorb7 all other kinds of light4 ,i throw a blue light2 you keep it1 and ,i get no light back4 ,i throw a red light2 you throw it back to me4 ,i throw a green light2 you keep it1 and ,i get no light back4 ,i throw a yellow light2 you keep it1 and ,i get no light back4 ,i throw two lights at the same time1 yellow and red2 you keep the yellow and throw back only the red4 ,but yellow and red together make orange2 so when ,i throw an orange light1 you throw back the red part of it and keep the yellow4 ,now if we suppose that instead of throwing lights to you ,i throw them to molecules of dye which are trained to throw back the red lights and keep all the other kinds 7absorb them and change them to heat71 we can understand what the dye in a red sweater does4 ,the dye is not really trained1 of course1 but for a reason which we do not entirely understand1 some kinds of dye always throw back 7reflect7 any red that is in the light that shines on them1 but they keep all other kinds of light1 changing them to heat4 ,other dyes or coloring matter always throw back any green that is in the light that shines on them1 keeping the other colors4 ,blue coloring matter throws back only the blue part of the light1 and so on through all the colors4 ,so if you throw a white light1 which contains all the colors1 on a red sweater1 the dye in the sweater picks out the red part of the white light and throws that back to your eyes 7reflects it to you7 but it keeps the rest of the colors of the white light1 changing them to heat2 and since only the red part of the light is reflected to your eyes1 that is the only part of it that you can see2 so the sweater looks red4 ,the green substance 7chlorophyll7 in grass acts in the same way2 only it throws the green part of the sunlight back to your eyes1 keeping the rest2 so the part of the light that reaches you from the grass is the green light1 and the grass looks green4 ,anything white1 like a piece of paper1 reflects all the light that strikes it2 so if all the colors 7white light7 strike it1 all are reflected to your eyes and the object looks white4 ,you have looked at people under the mercury-vapor lights in photo-postal studios1 have you not8 ,the lights are long1 inclined tubes which glow with a greenish-violet light4 ,no matter how good the color of a person is in ordinary light1 in that light it is ghastly4 ,illustration3 ,,fig4 #id4 ,a mercury-vapor lamp4 ,go into the kitchen tonight1 light a burner of the gas stove1 turn out the light and sprinkle salt on the blue gas flame4 ,the flame will leap up1 yellow4 ,look at your hands1 at some one's lips1 at a piece of red cloth1 in this light4 ,does anything look red8 ,the reason why nothing looks pink or red in these two kinds of light is this3 ,the light given by glowing salt vapor or mercury vapor has no red in it2 if you tried to make a rainbow from it with a prism1 you would find no red or orange color in it4 ,a thing looks red when it absorbs all the parts of the light that are not red and reflects the red light to your eyes4 ,if there is no red in the light to reflect1 obviously a thing cannot look red in that light4 ,when you look through a piece of colored glass1 the case is somewhat different4 ,a piece of blue glass1 for instance1 acts as a sort of strainer4 ,the coloring matter in it lets the blue light through it1 but it holds back 7absorbs7 the other kinds of light4 ,so if you look through a piece of blue glass you see everything blue2 that is1 only the blue part of the light from different objects can reach your eyes through this kind of glass4 ,anything that is transparent and colored acts in a similar way4 ,,why ,,the ,,sky ,,is ,,blue4 ,and that is why the sky looks blue4 ,air holds back all colors of light except blue2 that is1 it holds them back a little4 ,a room full of air holds the colors back hardly at all4 ,a few miles of air hold them back more2 mountains in the distance look bluish because only the blue light from them can reach you through the air4 ,the hundred or more miles of air above you hold back a considerable amount of the other colors of light1 letting through much more of blue than of any other color4 ,so the sky looks blue2 that is1 when the air scatters the sunlight above you1 it is chiefly the blue parts of the sunlight that it allows to reach your eyes4 ,,why ,,bodies ,,of ,,water ,,look ,,green ,,in ,,some ,,places ,,and ,,blue ,,in ,,others4 ,water acts in a similar way1 but it lets the green light through instead of the blue4 ,a little water holds back 7absorbs7 the other colors so slightly that you cannot notice the effect in a glass of water4 ,but in a swimming tank full of water1 or in a lake or an ocean1 you can notice it decidedly when you look straight down into the water itself4 ,when you look at a smooth body of water at a slant on a clear day1 the blue sky is reflected to you and the water looks blue instead of green4 ,and it may even look blue when you look straight down in it if it is too deep for you to see the bottom and the sky is reflected from the surface4 ,,why ,,the ,,sky ,,is ,,often ,,red ,,at ,,sunset4 ,dust lets more of red and yellow light through than of any other color1 and for this reason there is much red and yellow in the sunset4 ,just before the sun sets1 it shines through the low1 dusty air4 ,the dust filters out most of the light except the red and yellow4 ,the red light and yellow light are reflected by the clouds 7for the clouds are themselves white2 that is1 they reflect all the colors that strike them71 and you have the beautiful sunset clouds4 ,sometimes there is a purple in the sunset1 and even green4 ,but since the air itself is blue 7that is1 it lets mostly blue light go through71 it is easy to see how this blue can combine with the red or yellow that the dust lets through1 to form purple or green4 ,but we could not have sunset colors or all the colors we see on earth1 if it were not that the sunlight is mostly white--that it contains all colors4 ,and that1 too1 is why we can have a rainbow4 ,,how ,,rainbows ,,are ,,formed4 ,you already know fairly well how a rainbow is formed1 since you made an imitation of one with a prism4 ,a rainbow appears in the sky when the sun shines through the rain2 the plain white light of the sun is divided up into red1 orange1 yellow1 green1 blue1 indigo1 and violet4 ,as the white light of the sun passes through the raindrops1 the violet part of the light is bent more than any of the rest1 the indigo part is bent not quite so much1 and so on to the red1 which is bent least of all4 ,so all the colors fan out from the single beam of white light and form a band of color1 which we call the rainbow4 ,illustration3 ,,fig4 #ie4 ,explain why the breakers are white and the sea green or blue4 ,,how ,,we ,,can ,,tell ,,what ,,the ,,sun ,,and ,,stars ,,are ,,made ,,of4 ,when a gas or vapor becomes hot enough to give off light 7when it is incandescent71 it does not give off white light but light of different colors4 ,an experiment will let you see this for yourself4 ,,experiment #ec4 ,sprinkle a little copper sulfate 7bluestone7 in the flame of a ,bunsen burner4 ,what color does it make the flame8 ,copper vapor always gives this greenish-blue light when it is heated4 ,the photographer's mercury-vapor light gave a greenish-violet glow4 ,when you burn salt or soda in a gas flame1 you remember that you get a clear yellow light4 ,by breaking up these lights1 somewhat as you broke up the sunlight with the prism1 chemists and astronomers can tell what kind of gas is glowing4 ,the instrument they use to break up the light into its different colors is called a spectroscope1 and the band of colors formed is called the spectrum4 ,with the spectroscope they examine the light that comes from the sun and stars and by the colors of the spectra they can tell what these far-distant bodies are made of4 ,,application #ci4 ,if you were going to the tropics1 would it be better to wear outside clothes that were white or black8 ,,application #dj4 ,a dancer was to dance in a spotlight on the stage4 ,the light was to change colors constantly4 ,she wanted her robe to reflect each color that was thrown on it4 ,should she have worn a robe of red1 yellow1 white1 green1 or blue8 ,,application #da4 ,if you looked through a red glass at a purple flower 7purple is red mixed with blue71 would the flower look red1 blue1 purple1 black1 or white8 ,,inference ,,exercise ,explain the following3 #bda4 ,mercury is separated from its ore by heating the ore so strongly that the mercury rises from it as a vapor4 #bdb4 ,hothouses are built of glass4 #bdc4 ,a rainbow is sometimes seen in the spray of a garden hose4 #bdd4 ,your feet become hot when your shoes are being polished4 #bde4 ,doors into offices usually have windows of ground glass or frosted glass4 #bdf4 ,opera glasses are of value to those sitting at a distance from the stage4 #bdg4 ,in order to see clearly through opera glasses1 you have to adjust them4 #bdh4 ,it is warm inside an ,eskimo's hut although it is built of ice and snow4 #bdi4 ,it is usually cooler on a lawn than on dry ground4 #bej4 ,black clothes are warmer in the sunlight than clothes of any other color4 ,,chapter ,,six ,,sound ,,section #bh4 ,what sound is4 ,what makes a dictaphone or a phonograph repeat your words8 ,what makes the wind howl when it blows through the branches of trees8 ,why can you hear an approaching train better if you put your ear to the rail8 ,if you were to land on the moon tonight1 and had with you a tank containing a supply of air which you could breathe 7for there is no air to speak of on the moon71 you might try to speak4 ,but you would find that you had lost your voice completely4 ,you could not say a word4 ,you would open and close your mouth and not a sound would come4 ,then you might try to make a noise by clapping your hands2 but that would not work4 ,you could not make a sound4 ,am ,i deaf and dumb8 you might wonder4 ,the whole trouble would lie in the fact that the moon has practically no air4 ,and sound is usually a kind of motion of the air1--hundreds of quick1 sharp puffs in a second1 so close together that we cannot feel them with anything less sensitive than the tiny nerves in our ears4 ,if you can once realize the fact that sound is a series of quick1 sharp puffs of air1 or to use a more scientific term1 vibrations of air1 it will be easy for you to understand most of the laws of sound4 ,a phonograph seems almost miraculous4 ,yet it works on an exceedingly simple principle4 ,when you talk1 the breath passing out of your throat makes the vocal cords vibrate4 ,these and your tongue and lips make the air in front of you vibrate4 ,when you talk into a dictaphone horn1 the vibrating air causes the needle at the small end of the horn to vibrate so that it traces a wavy line in the soft wax of the cylinder as the cylinder turns4 ,then when you run the needle over the line again it follows the identical track made when you talked into the horn1 and it vibrates back and forth just as at first2 this makes the air in the horn vibrate exactly as when you talked into the horn1 and you have the same sound4 ,all this goes back to the fundamental principle that sound is vibrations of air2 different kinds of sounds are simply different kinds of vibrations4 ,the next experiments will prove this4 ,,experiment #ed4 ,turn the rotator rapidly1 holding the corner of a piece of stiff paper against the holes in the disk4 ,as you turn faster1 does the sound become higher or lower8 ,keep turning at a steady rate and move your paper from the inner row of holes to the outer row and back again4 ,which row has the most holes in it8 ,which makes the highest sound8 ,hold your paper against the teeth at the edge of the disk4 ,is the pitch higher or lower than before8 ,blow through a blowpipe against the different rows of holes while the disk is being whirled4 ,as the holes make the air vibrate do you get any sound8 ,this experiment shows that by making the air vibrate you get a sound4 ,the next experiment will show that when you have sound you are getting vibrations4 ,,experiment #ee4 ,tap a tuning fork against the desk1 then hold the prongs lightly against your lips4 ,can you feel them vibrate8 ,tap it again1 and hold the fork close to your ear4 ,can you hear the sound8 ,illustration3 ,,fig4 #if4 ,an interesting experiment in sound4 ,the experiment which follows will show that we usually must have air to do the vibrating to carry the sound4 ,,experiment #ef4 ,make a pad of not less than a dozen thicknesses of soft cloth so that you can stand an alarm clock on it on the plate of the air pump4 ,the pad is to keep the vibrations of the alarm from making the plate vibrate4 ,a still better way would be to set a tripod on the plate of the air pump and to suspend the alarm clock from the tripod by a rubber band4 ,set the alarm so that it will ring in #c or #d minutes1 put it under the bell jar1 and pump out the air4 ,before the alarm goes off1 be sure that the air is almost completely pumped out of the jar4 ,can you hear the bell ring8 ,distinguish between a dull trilling sound caused by the jarring of the air pump when the alarm is on1 and the actual ringing sound of the bell4 ,illustration3 ,,fig4 #ig4 ,when the air is pumped out of the jar1 you cannot hear the bell ring4 ,the experiment just completed shows how we know there would be no sound on the moon1 since there is practically no air around it4 ,the next experiment will show you more about the way in which phonographs work4 ,,experiment #eg4 ,put a blank cylinder on the dictaphone1 adjust the recording 7cutting7 needle and diaphragm at the end of the tube1 start the motor1 and talk into the dictaphone4 ,shut off the motor1 remove the cutting needle1 and put on the reproducing needle 7the cutting needle1 being sharp1 would spoil the cylinder74 ,start the reproducing needle where the recording needle started1 turn on the motor1 and listen to your own voice4 ,notice that in the dictaphone the air waves of your voice are all concentrated into a small space as they go down the tube4 ,at the end of the tube is a diaphragm1 a flat disk which is elastic and vibrates back and forth very easily4 ,the air waves from your voice would not vibrate the needle itself enough to make any record2 but they vibrate the diaphragm1 and the needle1 being fastened rigidly to it1 vibrates with it4 ,illustration3 ,,fig4 #ih4 ,making a phonograph record on an old-fashioned phonograph4 ,in the same way1 when the reproducing needle vibrates as it goes over the track made by the cutting needle1 it would make air vibrations too slight for you to hear if it were not fastened to the diaphragm4 ,when the diaphragm vibrates with the needle1 it makes a much larger surface of air vibrate than the needle alone could4 ,then the tube1 like an ear trumpet1 throws all the air vibrations in one direction1 so that you hear the sound easily4 ,,experiment #eh4 ,put a clean white sheet of paper around the recording drum1 pasting the two ends together to hold it in place4 ,put a small piece of gum camphor on a dish just under the paper1 light it1 and turn the drum so that all parts will be evenly smoked4 ,be sure to turn it rapidly enough to keep the paper from being burned4 ,melt a piece of glass over a burner and draw it out into a thread4 ,break off about #h inches of this glass thread and tie it firmly with cotton thread to the edge of one prong of a tuning fork4 ,clamp the top of the tuning fork firmly above the smoked drum1 adjusting it so that the point of the glass thread rests on the smoked paper4 ,turn the handle slightly to see if the glass is making a mark4 ,if it is not1 adjust it so that it will4 ,now let some one turn the cylinder quickly and steadily4 ,while it is turning1 tap the tuning fork on the prong which has not the glass thread fastened to it4 ,the glass point should trace a white1 wavy line through the smoke on the paper4 ,if it does not1 keep on trying1 adjusting the apparatus until the point makes a wavy line4 ,illustration3 ,,fig4 #ii4 ,a modern dictaphone4 ,making a record in this way is1 on a large scale1 almost exactly like the making of a phonograph record4 ,the smoked paper on which a tracing can easily be made as it turns is like the soft wax cylinder4 ,the glass needle is like the recording needle of a phonograph4 ,the chief difference is that you have struck the tuning fork to make it and the needle vibrate1 instead of making it vibrate by air waves set in motion by your talking4 ,it is because these vibrations of the tuning fork are more powerful and larger than are those of the recording needle of a phonograph that you can see the record on the recording drum1 while you cannot see it clearly on the phonograph cylinder4 ,illustration3 ,,fig4 #ajj4 ,how the apparatus is set up4 ,in all ordinary circumstances1 sound is the vibration of air4 ,but in swimming we can hear with our ears under water1 and fishes hear without any air4 ,so1 to be accurate1 we should say that sound is vibrations of any kind of matter4 ,and the vibrations travel better in most other kinds of matter than they do in air4 ,vibrations move rather slowly in air1 compared with the speed at which they travel in other substances4 ,it takes sound about #e seconds to go a mile in air2 in other words1 it would go #ab miles while an express train went one4 ,but it travels faster in water and still faster in anything hard like steel4 ,that is why you can hear the noise of an approaching train better if you put your ear to the rail4 ,illustration3 ,,fig4 #aja4 ,when the tuning fork vibrates1 the glass needle makes a wavy line on the smoked paper on the drum4 ,,why ,,we ,,see ,,steam ,,rise ,,before ,,we ,,hear ,a ,,whistle ,,blow4 ,but even through steel1 sound does not travel with anything like the speed of light4 ,in the time that it takes sound to go a mile1 light goes hundreds of thousands of miles1 easily coming all the way from the moon to the earth4 ,that is why we see the steam rise from the whistle of a train or a boat before we hear the sound4 ,the sound and the light start together2 but the light that shows us the steam is in our eyes almost at the instant when the steam leaves the whistle2 the sound lags behind1 and we hear it later4 ,,application #db4 ,explain why a bell rung in a vacuum makes no noise2 why the clicking of two stones under water sounds louder if your head is under water1 than the clicking of the two stones in the air sounds if your head is in the air2 why you hear a buzzing sound when a bee or a fly comes near you2 how a phonograph can reproduce sounds4 ,,inference ,,exercise ,explain the following3 #bea4 ,the paint on woodwork blisters when hot4 #beb4 ,you can screw a nut on a bolt very much tighter with a wrench than with your fingers4 #bec4 ,when a pipe is being repaired in the basement of a house1 you can hear a scraping noise in the faucets upstairs4 #bed4 ,sunsets are unusually red after volcanic eruptions4 #bee4 ,thunder shakes a house4 #bef4 ,shooting stars are really stones flying through space4 ,when they come near the earth1 it pulls them swiftly down through the air4 ,explain why they glow4 #beg4 ,at night it is difficult to see out through a closed window of a room in which a lamp is lighted4 #beh4 ,when there is a breeze you cannot see clear reflections in a lake4 #bei4 ,rubbing with coarse sandpaper makes rough wood smooth4 #bfj4 ,a bow is bent backward to make the arrow go forward4 ,,section #bi4 ,echoes4 ,when you put a sea shell to your ear1 how is it that you hear a roar in the shell8 ,why can you sometimes hear an echo and sometimes not8 ,if it were not for the fact that sound travels rather slowly1 we should have no echoes1 for the sound would get back to us practically at the instant we made it4 ,an echo is merely a sound1 a series of air vibrations1 bounced back to us by something at a distance4 ,it takes time for the vibration which we start to reach the wall or cliff that bounces it back1 and it takes as much more time for the returning vibration to reach our ears4 ,so you have plenty of time to finish your shout before the sound bounces back again4 ,the next experiment shows pretty well how the waves1 or vibrations1 of sound are reflected2 only in the experiment we use waves of water because they go more slowly and we can watch them4 ,,experiment #ei4 ,fill the long laboratory sink 7or the bathtub at home7 half full of water and start a wave from one end4 ,watch it move along the side of the sink4 ,notice what happens when it reaches the other end4 ,air waves do the same thing2 when they strike against a flat surface1 they bounce back like a rubber ball4 ,if you are far enough away from a flat wall or cliff1 and shout1 the sound 7the air vibrations you start7 is reflected back to you and you hear the echo4 ,but if you are close to the walls1 as in an empty room1 the sound reverberates2 it bounces back and forth from one wall to the other so rapidly that no distinct echo is heard1 and there is merely a confusion of sound4 ,illustration3 ,,fig4 #ajb4 ,when the wave reaches the end of the sink1 it is reflected back4 ,sound waves are reflected in the same way4 ,when you drop a pebble in water1 the ripples spread in all directions4 ,in the same way1 when you make a sound in the open air1 the air waves spread in all directions4 ,but when you shout through a megaphone the air waves are all concentrated in one direction and consequently they are much stronger in that direction4 ,however1 while the megaphone intensifies sound1 the echoing from the sides of the megaphone makes the sound lose some of its distinctness4 ,,why ,,it ,,is ,,hard ,,to ,,understand ,a ,,speaker ,,in ,,an ,,empty ,,hall4 ,a speaker can be heard much more easily in a room full of people than in an empty hall4 ,the sound does not reflect well from the soft clothes of the audience and the uneven surfaces of their bodies1 just as a rubber ball does not bounce well in sand4 ,so the sound does not reverberate as in an empty hall4 ,,application #dc4 ,explain why a carpeted room is quieter than one with a bare floor2 why you shout through your hands when you want to be heard at a distance4 ,,inference ,,exercise ,explain the following3 #bfa4 ,it is harder to walk when you shuffle your feet4 #bfb4 ,the air over a lamp chimney1 or over a register in a furnace-heated house1 is moving upward rapidly4 #bfc4 ,the shooting of a gun sounds much louder within a room than it does outdoors4 #bfd4 ,a drum makes a loud1 clear sound when the tightened head is struck4 #bfe4 ,the pull of the moon causes the ocean tides4 #bff4 ,sand is sometimes put in the bottom of vases to keep them from falling over4 #bfg4 ,it is difficult to understand clearly the words of one who is speaking in an almost empty hall4 #bfh4 ,the ridges in a washboard help to clean the clothes that are rubbed over them4 #bfi4 ,one kind of mechanical toy has a heavy lead wheel inside4 ,when you start this to whirling1 the toy runs for a long time4 #bgj4 ,if you raise your finger slightly after touching the surface of water1 the water comes up with your finger4 ,,section #cj4 ,pitch4 ,what makes the keys of a piano give different sounds8 ,why does the moving of your fingers up and down on a violin string make it play different notes8 ,why is the whistle of a peanut roaster so shrill1 and why is the whistle of a boat so deep8 ,did you ever notice how tiresome the whistle on a peanut roaster gets8 ,well1 suppose that whenever you spoke you had to utter your words in exactly that pitch2 that every time a car came down the street its noise was like the whistle of the peanut roaster1 only louder2 that every step you took sounded like hitting a bell of the same pitch2 that when you went to the moving-picture theater the orchestra played only the one note2 that when any one sang1 his voice did not rise and fall2 in short1 that all the sounds in the world were in one pitch4 ,that is the way it would be if different kinds of air vibrations did not make different kinds of notes1--if there were no differences in pitch4 ,,pitch ,,due ,,to ,,rapidity ,,of ,,vibration4 ,when air vibrations are slow1--far apart1--the sound is low2 when they are faster1 the sound is higher2 when they are very quick indeed1 the sound is very shrill and high4 ,in various ways1 as by people talking and walking and by the running of street cars and automobiles1 all sorts of different vibrations are started1 giving us a pleasant variety of high and low and medium pitches in the sounds of the world around us4 ,an experiment will show how pitch varies and how it is regulated3 ,,experiment #fj4 ,move the slide of an adjustable tuning fork well up from the end of the prongs1 tap one prong lightly on the desk1 and listen4 ,move the slide somewhat toward the end of the prongs1 and repeat4 ,is a higher or a lower sound produced as the slide shortens the length of the prongs8 ,whistle a low note1 then a high one4 ,notice what you do with your lips2 when is the opening the smaller8 ,sing a low note1 then a high one4 ,when are the cords in your throat looser8 ,fill a drinking glass half full of water1 and strike it4 ,now pour half the water out1 and strike the glass again4 ,do you get the higher sound when the column of water is shorter or when it is longer8 ,stretch a rubber band across your thumb and forefinger4 ,pick the band as you make it tighter1 not making it longer1 but pulling it tighter with your other fingers4 ,does it make a higher or a lower sound as you increase the tightness8 ,stretch the band from your thumb to your little finger and pick it2 now put your middle finger under the band so as to divide it in halves1 and pick it again4 ,does a short strand give a higher or lower pitch than a long strand8 ,illustration3 ,,fig4 #ajc4 ,when the prongs of the tuning fork are made longer or shorter1 the pitch of the sound is changed4 ,a violinist tunes his violin by tightening the strings2 the tighter they are and the thinner they are1 the higher the note they give4 ,some of the strings are naturally higher than others2 the highest is a smaller1 finer string than the lowest4 ,when the violinist plays1 he shortens the strings by holding them down with his fingers1 and the shorter he makes them the higher the note4 ,a bass drum is much larger than a high-pitched kettledrum4 ,the pipes of an organ are long and large for the low notes1 shorter and smaller for the high ones4 ,in general1 the longer or larger the object is that vibrates1 the slower the rate of vibration and consequently the lower the pitch4 ,but the shorter or finer the object is that vibrates1 the higher the rate of vibration and the higher the pitch4 ,all musical instruments contain devices which can be made to vibrate1--either strings or columns of air1 or other things that swing to and fro and start waves in the air4 ,and by tightening them1 or making them smaller or shorter1 the pitch can be made higher2 that is1 the number of vibrations to each second can be increased4 ,,application #dd4 ,explain why a steamboat whistle is usually of much lower pitch than is a toy whistle2 why a banjo player moves his fingers toward the drum end of the banjo when he plays high notes2 why the sound made by a mosquito is higher in pitch than that made by a bumblebee4 ,,application #de4 ,a boy had a banjo given him for ,christmas4 ,he wanted to tune it4 ,to make a string give a higher note1 should he have tightened or loosened it8 ,or could he have secured the same result by moving his finger up and down the string to lengthen or shorten it8 ,,application #df4 ,a man was tuning a piano for a concert4 ,the hall was cold1 yet he knew it would be warm at the time of the concert4 ,should he have tuned the piano to a higher pitch than he wanted it to have on the concert night1 to the exact pitch1 or to a lower pitch8 ,,inference ,,exercise ,explain the following3 #bga4 ,a cowboy whirls his lasso around and around his head before he throws it4 #bgb4 ,furnaces are always placed in the basements of buildings1 never on top floors4 #bgc4 ,a rather slight contraction of a muscle lifts your arm a considerable distance4 #bgd4 ,a player on a slide trombone changes the pitch of the notes by lengthening and shortening the tube while he blows through it4 #bge4 ,rain runs off a tar roof in droplets1 while on shingles it soaks in somewhat and spreads4 #bgf4 ,there is a sighing sound as the wind blows through the branches of trees1 or through stretched wires or ropes4 #bgg4 ,sometimes a very violent noise breaks the membrane in the drum of a person's ear4 #bgh4 ,as a street car goes faster and faster1 the hum of its motor is higher and higher4 #bgi4 ,if a street is partly dry1 the wet spots shine more than the dry spots do4 #bhj4 ,molten type metal1 when poured into a mold1 becomes hard1 solid type when it cools4 ,,chapter ,,seven ,,magnetism ,,and ,,electricity ,,section #ca4 ,magnets2 the compass4 ,what makes the needle of a compass point north8 ,what causes the ,northern ,lights8 ,for many hundreds of years sailors have used the compass to determine directions4 ,during all this time men have known that one point of the needle always swings toward the north if there is no iron near to pull it some other way1 but until within the past century they did not know why4 ,now we have found the explanation in the fact that the earth is a great big magnet4 ,the experiment which follows will help you to understand why the earth's being a magnet should make the compass needle point north and south4 ,,experiment #fa4 ,lay a magnetic compass flat on the table4 ,notice which point swings to the north4 ,now hold a horseshoe magnet1 points down1 over the compass4 ,turn the magnet around and watch the compass needle2 see which end of the magnet attracts the north point2 hold that end of it toward the south point and note the effect4 ,hold the magnet1 ends up1 under the table directly below the compass and turn the magnet1 watching the compass needle4 ,the earth is a magnet1 and it acts just as your magnet does3 one end attracts one point of the compass1 and the other end attracts the other point4 ,that ought to make it clear why the compass points north4 ,but how is the compass made8 ,the next experiment will show this plainly4 ,,experiment #fb4 ,take a long shoestring and make a loop in one end of it4 ,slip the magnet through the loop and suspend it1 ends down4 ,fasten the shoestring to the top of a doorway so that the magnet can swing easily4 ,steady the magnet and let it turn until it comes to a rest4 ,mark the end that swings to the north4 ,turn this end around to the south2 let go and watch it4 ,place the magnet the other way around in the loop so that you can be sure that it is not twisting of the shoestring that makes the magnet turn in this direction4 ,now stroke a needle several times along one arm of the magnet1 always in the same direction1 as shown in ,figure #aje4 ,hold the needle over some iron filings or touch any bit of iron or steel with it4 ,what has the needle become8 ,lay it on a cardboard milk-bottle top of the flat kind1 and on that float it in the middle of a glass or earthenware dish of water4 ,notice which end turns north4 ,turn this end to the south and see what happens4 ,hold your magnet1 ends up1 under the dish1 and turn the magnet4 ,what does the needle do8 ,illustration3 ,,fig4 #ajd4 ,the compass needle follows the magnet4 ,now it should be easy to understand why the compass points north4 ,one end of any magnet pulls on one end of another magnet and drives the other end away4 ,the earth is a big magnet4 ,so if you make a magnet and balance it in such a way that it is free to swing1 the north end of the big earth magnet pulls one end of the little magnet toward it and pushes the other end away4 ,therefore one end of your compass always points north4 ,,other ,,effects ,,of ,,the ,,earth',s ,,magnetism4 ,another interesting effect of the earth's being a big magnet is to be seen if you lay a piece of steel so that it points north and south1 and then pound it on one end4 ,it becomes magnetized just as your needle became magnetized when it was rubbed on the small magnet4 ,illustration3 ,,fig4 #aje4 ,magnetizing a needle4 ,illustration3 ,,fig4 #ajf4 ,a compass made of a needle and a piece of cardboard4 ,and still another effect of the earth's magnetism is this3 ,tiny particles of electricity1 called electrons1 are probably shooting through space from the sun4 ,it is believed that as they come near the earth1 the magnetism of the north and south polar regions attracts them toward the poles1 and that as they rush through the thin1 dry upper air1 they make it glow4 ,and this is probably what causes the ,northern ,lights or ,aurora ,borealis4 ,,what ,,happens ,,when ,a ,,needle ,,is ,,magnetized4 ,the reason that a needle becomes magnetic if it is rubbed over a magnet is probably this3 ,every molecule of iron may be an extremely tiny magnet2 if it is1 each molecule has a north and south pole like the needle of a compass4 ,in an ordinary needle 7or in any unmagnetized piece of iron or steel7 these molecules would be facing every way1 as shown in ,figure #ajg4 ,illustration3 ,,fig4 #ajg4 ,diagram of molecules in unmagnetized iron4 ,the north and south poles of the molecules are supposed to be pointing in all directions4 ,illustration3 ,,fig4 #ajh4 ,diagram of magnetized iron4 ,the north and south poles of the molecules are all supposed to point in the same direction4 ,but when a piece of steel or iron that is already magnetized is brought near the unmagnetized needle1 all the north poles of the molecules of the needle are pulled in the same direction--it is almost like combing tangled hair to stroke a needle over a magnet4 ,then the molecules are arranged more as shown in ,figure #ajh4 ,when all the molecules1 each of which is a tiny magnet1 pull in the same direction1 they make a strong magnet1 and they magnetize any iron that comes near them just as they were magnetized4 ,steel will stay magnetized a long time2 but ordinary soft iron loses magnetism almost as soon as another magnet is taken away from it1--the molecules become all disarranged again4 ,in a later section you will find that whenever electricity flows through a wire that is coiled around a piece of iron1 the iron becomes magnetized just as when it is rubbed with a magnet4 ,,application #dg4 ,an explorer lost his compass4 ,in clear weather he could tell the directions by the sun and stars1 but in cloudy weather he was badly handicapped4 ,he had with him a gun1 plenty of ammunition1 a sewing kit1 a hunting knife1 and some provisions4 ,how could he have made a compass8 ,,inference ,,exercise ,explain the following3 #bha4 ,snow turns to water in the first warm weather4 #bhb4 ,a person's face looks ghastly by the greenish light of a mercury-vapor lamp4 #bhc4 ,if a red-hot coal is touched with a cold poker1 the coal turns black at the place touched4 #bhd4 ,stereopticon slides are put in upside down1 yet the picture on the screen is right side up4 #bhe4 ,if the vocal cords of your throat did not vibrate1 you could not talk out loud4 #bhf4 ,a watch is sometimes put out of order if it is held near a magnet4 #bhg4 ,the water will be no higher on the inside of a leaky boat than it is on the outside4 #bhh4 ,a bass viol is considerably larger than a violin4 #bhi4 ,ships that are used by men testing the earth's magnetism carry very sensitive compasses4 ,explain why such ships are made entirely of wood and brass4 #bij4 ,thunder rolls2 that is1 after the first peal there is a reverberating sound that becomes less and less distinct4 ,,section #cb4 ,static electricity4 ,what is electricity8 ,what makes thunder and lightning8 ,why does the barrel or cap of a fountain pen pick up small bits of paper after it has been rubbed on your coat sleeve8 ,why do sparks fly from the fur of a cat when you stroke it in the dark8 ,the ,greeks1 #bjjj years ago1 knew that there was such a thing as electricity1 and they used to get it by rubbing amber with silk4 ,in the past century men have learned how to make electricity do all sorts of useful work3 making boats and cars and automobiles go1 ringing bells1 furnishing light1 and1 in the telephone and telegraph1 carrying messages4 ,but no one knew what electricity really was until1 within the last #be years1 scientists found out4 ,,atoms ,,and ,,electrons4 ,when we talked about molecules1 we said that they were as much smaller than a germ as a germ is smaller than a mountain4 ,well1 a molecule is made up1 probably1 of some things that are much smaller still1--so small that people thought that nothing could be smaller4 ,those unthinkably tiny things are called atoms2 you will hear more about them when you come to the parts of this book that tell about chemistry4 ,but if you took the smallest atom in the world and divided it into #agjj pieces1 each one of these would be about the size of a piece of electricity4 ,electricity is made up of the tiniest things known to man--things so small that nobody really can think of their smallness4 ,these little pieces of electricity are called electrons1 and for all their smallness1 scientists have been able to find out a good deal about them4 ,they have managed to get one electron all by itself on a droplet of oil and they have seen how it made the oil behave4 ,of course they could not see the electron1 but they could tell from various experiments that they had just one4 ,scientists know how many trillions of electrons flow through an incandescent electric lamp in a second and how many quadrillions of them it would take to weigh as much as a feather4 ,they know what the electrons do when they move1 how fast they can move1 and what substances let electrons move through them easily and what substances hold them back2 and they know perfectly well how to set them in motion4 ,how the scientists came to know all these things you will learn in the study of physics2 it is a long story4 ,but you can find out some things about electrons yourself4 ,the first experiment is a simple one such as the ,greeks used to do with amber4 ,,experiment #fc4 ,rub a hard rubber comb on a piece of woolen cloth4 ,the sleeve of a woolen coat or sweater will do4 ,rub the comb quickly in the same direction several times4 ,now hold it over some small bits of paper or sawdust4 ,what does it do to them8 ,hold it over some one's hair4 ,the rest of this experiment will work well only on cool1 clear days4 ,rub the comb again1 a dozen or more times in quick succession4 ,now touch it gently to the lobe of your ear4 ,do you hear the snap as the small spark jumps from the comb to your ear8 ,pull a dry hair out of your head and hold it by one end4 ,charge your comb by rubbing it again1 and bring it near the loose end of the hair4 ,if the end of the hair clings to the comb at first1 leave it clinging until it flies off4 ,now try to touch the hair with the comb4 ,next1 pinch the end of the hair between your thumb and finger and again bring the charged comb near it4 ,is the hair attracted or repelled8 ,after touching the comb what does it do8 ,you can get the same effects by rubbing glass or amber on silk4 ,illustration3 ,,fig4 #aji4 ,when the comb is rubbed on the coat1 it becomes charged with electricity4 ,,objects ,,negatively ,,and ,,positively ,,charged ,,with ,,electricity4 ,there are probably electrons in everything4 ,but when there is just the usual number of electrons in an object1 it acts in an ordinary way and we say that it is not charged with electricity4 ,if there are more than the usual number of electrons on an object1 however1 we say that it is negatively charged1 or that it has a negative charge of electricity on it4 ,but if there are fewer electrons than usual in an object1 we say that it has a positive charge of electricity on it1 or that it is positively charged4 ,you might expect a negative charge to indicate fewer electrons than usual1 not more4 ,but people called the charge negative long before they knew anything about electrons2 and it is easier to keep the old name than to change all the books that have been written about electricity4 ,so we still call a charge negative when there are unusually many electrons1 and we call it positive when there are unusually few4 ,a negative charge means that more electrons are present than usual4 ,a positive charge means that fewer electrons are present than usual4 ,illustration3 ,,fig4 #aaj4 ,the charged comb picks up pieces of paper4 ,before you rubbed your comb on wool1 neither the comb nor the wool was charged2 both had just the usual number of electrons4 ,but when you rubbed them together1 you rubbed some of the electrons off the wool on to the comb4 ,then the comb had a negative charge2 that is1 it had too many electrons--too many little particles of electricity4 ,when you brought the comb near the hair1 the hair had fewer electrons than the comb4 ,whenever one object has more electrons on it than another1 the two objects are pulled toward each other2 so there was an attraction between the comb and the hair1 and the hair came over to the comb4 ,as soon as it touched the comb1 some of the extra electrons jumped from the comb to the hair4 ,the electrons could not get off the hair easily1 so they stayed there4 ,electrons repel each other--drive each other away4 ,so when you had a number of electrons on the end of the comb and a number on the end of the hair1 they pushed each other away1 and the hair flew from the comb4 ,but when you pinched the hair1 the electrons could get off it to your moist hand1 which lets electricity through it fairly easily4 ,then the comb had extra electrons on it and the hair did not2 so the comb pulled the hair over toward it again4 ,when you brought the charged comb near your ear1 some of the electrons on the comb pushed the others off to your ear1 and you heard them snap as they rushed through the air1 making it vibrate4 ,,how ,,lightning ,,and ,,thunder ,,are ,,caused4 ,in thunderstorms the strong currents of rising air blow some of the forming raindrops in the clouds into bits of spray4 ,the tinier droplets get more than their share of electrons when this happens and are carried on up to higher clouds4 ,in this way clouds become charged with electricity4 ,one cloud has on it many more electrons than another cloud that is made1 perhaps1 of lower1 larger droplets4 ,the electricity leaps from the cloud that has the greater number of electrons to the cloud that has the less number1 or it leaps from the heavily charged cloud down to a tree or house or the ground4 ,you see the electricity leap and call it lightning4 ,much more leaps1 however1 than leaped from the comb to your ear1 and so it makes a very much louder snap4 ,the snap is caused in this way3 ,as the electric spark leaps through the air1 it leaves an empty space or vacuum immediately behind it4 ,the air from all sides rushes into the vacuum and collides there2 then it bounces back4 ,this again leaves a partial vacuum2 so the air rushes in once more1 coming from all sides at once1 and again bounces back4 ,this starts the air vibrations which we call sound4 ,then the sound is echoed from cloud to cloud and from the clouds to the earth and back again1 and we call it thunder4 ,the electricity you have been reading about and experimenting with in this section is called static electricity4 ,static means standing still4 ,the electricity you rubbed up to the surface of the comb or glass stayed still until it jumped to the bit of paper or hair2 then it stayed still on that4 ,this was the only kind of electricity most people knew anything about until the nineteenth century2 and it is not of any great use4 ,electricity must be flowing through things to do work4 ,that is why people could not invent electric cars and electric lights and telephones before they knew how to make electricity flow steadily rather than just to stand still on one thing until it jumped across to another and stood there4 ,in the next chapter we shall take up the ways in which electrons are made to flow and to do work4 ,,application #dh4 ,explain why the stroking of a cat's back will sometimes cause sparks and make the cat's hairs stand apart2 why combing sometimes makes your hairs fly apart4 ,both of these effects are best secured on a dry day1 because on a damp day the water particles in the air will let the electrons pass to them as fast as they are rubbed up to the surface of the hair4 ,,inference ,,exercise ,explain the following3 #bia4 ,if you shuffle your feet on a carpet in clear1 cold weather and then touch a person's nose or ear1 a slight spark passes from your finger and stings him4 #bib4 ,if you stay out in the cold long1 you get chilled through4 #bic4 ,the air and earth in a greenhouse are warmed by the sun through the glass even when it is cold outside and when the glass itself remains cold4 #bid4 ,when you hold a blade of grass taut between your thumbs and blow on it1 you get a noise4 #bie4 ,shadows are usually black4 #bif4 ,some women keep magnets with which to find lost needles4 #big4 ,you can grasp objects much more firmly with pliers than with your fingers4 #bih4 ,if the glass in a mirror is uneven1 the image of your face is unnatural4 #bii4 ,a sweater clings close to your body4 #cjj4 ,kitchens1 bathrooms1 and hospitals should have painted walls4 ,,chapter ,,eight ,,electricity ,,section #cc4 ,making electricity flow4 ,what causes a battery to produce electricity8 ,what makes electricity come into our houses8 ,the kind of electricity you get from rubbing 7friction7 is not of much practical use1 you remember4 ,men had to find a way to get a steady current of electricity before they could make electricity do any work for them4 ,the difference between static electricity--when it leaps from one thing to another--and flowing electricity is a good deal like the difference between a short shower of rain and a river4 ,both rain and river are water1 and the water of each is moving from one place to another2 but you cannot get the raindrops to make any really practical machine go1 while the rivers can do real work by turning the wheels in factories and mills4 ,within the past century two devices for making electricity flow and do work have been perfected3 ,one of these is the electric battery2 the other is the dynamo4 ,,the ,,electric ,,battery4 ,a battery consists of two pieces of different kinds of metal1 or a metal and some carbon1 in a chemical solution4 ,if you hang a piece of zinc and a carbon1 such as comes from an arc light1 in some water1 and then dissolve sal ammoniac in the water1 you will have a battery4 ,some of the molecules of the sal ammoniac divide into two parts when the sal ammoniac gets into the water1 and the molecules continue to divide as long as the battery is in use or until it wears out4 ,one part of each molecule has an unusually large number of electrons2 the other part has unusually few4 ,the parts with unusually large numbers of electrons gather around the zinc2 so the zinc is negatively charged1--it has more than the ordinary number of electrons4 ,the part of the sal ammoniac with unusually few electrons goes over to the carbon2 so the carbon is positively charged1--it has fewer than the ordinary number of electrons4 ,,making ,,the ,,current ,,flow4 ,now if we can make some kind of bridge between the carbon and the zinc1 the electrons will flow from the place where there are many to the place where there are few4 ,electrons can flow through copper wire very easily4 ,so if we fasten one end of the copper wire to the carbon and the other end to the zinc1 the electrons will flow from the zinc to the carbon as long as there are more electrons on the zinc2 that is1 until the battery wears out4 ,therefore we have a steady flow of electricity through the wire4 ,while the electricity is flowing from one pole to the other1 we can make it do work4 ,,experiment #fd4 ,set up two or three ,samson cells4 ,they consist of a glass jar1 an open zinc cylinder1 and a smaller carbon cylinder4 ,dissolve a little over half a cup of sal ammoniac in water and put it into the glass jar2 then fill the jar with water up to the line that is marked on it4 ,put the carbon and zinc which are attached to the black jar cover into the jar4 ,be careful not to let the carbon touch the zinc4 ,one of these cells will probably not be strong enough to ring a doorbell for you2 so connect two or three together in series as follows3 ,fasten a piece of copper wire from the carbon of the first cell to the zinc of the second4 ,if you have three cells1 fasten another piece of wire from the carbon of the second cell to the zinc of the third1 as shown in ,figure #aaa4 ,fasten one end of a copper wire to the zinc of the first cell and the other end of this wire to one binding post of an electric bell4 ,fasten one end of another piece of copper wire to the carbon of the third cell1 if you have three1 and touch the other end of this wire to the free binding post of the electric bell4 ,if you have everything connected rightly1 the bell should ring4 ,illustration3 ,,fig4 #aaa4 ,a wet battery of three cells connected to ring a bell4 ,,different ,,kinds ,,of ,,batteries4 ,there are many different kinds of batteries4 ,the one you have just made is a simple one frequently used for doorbells4 ,other batteries are more complicated4 ,some are made with copper and zinc in a solution of copper sulfate2 some1 even1 are made by letting electricity from a dynamo run through a solution from one lead plate to another until a chemical substance is stored on one of them2 then1 when the two lead plates are connected by a wire1 the electrons run from one to the other4 ,this kind of battery is called a storage battery1 and it is much used in submarines and automobiles4 ,illustration3 ,,fig4 #aab4 ,a battery of three dry cells4 ,but all the different batteries work on the same general principle3 ,a chemical solution divides into two parts1 one with many electrons and the other with a less number4 ,one part of the solution gathers on one pole 7piece of metal in the solution7 and charges it positively2 the other part gathers on the other pole and charges it negatively4 ,then the electricity flows from one pole to the other4 ,,positive ,,and ,,negative ,,poles4 ,before people knew anything about electrons1 they knew that electricity flowed from one pole of a battery to the other4 ,but they always said that it flowed from the carbon to the zinc2 and they called the carbon the positive pole and the zinc the negative4 ,although we now know that the electrons flow from the zinc to the carbon1 it is much more convenient to use the old way of speaking1 as was explained on page #aii4 ,practically1 it makes no difference which way the electrons are going as long as a current of electricity is flowing through the wire from one pole of the battery to the other pole4 ,so every one speaks of electricity as flowing from the positive pole of a battery 7usually the carbon or copper7 to the negative pole 7usually the zinc71 although the electrons actually move in the other direction4 ,illustration3 ,,fig4 #aac4 ,a storage battery4 ,batteries make enough electricity flow to do a good deal of work4 ,but they are rather expensive1 and it takes a great many to give a flow of electricity sufficient for really heavy work1 such as running street cars or lighting a city4 ,fortunately there is another way of getting large amounts of electricity to flow4 ,this is by means of dynamos4 ,,how ,a ,,dynamo ,,makes ,a ,,current ,,flow4 ,to understand a dynamo1 you must first realize that there are countless electrons in the world--perhaps all things are made entirely of them4 ,but you remember that when we want to get these electrons to do work we must make them flow4 ,this can be done by spinning a loop of wire between the poles of a magnet4 ,whenever a loop of wire is turned between the two poles of a magnet1 the magnetism pushes the electrons that are already in the wire around and around the loop4 ,as long as we keep the loop spinning1 a current of electricity flows4 ,illustration3 ,,fig4 #aad4 ,spinning loops of wire between the poles of a magnet causes a current of electricity to flow through the wire4 ,if only one loop of wire is spun between the poles of a magnet1 the current is very feeble4 ,if you loop the wire around twice1 as shown in ,figure #aad1 the magnet acts on twice as much of the wire at the same time2 so the current is stronger4 ,if a very long piece of wire is used and is looped around many times1 and the whole coil is spun rapidly between the poles of a powerful magnet1 myriads of the electrons in the wire rush around and around the loops--a powerful current of electricity flows through the wire4 ,illustration3 ,,fig4 #aae4 ,the more loops there are1 the stronger the current4 ,now suppose you bring one loop of the long wire out1 as shown in ,figure #aae1 and suppose you spin the rest of the loops between the poles of the magnet4 ,then1 to flow through the loops by the magnet the electricity will have to go clear out through the long loop and back again4 ,while it is flowing through this long loop1 we can make it work4 ,we can cut the long loop and attach one broken end to one part of an electric lamp and the other end to the other part1 so that the electricity has to flow through the lamp in order to get back to the spinning coil of wire1 as shown in ,figure #aaf4 ,such an arrangement as this is really an extremely simple dynamo4 ,illustration3 ,,fig4 #aaf4 ,if the electricity passes through a lamp on its way around the circuit the filament of the lamp glows4 ,illustration3 ,,fig4 #aag4 ,a dynamo in an electric light plant4 ,you could make a dynamo that would actually work1 by arranging such an apparatus so that the coil would spin between the poles of the magnet4 ,but of course the big commercial dynamos are very much more complicated in their construction4 ,figure #aaf shows only the general principle on which they work4 ,the main point to note is that by spinning a coil of wire between the poles of a magnet1 you can make electricity flow rapidly through the wire4 ,and it is in this way that most of the electricity we use is made4 ,the power spinning the coil of wire is sometimes steam1 and sometimes gasoline or distillate2 and water power is very often used4 ,a large amount of our electricity comes from places where there are waterfalls4 ,niagara1 for instance1 turns great dynamos and generates an enormous amount of electricity4 ,,why ,,many ,,automobiles ,,have ,,to ,,be ,,cranked4 ,in an automobile1 the magneto is a little dynamo that makes the sparks which explode the gasoline4 ,while the automobile is going the engine spins the coil of wire between the magnets1 but at starting you have to spin the coil yourself2 and doing that is called cranking the automobile4 ,self-starters have a battery and motor to spin the coil for you until the engine begins to go2 then the engine turns the coil of the magneto4 ,,how ,,old-,,fashioned ,,telephones ,,are ,,rung4 ,the old-fashioned telephones1 still often used in the country1 have little cranks that you turn to ring for central4 ,the crank turns a coil of wire between the poles of the magnet and generates the electricity for ringing the bell4 ,these little dynamos1 like those in automobiles1 are usually called magnetos4 ,illustration3 ,,fig4 #aah4 ,the magneto in an automobile is a small dynamo4 ,,alternating ,,current4 ,for the sake of simplicity and convenience we speak of electricity as always flowing in through one wire and out through the other4 ,with batteries this is actually the case4 ,it is also the case where people have what is called direct-current 7d4 c47 electricity4 ,but it is easier to raise and lower the voltage 7pressure7 of the current if instead of being direct it is alternating2 that is1 if for one instant the electricity flows in through one wire and out through the other1 the next instant flowing the opposite way1 then the first way again1 and so on4 ,this kind of current is called alternating current 7a4 c471 because the current alternates1 coming in the upper wire and out of the lower for a fraction of a second2 then coming in the lower and out of the upper for the next fraction of a second2 then coming in the upper again and out of the lower for a fraction of a second2 and so on1 back and forth1 all the time4 ,for heating and lighting1 this alternating current is just as good as the direct current1 and it is probably what you have in your own home4 ,for charging storage batteries and making electromagnets1 separating water into two gases1 and for running certain kinds of motors1 however1 the direct current is necessary4 ,find out whether the current in your laboratory is direct or alternating4 ,,application #di4 ,explain why we need fuel or water to generate large currents of electricity2 how we can get small amounts of electricity to flow without using dynamos2 why automobiles must be cranked unless they have batteries to start them4 ,,inference ,,exercise ,explain the following3 #cja4 ,mexican water jars are made of porous clay2 the water that seeps through keeps the water inside cool4 #cjb4 ,when you crank an automobile1 electricity is generated4 #cjc4 ,potatoes will not cook any more quickly in water that is boiling violently than in water that is boiling gently4 #cjd4 ,when you brush your hair on a winter morning1 it sometimes stands up and flies apart more and more as you continue to brush it4 #cje4 ,you cannot see a person clearly through a ground-glass window1 although it lets most of the light through4 #cjf4 ,there is a layer of coarse1 light-colored gravel over the tar on roofs1 to keep the tar from melting4 #cjg4 ,it is very easy to slip on a well-waxed hardwood floor4 #cjh4 ,if you have a silver filling in one of your teeth and you touch the filling with a fork or spoon1 you get a slight shock4 #cji4 ,you can shake a thing down into a bottle when it will not slip down by itself4 #caj4 ,if you rub a needle across one pole of a magnet three or four times in the same direction1 then float it on a cork in water one end of the needle will point north4 ,,section #cd4 ,conduction of electricity4 ,how does electricity travel8 ,why do you get a shock if your hands are wet when you touch a live wire8 ,if you were to use a piece of string instead of a copper wire to go from one pole of a battery to another or to spin between the poles of the magnet of the dynamo1 you could get no flow of electricity to speak of4 ,electrons do not flow through string easily1 but they flow through a copper wire very easily4 ,anything that carries1 or conducts1 electricity well is called a good conductor4 ,anything that carries it poorly is called a poor conductor4 ,anything that allows practically no electricity to pass through it is called an insulator4 ,,experiment #fe4e ,turn on an electric lamp4 ,turn it off by opening the knife switch4 ,cover the blade of the knife switch with a fold of paper and close it4 ,will the lamp glow8 ,try a fold of dry cloth2 a fold of the same cloth wet4 ,connect the blade to the slot with a piece of iron2 with a piece of glass2 with porcelain2 with rubber2 with dry wood2 with wood that is soaking wet2 with a coin4 ,which of these are good conductors of electricity8 ,which could be used as insulators8 ,footnote #e3 ,read footnote1 page #bbf1 before doing this experiment4 ,illustration3 ,,fig4 #aai4 ,electricity flows through the coin4 ,,how ,,you ,,can ,,get ,,an ,,electrical ,,shock4 ,a person's body is not a very good conductor of electricity1 but will conduct it somewhat4 ,when electricity goes through your body1 you get a shock4 ,the shock from the ordinary current of electricity1 #aaj volts1 is not enough to injure you at all2 in fact1 if you were standing on dry wood1 it would be safe1 although you would get a slight shock1 to connect the blade of a knife switch to the slot of the switch1 through your hand or body4 ,your body would not allow enough current to pass through it to light the lamp4 ,stronger currents1 like those of power lines and even trolley wires1 are extremely dangerous4 ,all the electric wires entering your house are made of copper4 ,they are all covered with cloth and rubber and are fastened with glass or porcelain knobs4 ,the reason is simple3 ,copper and practically all other metals are very good conductors of electricity2 that is1 they allow electricity to pass through them very easily4 ,cloth1 rubber1 glass1 and porcelain are very poor conductors1 and they are therefore used as insulators1--to keep the electricity from going where you do not want it to go4 ,illustration3 ,,fig4 #abj4 ,will electricity go through the glass8 ,,experiment #ff4 ,to each binding post of an electric bell fasten a piece of insulated copper wire with bare ends and at least #d feet long4 ,connect the free end of one of these wires with one pole of a battery1 using a regular laboratory battery or one you made yourself4 ,attach one end of another piece of wire a foot or so long1 with bare ends1 to the other pole of the battery4 ,touch the free end of this short wire to the free end of the long wire1 as shown in ,figure #abj4 ,does the bell ring8 ,if it does not1 something is wrong with the connection or with the battery2 fix them so that the bell will ring4 ,now leave a gap of about an inch between the free end of the long wire and the free end of the short wire4 ,try making the electricity flow from the short wire into the long one through a number of different things1 such as string1 a key1 a knife1 a piece of glass tubing1 wet cloth1 dry cloth1 rubber1 paper1 a nail1 a dish of mercury 7dip the ends of the wire into the dish so that they both touch the mercury at the same time71 a dish of water1 a stone1 a pail1 a pin1 and anything else that you may like to try4 ,illustration3 ,,fig4 #aba4 ,electrical apparatus3 ,a1 plug fuse2 ,b1 cartridge fuse2 ,c1 knife switch2 ,d1 snap switch2 ,e1 socket with nail plug in it2 ,f1 fuse gap2 ,g1 flush switch2 ,h1 lamp socket2 ,i1 ,j1 ,k1 resistance wire4 ,each thing that makes the bell ring is a good conductor4 ,each one that will not make it ring is a poor conductor or an insulator4 ,make a list of the things you have tried2 in one column note the good conductors1 and in another column note the insulators and poor conductors4 ,the water and wet cloth did not ring the bell1 but this is because the pressure or voltage of the electricity in the batteries is not very high4 ,in dealing with high-power wires it is much safer to consider water1 or anything wet1 as a pretty good conductor of electricity4 ,absolutely pure1 distilled water is an extremely poor conductor2 but most water has enough minerals dissolved in it to make it conduct electricity fairly well4 ,in your list you had better put water and wet things in the column with the good conductors4 ,,application #ej4 ,robbers had cut the telegraph line between two railroad stations 7,fig4 #abb74 ,the broken ends of the wire fell to the ground1 a number of feet apart4 ,a farmer caught sight of the men speeding away in an automobile and he saw the cut wires on the ground4 ,he guessed that they had some evil purpose and decided to repair the damage4 ,he could not bring the two ends of the wire together4 ,he ran to his barn and found the following things there3 ,a ball of cord1 a pickax1 a crowbar1 some harness1 a wooden wagon tongue1 a whip1 a piece of iron wire around a bale of hay 7the wire was not long enough to stretch the whole distance between the two ends of the telegraph wire1 even if you think he might have used it to patch the gap71 a barrel with four iron hoops1 and a rope4 ,which of these things could he have made use of in connecting the broken ends of the telegraph wire8 ,illustration3 ,,fig4 #abb4 ,which should he choose to connect the broken wires8 ,,application #ea4 ,a man was about to put in a new socket for an electric lamp in his home4 ,he did not want to turn off the current for the whole house1 as it was night and there was no gas to furnish light while he worked4 ,i've heard that if you keep your hands wet while you work1 the film of water on them will keep you from getting a shock1 his wife said4 ,don't you wet your hands1 ,father1 said his #ab-year-old boy2 keep them dry1 and handle the wires with your pliers1 so that you won't have to touch it4 ,i advise you to put on your canvas gloves while you work2 then you can't get a shock1 added another member of the family4 ,that's a good idea1 said the wife1 but wet the gloves1 then you will have the double protection of the water and the cloth4 ,the man laughed and went to work on the socket4 ,he did not get a shock4 ,which advice1 if any1 do you think he followed8 ,,inference ,,exercise ,explain the following3 #caa4 ,a red postage stamp looks greenish gray in the green light of a mercury-vapor lamp4 #cab4 ,cracks are left between sections of the roadbed in cement auto highways4 #cac4 ,electricity goes up a mountain through a wire4 #cad4 ,it is impossible to stand sidewise against a wall on one foot1 when that foot touches the wall4 #cae4 ,a charged storage battery will run an electric automobile4 #caf4 ,an empty house is noisier to walk in and talk in than is a furnished one4 #cag4 ,lightning rods are made of metal4 #cah4 ,it is harder to hold a frying pan by the end of the handle than by part of the handle close to the pan4 #cai4 ,diamonds flash many colors4 #cbj4 ,in swimming1 if you have hold of a fastened rope and try to pull it toward you1 you go toward it4 ,,section #ce4 ,complete circuits4 ,why does a doorbell ring when you push a button8 ,why is it that when you touch one electric wire you feel no shock1 while if you touch two wires you sometimes get a shock8 ,when a wire is broken in an electric light1 why does it not light8 ,suppose you have some water in an open circular trough like the one shown in ,figure #abc4 ,then suppose you have a paddle and keep pushing the water to your right from one point4 ,the water you push pushes the water next to it1 that pushes the water next to it1 and so on all around the trough until the water just behind your paddle pushes in toward the paddle2 the water goes around and around the trough in a complete circuit4 ,there never is too much water in one place2 you never run out of water4 ,but then suppose a partition is put across the trough somewhere along the circuit4 ,when the water reaches that1 it cannot pass2 it has no place to flow to1 and the current of water stops4 ,,the ,,electric ,,circuit4 ,the flow of electricity in an electric circuit may be compared to the flow of the water in the tank we have been imagining4 ,the long loop of wire extending out from the dynamo to your house and back again corresponds to the tank4 ,the electricity corresponds to the water4 ,your dynamo pushes the electricity around and around the circuit1 as the paddle pushes the water4 ,but let some one break the circuit by putting a partition between two parts of it1 and the electricity immediately stops flowing4 ,one of the most effective partitions we can put into an electric circuit is a gap of air4 ,it is very difficult for any electricity to flow through the air2 so if we simply cut the wire in two1 electricity can no longer flow from one part to the other1 and the current is broken4 ,illustration3 ,,fig4 #abc4 ,electricity flows around a completed circuit somewhat as water might be made to flow around this trough4 ,,breaking ,,and ,,making ,,the ,,circuit4 ,the most convenient way to put an air partition into an electric circuit and so to break it1 or to close the circuit again so it will be complete1 is to use a switch4 ,,experiment #fg4 ,in the laboratory1 examine the three different kinds of switches where the electricity flows into the lamp and resistance wire and then out again4 ,trace the path the electricity must take from the wire coming into the building down to the first switch that it meets2 then from one end of the wire through the brass or copper to which the wire is screwed1 through the switch and on out into the end of the next piece of wire4 ,turn the first switch off and see how a partition of air is made between the place where the electricity comes in and the place where it would get out if it could4 ,turn the switch on and notice how this gives the electricity a complete path through to the next piece of wire4 ,in this way follow the circuit on through all the switches to the electric lamp4 ,if you examine the socket into which the lamp screws and examine the lamp itself1 you will see that electricity which goes to the outer part of the socket passes into the rim of the lamp2 from here it goes into one end of the filament4 ,it passes through the filament to the other end1 which is connected to the little brass disk at the end of the lamp4 ,from this you can see that it goes into the center point of the socket1 and then on into the second wire that connects to the socket4 ,trace the current on back through this other wire until you see where this wire leads toward the dynamo4 ,you should understand that the electric lamp1 the switches1 the fuses1 all things along the circuit1 are simply parts of the long loop from the dynamo1 as shown in ,figure #abd4 ,,connecting ,,in ,,parallel4 ,the trouble with ,figure #abd is that it is a little too simple4 ,from looking at it you might think that the loop entered only one building4 ,and it might seem that turning off one switch would shut off the electricity all along the line4 ,it would1 too1 if the circuit were arranged exactly as shown above4 ,to avoid this1 and for other reasons1 the main loop from the dynamo has branches so that the electricity can go through any or all of them at the same time and so that shutting off one branch will not affect the others4 ,electricians call this connecting in parallel2 there are many parallel circuits from one power house4 ,illustration3 ,,fig4 #abd4 ,diagram of the complete circuit through the laboratory switches4 ,figure #abe illustrates the principle just explained4 ,as there diagrammed1 the electricity passes out from the dynamo along the lower wire and goes down the left-hand wire of circuit ,a through one of the electric lamps that is turned on1 and then it goes back through the right-hand wire of the ,a circuit to the upper wire of the main circuit and then on back to the dynamo4 ,but only a part of the electricity goes through the ,a circuit2 part goes on to the ,b circuit1 and there it passes partly through the electric iron4 ,then it goes back through the other wire to the dynamo4 ,no electricity can get through the electric lamp on the ,b circuit1 because the switch to the lamp is open4 ,the switch on the ,c circuit is open2 so no electricity can pass through it4 ,the purpose of the diagram is to show that electricity from the dynamo may go through several branch circuits and then get back to the dynamo1 and that shutting off the electricity from one branch circuit does not shut it off from the others4 ,and the purpose of this section is to make it clear that electricity can flow only through a complete circuit2 it must have an unbroken path from the dynamo back to the dynamo again or from one pole of the battery back to the other pole4 ,if the electricity does not have a complete circuit1 it will not flow4 ,,application #eb4 ,a small boy disconnected the doorbell batteries from the wires that ran to them1 and when he wanted to put the wires back1 he could not remember how they had been connected4 ,he tried fastening both wires to the carbon part of the battery1 connecting one wire to the carbon and one to the zinc1 and connecting both to the zinc4 ,then he decided that one wire was all that had to be connected anyway1 that the second was simply to make it stronger4 ,which of the ways he tried1 if any1 would have been right8 ,illustration3 ,,fig4 #abe4 ,parallel circuits4 ,illustration3 ,,fig4 #abf4 ,how should he connect them8 ,,application #ec4 ,dorothy was moving4 ,when they took out our telephone1 she said to her chum1 ,helen1 the electrician just cut the wires right off4 ,he must have turned off the electricity first1 ,helen answered1 or else it would all have run out of the cut ends of the wire and gone to waste4 ,why1 it couldn't1 ,dorothy said4 ,electricity won't flow off into the air4 ,of course it can if there is nothing to hold it in1 ,helen argued4 ,which was right8 ,,inference ,,exercise ,explain the following3 #cba4 ,it is very easy to get chilled when one is perspiring4 #cbb4 ,ice cream becomes liquid if you leave it in your dish too long4 #cbc4 ,you should face forward when alighting from a street car4 #cbd4 ,there are always at least two electric wires going into a building that is wired4 #cbe4 ,woolen sweaters keep you warm4 #cbf4 ,steel rails are not riveted to railroad ties but the spikes are driven close to each rail so that the heads hook over the edge and hold the rail down without absolutely preventing its movement forward and backward4 ,why should rails be laid in this way8 #cbg4 ,the earth keeps whirling around the sun without falling into it1 although the pull from the sun is very great4 #cbh4 ,electricity is brought down from power houses in the mountains by means of cables4 #cbi4 ,white clothes are cooler than black when the person wearing them is out in the sun4 #ccj4 ,all the street cars along one line are stopped when a trolley wire breaks4 ,,section #cf4 ,grounded circuits4 ,why can a bird sit on a live wire without getting a shock1 while a man would get a shock if he reached up and took hold of the same wire8 ,we have just been laying emphasis on the fact that for electricity to flow out of a dynamo or battery1 it must have a complete circuit back to the battery or dynamo4 ,yet only one wire is needed in order to telegraph between two stations4 ,likewise1 a single wire could be made to carry into a building the current for electric lights4 ,this is because the ground can carry electricity4 ,if you make all connections from a battery or dynamo just as for any complete circuit1 but use the earth for one wire1 the electricity will flow perfectly well 7,fig4 #abg74 ,to connect an electric wire with the earth1 the wire must go down deep into the ground and be well packed with earth2 but since water pipes go down deep and the earth is already packed around them1 the most convenient way to ground a circuit is to connect the wire that should go into the ground with the water pipe4 ,the next experiment1 the grounding of a circuit1 should be done by the class with the help of the teacher4 ,illustration3 ,,fig4 #abg4 ,the ground can be used in place of a wire to complete the circuit4 ,,experiment #fh4 ,caution3 ,keep the switches turned off throughout this experiment4#f ,footnote #f3 ,all through this chapter it is assumed that the electrical apparatus described in the appendix is being used4 ,in this apparatus all the switches are on one wire1 the other wire being alive even when the switches are turned off4 7a7 ,put a piece of fuse wire across the fuse gap4 ,screw the plug with nails in it into the lamp socket4 ,connect the bare end of a piece of insulated wire to the water faucet and touch the other end to one nail of the plug4 ,if nothing happens1 touch it to the other nail instead4 ,the electricity has gone down into the ground through the water pipe1 instead of into the other wire4 ,the ground carries the electricity back to the dynamo just as a wire would4 7b7 ,put a new piece of fuse wire across the gap4 ,keep switches turned off4 ,touch the brass disk at the bottom of an electric lamp to the nail which worked1 and touch the wire from the faucet to the other brass part of the lamp 7,fig4 #abi74 ,what happens8 ,caution3 ,under no circumstances allow the switch to be turned on while you are doing any part of this experiment4 ,under no circumstances touch the wire from the faucet to the binding posts of the fuse gap4 ,do only as directed4 ,explain what would happen if you disobeyed these rules4 ,illustration3 ,,fig4 #abh4 ,grounding the circuit4 ,the faucet and water pipe lead the electricity to the ground4 ,,why ,a ,,bird ,,is ,,not ,,electrocuted ,,when ,,it ,,sits ,,on ,a ,,live ,,wire4 ,if a man accidentally touches a live wire that carries a strong current of electricity he is electrocuted2 yet birds perch on such a wire in perfect safety4 ,if a man should leap into the air and grasp a live wire1 hanging from it without touching the ground1 he would be no more hurt by it than a bird is4 ,a person who is electrocuted by touching such a wire must at the same time be standing on the ground or on something connected with it4 ,the ground completes the electric circuit which passes through the body4 ,an electric circuit can always be completed through the ground1 and when this is done1 it is called grounding a circuit4 ,illustration3 ,,fig4 #abi4 ,how the lamp and wire are held to ground the circuit4 ,,application #ed4 ,explain why only one wire is needed to telegraph between two stations2 why you should not turn an electric light on or off while standing in a tub of water4 ,,application #ee4 ,in a house in the country1 the electric wires passed through a double wall4 ,they were separated from each other and well covered with insulation1 but they were not within an iron pipe1 as is now required in many cities4 ,the current was alternating4 ,one night when the lights were out a rat in the wall gnawed through the insulation of the wire and also gnawed clear through one of the wires4 ,did he get a shock8 ,the next morning1 the woman of the house wanted to use the electric iron in the kitchen and it would not work4 ,the kitchen had in it a gas stove1 a sink with running water1 a table1 a couple of chairs1 and the usual kitchen utensils4 ,there was also a piece of wire about long enough to reach across the kitchen4 ,the electrician could not come out for several hours1 and the woman wanted very much to do her ironing4 ,figure #acj is a diagram of the wires and the kitchen4 ,show what the woman might have done in order to use her iron until the electrician arrived4 ,illustration3 ,,fig4 #acj4 ,how can the electric iron be used after one wire has been cut8 ,,application #ef4 ,a man wanted to change the location of the wiring in his cement-floored garage4 ,while he was working1 would it have been best for him to stand on the bare cement floor1 on a wire mat1 on an old automobile tire1 on a wet rug1 or on some skid chains that were there8 ,,inference ,,exercise ,explain the following3 #cca4 ,an ungreased wheel squeaks4 #ccb4 ,lightning rods extend into the earth4 #ccc4 ,a banjo player moves his fingers toward the drum end of the banjo when he plays high notes4 #ccd4 ,when the filament breaks1 an electric lamp will no longer glow4 #cce4 ,an inverted image is formed by the lens of a camera4 #ccf4 ,a blown-out fuse may be replaced temporarily with a hairpin or with a copper cent4 #ccg4 ,sparks fly when a horse's shoe hits a stone4 #cch4 ,a room requires less artificial light if the wall paper is light than if it is dark4 #cci4 ,phonographs usually have horns1 either inside or outside4 #cdj4 ,an electric car needs only one wire to make it go4 ,,section #cg4 ,resistance4 ,what makes an electric heater hot8 ,why does lightning kill people when it strikes them8 ,what makes an electric light glow8 ,we have talked about making electricity work when it flows in a steady stream1 and everybody knows that it makes lights glow1 makes toasters and electric stoves hot1 and heats electric irons4 ,but did it ever strike you as remarkable that the same electricity that flows harmlessly through the wires in your house without heating them1 suddenly makes the wire in your toaster or the filament in your incandescent lamp glowing hot8 ,the insulation is not what keeps the wire cool1 as you can see by the next experiment4 ,,experiment #fi4 ,between two of the laboratory switches you will find one piece of wire which has no insulation4 ,turn on the electricity and make the lamp glow2 see that you are standing on dry wood and are not touching any pipes or anything connected to the ground4 ,feel the bare piece of wire with your fingers4 ,why does this not give you a shock8 ,what would happen if you touched your other hand to the gas pipe or water pipe8 ,do not try it6 ,but what would happen if you did8 ,the reason that the filament of the electric lamp gets white hot while the copper wire stays cool is this3 ,all substances that conduct electricity resist the flow somewhat2 there is something like friction between the wire and the electricity passing through it4 ,the smaller around a wire is1 the greater resistance it offers to the passing of an electric current4 ,the filament of an electric lamp is very fine and therefore offers considerable resistance4 ,however1 if the filament were made of copper1 even as fine as it is1 it would take a much greater flow of electricity to make it white hot1 and it would be very expensive to use4 ,so filaments are not made of copper but of substances which do not conduct electricity nearly as well and which therefore have much higher resistance4 ,carbon was once used1 but now a metal called tungsten is used for most incandescent lamps4 ,both carbon and tungsten resist an electric current so much that they are easily heated white hot by it4 ,on the other hand1 they let so little current through that what does pass flows through the larger copper wires very easily and does not heat them noticeably4 ,illustration3 ,,fig4 #aca4 ,feeling one live wire does not give her a shock1 but what would happen if she touched the gas pipe with her other hand8 ,,experiment #gj4 ,turn on the switch that lets the electricity flow through the long resistance wire that passes around the porcelain posts4 ,watch the wire4 ,the resistance wire you are using is an alloy1 a mixture of metals that will resist electricity much more than ordinary metals will4 ,this is the same kind of wire that is used in electric irons and toasters and heaters4 ,it has so great a resistance to the electricity that it is heated red hot1 or almost white hot1 by the electricity passing through it4 ,,application #eg4 ,a power company wanted to send large quantities of electricity down from a mountain4 ,should the company have obtained resistance wire or copper wire to carry it8 ,should the wire have been large or fine8 ,,application #eh4 ,a firm was making electric toasters4 ,in the experimental laboratory they tried various weights of resistance wire for the toasters4 ,they tried a very fine wire1 ,no4 #cj2 a medium weight wire1 ,no4 #bd2 and a heavy wire1 ,no4 #ah4 ,one of these wires did not get hot enough1 and it took so much electricity that it would have been too expensive to run2 another got so hot that it soon burned out4 ,one worked satisfactorily4 ,which of the three sizes burned out8 ,which was satisfactory8 ,,inference ,,exercise ,explain the following3 #cda4 ,if you attach one end of a wire to a water faucet and connect the other end to an electric lamp in place of one of the regular lighting wires1 the lamp will light4 #cdb4 ,the needle of a sewing machine goes up and down many times to each stroke of the treadle4 #cdc4 ,trolley wires are bare4 #cdd4 ,if you had rubbers on your feet1 you could take hold of one live wire with perfect safety1 provided you touched nothing else4 #cde4 ,if you were on the moon1 you would look up at the earth4 #cdf4 ,toy balloons burst when they go high up where the air is thin4 #cdg4 ,you have to put on the brakes to stop a car quickly4 #cdh4 ,telephone wires are strung on glass supporters4 #cdi4 ,if you pour boiling water into a drinking glass1 frequently the glass will crack4 #cej4 ,an asbestos mat tends to keep food from burning4 ,illustration3 ,,fig4 #acb4 ,pencils ready for making an arc light4 ,,section #ch4 ,the electric arc4 ,how can electricity set a house on fire8 ,,this ,,is ,,one ,,of ,,the ,,most ,,important ,,sections ,,in ,,the ,,book4 ,do you know that you can make an arc light with two ordinary pencils8 ,the next experiment1 which should be done by the class with the help of the teacher1 shows how to do it4 ,,experiment #ga4 ,sharpen two pencils4 ,about halfway between the point and the other end of each pencil cut a notch all the way around and down to the lead1 or burn a notch down by means of the glowing resistance wire4 ,what you call the lead of the pencil is really graphite1 a form of carbon4 ,the leads of your two pencils are almost exactly like the carbons used in arc lights1 except1 of course1 that they are much smaller4 ,turn off the electricity both at the snap switch and at the knife switch4 ,fasten the bare end of a #b-;foot piece of fine insulated wire 7about ,no4 #bd7 around the center of the lead in each pencil so that you get a good contact1 as shown in ,figure #acb4 ,fasten the other bare end of each wire to either side of the open knife switch so that when this switch is open the electricity will have to pass down one wire to the lead of one pencil1 from that to the lead of the other pencil1 and from that back through the second wire to the other side of the knife switch and on around the circuit1 as shown in ,figure #acc4 ,keep the two pencils apart and off the desk1 while some one turns on the snap switch and the flush switch that lets the electricity through the resistance wire4 ,now bring the pencil points together for an instant1 immediately drawing them apart about half an inch4 ,you should get a brilliant white arc light4 ,caution3 ,do not look at this brilliant arc for more than a fraction of a second unless you look through a piece of smoked or colored glass4 ,blow out the flame when the wood catches fire4 ,after you have done this two or three times1 the inside of the wood below the notches will be burned out so completely that you can pull it off with your fingers1 leaving the lead bare all the way up to the wires4 ,let the class stand well back and watch the teacher do the next part of the experiment4 ,connect two heavy insulated copper wires1 about ,no4 #ab1 to the sides of the knife switch just as you connected the fine wires4 ,but this time bring the ends of the copper wires themselves together for an instant1 then draw them apart4 ,hold the ends of the wires over the zinc of the table while you do this1 as melted copper will drop from them4 ,illustration3 ,,fig4 #acc4 ,the pencil points are touched together and immediately drawn apart4 ,illustration3 ,,fig4 #acd4 ,a brilliant arc light is the result4 ,,what ,,happens ,,when ,,an ,,arc ,,is ,,formed4 ,what happens when you form an electric arc is this3 ,as you draw the two ends of the pencils apart1 only a speck of the lead in each touches the other4 ,the electricity passing for an instant through the last speck at the end of the pencil makes it so hot that it turns to vapor4 ,the vapor will let electricity go through it1 and makes a bridge from one pencil point to the other4 ,but the vapor gets very hot1 because it has a rather high resistance4 ,this heat vaporizes more carbon and makes more vapor for the electricity to pass through1 and so on4 ,the electricity passing through the carbon vapor makes it white hot1 and that is what causes the brilliant glow4 ,regular arc lights are made exactly like this experimental one1 except that the carbons used are much bigger and are made to stand the heat better than the small carbons in your pencil4 ,carbon is one of those substances that turn directly from a solid to a gas without first melting4 ,that is one reason why it is used for arc lights4 ,but copper melts when it becomes very hot1 as you saw when you made an arc light with the copper wires4 ,so copper cannot be used for practical arc lights4 ,,fires ,,caused ,,by ,,arcs4 ,there is one extremely important point about this experiment with arcs3 most fires that result from defective wiring are caused by the forming of arcs4 ,you see1 if two wires touch each other while the current is passing and then move apart a little1 an arc is formed4 ,and you have seen how intensely hot such an arc is4 ,two wires rubbing against each other1 or a wire not screwed tightly to its connection1 can arc4 ,a wire broken1 but with its ends close enough together to touch and then go apart1 can cause an arc4 ,and an arc is very dangerous in a house if there is anything burnable near it4 ,wires should never be just twisted together and then bound with tape to form a joint4 ,twisted wires sometimes break and sometimes come loose2 then an arc forms1 and the house catches fire4 ,good wiring always means soldering every joint and screwing the ends of the wires tightly into the switches or sockets to which they lead4 ,illustration3 ,,fig4 #ace4 ,an arc lamp4 ,the carbons are much larger than the carbons in the pencils1 and the arc gives an intense light4 ,,keeping ,,arcs ,,from ,,forming4 ,well-wired houses have the wires brought in through iron pipes1 called conduits1 and the conduits are always grounded2 so if an arc should form anywhere along the line1 the house would be protected by an iron conduit and if one of the loose ends of wire came in contact with the conduit1 the current would rush to the ground through it1 blowing out a fuse4 ,the next section tells about the purpose of fuses4 ,the directions that usually come with electric irons1 toasters1 and stoves say that the connection should be broken by pulling out the plug rather than by turning off the switch4 ,this is because the switch in the electric-light socket sometimes loses its spring and instead of snapping all the way around and quickly leaving a big gap1 it moves only a little way around and an arc is formed in the socket2 if you hear a sizzling sound in a socket1 you may be pretty sure that an arc has been formed4 ,but when you pull the plug entirely out of the iron or stove1 the gap is too big for an arc to form and you are perfectly safe4 ,fire commissions usually condemn extension lights1 because if the insulation wears out on a lamp cord so that the two wires can come in contact1 a dangerous arc may easily form4 ,and the insulation might suddenly be scraped off by something heavy moving across the cord4 ,this can happen whether the light at the end of the cord is turned on or off4 ,so it is best if you have an extension light always to turn it off at the socket from which the cord leads1 not at the lamp itself4 ,many people do not do this1 and go for years without having a fire4 ,but so might you live for years with a stick of dynamite in your bureau drawer and never have an explosion4 ,still1 it is not wise to keep dynamite in your bureau4 ,arc lights themselves1 of course1 are no more dangerous than is a fire in a kitchen stove4 ,for an arc light is placed in such a way that nothing can well come near it to catch fire4 ,the danger from the electric arc is like the danger from gasoline spilled and matches dropped where you are not expecting them1 so that you are not protected against them4 ,fortunately ordinary batteries have not enough voltage to cause dangerous arcs4 ,so you do not have to be as careful in wiring for electric bells and telegraph instruments4 ,it requires the high voltage of a city power line to make a dangerous electric arc4 ,so many fires are caused by electric arcs forming in buildings1 that you had better go back to the beginning of this section and read it all through again carefully4 ,it may save your home and even your life4 ,after you have reread this section1 test your understanding of it by answering the following questions3 #a4 ,how can you make an electric arc8 #b4 ,why should wires not be twisted together to make electric connections8 #c4 ,why should wires be brought into houses and through walls in iron conduits8 #d4 ,why should you pull out the plug of an electric iron1 percolator1 toaster1 heater1 or stove8 #e4 ,why do fire commissions condemn extension lights8 #f4 ,if you use an extension light1 where should it be turned off8 #g4 ,if you hear a sizzling and sputtering in your electric-light socket1 what does it mean8 ,what should you do8 #h4 ,is there any danger in defective sockets with switches that do not snap off completely8 ,what is the danger8 #i4 ,in ,application #ee1 page #bbh1 if the rat had gnawed the wire in two while the electric iron was being used1 would anything have happened to the rat8 ,would there have been any danger to the house8 #aj4 ,where a wire is screwed into an electric-light socket1 what harm1 if any1 might result from not screwing it in tightly8 #aa4 ,how can a wire be safely spliced8 #ab4 ,why is an electric arc in a circuit dangerous8 ,,inference ,,exercise ,explain the following3 #cea4 ,white objects look blue when seen through a blue glass4 #ceb4 ,when you pull the plug out of an electric iron1 the iron cools4 #cec4 ,people who do not hear well sometimes use speaking trumpets4 #ced4 ,the sounding board of a piano is roughly triangular2 the longest strings are the extreme left1 and those to the right get shorter and shorter4 #cee4 ,birds can sit on live wires without getting a shock4 #cef4 ,deaf people can sometimes identify musical selections by holding their hands on the piano4 #ceg4 ,an electric toaster gets hot when a current passes through it4 #ceh4 ,the cord of an electric iron sometimes catches fire while the iron is in use1 especially if the cord is old4 #cei4 ,if a live wire touches the earth or anything connected with it1 the current rushes into the earth4 #cfj4 ,when you stub your toe1 you have to run forward to keep from falling4 ,,section #ci4 ,short circuits and fuses4 ,why does a fuse blow out8 ,sometimes during the evening when the lights are all on in your home1 some one tinkers with a part of the electric circuit or turns on an electric heater or iron1 and suddenly all the lights in that part of the house go out4 ,a fuse has blown out4 ,if you have no extra fuses on hand1 it may be necessary to wait till the next day to replace the one that is blown out4 ,it is always a good idea to keep a couple of extra fuses2 they cost only #aj cents each4 ,and if you do not happen to know how fuses work or how to replace them when they blow out1 it will cost a dollar or so to get an electrician to put in a new fuse4 ,the next three experiments will help you to understand fuses4 ,illustration3 ,,fig4 #acf4 ,a1 the fuse gap and ,b1 the nail plug4 ,,experiment #gb4 ,on the lower wire leading to the electric lamp in the laboratory you will find a gap1 a place where the wire ends in a piece of a knife switch1 and then begins again about an inch away in another piece of the switch1 as shown in ,figure #acf4 ,there must be some kind of wire or metal that will conduct electricity across this gap4 ,but the gap is there to prevent as much electricity from flowing through as might flow through copper wire4 ,so never put copper wire across this gap4 ,if you do1 you will have to pay for the other fuses which may blow out4 ,always keep a piece of fuse wire stretched across the gap4 ,fuse wire is a soft leadlike wire1 which melts as soon as too much electricity passes through it4 ,unscrew the lamp1 and into the socket where it was1 screw the plug with the two nails sticking out of it4 ,turn the electricity on4 ,does anything happen8 ,turn the electricity off4 ,now touch the heads of the two nails together1 or connect them with a piece of any metal1 and turn on the electricity4 ,what happens8 ,examine the pieces of the fuse wire that are left4 ,it was so easy for the electricity to pass through the nails and wire1 that it gushed through at a tremendous rate4 ,this melted the fuse wire1 or blew out the fuse4 ,if the fuse across the gap by the socket had not been the more easily burned out1 one or perhaps both of the more expensive fuses up above1 where the wire comes in1 would have blown out4 ,these cost about #aj cents each to replace1 while the fuse wire you burned out costs only a fraction of a cent4 ,if there were no fuses in the laboratory wirings and you had short circuited the electricity 7given it an easy enough path71 it would have blown out the much more expensive fuses where the electricity enters the building4 ,if there were no big fuses where the electricity enters the building1 the rush of electricity would make all the copper wires through which it flowed inside the building so hot that they would melt and set fire to the building4 ,as long as you keep a piece of fuse wire across the gap1 there is no danger from short circuits4 ,,why ,,fuse ,,wire ,,melts4 ,for two reasons1 the fuse wire melts when ordinary wire would not4 ,first1 it has enough resistance to electricity so that if many amperes 7much current7 flow through1 it gets heated4 ,it has not nearly as much resistance1 however1 as the filament in an electric lamp or even as has the long resistance wire4 ,it does not become white hot as they do4 ,second1 it has a low melting point4 ,it melts immediately if you hold a match to it2 try this and see4 ,consequently1 long before the fuse wire becomes red hot1 it melts in two4 ,it has enough resistance to make it hot as soon as too many amperes flow through2 and it has such a low melting point that as soon as it gets hot it melts in two1 or blows out4 ,this breaks the circuit1 of course1 so that no more electricity can flow4 ,in this way the fuse protects houses from catching fire through short circuits4 ,illustration3 ,,fig4 #acg4 ,what will happen when the pin is thrust through the cords and the electricity turned on8 ,unfortunately1 however1 the fuse is almost no protection against an electric arc4 ,the copper vapor through which the electricity passes in an arc has enough resistance to keep the amperage 7current7 low2 so the arc may not blow out the fuse at all4 ,but if it were not for fuses1 there would be about as much danger of houses being set on fire by short circuits as by arcs4 ,perhaps there would be more danger1 because short circuits are the more common4 ,,experiment #gc4 ,put a new piece of fuse wire across the fuse gap4 ,leave the nail plug screwed in the socket4 ,use a piece of flexible lamp cord--the kind that is made of two strands of wire twisted together 7see ,fig4 #acg74 ,fasten one bared end of each wire around each nail of the nail plug4 ,see that the other ends of the lamp cord are not touching each other4 ,turn on the electricity4 ,does anything happen8 ,turn off the electricity4 ,now put a pin straight through the middle of the two wires4 ,turn on the electricity again4 ,what happens8 ,there is not much resistance in the pin1 and so it allows the electricity to rush through it4 ,people sometimes cause fuses to blow out by pinning pictures to electric lamp wires or by pinning the wires up out of the way4 ,a ,,short ,,circuit ,,an ,,easy ,,circuit4 ,you always get a short circuit when you give electricity an easy way to get from one wire to the other4 ,but you get no current unless you give it some way to pass from one wire to the other1 thus completing the circuit4 ,therefore you should always complete the circuit through something which resists the flow of electricity1 like an electric lamp1 a heater1 or an iron4 ,remember this and you will have the key to an understanding of the practical use of electricity4 ,the term short circuit is a little confusing1 in that electricity may have to go a longer way to be short circuited than to pass through some resistance1 such as a lamp4 ,really a short circuit should be called an easy circuit or something like that1 to indicate that it is the path of least resistance4 ,wherever the electricity has a chance to complete its circuit without going through any considerable resistance1 no matter how far it goes1 we have a short circuit4 ,and since everything resists electricity a little1 a large enough flow of electricity would even heat a copper wire red hot2 that is why a short circuit would be dangerous if you had no fuses4 ,,application #ei4 ,to test your knowledge of short circuits and fuses1 trace the current carefully from the upper wire as it enters the laboratory1 through the plug fuse4 ,show where it comes from to enter the plug fuse1 exactly how it goes through the fuse1 where it comes out1 and where it goes from there4 ,trace it on through the cartridge fuse in the same way1 through all the switches into the lamp socket1 through the lamp1 out of the lamp socket to the fuse gap1 across this to the other wire1 and on out of the room4 ,it goes on from there through more fuses and back to the dynamo from which the other wire comes4 ,test yourself further with the following questions3 #a4 ,where in this circuit is the resistance supposed to be8 #b4 ,what happens when you put a good conductor in place of this resistance if the electricity can get from one wire to the other without passing through this resistance8 #c4 ,why do we use fuses8 #d4 ,what is a short circuit8 #e4 ,what makes an electric toaster get hot8 #f4 ,why should you not stick pins through electric cords8 ,,experiment #gd4 ,take the fuse wire out of the fuse gap and put a single strand of zinc shaving in its place4 ,instead of the nail plug1 screw the lamp into the socket4 ,do not turn on the switch that lets the electricity flow through the resistance wire1 but turn on the electricity so that the lamp will glow4 ,does the zinc shaving work satisfactorily as a fuse wire8 ,now turn the electricity on through the resistance wire4 ,what happens8 ,when are the greater number of amperes of electricity flowing through the zinc shaving8 7,,note4 ,amperes means the amount of current flowing47 ,can the zinc shaving stand as many amperes as the fuse wire you ordinarily use8 ,which lets more electricity pass through it1 the lamp or the resistance wire8 ,why do electric irons and toasters often blow out fuses8 ,if this happens at your home1 examine the fuse and see how many amperes 7how much current7 it will allow to flow through it4 ,it will say #f;,a if it allows #f amperes to pass through it2 #be;,a if it allows #be amperes to pass through it1 etc4 ,the fuse wire across the fuse gap allows about #h amperes to pass through before it melts4 ,the zinc shaving allows only about #b4 ,read the marks on the cartridge and plug fuses4 ,how many amperes will they stand8 ,,application #fj4 ,a family had just secured an electric heater4 ,the first night it was used1 the fuse blew out4 ,the boy said3 ,let's put a piece of copper wire across the fuse socket2 then there can't be any more trouble4 ,the father said that they had better get a new fuse to replace the old one4 ,the old fuse was marked #aj;,a4 ,was the boy or was the father right8 ,if the father was right1 should they have got a fuse marked #f;,a1 one marked #aj;,a1 or one marked #ae;,a8 ,,application #fa4 ,the family were putting up an extension light4 ,they wanted the cord held firmly up out of the way4 ,one suggested that they drive a nail through both parts of the cord and into the wall4 ,another thought it would be better to put a loop of string around the cord and fasten the loop to the wall4 ,a third suggested the use of a double-pointed carpet tack that would go across the wires1 but not through them1 and if driven tightly into the wall would hold the wire more firmly than would the loop4 ,which way was best8 ,,inference ,,exercise ,explain the following3 #cfa4 ,if the insulation wears off both wires of a lamp cord1 the fuse will blow out4 #cfb4 ,street cars are heated by electricity4 #cfc4 ,the handles of pancake turners are often made of wood4 #cfd4 ,glue soaks into the pores of pieces of wood and gradually hardens4 #cfe4 ,the glue then holds the pieces tightly together4 #cff4 ,you need a fuse of higher amperage1 as a #aj-;ampere fuse1 instead of a #f-;ampere one1 where you use electricity for an iron1 and one of still higher amperage for an electric stove4 #cfg4 ,you should be careful about turning on electric lights or doing anything with electric wires when you are on a cement1 iron1 or earthen floor1 or if you are standing in water4 #cfh4 ,the keys and buttons with which you turn on electric lights are usually made of a rubber composition4 #cfi4 ,defective wiring1 because of which bare wires may touch1 has caused many fires4 #cgj4 ,a person wearing glasses can sometimes see in them the image of a person behind him4 ,,section #dj4 ,electromagnets4 ,how is a telegram sent8 ,what carries your voice when you telephone8 ,so far we have talked about electricity only making heat and light by being forced through something that resists it4 ,but everybody knows that electricity can be made to do another kind of work4 ,it can be made to move things1--to run street cars1 to click telegraph instruments1 to vibrate the thin metal disk in a telephone receiver1 and so on4 ,the following experiments will show you how electricity moves things3 ,illustration3 ,,fig4 #ach4 ,the magnetized bolt picks up the iron filings4 ,,experiment #ge4 ,bare an inch of each end of a piece of insulated wire about #aj feet long4 ,fasten one end to the zinc of your battery or to one wire from the storage battery2 wrap the wire around and around an iron machine bolt1 leaving the bolt a foot or so from the battery1 until you have only about a foot of wire left4 ,hold your bolt over some iron filings4 ,is it a magnet8 ,now touch the free end of your wire to the carbon of your battery or to the other wire from the storage battery1 and hold the bolt over the iron filings4 ,is it a magnet now8 ,you have completed the circuit by touching the free end of the wire to the free pole of your battery2 so the electricity flows through the wire1 around the bolt1 and back to the battery4 ,disconnect one end of the wire from the battery4 ,you have now broken the circuit1 and the electricity can no longer flow around the bolt to magnetize it4 ,see if the bolt will pick up the iron filings any more2 it may keep a little of its magnetism even when no electricity is flowing1 but the magnetism will be noticeably less4 ,when you disconnect the wire so that the electricity can no longer flow through a complete circuit from its source back to its source again1 you are said to break the circuit4 ,illustration3 ,,fig4 #aci4 ,sending a message with a cigar-box telegraph4 ,,experiment #gf4 ,examine the cigar-box telegraph 7see ,appendix ,b7 and notice that it is made on the same principle as was the magnetized bolt in ,experiment #ge4 ,complete the circuit through the electromagnet 7the bolt wound with wire7 by connecting the two ends of the wire that is wrapped around the bolt1 with wires from the two poles of the battery4 ,by making and breaking the circuit 7connecting and disconnecting one of the wires7 you should be able to make the lower bolt jump up and down and give the characteristic click of the telegraph instrument4 ,in this experiment it does not matter how long the wires are if the batteries are strong enough4 ,of course it makes no difference where you break the circuit4 ,so you could have the batteries in the laboratory and the cigar box a hundred miles away1 with the wire going from the batteries to the bolt and back again4 ,then if you made and broke the circuit at the laboratory1 the instrument would click a hundred miles away4 ,if you want to1 you may take the cigar-box telegraph out into the yard1 leaving the batteries in the laboratory1 while you try to telegraph this short distance4 ,examine a regular telegraph instrument4 ,trace the wire from one binding post1 around the coil and through the key1 back to the other binding post1 and notice how pushing down the key completes the circuit and how raising it up breaks the circuit4 ,illustration3 ,,fig4 #adj4 ,connecting up a real telegraph instrument4 ,,experiment #gg4 ,connect two regular telegraph instruments1 leaving one at each end of the long laboratory table4 ,make the connections as follows3 ,take a wire long enough to go from one instrument to the other4 ,fasten the bare ends of this wire into the right-hand binding post of the instrument at your left1 and into the left-hand binding post of the instrument at your right2 that is1 connect the binding posts that are nearest together1 as in ,figure #ada4 ,now connect one wire from the laboratory battery to the free post of the right-hand instrument4 ,connect the other wire from the laboratory battery to the ground through a faucet1 radiator1 or gas pipe1 making the connection firm and being sure that there is a good1 clear contact between the bare end of the wire and the metal to which the wire is attached4 ,make another ground connection near the left-hand instrument2 that is1 take a wire long enough to reach from some pipe or radiator to the left-hand telegraph instrument1 bind one bare end of this wire firmly to a clean part of the pipe and bring the other end toward the instrument4 ,before attaching this other end to the free binding post of the left-hand instrument1 be sure to open the switch beside the telegraph key by pushing it to your right4 ,close the switch on the other instrument4 ,now attach the free ground wire to the free binding post of your telegraph instrument1 and press the key4 ,does the other instrument click8 ,if not1 disconnect the ground wire and examine all connections4 ,also press the sounder of each instrument down and see if it springs back readily4 ,it may be that some screw is too tight1 or too loose1 or that a spring has come off2 tinker awhile and see if you cannot make the instrument work4 ,if you are unable to do so1 ask for help4 ,figure #ada is a diagram of all the connections4 ,when you want to telegraph1 open the switch of the instrument you want to send from and close the switch of the instrument which is to receive the message4 ,holding the key down a little while1 then letting it up1 makes a dash1 while letting it spring up instantly1 makes a dot4 ,practice making dots and dashes4 ,telegraph the word cat1 using the alphabet shown on the next page4 ,telegraph your own name2 your address4 ,illustration3 ,,fig4 #ada4 ,diagram showing how to connect up two telegraph instruments4 ,the circles on the tables represent the binding posts of the instruments4 ,illustration3 ,,fig4 #adb4 ,telegraphing across the room4 ,here is the ,morse telegraph code in dots and dashes3 ,,letters ,a ,b ,c ,d ,e ,f ,g - - - - -- ,h ,i ,j ,k ,l ,m ,n -- -- -- - - - ,o ,p ,q ,r ,s ,t ,u - - - ,v ,w ,x ,y ,z - -- - ,,numerals #a #b #c #d #e -- - - - --- #f #g #h #i #j -- - -- ---- ,by using the ,morse code1 telegraph and cable messages are sent all over the world in a few seconds4 ,the ability to send messages in this way arose from the simple discovery that when an electric current passes around a piece of iron1 it turns the iron into a magnet4 ,,how ,a ,,telephone ,,works4 ,a telephone is much like a delicate and complicated telegraph in which the vibrations started by your voice press the key1 and in which the sounder can vibrate swiftly in response to the electric currents passing through the wire4 ,the key in the telephone is a thin metal disk that vibrates easily1 back of the rubber mouthpiece4 ,each time an air vibration from your voice presses against it1 it increases the current flowing in the circuit4 ,and each time the current in the circuit is increased1 the disk in the receiver is pulled down1 just as the sounder of a telegraph is pulled down4 ,so every vibration of the disk back of the mouthpiece causes a vibration of the disk in the receiver of the other telephone2 this makes the air over it vibrate just as your voice made the mouthpiece vibrate1 and you get the same sound4 ,to make a difference between slight vibrations and larger ones in telephones1 there are some carbon granules between the mouthpiece disk and a disk behind it2 and there are various other complications1 such as the bell-ringing apparatus and the connections in the central office4 ,but the principle of the telephone is almost exactly the same as the principle of the telegraph4 ,both depend entirely on the fact that an electric current passing around a piece of iron magnetizes the iron4 ,,experiment #gh4 ,by means of your battery1 make an electric bell ring4 ,examine the bell and trace the current through it4 ,notice how the current passes around two iron bars and magnetizes them1 as it did in the telegraph instrument4 ,notice that the circuit is completed through a little metal attachment on the base of the clapper1 and that when the clapper is pulled toward the electromagnet the circuit is broken4 ,the iron bars are then no longer magnetized4 ,notice that a spring pulls the clapper back into place as soon as the iron stops attracting it4 ,this completes the circuit again and the clapper is pulled down4 ,that breaks the circuit and the clapper springs back4 ,see how this constant making and breaking of the circuit causes the bell clapper to fly back and forth4 ,illustration3 ,,fig4 #adc4 ,the bell is rung by electromagnets4 ,the electric bell1 like the telephone and telegraph1 works on the simple principle that electricity flowing through a wire that is wrapped around and around a piece of iron will turn that piece of iron into a magnet as long as the electricity flows4 ,,the ,,electric ,,motor4 ,the motor of a street car is a still more complicated carrying out of the same principle4 ,in the next experiment you will see the working of a motor4 ,,experiment #gi4 ,connect the wires from the laboratory battery to the two binding posts of the toy motor1 and make the motor run4 ,examine the motor and see that it is made of several electromagnets which keep attracting each other around and around4 ,motors1 and therefore all things that are moved by electricity1 including trolley cars and electric railways1 submarines while submerged1 electric automobiles1 electric sewing machines1 electric vacuum cleaners1 and electric player-pianos1 are moved by magnetizing a piece of iron and letting this pull on another piece of iron4 ,and the iron is magnetized by letting a current of electricity flow around and around it4 ,illustration3 ,,fig4 #add4 ,a toy electric motor that goes4 ,the making of various kinds of electromagnets and putting currents of electricity to work is becoming one of the great industries of mankind4 ,waterfalls are being hitched up to dynamos everywhere1 and the water power that once turned the mill wheels now turns millions of coils of wire between the poles of powerful magnets4 ,the current generated in this way is used for all kinds of work--not only for furnishing light to cities1 and cooking meals1 heating homes1 and ironing clothes1 but for running powerful motors in factories1 for driving interurban trains swiftly across the country1 for carrying people back and forth to work in city street cars1 for lifting great pieces of iron and steel in the yards where huge electromagnets are used1--for countless pieces of work in all parts of the globe4 ,yet the use of electricity is still only in its beginning4 ,tremendous amounts of water power are still running to waste2 there is almost no limit to the amount of electricity we shall be able to generate as we use the world's water power to turn our dynamos4 ,illustration3 ,,fig4 #ade4 ,an electric motor of commercial size4 ,,application #fb4 ,explain how pressing a telegraph key can make another instrument click hundreds of miles away1 and how you can hear over the telephone4 ,is it vibrations of sound or of electricity that go through the telephone wire1 or does your voice travel over it1 or does the wire itself vibrate8 ,explain how electricity can make a car go4 ,,inference ,,exercise ,explain the following3 #cga4 ,when a fuse blows out1 you can get no light4 #cgb4 ,if you lay your ear on a desk1 you hear the sounds in the room clearly4 #cgc4 ,if you touch a live wire with wet hands1 you get a much worse shock than if you touch it with dry hands4 #cgd4 ,a park music stand is backed by a sounding board4 #cge4 ,the clapper of an electric bell is pulled against the bell when you push the button4 #cgf4 ,a hot iron tire put on a wagon wheel fits very tightly when it cools4 #cgg4 ,candy will cool more rapidly in a tin plate than in a china plate4 #cgh4 ,when a trolley wire breaks and falls to the ground it melts and burns at the point at which it touches the ground4 #cgi4 ,by allowing the electricity from the trolley wire to flow down through an underground coil of wire1 a motorman can open a switch in the track4 #chj4 ,the bare ends of the two wires leading to your electric lamp should never be allowed to touch each other4 ,,chapter ,,nine ,,mingling ,,of ,,molecules ,,section #da4 ,solutions and emulsions4 ,how does soap make your hands clean8 ,why will gasoline take a grease spot out of your clothes8 ,if we were to go back to our convenient imaginary switchboard to turn off another law1 we should find near the heat switches1 and not far from the chemistry ones1 a switch labeled ,,solution4 ,suppose we turned it off3 ,the fishes in the sea are among the first creatures to be surprised by our action4 ,for instantly all the salt in the ocean drops to the bottom like so much sand1 and most salt-water fishes soon perish in the fresh water4 ,if some one is about to drink a cup of tea and has sweetened it just to his taste1 you can imagine his amazement when1 bringing it to his lips1 he finds himself drinking tasteless1 white1 milky water4 ,down in the bottom of the cup is a sediment of sugar1 like so much fine gravel1 with a brownish dust of tea covering it4 ,to see whether or not the trouble is with the sugar itself1 he may take some sugar out of the bowl and taste it1--it is just like white sand4 ,wondering what has happened1 and whether he or the sugar is at fault1 he reaches for the vinegar cruet4 ,the vinegar is no longer clear1 but is a colorless liquid with tiny specks of brown floating about in it4 ,tasting it1 he thinks it must be dusty water4 ,salt1 pepper1 mustard1 onions1 or anything he eats1 is absolutely tasteless1 although some of the things smell as strong as ever4 ,to tell the truth1 ,i doubt if the man has a chance to do all of this experimenting4 ,for the salt in his blood turns to solid hard grains1 and the dissolved food in the blood turns to dustlike particles4 ,his blood flows through him1 a muddy stream of sterile water4 ,the cells of his body get no food1 and even before they miss the food1 most of the cells shrivel to drops of muddy water4 ,the whole man collapses4 ,plants are as badly off4 ,the life-giving sap turns to water with specks of the one-time nourishment floating uselessly through it4 ,most plant cells1 like the cells in the man1 turn to water1 with fibers and dust flecks making it cloudy4 ,within a few seconds there is not a living thing left in the world1 and the saltless waves dash up on a barren shore4 ,probably we had better let the ,,solution switch alone1 after all4 ,instead1 here are a couple of experiments that will help to make clear what happens when anything dissolves to make a solution4 ,,experiment #hj4 ,fill a test tube one fourth full of cold water4 ,slowly stir in salt until no more will dissolve4 ,add half a teaspoonful more of salt than will dissolve4 ,dry the outside of the test tube and heat the salty water over the ,bunsen burner4 ,will hot water dissolve things more readily or less readily than cold8 ,why do you wash dishes in hot water8 ,,experiment #ha4 ,fill a test tube one fourth full of any kind of oil1 and one fourth full of water4 ,hold your thumb over the top of the test tube and shake it hard for a minute or two4 ,now look at it4 ,pour it out1 and shake some prepared cleanser into the test tube1 adding a little more water4 ,shake the test tube thoroughly and rinse4 ,put it away clean4 ,when you shake the oil with the water1 the oil breaks up into tiny droplets4 ,these droplets are so small that they reflect the light that strikes them and so look white1 or pale yellow4 ,this milky mixture is called an emulsion4 ,milk is an emulsion2 there are tiny droplets of butter fat and other substances scattered all through the milk4 ,the butter fat is not dissolved in the rest of the milk1 and the oil is not dissolved in the water4 ,but the droplets may be so small that an emulsion acts almost exactly like a solution4 ,illustration3 ,,fig4 #adf4 ,will heating the water make more salt dissolve8 ,but when you shake or stir salt or sugar in water1 the particles divide up into smaller and smaller pieces1 until probably each piece is just a single molecule of the salt or sugar4 ,and these molecules get into the spaces between the water molecules and bounce around among them4 ,they therefore act like the water and let the light through4 ,this is a solution4 ,the salt or sugar is dissolved in the water4 ,any liquid mixture which remains clear is a solution1 no matter what the color4 ,most red ink1 most blueing1 clear coffee1 tea1 and ocean water are solutions4 ,if a liquid is clear1 no matter what the color1 you can be sure that whatever things may be in it are dissolved4 ,illustration3 ,,fig4 #adg4 ,will the volume be doubled when the alcohol and water are poured together8 ,,experiment #hb4 ,pour alcohol into a test tube 7square-bottomed test tubes are best for this experiment71 standing the tube up beside a ruler4 ,when the alcohol is just #a inch high in the tube1 stop pouring4 ,put exactly the same amount of water in another test tube of the same size4 ,when you pour them together1 how many inches high do you think the mixture will be8 ,pour the water into the alcohol1 shake the mixture a little1 and measure to see how high it comes in the test tube4 ,did you notice the warmth when you shook the tube8 ,if you use denatured alcohol1 you are likely to have an emulsion as a result of the mixing4 ,the alcohol part of the denatured alcohol dissolves in the water well enough1 but the denaturing substance in the alcohol will not dissolve in water2 so it forms tiny droplets that make the mixture of alcohol and water cloudy4 ,the purpose of this experiment is to show that the molecules of water get into the spaces between the molecules of alcohol4 ,it is as if you were to add a pail of pebbles to a pail of apples4 ,the pebbles would fill in between the apples1 and the mixture would not nearly fill two pails4 ,the most important difference between a solution and an emulsion is that the particles in an emulsion are very much larger than those in a solution2 but for practical purposes that often does not make much difference4 ,you dissolve a grease spot from your clothes with gasoline2 you make an emulsion when you take it off with soap and water2 but by either method you remove the spot4 ,you dissolve part of the coffee or tea in boiling water2 you make an emulsion with cocoa2 but in both cases the flavor is distributed through the liquid4 ,milk is an emulsion1 vinegar is a solution2 but in both1 the particles are so thoroughly mixed with the water that the flavor is the same throughout4 ,therefore in working out inferences that are explained in terms of solutions and emulsions1 it is not especially important for you to decide whether you have a solution or an emulsion if you know that it is one or the other4 ,,how ,,precious ,,stones ,,are ,,formed4 ,colored glass is made by dissolving coloring matter in the glass while it is molten4 ,rubies1 sapphires1 emeralds1 topazes1 and amethysts were colored in the same way1 but by nature4 ,when the part of the earth where they are found was hot enough to melt stone1 the liquid ruby or sapphire or emerald1 or whatever the stone was to be1 happened to be near some coloring matter that dissolved in it and gave it color4 ,several of these stones are made of exactly the same kind of material1 but different kinds of coloring matter dissolved in them when they were melted4 ,many articles are much used chiefly because they are good emulsifiers or good solvents 7dissolve things well74 ,soap is a first-rate emulsifier2 water is the best solvent in the world2 but it will not dissolve oil and gummy things sufficiently to be of use when we want them dissolved4 ,turpentine1 alcohol1 and gasoline find one of their chief uses as solvents for gums and oils4 ,almost all cleaning is simply a process of dissolving or emulsifying the dirt you want to get rid of1 and washing it away with the liquid4 ,do not forget that heat helps to dissolve most things4 ,,application #fc4 ,explain why clothes are washed in hot suds2 why sugar disappears in hot coffee or tea2 why it does not disappear as quickly in cold lemonade2 why you cannot see through milk as you can through water4 ,,inference ,,exercise ,explain the following3 #cha4 ,a kind of lamp bracket is made with a rubber cup4 ,when you press this cup against the wall or against a piece of furniture and exhaust the air from the cup1 the cup sticks fast to the wall and supports the lamp bracket4 #chb4 ,you can take a vaseline stain out with kerosene4 #chc4 ,if the two poles of an electric battery are connected with a copper wire1 the battery soon becomes discharged4 #chd4 ,electric bells have iron bars wound around and around with insulated copper wire4 #che4 ,piano keys may be cleaned with alcohol4 #chf4 ,linemen working with live wires wear heavy rubber gloves4 #chg4 ,crayon will not write on the smooth1 glazed parts of a blackboard4 #chh4 ,varnish and shellac may be thinned with alcohol4 #chi4 ,filtering will take mud out of water1 but it will not remove salt4 #cij4 ,explain why only one wire is needed to telegraph between two stations4 ,,section #db4 ,crystals4 ,how is rock candy made8 ,why is there sugar around the mouth of a syrup jug8 ,how are jewels formed in the earth8 ,you can learn how crystals are formed--and many gems and rock candy and the sugar on a syrup jug are all crystals--by making some4 ,try this experiment3 ,,experiment #hc4 ,fill a test tube one fourth full of powdered alum2 cover the alum with boiling water2 hold the tube over a flame so that the mixture will boil gently2 and slowly add boiling-hot water until all of the alum is dissolved4 ,do not add any more water than you have to1 and keep stirring the alum with a glass rod while you are adding the water4 ,pour half of the solution into another test tube for the next experiment4 ,hang a string in the first test tube so that it touches the bottom of the tube4 ,set it aside to cool1 uncovered4 ,the next day examine the string and the bottom of the tube4 ,,experiment #hd4 ,while the solution of alum in the second test tube 7,experiment #hc7 is still hot1 hold the tube in a pan of cold water and shake or stir it until it cools4 ,when white specks appear in the clear solution1 pour off as much of the clear part of the liquid as you can2 then pour a little of the rest on a glass slide1 and examine the specks under a microscope4 ,illustration3 ,,fig4 #adh4 ,alum crystals4 ,in both of the above experiments1 the hot water was able to dissolve more of the alum than the cold water could possibly hold4 ,so when the water cooled it could no longer hold the alum in solution4 ,therefore part of the alum turned to solid particles4 ,when the string was in the cooling liquid1 it attracted the particles of alum as they crystallized out of the solution4 ,the force of adhesion drew the near-by molecules to the string1 then these drew the next1 and these drew more1 and so on until the crystals were formed4 ,but when you kept stirring the liquid while it cooled1 the crystals never had time to grow large before they were jostled around to some other part of the liquid or were broken by your stirring rod4 ,therefore they were small instead of large4 ,stirring or shaking a solution will always make crystals form more quickly1 but it will also make them smaller4 ,,how ,,rock ,,candy ,,is ,,made4 ,rock candy is made by hanging a string in a strong sugar solution or syrup and letting the water evaporate slowly until there is not enough water to hold all the sugar in solution4 ,then the sugar crystals gather slowly around the string1 forming the large1 clear pieces of rock candy4 ,the sugar around the mouth of a syrup jug is formed in the same way4 ,you always get crystallization when you make a liquid too cool to hold the solid thing in solution1 or when you evaporate so much of the liquid that there is not enough left to keep the solid thing dissolved4 ,when you make fudge1 the sugar forms small crystals as the liquid cools4 ,when a boat has been on the ocean1 salt crystals form on the sails when the spray that has wet them evaporates4 ,but crystals may form also in the air4 ,there is always some moisture in the air1 and when it becomes very cold1 some of this moisture forms crystals of ice4 ,if they form up in the clouds1 they fall as snow4 ,if they form around blades of grass or on the sidewalk1 as the alum crystals formed on the string1 we have frost4 ,still another place that crystals occur is in the earth4 ,when the rocks in the earth were hot enough to be melted and then began to cool1 certain substances in the rocks crystallized4 ,some of these crystals that are especially hard and clear constitute precious and semi-precious stones4 ,,application #fd4 ,explain why you beat fudge as it cools2 why the paper around butter becomes encrusted with salt if it is exposed to the air for some time4 ,,inference ,,exercise ,explain the following3 #cia4 ,dynamos have copper brushes to lead the current from the coils of wire to the line wires4 #cib4 ,a megaphone makes the voice carry farther than usual4 #cic4 ,copper wire is used to conduct electricity1 although iron wire costs much less4 #cid4 ,a flute gives notes that differ in pitch according to the stops that are opened4 #cie4 ,there are usually solid pieces of sugar around the mouth of a syrup jar4 #cif4 ,you can beat eggs quickly with a ,dover egg beater4 #cig4 ,when ocean water stands in shallow open tanks for some time1 salt begins to form before the water has all evaporated4 #cih4 ,in a coffee percolator the boiling water goes up through a tube4 ,as this water drips back through the ground coffee beans1 it becomes brown and flavored1 and the coffee is made4 #cii4 ,kerosene will clean off the rim of soap and grease that forms in bathtubs4 #djj4 ,beating cake frosting or candy causes it to sugar4 ,,section #dc4 ,diffusion4 ,how does food get into the blood8 ,why can you so quickly smell gas that is escaping at the opposite side of a room8 ,on our imaginary switchboard the ,,diffusion switch would not be safe to tamper with4 ,it would be near the ,,solution switch1 and almost as dangerous4 ,for if you were to make diffusion cease in the world1 the dissolved food and oxygen in your blood would do no good2 it could not get out of the blood vessels or into the cells of your body4 ,you might breathe all you liked1 but breathing would not help you2 the air could not get through the walls of your lungs into the blood4 ,plants would begin to wither and droop1 although they would not die quite as quickly as animals and fishes and people4 ,but no sap could enter their roots and none could pass from cell to cell4 ,the plants would be as little able to breathe through their leaves as we through our lungs4 ,if gas escaped in the room where you were1 you could not smell it even if you stayed alive long enough to try2 the gas would rise to the top of the room and stay there4 ,all gases and all liquids would stay as they were1 and neither would ever form mixtures4 ,it would not make so much difference in the dead parts of the world if diffusion ceased2 the rocks1 mountains1 earth1 and sea would not be changed at all at first4 ,to be sure1 the rivers where they flowed into the oceans would make big spaces of saltless water2 and when water evaporated from the ocean the vapor would push aside the air and stay in a layer over the ocean1 instead of mixing with the air and rising to great heights4 ,but the real disaster would be to living things4 ,all of them would be smothered and starved to death as soon as diffusion ceased4 ,here is an experiment that shows how gases diffuse3 ,,experiment #he4 ,take two test tubes with mouths of the same size so that you can fit them snugly against each other when you want to4 ,fill one to the brim with water and hold your thumb or a piece of cardboard over its mouth while you place it upside down in a pan of water4 ,take the free end of a rubber tube that is attached to a gas pipe and put it into the test tube a short distance1 so that the gas will go up into the tube1 as shown in ,figure #adi4 ,now turn on the gas gently4 ,when all the water has been forced out of the tube and the gas bubbles begin to come up on the outside1 turn off the gas4 ,put a piece of cardboard1 about an inch or so square1 over the mouth of the tube so that no air can get into it1 and take the tube out of the water1 keeping the mouth down and covered4 ,bring the empty test tube1 which of course is full of air1 mouth up under the test tube full of gas1 making the mouths of the two tubes meet with the cardboard between them1 as shown in ,figure #aej4 ,now have some one pull the cardboard gently from between the two test tubes1 so that the mouths of the tubes will be pressed against each other and so that practically no gas will escape4 ,hold them quietly this way1 the tube of gas uppermost1 for not less than one full minute by the clock4 ,a minute and a half is not too much time4 ,now have some one light a match for you1 or else go to a lighted ,bunsen burner4 ,take the test tubes apart gently and hold the lower one1 which was full of air1 with its mouth to the flame4 ,what has the gas in the upper tube done8 ,now hold the flame to the upper test tube1 which was full of gas4 ,what happens8 ,has all the gas gone out of it8 ,illustration3 ,,fig4 #adi4 ,filling a test tube with gas4 ,illustration3 ,,fig4 #aej4 ,the lower test tube is full of air2 the upper1 of gas4 ,what will happen when the cardboard is withdrawn8 ,as you well know1 gas is much lighter than air2 you can make a balloon rise by filling it with gas4 ,yet part of the gas went down into the lower tube4 ,the explanation is that the molecules of gas and those of air were flying around at such a rate that many of the gas molecules went shooting down among the air molecules1 and many of the molecules of air went shooting up among those of gas1 so that the gas and the air became mixed4 ,,diffusion ,,in ,,liquids4 ,diffusion takes place in liquids1 as you know4 ,for when you put sugar in coffee or tea and do not stir it1 although the upper part of the tea or coffee is not sweetened1 the part nearer the sugar is very sweet4 ,if you should let the coffee or tea1 with the sugar in the bottom1 stand for a few months1 it would get sweet all through4 ,diffusion is slower in liquids than in gases1 because the molecules are so very much closer together4 ,,osmosis4 ,one of the most striking and important facts about diffusion is that it can take place right through a membrane4 ,try this experiment3 ,,experiment #hf4 ,with a rubber band fasten a piece of parchment paper1 made into a little bag1 to the end of a piece of glass tubing about #aj inches long4 ,or make a small hole in one end of a raw egg and empty the shell2 then1 to get the hard part off the shell1 soak it overnight in strong vinegar or hydrochloric acid diluted about #a to #d4 ,this will leave a membranous bag that can be used in place of the parchment bag4 ,fill a tumbler half full of water colored with red ink1 and add enough cornstarch to make the water milky4 ,pour into the tube enough of a strong sugar solution to fill the membranous bag at its base and to rise half an inch in the tube4 ,put the membranous bag down into the pink1 milky water1 supporting the tube by passing it through a square cardboard and clamping it with a spring clothespin as shown in ,figure #aea4 ,every few minutes look to see what is happening4 ,does any of the red ink pass through the membrane8 ,does any of the cornstarch pass through8 ,this is an example of diffusion through a membrane4 ,the process is called osmosis1 and the pressure that forces the liquid up the tube is called osmotic pressure4 ,it is by this sort of diffusion that chicks which are being incubated get air1 and that growing plants get food4 ,it is in this way that the cells of our body secure food and oxygen and get rid of their wastes4 ,there are no little holes in our blood vessels to let the air get into them from our lungs4 ,the air simply diffuses through the thin walls of the blood vessels4 ,there are no holes from the intestinal tract into the blood vessels4 ,yet the dissolved food diffuses right through the intestinal wall and through the walls of the blood vessels4 ,and later on1 when it reaches the body cells that need nourishment1 the dissolved food diffuses out through the walls of the blood vessels again and through the cell walls into the cells4 ,waste is taken out of the cells into the blood and passes from the blood into the lungs and kidneys by this same process of diffusion4 ,so you can readily see why everything would die if diffusion stopped4 ,illustration3 ,,fig4 #aea4 ,pouring the syrup into the osmosis tube4 ,,application #fe4 ,explain how the roots of a plant can take in water and food when there are no holes from the outside of the root to the inside2 how bees can smell flowers for a considerable distance4 ,,inference ,,exercise ,explain the following3 #dja4 ,a shell in the bottom of a teakettle gathers most of the scale around it and so keeps the scale from caking at the bottom of the kettle4 #djb4 ,there is oxygen dissolved in water4 ,when the water comes in contact with the fine blood vessels in a fish's gills1 some of this oxygen passes through the walls of the blood vessels into the blood4 ,explain how it does so4 #djc4 ,asphalt becomes soft in summer4 #djd4 ,when the trolley comes off the wire the car soon stops4 #dje4 ,you cannot see stars in the daytime on earth1 yet you could see them in the daytime on the airless moon4 #djf4 ,although the carbon dioxid you breathe out is heavier than the rest of the air1 part of it goes up and mixes with the air above4 #djg4 ,on a cold day wood does not feel as cold as iron4 #djh4 ,to make mayonnaise dressing1 the oil1 egg1 and vinegar are thoroughly beaten together4 #dji4 ,a solution of iodin becomes stronger if it is allowed to stand open to the air4 #daj4 ,a drop of milk in a glass of water clouds all the water slightly4 ,,section #dd4 ,clouds1 rain1 and dew3 ,humidity4 ,why is it that you can see your breath on a cold day8 ,where do rain and snow come from8 ,what makes the clouds8 ,there is water vapor in the air all around us--invisible water vapor1 its molecules mingling with those of the air--water that has evaporated from the oceans and lakes and all wet places4 ,this water vapor changes into droplets of water when it gets cool enough4 ,and those droplets of water make up our clouds and fogs2 they join together to form our rain and snow high in the air1 or gather as dew or frost on the grass at night4 ,if the water vapor should suddenly lose its power of changing into droplets of water when it cooled1--well1 let us pretend it has lost this power but that any amount of water can evaporate1 and see what happens3 ,what fine weather it is6 ,there is not a cloud in the sky4 ,as evening closes in1 the stars come out with intense brightness4 ,the whole sky is gleaming with stars--more than we have ever seen at night before4 ,the next morning we find no dew or frost on the grass4 ,all the green things look dry4 ,as the day goes on1 they begin to wilt and wither4 ,we all wish the day were not quite so fine--a little rain would help things wonderfully4 ,not a cloud appears1 however1 and we water as much of our gardens as we can4 ,they drink the water greedily1 and that night1 again no dew or fog1 and not the faintest cloud or mist to dim the stars4 ,and the new day once more brings the blazing sun further to parch the land and plants4 ,day after day and night after night the drought gets worse4 ,the rivers sink low2 brooks run dry2 the edges of the lakes become marshes4 ,the marshes dry out to hardened mud4 ,the dry leaves of the trees rustle and crumble4 ,all the animals and wood creatures gather around the muddy pools that once were lakes or rivers4 ,people begin saving water and buying it and selling it as the most precious of articles4 ,as the months go by1 winter freezes the few pools that remain4 ,no snow falls4 ,living creatures die by the tens of thousands4 ,but the winter is less cold than usual1 because there is now so much water vapor in the air that it acts like a great blanket holding in the earth's heat4 ,with spring no showers come4 ,the dead trees send forth no buds4 ,no birds herald the coming of warm weather4 ,the continents of the world have become vast1 uninhabitable deserts4 ,people have all moved to the shores of the ocean1 where their chemists are extracting salt from the water in order to give them something to drink4 ,by using this saltless water they can irrigate the land near the oceans and grow some food to live on4 ,each continent is encircled by a strip of irrigated land and densely populated cities close to the water's edge4 ,it is many years before the oceans disappear4 ,but in time they too are transformed into water vapor1 and no more life as we know it is possible in the world4 ,the earth has become a great rocky and sandy ball1 whirling through space1 lifeless and utterly dry4 ,that which prevents this from really happening is very simple3 ,in the world as it is1 water vapor condenses and changes to drops of water whenever it gets cool enough4 ,,how ,,water ,,vapor ,,gets ,,into ,,the ,,air4 ,the water vapor gets into the air by evaporation4 ,when we say that water evaporates1 we mean that it changes into water vapor4 ,as you already know1 it is heat that makes water evaporate2 that is why you hang wet clothes in the sun or by the fire to dry3 you want to change the water in them to water vapor4 ,the sun does not suck up the water from the ocean1 as some people say2 but it warms the water and turns part of it to vapor4 ,what happens down among the molecules when water evaporates is this3 ,the heat makes the molecules dance around faster and faster2 then the ones with the swiftest motion near the top shoot off into the air4 ,the molecules that have shot off into the air make up the water vapor4 ,the water vapor is entirely invisible4 ,no matter how much of it there is1 you cannot see it4 ,the weather is just as clear when there is a great deal of water vapor in the air as when there is very little1 as long as none of the vapor condenses4 ,,how ,,clouds ,,are ,,formed4 ,but when water vapor condenses1 it forms into extremely small drops of real water4 ,each of these drops is so small that it is usually impossible to see one2 they are so tiny that you could lay about #cjjj of them side by side in one inch6 ,yet1 small as they are1 when there are many of them they become distinctly visible4 ,we see them floating around us sometimes and call them fog or mist4 ,and when there are millions of them floating in the air high above us1 we call them a cloud4 ,the reason clouds form so high in the air is this3 ,when air or any gas expands1 it cools4 ,do you remember ,experiment #ca1 where you let the gas from a tank expand into a wet test tube and it became so cold that the water on the test tube froze8 ,well1 it is much the same way with rising air4 ,when air rises1 there is less air above it to keep it compressed2 so it expands and cools4 ,then the water vapor in it condenses into droplets of water1 and these form a cloud4 ,each droplet forms a gathering place for more condensing water vapor1 and therefore grows4 ,when the droplets of water in a cloud are very close together1 some may be jostled against one another by the wind4 ,and when they touch each other1 they stick together1 forming a larger drop4 ,when a drop grows large enough it begins to fall through the cloud1 gathering up the small droplets as it goes4 ,by the time it gets out of the cloud it has grown to a full-sized raindrop1 and falls to earth4 ,the complete story of rain1 then1 is this3 ,,how ,,rain ,,is ,,caused4 ,the surface of the oceans and lakes is warmed by the sun4 ,the water evaporates1 turning to invisible water vapor4 ,this water vapor mingles with the air4 ,after a while the air is caught in a rising current and swept up high1 carrying the water vapor with it4 ,as the air rises1 there is less air above it to press down on it2 so it expands4 ,when air expands it cools1 and the water vapor which is mingled with it likewise cools4 ,when the water vapor gets cool enough it condenses1 changing to myriads of extremely small drops of water4 ,these make a cloud4 ,a wind comes along2 that is1 the air in which the cloud is floating moves4 ,the wind carries the cloud along with it4 ,more rising air1 full of evaporated water from the ocean1 joins the cloud and cools1 and the water forms into more tiny droplets4 ,the droplets get so close together that they shut out the sun's light from the earth1 and people say that the sky is darkening4 ,meanwhile some of the droplets begin to touch each other and to stick together4 ,little by little the drops grow bigger by joining together4 ,pretty soon they get so big and heavy that they can no longer float high in the air1 and they fall to the ground as rain4 ,part of the rain soaks into the ground4 ,some of it gradually seeps down through the ground to an underground stream4 ,this has its outlet in a spring or well1 or in an open lake or the ocean4 ,but the rain does not all soak in4 ,after the storm1 some of the water again evaporates from the top of the ground and mixes with the warm air1 and it goes through the same round4 ,other raindrops join on the ground to form rivulets that trickle along until they meet and join other rivulets2 and all go on together as a brook4 ,the brook joins others until the brooks form a river2 and the river flows into a lake or into the ocean4 ,then again the sun warms the surface of the ocean or lake2 the water evaporates and mixes with the air1 which rises1 expands1 and cools2 the droplets form and make clouds2 the droplets join1 forming big drops1 and they fall once more as rain4 ,the rain soaks into the ground or runs off in rivulets1 and sooner or later it is once more evaporated4 ,and so the cycle is repeated again and again4 ,and all this is accounted for by the simple fact that when water evaporates its vapor mingles with the air2 and when this vapor is sufficiently cooled it condenses and forms droplets of water4 ,,the ,,barometer4 ,in predicting the weather a great deal of use is made of an instrument called the barometer4 ,the barometer shows how hard the air around it is pressing4 ,if the air is pressing hard1 the mercury in the barometer rises4 ,if the air is not pressing hard the mercury sinks4 ,just before a storm1 the air usually does not press so hard on things as at other times2 so usually1 just before a storm1 the mercury in the barometer is lower than in clear weather4 ,you will understand the barometer better after you make one4 ,here are the directions for making a barometer3 ,,experiment #hg4 ,to be done by the class with the aid of the teacher4 ,use a piece of glass tubing not less than #cb inches long1 sealed at one end4 ,fill this tube to the brim with mercury 7quicksilver71 by pouring the mercury into it through a paper funnel4 ,have the sealed end of the tube in a cup1 to catch any mercury that spills4#g ,when the tube is full1 pour mercury into the cup until there is at least half an inch of it at the bottom4 ,now put your forefinger very tightly over the open end of the tube1 take hold of the sealed end with your other hand1 and turn the tube over4 ,lower the open end1 with your finger over it1 into the cup4 ,when the mercury in the cup completely covers your finger and the end of the tube1 remove your finger carefully so that no air can get up into the tube of mercury4 ,let the open end of the tube rest gently on the bottom of the cup1 and hold the tube upright with your hand or by clamping it to a ring stand4 ,hold a yardstick or meter stick beside the tube1 remembering to keep the tube straight up and down4 ,measure accurately the height of the mercury column from the surface of the mercury in the cup4 ,then go to the regular barometer hanging on the wall1 and read it4 ,footnote #g3 ,if mercury spills on the floor or table during this experiment1 gather it all into a piece of paper by brushing even the tiny droplets together with a soft brush2 squeeze it through a towel into a cup to clean it4 ,it is expensive2 so try not to lose any of it4 ,the reason your barometer may not read exactly the same as the expensive laboratory instrument is that a little air and water vapor stick to the inside of the tube and rise into the vacuum above the mercury2 also1 the tube may not be quite straight up and down4 ,otherwise the readings would be the same4 ,illustration3 ,,fig4 #aeb4 ,filling the barometer tube with mercury4 ,of course you understand what holds the mercury up in the tube4 ,if you could put the cup of mercury into a vacuum1 the mercury in the tube would sink down into the cup4 ,but the pressure of the air on the surface of the mercury in the cup keeps the mercury from flowing out of the tube and so leaving a vacuum in there4 ,if the air pushes down hard on the mercury in the cup1 the mercury will stand high in the tube4 ,this is called high pressure4 ,if the air does not press hard on the mercury in the cup1 the mercury stands low in the tube4 ,this is called low pressure4 ,illustration3 ,,fig4 #aec4 ,inverting the filled tube in the cup of mercury4 ,,how ,,weather ,,is ,,forecast4 ,weather forecasters make a great deal of use of the barometer1 for storms are usually accompanied by low pressure1 and clear weather nearly always goes with high pressure4 ,the reason storms are usually accompanied by low pressure is this3 ,a storm is almost always due to the rising of air1 for the rising air expands and cools1 and if there is much water vapor in it1 this condenses when it cools and forms clouds and rain4 ,now air rises only when there is comparatively little pressure from above4 ,therefore1 before and during a storm there is not so much pressure on the mercury of the barometer and the barometer is low4 ,clear weather1 on the other hand1 is often the result of air being compressed1 for compressing air warms it4 ,when air is being warmed1 the water vapor in it will not condense2 so the air remains clear4 ,but when the air is being compressed1 it presses hard on the mercury of the barometer2 the pressure is high1 and the mercury in the barometer rises high4 ,therefore when the mercury in the barometer is rising1 the weather is usually clear4 ,illustration3 ,,fig4 #aed4 ,finding the pressure of the air by measuring the height of the mercury in the tube4 ,these two statements are true only in a very general way1 however4 ,if weather forecasters had only their own barometers to go by1 they would not be of much value2 for one thing1 they could not tell us that a storm was coming much before it reached us4 ,but there are weather stations all over the civilized world1 and they keep in touch with each other by telegraph4 ,it is known that storms travel from west to east in our part of the world4 ,if one weather man reports a storm at his station1 and tells how his barometer stands1 the weather men to the east of him know that the storm is coming their way4 ,from several such reports the weather men to the east can tell how fast the storm is traveling and exactly which way it is going4 ,then they can tell when it will reach their station and can make the correct prediction4 ,illustration3 ,,fig4 #aee4 ,the kind of mercury barometer that you buy4 ,weather men do not have to wait for an actual storm to be reported4 ,if the reports from the west show that the air is rising as it swirls along--that is1 if the barometer readings in the west are low--they know that this low-pressure air is approaching them4 ,and they know that low pressure usually means air that is rising and cooling and therefore likely to drop its moisture4 ,in the same way1 if the barometers to the west show high pressure1 the eastern weather men know that the air that is blowing toward them is being compressed and warmed1 and is therefore not at all likely to drop its moisture2 so they predict fair weather4 ,the weather man is not ever certain of his forecasts1 however4 ,sometimes the air will begin to rise just before it gets to him4 ,then there may be a shower of rain when he has predicted fair weather4 ,or sometimes the air that has been rising to the west1 and which has made him predict bad weather1 may stop rising2 the storm may be over before it reaches his station4 ,then his prediction of bad weather is wrong4 ,or sometimes the storm unexpectedly changes its path4 ,there are many ways in which a weather prophecy may go wrong2 and then we blame the weather man4 ,we are likely to remember the times that his prophecy is mistaken and to forget the many1 many times when it is right4 ,illustration3 ,,fig4 #aef4 ,an aneroid barometer is more convenient than one made with mercury4 ,the walls are forced in or spring back out according to the pressure of the air4 ,this movement of the walls forces the hand around4 ,,how ,,snow ,,is ,,formed4 ,the difference between the ways in which snow and rain are formed is very slight4 ,in both cases water evaporates and its vapor mingles with the warm air4 ,the warm air rises and expands4 ,it cools as it expands1 and when it gets cool enough the water vapor begins to condense4 ,but if the air as it expands becomes very cold1 so cold that the droplets of water freeze as they form and gather together to make delicate crystals of ice1 snow is formed4 ,the ice crystals found in snow are always six-sided or six-pointed1 because1 probably1 the water or ice molecules pull from six directions and therefore gather each other together along the six lines of this pull4 ,at any rate1 the tiny crystals of frozen water are formed and come floating down to the ground2 and we call them snowflakes4 ,after the snow melts it goes through the same cycle as the rain1 most of it finally getting back to the ocean through rivers1 and there1 in time1 being evaporated once more4 ,illustration3 ,,fig4 #aeg4 ,different forms of snowflakes4 ,each snowflake is a collection of small ice crystals4 ,hail is rain that happens to be caught in a powerful current of rising air as it forms1 and is carried up so high that it freezes in the cold1 expanding air into little balls of ice1 or hail stones1 which fall to the ground before they have time to melt4 ,,why ,,one ,,side ,,of ,a ,,mountain ,,range ,,usually ,,has ,,rainfall4 ,when air that is moving along reaches a mountain range1 it either would have to stop1 or rise and go over the mountain4 ,the pressure of the air behind it1 moving in the same direction1 keeps it from stopping1 and so it has to go up the slopes and over the range4 ,but as it goes up1 there is less air above it to push down on it2 so it expands4 ,this makes it cool1 and the water vapor in it begins to condense and form snow or rain4 ,therefore the side of mountain ranges against which the wind usually blows1 almost always has plenty of rainfall4 ,it is different on the farther side of the mountain range4 ,for here the air is sinking4 ,as it sinks it is being compressed4 ,and as it is compressed it is heated4 ,if you hold your finger over the mouth of a bicycle pump and compress the air in the pump by pushing down on the handle1 you will find that the pump is decidedly warmed4 ,when the air1 sinking down on the farther side of the mountain range1 is heated1 the water vapor in it is not at all likely to condense4 ,therefore rain seldom falls on the side of the mountains which is turned away from the prevailing winds4 ,,how ,,dew ,,and ,,frost ,,are ,,formed4 ,the heat of the earth radiates out into the air and on out into space4 ,at night1 when the earth loses its heat this way and does not receive heat from the sun1 it becomes cooler4 ,when the air1 carrying its water vapor1 touches the cool leaves and flowers1 the water vapor is condensed by the coolness and forms drops of dew upon them4 ,or1 if the night is colder1 the droplets freeze as they form1 and in the morning we see the grass and shrubs all covered with frost4 ,,the ,,cause ,,of ,,fogs4 ,when warm air is cooled while it is down around us1 the water vapor in it condenses into myriads of droplets that float in the air and make it foggy4 ,the air may be cooled by blowing in from the warm lake or ocean in the early morning1 for at night the land cools more rapidly than the water does4 ,this accounts for the early morning fogs in many cities that are on the coasts4 ,likewise when the wind has been blowing over a warm ocean current1 the surface of the warm water evaporates and fills the air with water vapor4 ,then when this air passes over a cold current1 the cold current cools the air so much that the moisture in it condenses and forms fog4 ,that is why there are fog banks1 dangerous to navigation1 in parts of the ocean1 particularly off ,labrador4 ,,why ,,you ,,can ,,see ,,your ,,breath ,,on ,,cold ,,days4 ,you really make a little fog when you breathe on a cold morning4 ,the air in your lungs is warm4 ,the moisture in the lungs evaporates into this warm air1 and you breathe it out4 ,if the outside air is cold1 your breath is cooled2 so some of the water vapor in it condenses into very small droplets1 and you see your breath4 ,here are two experiments in condensing water vapor by cooling the air with which it is mixed4 ,both work best if the weather is warm or the air damp4 ,,experiment #hh4 ,put the bell jar on the plate of the air pump and begin to pump the air out of it4 ,watch the air in the jar4 ,if the day is warm or damp1 a slight mist will form4 ,as part of the air is pumped out1 the rest expands and cools1 as warm air does when it rises and is no longer pressed on so hard by the air above it4 ,and as in the case of the rising warm air1 the water vapor condenses when it cools1 and forms the mist that you see4 ,this mist1 like all clouds and fog1 consists of thousands of extremely small droplets4 ,,experiment #hi4 ,hold a saucer of ice just below your mouth4 ,open your mouth wide and breathe gently over the ice4 ,can you see your breath8 ,now put the ice into half a glass of water and cover the glass4 ,be sure the outside of the glass is thoroughly dry4 ,set it aside and look at it again in a few minutes4 ,what caused the mist when you breathed across the ice8 ,where did the water on the outside of the glass of ice water come from8 ,what made it condense8 ,illustration3 ,,fig4 #aeh4 ,if you blow gently over ice1 you can see your breath4 ,,application #ff4 ,explain why clouds are formed high in the atmosphere2 why we have dew at night instead of in the daytime2 why clothes dry more quickly in a breeze than in still air2 why clothes dry more quickly on a sunny day than on a foggy one4 ,illustration3 ,,fig4 #aei4 ,the glass does not leak2 the moisture on it comes from the air4 ,,inference ,,exercise ,explain the following3 #daa4 ,a gas-filled electric lamp gets hotter than a vacuum lamp4 #dab4 ,you can remove a stamp from an envelope by soaking it in water4 #dac4 ,we see our breath on cold days and not on warm days4 #dad4 ,the electric arc is exceedingly hot4 #dae4 ,rock candy is made by hanging a string in a strong syrup left open to the air4 #daf4 ,dishes in which candy has been made should be put to soak4 #dag4 ,moisture gathers on eyeglasses when the wearer comes from a cold room into a warm one4 #dah4 ,sprinkling the street on a hot day makes the air cool4 #dai4 ,you cannot see things in a dark room4 #dbj4 ,where air is rising there is likely to be rain4 ,,section #de4 ,softening due to oil or water4 ,why does fog deaden a tennis racket8 ,how does cold cream keep your face from becoming chapped8 ,let us now imagine that animal and plant substances have suddenly lost their ability to be softened by oil or water4 ,all living things soon feel very uncomfortable4 ,your face and hands sting and crack2 the skin all over your body becomes harsh and dry2 your mouth feels parched4 ,the shoes you are wearing feel as if they had been dried over a radiator after being very wet1 only they are still harder and more uncomfortable4 ,a man driving a horse feels the lines stiffening in his hands2 and the harness soon becomes so dry and brittle that it cracks and perhaps breaks if the horse stops suddenly4 ,the leaves on the trees begin to rattle and break into pieces as the wind blows against them4 ,although they keep their greenness1 they act like the driest leaves of autumn4 ,i doubt whether you or any one can stay alive long enough to notice such effects4 ,for the muscles of your body1 including those that make you breathe and make your heart beat1 probably become so harsh and stiff that they entirely fail to work1 and you drop dead among thousands of other stiff1 harsh-skinned animals and people4 ,so it is well that in the real world oil and water soften practically all plant and animal tissues4 ,of course1 in living plants and animals the oil and water come largely from within themselves4 ,your skin is kept moist and slightly oily all the time by little glands within it1 some of which1 called sweat glands1 secrete perspiration and others of which secrete oil4 ,but sometimes the oil is washed off the surface of your hands1 as when you wash an article in gasoline or strong soap4 ,then you feel that your skin is dry and harsh4 ,and when you want to soften it again you rub into it oily substances1 like cold cream or vaseline4 ,in the same way if harness or shoes get wet and then are dried out1 they can be made properly flexible by oiling4 ,you could wet them1 of course1 and this would soften them as long as they stayed wet4 ,but water evaporates rather quickly2 so when you want a thing to stay soft1 you usually apply some kind of oil or grease4 ,just as diffusion and the forming of solutions are increased by heat1 this softening by oil and water works better if the oil or water is warm4 ,that is why you soak your hands in warm water before manicuring your nails4 ,,application #fg4 ,explain why women dampen clothes before ironing them2 why crackers are put up in waterproof cartons2 why an oil shoe polish is better than one containing water4 ,,inference ,,exercise ,explain the following3 #dba4 ,you can shorten your finger nails by filing them4 #dbb4 ,you can do it more quickly after washing them than before4 #dbc4 ,after a flashlight picture is taken1 the smoke soon reaches all parts of the room4 #dbd4 ,a jeweler wears a convex lens on his eye when he works with small objects4 #dbe4 ,shoemakers soak the leather before half-soling shoes4 #dbf4 ,lightning often sets fire to houses or trees that it strikes4 #dbg4 ,the directions on many bottles of medicine and of preparations for household use say1 ,shake well before using4 #dbh4 ,if you set a cold tumbler inside of one that has just been washed in hot water1 the outer one will crack in a few minutes4 #dbi4 ,a dry cloth hung out at night becomes wet1 while a wet cloth hung out on a clear day dries4 #dcj4 ,putting cold cream or tallow around the roots of your finger nails will help to prevent hangnails4 ,,chapter ,,ten ,,chemical ,,change ,,and ,,energy ,,section #df4 ,what things are made of3 ,elements4 ,what is water made of8 ,what is iron made of8 ,is everything made out of dust8 ,one of the most natural questions in the world is1 ,what is this made of8 ,if we are talking about a piece of bread1 the answer is1 of course1 flour1 water1 milk1 shortening1 sugar1 salt1 and yeast4 ,but what is each of these made of8 ,flour is made of wheat1 and the wheat is made of materials that the plant gets from the earth1 water1 and air4 ,then what are the earth1 water1 and air made of8 ,a chemist is a person who can answer these questions and who can tell what almost everything is made of4 ,and a strange thing that chemists have found out is this3 ,everything in the world is made out of one or more of about eighty-five simple substances called elements4 ,,what ,,an ,,element ,,is4 ,an element is a substance that is not made of anything else but itself4 ,gold is one of the eighty-five elements2 there are no other substances known to man that you can put together to make gold4 ,it is made of gold and that is all4 ,there is a theory that maybe all the elements are made of electrons in different arrangements1 or of electrons and one other thing2 but we do not know that1 it is only a theory4 ,carbon is another element2 pure charcoal is carbon4 ,the part of the air that we use when we breathe or when we burn things is called oxygen4 ,oxygen is an element2 it is not made of anything but itself4 ,there is another gas which is often used to fill balloons that are to go very high2 it is the lightest in the world and is called hydrogen4 ,hydrogen is an element4 ,for a long time people thought that water was an element4 ,water certainly looks and seems as if it were made only of itself4 ,yet during the thousands of years that people believed water was an element1 they were daily putting two elements together and making water out of them4 ,when you put a kettle1 or anything cold1 over a fire1 tiny drops of water always form on it4 ,these are not drops of water that were dissolved in the air1 and that condense on the sides of the cold kettle2 if they were1 they would gather on the kettle better in the open air than over the hot fire4 ,really there is some of that very light gas1 hydrogen1 in the wood or coal or gas that you use1 and this hydrogen joins the oxygen in the air to make water whenever we burn ordinary fuel4 ,but the best way to prove that water is made of two gases is to take the water apart and get the gases from it4 ,here are the directions for doing this3 ,,experiment #ij4 ,a regular bought electrolysis apparatus may be used1 or you can make a simple one as follows3 ,use a tumbler and two test tubes4 ,if the test tubes are rather small 7#c_/h'' ,x #c''7 they will fill more quickly4 ,dissolve a little lye 7about #a_/h teaspoonful7 in half a pint of water to make the water conduct electricity easily1 or you may use sulfuric acid in place of lye4 ,pour half of this solution into the tumbler4 ,pour as much more as possible into the test tubes1 filling both tubes brim full4 ,cover the mouth of each test tube with a small square of dry paper or cardboard1 and turn it upside down1 lowering it into the tumbler4 ,the electrodes are two #c_/d'' pieces of platinum wire 7#cj71 which are soldered to two pieces of insulated copper wire1 each about #b feet long4#h ,the other ends of the copper wire are bare4 ,fasten the bare end of one copper wire to one nail of the nail plug if you have direct current 7d4 c47 in the laboratory1 and fasten the bare end of the other wire to the other nail2 then turn on the electricity4 ,if you do not have direct current in the laboratory1 attach the copper wires to the two poles of a battery instead4 ,footnote #h3 ,if the copper wire is drawn through a piece of #a_/d-;inch soft glass tubing so that only the platinum wire projects from the end of the tube1 and the tube is then sealed around the platinum by holding it in a ,bunsen burner a few minutes1 your electrodes will be more permanent and more satisfactory4 ,the pieces of glass tubing should be about #f inches long 7see ,fig4 #afj74 ,bend the platinum electrodes up so that they will stick up into the test tubes from below4 ,bubbles should immediately begin to gather on the platinum wire and to rise in the test tubes4 ,as the test tubes fill with gas1 the water is forced out2 so you can tell how much gas has collected at any time by seeing how much water is left in each tube4 ,one tube should fill with gas twice as fast as the other4 ,the gas in this tube is hydrogen2 there is twice as much hydrogen as there is oxygen in water4 ,the tube that fills more slowly contains oxygen4 ,when the faster-filling tube is full of hydrogen--that is1 when all of the water has been forced out of it--take the electrode out and let it hang loose in the glass4 ,put a piece of cardboard about #a inch square over the mouth of the test tube2 take the test tube out of the water and turn it right side up1 keeping it covered with the cardboard4 ,light a match1 remove the cardboard cover1 and hold the match over the open test tube4 ,does the hydrogen in it burn8 ,when the tube containing the oxygen is full1 take it out1 covered1 just as you did the hydrogen test tube4 ,but in this case make the end of a stick of charcoal glow1 remove the cardboard from the tube1 and then plunge the glowing charcoal into the test tube full of oxygen4 ,illustration3 ,,fig4 #afj4 ,the electrodes are made of loops of platinum wire sealed in glass tubes4 ,only oxygen will make charcoal burst into flame like this4 ,when people found that they could take water apart in this way and turn it into hydrogen and oxygen1 and when they found that whenever they combined hydrogen with oxygen they got water1 they knew1 of course1 that water was not an element4 ,maybe some day they will find that some of the eighty-five or so substances that we now consider elements can really be divided into two or more elements2 but so far the elements we know show no signs of being made of anything except themselves4 ,the last section of this book will explain something about the way the chemist goes to work to find out what elements are hidden in compounds4 ,illustration3 ,,fig4 #afa4 ,water can be separated into two gases by a current of electricity4 ,,the ,,quick ,,way ,,chemists ,,write ,,about ,,elements4 ,since everything in the world is made of a combination or a mixture of elements1 chemists have found it very convenient to make abbreviations for the names of the elements so that they can quickly write what a thing is made of4 ,they indicate hydrogen by the letter ,h4 ,o always means oxygen to the chemist2 ,c means carbon2 and ,cl means chlorine1 the poison gas so much used in the ,world ,war4 ,the abbreviation stands for the ,latin name of the element instead of for the ,english name1 but they are often almost alike4 ,the ,latin name for the metal sodium1 however1 is natrum1 and chemists always write ,na when they mean sodium2 this is fortunate1 because ,s already stands for the element sulfur4 ,fe means iron 7,latin1 ferrum74 ,but ,i stands for the element iodine4 7,the iodine you use when you get scratched is the element iodine dissolved in alcohol47 ,it is not necessary for you to remember the chemical symbols unless you mean to become a chemist or unless you read a good deal about chemistry4 ,but almost every one knows at least that ,h means hydrogen1 ,o means oxygen1 and ,c means carbon4 ,when a chemist wants to show that water is made of hydrogen two parts and oxygen one part1 he writes it very quickly like this3 ,h#b,o 7pronounced ,h two ,o74 ,h#b,o means to a chemist just as much as w-a-t-e-r means to you2 and it means even more1 because it tells that water is made of two parts hydrogen and one part oxygen4 ,if a chemist wanted to write1 ,you can take water apart and it will give you two parts of hydrogen and also one part of oxygen1 this is what he would put down3 ,h#b,o - #b;,h,o4 ,if he wanted to show that you could combine two parts of hydrogen and one part of oxygen to form water1 he would write it quickly like this3 #b;,h,o - ,h#b,o4 ,these are called chemical equations4 ,you do not need to remember them2 they are put here merely so that you will know what they look like4 ,some of them are much longer and more complicated1 like this3 ,,hc#b;,h#c,o#b,na,h,c,o#c - ,h#b,o,,co#b,na,c#b;,h#c,o#b4 ,this is the chemist's way of saying1 ,vinegar is made of one part of hydrogen gas that will come off easily and that gives it its sour taste1 two parts of carbon1 three parts of hydrogen that does not come off so easily1 and two parts of oxygen4 ,when you put this with baking soda1 which is made of one part of the metal sodium1 one part of hydrogen1 one part of carbon1 and three parts of oxygen1 you get water and carbon dioxid gas and a kind of salt called sodium acetate4 ,or1 more briefly1 ,if you put baking soda with vinegar1 you get water1 a gas called carbon dioxid1 and a salt4 ,you can see how much shorter the chemist's way of writing it is4 ,,some ,,elements ,,you ,,already ,,know4 ,here is a list of some elements that you are already pretty well acquainted with4 ,the abbreviation is put after the name for each4 ,this list is only for reference and need not be learned4 ,aluminum 7,al7 ,carbon 7,c7 ,charcoal1 diamonds1 graphite 7the lead in a pencil is graphite71 hard coal1 and soot are all made of carbon4 ,chlorine 7,cl7 ,a poison gas that was used in the war4 ,copper 7,cu7 ,gold 7,au7 ,hydrogen 7,h7 ,the lightest gas in the world2 you got it from water in the last experiment and will get it from an acid in the next4 ,iodine 7,i7 ,it is a solid2 what you use is iodine dissolved in alcohol4 ,iron 7,fe7 ,lead 7,pb7 ,mercury 7,hg7 ,this is another name for quicksilver4 ,nickel 7,ni7 ,nitrogen 7,n7 ,about four fifths of the air is pure nitrogen4 ,oxygen 7,o7 ,this is the part of the air we use in breathing4 ,you got some out of water1 and you will have it to deal with in another experiment4 ,phosphorus 7,p7 ,phosphorus makes matches glow in the dark1 and it makes them strike easily4 ,platinum 7,pt7 ,radium 7,ra7 ,silver 7,ag7 ,sodium 7,na7 ,you are not acquainted with sodium by itself1 but when it is combined with the poison gas1 chlorine1 it makes ordinary table salt4 ,sulfur 7,s7 ,tin 7,sn7 ,zinc 7,zn7 ,for the rest of the elements you can refer to any textbook on chemistry4 ,,how ,,elements ,,hide ,,in ,,compounds4 ,one strange thing about an element is that it can hide so completely1 by combining with another element1 that you would never know it was present unless you took the combination apart4 ,take the black element carbon1 for instance4 ,sugar is made entirely of carbon and water4 ,you can tell this by making sugar very hot4 ,when it is hot enough1 it turns black2 the water part is driven off and the carbon is left behind4 ,yet to look at dry1 white sugar1 or to taste its sweetness1 one would never suspect that it was made of pure black1 tasteless carbon and colorless1 tasteless water4 ,mixing carbon and water would never give you sugar4 ,but combining them in the right proportions into a chemical compound does produce sugar4 ,not only is carbon concealed in sugar1 but it is present in all plant and animal matter4 ,that is why burning almost any kind of food makes it black4 ,you drive off most of the other elements and separate the food into its parts by getting it too hot2 the water evaporates and so does the nitrogen2 what is left is mainly black carbon4 ,,making ,,hydrogen ,,come ,,out ,,of ,,hiding4 ,the light gas1 hydrogen1 conceals itself as perfectly as carbon does by combining with other elements4 ,it is hiding in everything that is sour and in many things that are not sour4 ,and you can get it out of sour things with metals4 ,in some cases it is harder to separate than in others2 and some metals separate it better than others do4 ,but one sour compound that you can easily get the hydrogen out of is hydrochloric acid 7,h,cl71 which is hydrogen combined with the poison gas1 chlorine4 ,one of the best metals to get the hydrogen out with is zinc4 ,here are the directions for doing it and incidentally for making a toy balloon3 ,,experiment #ia4 ,do this experiment on the side of the laboratory farthest from any flames or fire4 ,do not let any flame come near the flask in which you are making hydrogen4 ,in the bottom of a flask put two or three wads of zinc shavings1 each about the size of your thumb4 ,fit a one-hole rubber stopper to the flask4 ,take the stopper out and put a piece of glass tubing about #e inches long through the hole of the stopper1 letting half an inch or so stick down into the flask when the stopper is in place 7,fig4 #afb74 ,with a rubber band fasten the mouth of a rubber balloon over the end of the glass tube that will be uppermost4 ,fill the balloon by blowing through the glass tube to see if all connections are tight1 and to see how far it may be expanded without danger of breaking4 ,you can tell when the balloon has about all it will hold1 by pressing gently with your fingers4 ,if the rubber feels tight1 do not blow any more4 ,let the air out of the balloon again4 ,now get some hydrochloric acid 7,h,cl7 diluted with three parts of water4 ,find the bottle marked ,h,cl1 dilute #a-c1 in which the acid is already diluted4 ,before you open the bottle1 get some solution of soda1 and keep it near you2 if in this experiment or any other you spatter acid on your hands or face or clothes1 wash it off immediately with soda solution4 ,remember this4 ,ammonia will do as well as the soda solution to wash off the acid1 but be careful not to get it into your eyes4 ,pour the hydrochloric acid 7,h,cl7 on the zinc shavings in the bottom of the flask1 until the acid stands about an inch deep4 ,then quickly put the rubber stopper with its attachments into the flask1 so that the gas that bubbles up will blow up the balloon4 ,if the bubbles do not form rapidly1 ask the teacher to pour a little strong hydrochloric acid into the flask2 but this will probably not be necessary4 ,let the balloon keep filling until it is as large as you blew it4 ,but if the bubbles stop coming before it gets as large as that1 close the neck of the balloon by pinching it tightly1 and take the stopper out4 ,let some one add more zinc shavings and more acid to the flask2 put the stopper back in1 and stop pinching the neck of the balloon4 ,in this and all other experiments when you use strong acids1 pour the used acids into the crockery jar that is provided for such wastes4 ,do not pour them into the sink1 as acids ruin sink drainpipes4 ,when the balloon is full1 close the neck by slipping the rubber band up from the part of the neck that is over the glass tube on to the upper part of the neck4 ,pull the balloon off the glass tube and pinch the neck firmly shut4 ,take the stopper out and rinse the flask several times with running water4 ,any zinc that is left should be rinsed thoroughly1 dried1 and set aside so that it may be used again4 ,now tie one end of a long thread firmly around the mouth of the balloon and let the balloon go4 ,does it rise8 ,if it does not1 the reason is that you did not get it full enough4 ,in that case make more hydrogen and fill it fuller1 as explained above4 ,illustration3 ,,fig4 #afb4 ,filling a balloon with hydrogen4 ,illustration3 ,,fig4 #afc4 ,adding more acid without losing the gas4 ,here is another experiment with hydrogen3 ,,experiment #ib4 ,put a wad of zinc shavings1 about the size of the end of your little finger1 into the bottom of a test tube4 ,cover it with hydrochloric acid 7,h,cl7 diluted one to three1 as in the preceding experiment4 ,after the bubbles have been rising for a couple of minutes1 take the test tube to the side of the laboratory where the burners are1 and hold a lighted match at its mouth4 ,will hydrogen burn8 ,remember that the hydrogen which the zinc is driving out of the acid is exactly the same as the hydrogen you drove out of water with an electric current4 ,there is a metal called sodium 7,na7 and another called potassium 7,k7 which are as soft as stiff putty and as shiny as silver2 if you put a tiny piece of sodium 7,na7 or potassium 7,k7 on water1 it will drive the hydrogen out of the water just as zinc drove it out of the acid4 ,the action is so swift and violent and releases so much heat that the hydrogen which is set free catches fire4 ,this makes it look as if the metal were burning as it sputters around on top of the water4 ,there is so much sputtering that the experiment is dangerous2 people have been blinded by the hot alkaline water spattering into their eyes4 ,so you cannot try this until sometime when you take a regular course in chemistry4 ,illustration3 ,,fig4 #afd4 ,trying to see if hydrogen will burn4 ,,getting ,,oxygen1 ,a ,,gas1 ,,from ,,two ,,solids4 ,oxygen 7,o7 can hide just as successfully as hydrogen4 ,practically all elements can do the same by combining with others4 ,here is an experiment in which you can get the gas1 oxygen1 out of a couple of solids4 ,if you went to the moon or some other place where there is no air1 you could carry oxygen very conveniently locked up in these solid substances4 ,oxygen1 you remember1 is the part of the air that keeps us alive when we breathe it4 ,,experiment #ic4 ,in a test tube mix about one half teaspoonful each of white potassium chlorate crystals and black grains of manganese dioxid4 ,put a piece of glass tubing through a cork so that the tubing will stick down a little way into the test tube4 ,do not put the glass tubing through the cork while the cork is in the test tube3 insert the glass tubing first1 then put the cork into the test tube4 ,put one end of a #b-;foot piece of rubber tubing over the glass tube and put the other end into a pan of water4 ,fill a flask or bottle to the brim with water1 letting it overflow a little2 hold a piece of cardboard firmly over the mouth of the bottle2 turn the bottle upside down quickly1 putting the mouth of it under water in the pan2 take the cardboard away4 ,the water should all stay in the bottle4 ,now shove the rubber tube into the neck of the bottle until it sticks up an inch or two4 ,during this experiment1 be careful not to let the neck of the bottle or flask pinch the rubber tubing2 small pieces of wood or glass tubing laid beside the rubber tubing where it goes under the run of the neck will prevent this4 ,hold1 the test tube1 tightly corked1 over the flame of a burner1 keeping the tube at a slant and moving it slightly back and forth so that all the material in it will be thoroughly heated4 ,if you stop heating the test tube even for a couple of seconds1 take the cork out2 if you do not remove the cork1 the cooling gas in the test tube will shrink and allow the water from the pan to be forced through the rubber tube into the test tube1 breaking it into pieces4 ,when enough gas has bubbled up into the bottle to force all the water out1 and when bubbles begin to come up outside the bottle1 uncork the test tube and lay it aside where it will not burn anything2 then slide the cardboard under the mouth of the bottle and turn it right side up2 leave the cardboard on the bottle4 ,light a piece of charcoal1 or let a splinter of wood burn a few minutes and then blow it out so that a glowing coal will be left on the end of it4 ,lift the cardboard off the bottle and plunge the glowing stick into it for a couple of seconds4 ,cover the bottle after taking out the stick1 and repeat1 using a lighted match or a burning piece of wood instead of the glowing stick4 ,if you dip a piece of iron picture wire in sulfur and light it1 and then plunge it into the bottle1 you will see iron burn4 ,illustration3 ,,fig4 #afe4 ,filling a bottle with oxygen4 ,illustration3 ,,fig4 #aff4 ,the iron really burns in the jar of oxygen4 ,both manganese dioxid and potassium chlorate have a great deal of oxygen bound up in them4 ,when they join together1 as they do when you heat them1 they cannot hold so much oxygen1 and it escapes as a gas4 ,in the experiment1 the escaping oxygen passed through the tube1 filled the bottle1 and forced the water out4 ,,what ,,burning ,,is4 ,when anything burns1 it is simply joining oxygen4 ,when a thing burns in air1 it cannot join the oxygen of the air very fast1 for every quart of oxygen in the air is diluted with a gallon of a gas called nitrogen4 ,nitrogen will not burn and it will not help anything else to burn4 ,but when you have pure oxygen1 as in the bottle1 the particles of wood or charcoal or picture wire can join it easily2 so there is a very bright blaze4 ,although free oxygen helps things to burn so brilliantly1 a match applied to the solids from which you got it would go out4 ,and while hydrogen burns very easily1 you cannot burn water although it is two-thirds hydrogen4 ,water is ,h#b,o1 you remember4 ,,what ,,compounds ,,are4 ,when elements are combined with other elements1 the new substances that are formed are called compounds4 ,water 7,h#b,o7 is a compound1 because it is made of hydrogen and oxygen combined4 ,when elements unite to form compounds1 they lose their original qualities4 ,the oxygen in water will not let things burn in it2 the hydrogen in water will not burn4 ,salt 7,na,cl7 is a compound4 ,it is made of the soft metal sodium 7,na71 which when placed on water sputters and drives hydrogen out of the water1 and the poison gas chlorine 7,cl71 combined with each other4 ,and salt is neither dangerous to put in water like sodium1 nor is it a greenish poison gas like chlorine4 ,,mixtures4 ,but sometimes elements can be mixed without their combining to form compounds1 in such a way that they keep most of their original properties4 ,air is a mixture4 ,it is made of oxygen 7,o7 and nitrogen 7,n74 ,if they were combined1 instead of mixed1 they might form laughing gas1--the gas dentists use in putting people to sleep when they pull teeth4 ,so it is well for us that air is only a mixture of oxygen and nitrogen1 and not a compound4 ,you found that things burned brilliantly in oxygen4 ,well1 things burn in air too1 because a fifth of the air is oxygen and the oxygen of the air has all its original properties left4 ,things do not burn as brightly in air as they do in pure oxygen for the same reason that a teaspoonful of sugar mixed with #d teaspoonfuls of boiled rice does not taste as sweet as pure sugar4 ,the sugar itself is as sweet1 but it is not as concentrated4 ,likewise the oxygen in the air is as able to help things burn as pure oxygen is2 but it is diluted with four times its own volume of nitrogen4 ,a solution is a mixture1 too2 for although substances disappear when they dissolve1 they keep their own properties4 ,sugar is sweet whether it is dissolved or not4 ,salt dissolved in water makes brine2 but the water will act in the way that it did before4 ,it will still help to make iron rust2 and salt will be salty1 whether or not it is dissolved in water4 ,that is why solutions are only mixtures and are not chemical compounds4 ,,everything ,,in ,,the ,,world ,,is ,,made ,,of ,,atoms4 ,everything in the world is either an element or a compound or a mixture4 ,most plant and animal matter is made of very complicated compounds1 or mixtures of compounds4 ,all pure metals are elements2 but metals1 when they are melted1 can be dissolved in each other to form alloys1 which really are mixtures4 ,most of the so-called gold and silver and nickel articles are really made of alloys2 that is1 the gold1 silver1 or nickel has some other elements dissolved in it to make it harder1 or to impart some other quality4 ,bronze and brass are always alloys2 steel is generally an alloy made chiefly of iron but with other elements such as tungsten1 of which electric lamp filaments are made1 dissolved in it to make it harder4 ,an alloy is a special kind of solution not quite like an ordinary solution4 ,you remember that in the opening chapters we often spoke of molecules1 the tiny particles of matter that are always moving rapidly back and forth4 ,well1 if you were to examine a molecule of water with the microscope which we imagined could show us molecules1 you would find that the molecule of water was made of three still smaller particles1 called atoms4 ,two of these would be atoms of hydrogen and would probably be especially small2 the third would be larger and would be an oxygen atom4 ,in the same way if you looked at a molecule of salt under this imaginary microscope1 you would probably find it made of two atoms1 one of sodium 7,na7 and one of chlorine 7,cl71 held fast together in some way which we do not entirely understand4 ,the smallest particle of an element is called an atom4 ,the smallest particle of a compound is called a molecule4 ,molecules are usually made of two or more atoms joined together4 ,,application #fh4 ,in the following list tell which things are elements1 which are compounds1 and which are mixtures1 remembering that both solutions and alloys are mixtures3 ,air1 water1 salt1 gold1 hydrogen1 milk1 oxygen1 radium1 nitrogen1 sulfur1 baking soda1 sodium1 diamonds1 sweetened coffee1 phosphorus1 hydrochloric acid1 brass4 ,,inference ,,exercise ,explain the following3 #dca4 ,although in most electric lamps there is a vacuum between the glowing filaments and the glass1 the glass nevertheless becomes warm4 #dcb4 ,clothes left out on the line overnight usually become damp4 #dcc4 ,you can separate water into hydrogen and oxygen1 yet you cannot separate the hydrogen or the oxygen into any other substances4 #dcd4 ,wet paper tears easily4 #dce4 ,windows are soiled on the outside much more quickly in rainy weather than in clear weather4 #dcf4 ,if you stir iron and sand together1 the iron will rust as if alone4 #dcg4 ,rust is made of iron and oxygen1 yet you cannot separate the iron from the oxygen with a magnet4 #dch4 ,a reading glass helps you to read fine print4 #dci4 ,stretching the string of a musical instrument more tightly makes the note higher4 #ddj4 ,mayonnaise dressing1 although it contains much oil1 can readily be washed off a plate with cold water4 ,,section #dg4 ,burning3 ,oxidation4 ,what makes smoke8 ,what makes fire burn8 ,why does air keep us alive8 ,why does an apple turn brown after you peel it8 ,if oxygen should suddenly lose its power of combining with other things to form compounds1 every fire in the world would go out at once4 ,you could go on breathing at first1 but your breathing would be useless4 ,you would shiver1 begin to struggle1 and death would come1 all within a minute or two4 ,plants and trees would die1 but they would remain standing until blown down by the wind4 ,even the fish in the water would all die in a few minutes1--more quickly than they usually do when we take them out of the water4 ,in a very short time everything in the world would be dead4 ,then suppose that this condition lasted for hundreds and hundreds of years1 the oxygen remaining unable to combine with other elements4 ,during all that time nothing would decay4 ,the trees would stay as they fell4 ,the corpses of people would dry and shrivel1 but they would lie where they dropped as perfectly preserved as the best of mummies4 ,the dead fish would float about in the oceans and lakes4 ,this is all because life is kept up by burning4 ,and burning is simply the combining of different things with oxygen4 ,if oxygen ceased to combine with the wood or gas or whatever fuel you use1 that fuel could not burn2 how could it when burning means combining with oxygen8 ,the heat in your body and the energy with which you move come entirely from the burning 7oxidation7 of materials in your body2 and that is why you have to breathe2 you need to get more and more oxygen into your body all the time to combine with the carbon and hydrogen in the cells of which your body is made4 ,plants breathe1 too4 ,they do not need so much oxygen1 since they do not keep warm and do not move around2 but each plant cell needs oxygen to live2 there is burning 7oxidation7 going on in every living cell4 ,fishes breathe oxygen through their gills1 absorbing the oxygen that is dissolved in the water4 ,they do not take the water apart to get some of the combined oxygen from it2 there is always some free oxygen dissolved in any water that is open to the air4 ,it is clear that fires would all go out and everything would die if burning 7combining with oxygen7 stopped4 ,the reason things would not decay is that decay usually is a slow kind of oxidation 7burning74 ,when it is not this1 it is the action of bacteria4 ,but bacteria themselves could not live if they had no oxygen2 so they could not make things decay4 ,not only would the dead plants and animals remain in good condition1 but the clothes people were wearing when they dropped dead would stay unfaded and bright colored through all the storms and sunshine4 ,and the iron poles and car tracks and window bars would remain unrusted4 ,for bleaching and rusting are slow kinds of oxidation or burning 7combining with oxygen74 ,here are two experiments which show that you cannot make things burn unless you have oxygen to combine with them3 ,,experiment #id4 ,light a candle not more than #d inches long and stand it on the plate of the air pump4 ,cover it with the bell jar and pump the air out4 ,what happens to the flame8 ,,experiment #ie4 ,fasten a piece of candle #c or #d inches long to the bottom of a pan4 ,pour water into the pan until it is about an inch deep4 ,light the candle4 ,turn an empty milk bottle upside down over the candle4 ,watch the flame4 ,leave the bottle over the candle until the bottle cools4 ,watch the water around the bottom of the bottle4 ,lift the bottle partly out of the water1 keeping the mouth under water4 ,the bubbles that came out for a few seconds at the beginning of the experiment were caused by the air in the bottle being heated and expanded by the flame4 ,soon1 however1 the oxygen in the air was used so fast that it made up for this expansion1 and the bubbles stopped going out4 ,when practically all the oxygen was used1 the flame went out4 ,the candle is made mostly of a combination of hydrogen and carbon4 ,the hydrogen combines with part of the oxygen in the air that is in the bottle to form a little water4 ,the carbon combines with the rest of the oxygen to make carbon dioxid1 much of which dissolves in the water below4 ,so there is practically empty space in the bottle where the oxygen was1 and the air outside forces the water up into this space4 ,the rest of the bottle is filled with the nitrogen that was in the air and that has remained unchanged4 ,about how much of the air was oxygen is indicated by the space that the water filled after the oxygen was combined with the candle4 ,illustration3 ,,fig4 #afg4 ,the water rises in the bottle after the burning candle uses up the oxygen4 ,,carbon ,,and ,,hydrogen ,,the ,,chief ,,elements ,,in ,,fuel4 ,carbon and hydrogen make up the larger part of almost every substance that is used for fuel1 including gas1 gasoline1 wood1 and soft coal2 alcohol1 crude oil1 kerosene1 paper1 peat1 and the acetylene used in automobile and bicycle lamps4 ,hard coal1 coke1 and charcoal are1 however1 chiefly plain carbon4 ,since burning is simply the combining of things with oxygen1 it is plain that when the carbon of fuel joins oxygen we shall get carbon dioxid 7,,co#b74 ,when the hydrogen in the fuel joins oxygen1 what must we get8 ,when things do not burn up completely1 the carbon may be left behind as charcoal4 ,that is what happens when food burns on the stove4 ,but if anything burns up entirely1 the carbon or charcoal burns too1 passing off as the invisible gas1 carbon dioxid1 just as the hydrogen burns to form steam or water4 ,it is because almost every fuel forms water when it burns1 that we find drops of water gathering on the outside of a cold kettle or cold flatiron if either is put directly over a flame4 ,the hydrogen in the fuel combines with the oxygen of the air to form steam4 ,as the steam strikes the cold kettle or iron1 it condenses and forms drops of water4 ,,nothing ,,ever ,,destroyed4 ,one important result of the discovery that burning is only a combining of oxygen with the fuel was that people began to see that nothing is ever destroyed4 ,there is exactly as much carbon in the carbon dioxid that floats off from a fire as there was in the wood that was burned up2 and there is exactly as much hydrogen in the water vapor that floats off from the fire as there was in the wood4 ,chemists have caught all the carbon dioxid and the water vapor and weighed them and added their weight to the weight of the ashes2 and they have found them to weigh even more than the original piece of wood1 because of the presence of the oxygen that combined with them in the burning4 ,if everything in the world were to burn up1 using the oxygen that is already here1 the world would not weigh one ounce more or less than it does now4 ,all the elements that were here before would still be here2 but they would be combined in different compounds4 ,instead of wood and coal and oxygen we should have water and carbon dioxid2 instead of diamonds1 we should have just carbon dioxid2 and so on with everything that can burn4 ,,why ,,water ,,puts ,,out ,a ,,fire4 ,water puts out a fire because it will not let enough free oxygen get to the wood1 or whatever is burning1 to combine with it4 ,the oxygen that is locked up in a compound1 like water1 you remember1 has lost its ability to combine with other things4 ,sand puts out a fire in the same way that water does4 ,most fire extinguishers make a foam of carbon dioxid 7,,co#b7 which covers the burning material and keeps the free oxygen in the air from coming near enough to combine with it4 ,water will not put out burning oil1 however1 as the oil floats up on top of the water and still combines with the oxygen in the air4 ,,why ,,electric ,,lamps ,,are ,,usually ,,vacuums4 ,electric lamps usually have vacuums inside because the filament gets so hot that it would burn up if there were any oxygen to combine with it4 ,but in a globe containing no oxygen the filament may be made ever so hot and it cannot possibly burn4 ,high-power electric lamps are not made with vacuums but are gas-filled4 ,the gas that is oftenest put into lamps is nitrogen1--the same gas that is mixed with the oxygen in air4 ,by taking all the oxygen out of a quantity of air1 the lamp manufacturers can use in perfect safety the nitrogen that is left4 ,it will not combine with the glowing filament4 ,there is no oxygen to combine with the filament2 so the lamp does not burn out4 ,,what ,,flames ,,are4 ,when you look at a flame1 it seems as if fire were a real thing and not merely a process of combining something with oxygen4 ,the flame is a real thing4 ,it is made up of hot gases1 rising from the hot fuel1 and it is usually filled with tiny glowing particles of carbon4 ,when you burn a piece of wood1 the heat partly separates its elements1 just as heating sugar separates the carbon from the water4 ,some of the hydrogen gas in the wood and some of the carbon too are separated from the wood by the heat4 ,these are pushed up by the cooler air around and combine with the oxygen as they rise4 ,the hydrogen combines more easily than the carbon2 part of the carbon may remain behind as charcoal if your wood does not all burn up1 and many of the smaller carbon particles only glow in the burning hydrogen1 instead of burning4 ,that is what makes the flame yellow4 ,if you hold anything white over a yellow flame1 it will soon be covered with black soot1 which is carbon4 ,,what ,,smoke ,,is4 ,smoke consists mostly of little specks of unburned carbon4 ,that is why it is gray or black4 ,when you have black smoke1 you may always be sure that some of the carbon particles are not combining properly with oxygen4 ,yellow flames are usually smoky2 that is1 they usually are full of unburned bits of carbon that float off above the flame4 ,but by letting enough air in with the flame1 it is possible to make all the little pieces of carbon burn 7combine with the oxygen of the air7 before they leave the heat of the burning hydrogen4 ,that is why kerosene lamps do not smoke when the chimney is on4 ,the chimney keeps all the hot gases together1 and this causes a draft of fresh air to blow up the chimney to push the hot gases on up4 ,the fresh air blowing up past the flame gives plenty of oxygen to combine with the carbon4 ,the drum part of an oil heater acts in the same way2 when the drum is open1 the heater smokes badly2 when it is closed up1 enough air goes past the flame to burn up all the carbon4 ,but if you turn either lamp or heater too high1 it will smoke anyway2 you cannot get enough air through to combine with all the carbon4 ,the hottest flames are the blue flames4 ,that is because in a blue flame all the carbon is burning up along with the hydrogen of the fuel--both are combining with the oxygen of the air as rapidly as possible4 ,a gas or gasoline stove is so arranged that air is fed into the burner with the gas4 ,you will see this in the following experiment3 ,,experiment #if4 ,light the ,bunsen burner in the laboratory4 ,open wide the little valve in the bottom4 ,now put your finger and thumb over the hole in the bottom of the burner4 ,what happens to the flame8 ,turn the valve so that it will close the hole in the same way4 ,now hold a white saucer over the flame1 being careful not to get it hot enough to break4 ,what is the black stuff on the bottom of the saucer8 ,examine the gas plate 7small gas stove7 in the laboratory4 ,light it1 and see if you can find the place where the air is fed in with the gas4 ,close this place and see what happens4 ,open it wider and see what happens4 ,if the air opening is too large1 the flame blows2 there is too much cold air coming in with the gas1 and your flame is not as hot as it would be if it did not blow4 ,also1 the stove is liable to back-fire 7catch fire at the air opening7 when the air opening is too wide4 ,illustration3 ,,fig4 #afh4 ,the ,bunsen burner smokes when the air holes are closed4 ,,application #fi4 ,an oil lamp tipped over and the burning oil spread over the floor4 ,near by were a pail of water1 a pan of ashes1 a rug1 and a seltzer siphon4 ,which of these might have been used to advantage in putting out the fire8 ,,application #gj4 ,my finger was burned4 ,i wanted the flesh around it to heal and new skin cells to live and grow rapidly around the burn4 ,put a rubber finger cot on the finger and keep all air out1 one friend advised me4 ,air causes decay and will therefore be bad for the burn4 ,he's wrong2 you should bandage it with clean cloth2 you want air to reach the finger1 ,i've heard1 said another friend4 ,oh1 no1 you don't2 air makes things burn1 and the burn will therefore get worse1 still another one said4 ,what should ,i have done8 ,,application #ga4 ,two students were discussing how coal was formed4 ,the trees must have fallen into water and been completely covered by it1 or they would have decayed1 said one4 ,water makes things decay more quickly2 there must have been a drought and the trees must have fallen on dry ground1 said the second4 ,which was right8 ,illustration3 ,,fig4 #afi4 ,regulating the air opening in a gas stove4 ,,application #gb4 ,a gas stove had a yellow flame4 ,in front1 by the handles1 was a metal disk with holes so arranged that turning it to the left allowed air to mix with the gas on the way to the flame1 and turning it to the right shut the air off 7see ,fig4 #agj74 ,one member of the family said1 ,turn the disk to the left and let more air mix with the gas4 ,but another objected4 ,it has too much air already2 that's why the flame is yellow4 ,turn it to the right and shut off the air from below4 ,you're both wrong4 ,why do you want to change it8 said a third member of the family4 ,the yellow flame is the hottest1 anyway4 ,can't you see that the yellow flame gives more light8 ,and don't you know that light is just a kind of radiant heat8 ,of course the yellow flame is the hottest4 ,leave the stove alone4 ,who was right8 ,illustration3 ,,fig4 #agj4 ,the air openings in the front of a gas stove4 ,,inference ,,exercise ,explain the following3 #dda4 ,iron tracks are welded together with an electric arc4 #ddb4 ,the cool mirror in a bathroom becomes covered with moisture when you take a hot bath4 #ddc4 ,this prevents you from seeing yourself in the mirror4 #ddd4 ,carbon dioxid has oxygen in it1 yet a burning match dropped into a bottle of it will go out4 #dde4 ,a ship that sinks to the bottom of the ocean does not decay4 #ddf4 ,when women put their hair in curlers1 they usually moisten the hair slightly4 #ddg4 ,to dry a pan after washing it1 a person often sets it on the hot stove for a few minutes4 #ddh4 ,when you put a kettle of cold water over a gas flame1 drops of water appear on the lower part of the sides of the kettle4 #ddi4 ,electric power plants are often situated where running water will turn the dynamo4 ,explain the necessity of turning the dynamo4 #dej4 ,we make carbon dioxid by burning carbon1 but you cannot put different things together to make carbon4 ,,section #dh4 ,chemical change caused by heat4 ,why do you have to strike a match to make it burn8 ,how does pulling the trigger make a gun go off8 ,what makes cooked foods taste different from raw ones8 ,has it struck you as strange that we do not all burn up1 since burning is a combining with oxygen1 and we are walking around in oxygen all the time8 ,the only reason we do not burn up is that it usually requires heat to start a chemical change4 ,you already know this in a practical way4 ,you know that you have to rub the head of a match and get it hot before it will begin to burn2 that gunpowder does not go off unless you heat it by the sudden blow of the gun hammer which you release when you pull the trigger2 that you have to concentrate the sun's rays with a magnifying glass to make it set a piece of paper on fire2 and that to change raw food into food that tastes pleasant you have to heat it4 ,if heat did not start chemical change1 you could never cook food1--partly because the fire would not burn1 and partly because the food would not change its taste even if heated by electricity or concentrated sunlight4 ,here is an experiment to show that gas will not burn unless it gets hot enough3 ,,experiment #ig4 ,hold a wire screen #b or #c inches above the mouth of a ,bunsen burner4 ,turn on the gas and light a match1 holding the lighted match above the screen4 ,why1 do you suppose1 does the gas below the screen not burn8 ,hold a lighted match to the gas below the screen4 ,does it burn now8 ,the reason the screen kept the gas below it from catching fire although the gas above it was burning was this3 ,the heat from the flame above was conducted out to the sides by the wire screen as soon as it reached the screen2 so very little heat could get through the screen to the gas below4 ,therefore the gas below the screen never got hot enough for the chemical change of oxidation1 or burning1 to take place4 ,so the gas below it did not catch fire4 ,another simple experiment with the ,bunsen burner1 that shows the same thing in a different way1 is this3 ,illustration3 ,,fig4 #aga4 ,why doesn't the flame above the wire gauze set fire to the gas below8 ,,experiment #ih4 ,light the ,bunsen burner4 ,open the air valve at the bottom all the way4 ,hold the wood end of a match 7not the head7 in the center of the inner greenish cone of flame1 about half an inch above the mouth of the burner4 ,does the part of the match in the center of the flame catch fire8 ,does the part on the edge8 ,what do you suppose is the reason for this8 ,where are the cold gas and air rushing in8 ,can they get hot all at once1 or will they have to travel out or up a way before they have time to get hot enough to combine8 ,illustration3 ,fig4 #agb4 ,the part of the match in the middle of the flame does not burn4 ,,application #gc4 ,explain why boiled milk has a different taste from fresh milk2 why blowing on a match will put it out2 why food gets black if it is left on the stove too long4 ,,inference ,,exercise ,explain the following3 #dea4 ,when you want bread dough to rise1 you put it in a warm place4 #deb4 ,ink left long in an open inkwell becomes thick4 #dec4 ,a ball bounces up when you throw it down4 #ded4 ,when the warm ocean air blows over the cool land in the early morning1 there is a heavy fog4 #dee4 ,striking a match makes it burn4 #def4 ,when you have something hard to cut1 you put it in the part of the scissors nearest the handles4 #deg4 ,a magnet held over iron filings makes them leap up4 #deh4 ,dishes in which flour thickening or dough has been mixed should be washed out with cold water4 #dei4 ,a woolen sweater is liable to stretch out of shape after being washed4 #dfj4 ,when a telegraph operator presses a key in his set1 a piece of iron is pulled down in the set of another operator4 ,,section #di4 ,chemical change caused by light4 ,how can a camera take a picture8 ,why does cloth fade in the sun8 ,what makes freckles8 ,if light could not help chemical change1 nothing would ever fade when hung in the sun2 wall paper and curtains would be as bright colored after #bj years as on the day they were put up1 if they were kept clean2 you would never become freckled1 tanned1 or sunburned2 all photographers and moving-picture operators would have to go out of business2 but worst of all1 every green plant would immediately stop growing and would soon die4 ,therefore1 all cows and horses and other plant-eating animals would die2 and then the flesh-eating animals would have nothing to eat and they would die2 and then all people would die4 ,you will be able better to understand why all this would happen after you do the following experiments1 the first of which will show that light helps the chemical change called bleaching or fading4 ,,experiment #ii4 ,rinse two small pieces of light-colored cloth4 7,lavender is a good color for this experiment47 ,lay one piece in the bright sun to dry2 dry the other in a dark cabinet or closet4 ,the next day compare the two cloths4 ,which has kept its color the better8 ,if the difference is not marked1 repeat the experiment for #b or #c days in succession1 putting the same cloth1 wet1 in the sun each time4 ,bleaching is usually a very slow kind of burning4 ,it is the dye that is oxidized 7burned71 not the cloth4 ,most dyes will combine with the oxygen in the air if they are exposed to the sunlight4 ,the dampness quickens the action4 ,,why ,,some ,,people ,,freckle ,,in ,,the ,,sun4 ,when the sunlight falls for a long time on the skin1 it often causes the cells in the under part of the skin to produce some dark coloring matter1 or pigment4 ,this dark pigment shows through the outer layer of skin1 and we call the little spots of it freckles4 ,some people are born with these pigment spots2 but when the freckles come out from long exposure to the sunlight1 they are an example right in our own skins of chemical change caused by the action of light4 ,tan also is due to pigment in the skin and is caused by light4 ,the next experiments with their explanations will show you how cameras can take pictures4 ,if you are not interested in knowing how photographs are made1 do the experiments and skip the explanations down to the middle of page #ccb4 ,,experiment #ajj4 ,dissolve a small crystal of silver nitrate 7,ag,n,o#c7 in about half an inch of pure water in the bottom of a test tube4 ,distilled water is best for this purpose4 ,now add one drop of hydrochloric acid 7,h,cl74 ,the white powder formed is a silver salt1 called silver chlorid 7,ag,cl72 the rest of the liquid is now a diluted nitric acid 7,,hno#c74 ,pour the suspension of silver chlorid 7,ag,cl7 on a piece of blotting paper or on a paper towel1 so that the water will be absorbed4 ,spread the remaining white paste of silver chlorid 7,ag,cl7 out over the blotter as well as you can4 ,cover part of it with a key 7or anything that will shut off the light71 and leave the other part exposed4 ,if the sun is shining1 put the blotter in the sunlight for #e minutes4 ,otherwise1 let as much daylight fall on it as possible for about #aj minutes4 ,now take the key off the part of the silver chlorid 7,ag,cl7 that it was covering and compare this with the part that was exposed to the light4 ,what has the light done to the silver chlorid 7,ag,cl7 that it shone on8 ,what has happened is that the light has made the silver 7,ag7 separate from the chlorine 7,cl7 of the silver chlorid 7,ag,cl74 ,chemists would write this3 ,ag,cl - ,ag ,cl4 ,that is1 silver chlorid 7,ag,cl7 has changed into silver 7,ag7 and chlorine 7,cl74 ,chlorine1 as you know1 is a poisonous gas1 and it floats off in the air1 leaving the fine particles of silver behind4 ,when silver is divided into very tiny particles1 it absorbs light instead of reflecting it2 so it looks dark gray or black4 ,,how ,,photographs ,,are ,,made4 ,all photography depends on this action of light4 ,the plates or films are coated with a silver salt1--usually a more sensitive salt than silver chlorid4 ,this is exposed to the light that shines through the lens of the camera4 ,as you have learned1 the lens brings the light from the object to a focus and makes an image on the film or plate4 ,the light parts of this image will change the silver salt to silver2 the dark parts will not change it4 ,so wherever there is a white place on the object you are photographing1 there will be a dark patch of silver on the film or plate1 and wherever there is a dark spot on the object1 there will be no change on the film or plate4 ,illustration3 ,,fig4 #agc4 ,the silver salt on the paper remains white where it was shaded by the key4 ,as a matter of fact1 the film or plate is exposed such a short time that there is not time for the change to be completed4 ,so the photographer develops the negative2 he washes it in some chemicals that finish the process which the light started4 ,if he exposed the whole plate to the light now1 however1 all the unchanged parts of the silver salt would also be changed by the light1 and there would be no picture left4 ,so before he lets any light shine on it1 except red light which has no effect on the silver salt1 he dissolves off all the white unchanged part of the silver salt1 in another kind of chemical called the fixing bath4 ,this is called fixing the negative4 ,the only trouble with the picture now is that wherever there should be a patch of white1 there is a patch of dark silver particles2 and wherever there should be a dark place1 there is just the clear glass or celluloid1 with all the silver salt dissolved off4 ,this kind of picture is called a negative2 everything is just the opposite shade from what it should be4 ,a white man dressed in a black suit looks like a negro dressed in a white suit4 ,,how ,a ,,photographic ,,print ,,is ,,made4 ,the negative not only has the lights and shadows reversed1 but it is on celluloid or glass1 and except for moving pictures and stereopticons1 we usually want the picture on paper4 ,so a print is made of the negative4 ,the next experiment will show you how this is done4 ,,experiment #aja4 ,in a dark room or closet1 take a sheet of blueprint paper from the package1 afterwards closing the package carefully so that no light can get to the papers inside4 ,hold the piece of blueprint paper under your waist or coat1 to keep it dark when you go into the light4 ,now lay it1 greenish side downward1 on a negative4 ,hold the two together1 or place them in a printing frame1 and turn them over so that the light will shine through the negative upon the greenish side of the blueprint paper4 ,be sure that the paper is held firmly against the negative and not moved around4 ,let the sun shine through the negative upon the paper for #a or #b minutes according to the brightness of the sun1 or let the gray light of the sky1 if it is cloudy1 shine on it for #e or #aj minutes4 ,now quickly put the blueprint paper 7not the negative7 into a basin of water1 face down4 ,wash for a couple of minutes4 ,turn it over and examine it4 ,if it has been exposed to the light too long1 it will be dark2 if it has been exposed too short a time1 it will be too light2 in either case1 if the print is not clear1 repeat with a fresh piece of blueprint paper1 altering the time of exposure to the sunlight to improve the print4 ,you can make pretty outline pictures of leaves and pressed flowers1 or of lace1 by laying these on the blueprint paper in place of the negative and in other respects doing as directed above4 ,illustration3 ,,figs4 #agd and #age4 ,where the negative is dark1 the print is light4 ,in making blueprints you are changing an iron salt instead of a silver salt1 by the action of light4 ,regular photographic prints are usually made on paper treated with a silver salt rather than with iron salt1 and sometimes a gold or platinum salt is used4 ,but these other salts have to be washed off with chemicals since they do not come off in water1 as the unchanged part of the iron salt comes off when you fix the blueprint paper in the water bath4 ,since the light cannot get through the black part of a negative1 the coating on the paper behind that part is not affected and it stays light colored2 and since the light can get through the clear parts of the negative1 the coating on the paper back of those parts is affected and becomes dark4 ,therefore1 the print is right side out1--there is a light place on the print for every white place on the object photographed1 and there is a dark place on the print for every black place on the object4 ,moving-picture films are printed from one film to another1 just as you printed from a negative to a piece of paper4 ,the negative is taken on one film1 then this is printed on another film4 ,the second film is right side out4 ,,light ,,and ,,the ,,manufacture ,,of ,,food ,,in ,,plants4 ,much the most important chemical effect of light1 however1 is not in making photographs1 in bleaching things1 or in burning your skin4 ,it is in the putting together of carbon and water to make sugar in plants4 ,plants get water 7,h#b,o7 from the earth and carbon dioxid 7,,co#b7 from the air4 ,when the sun shines on chlorophyll1 the green substance in plants1 the chlorophyll puts them together and makes sugar4 ,the plant changes this sugar into starch and other foods1 and into the tissues of the plant itself4 ,nothing in the world can put carbon dioxid and water together and make food out of them except certain bacteria and the chlorophyll of plants4 ,and light is absolutely necessary for this chemical action4 ,try this experiment3 ,,experiment #ajb4 ,pin together two pieces of cork on opposite sides of a leaf that is exposed to the sun4 ,the next day take this leaf from the plant and heat it in a beaker of alcohol until the green coloring matter is removed from the leaf4 ,then place the leaf in a glass of water that contains iodine4 ,the iodine will color the leaf dark where the cells contain starch4 7,see ,experiment #aae1 page #cgc47 ,is starch formed where the light does not reach the leaf8 ,no plant can make food except with the help of light4 ,the part of the plant that can put carbon dioxid and water together is the green stuff or chlorophyll1 and this can work only when light is shining on it4 ,so all plants would die without light4 ,but if all plants should die1 all animals would die also1 for animals cannot make food out of carbon dioxid and water1 as they do not have the chlorophyll that puts these things together4 ,a lion does not live on leaves1 it is true1 but he lives on deer and other animals that do live on leaves and plants4 ,if the plants died1 all plant-eating animals would die4 ,then there would be nothing for the flesh-eating animals to eat except each other1 and in time no animals would be left in the world4 ,the same thing would happen to the fish4 ,and man1 of course1 could no longer exist4 ,the food supply of the world depends on the fact that light can start chemical change4 ,,oxygen ,,released ,,in ,,the ,,manufacture ,,of ,,plant ,,food4 ,besides in one way or another giving us all of our food1 plants1 helped by light1 also give us most of the free oxygen that we breathe4 ,we and all animals get the energy by which we live by combining oxygen with the hydrogen of our food 7forming water7 and by combining oxygen with the carbon in our food 7forming carbon dioxid74 ,this combining 7burning or oxidizing7 gives us our body heat and the energy to move4 ,the free oxygen is carried to the different parts of our bodies by the red blood corpuscles that float in the liquid part of the blood4 ,the liquid part of the blood also carries the food to the different parts of the body1 and the food contains the carbon and hydrogen that is to be burned4 ,then in a muscle1 for instance1 the oxygen that has been carried by the corpuscles combines with the carbon to form carbon dioxid1 and with the hydrogen to form water4 ,the corpuscles carry part of the carbon dioxid back to the lungs1 and the water is carried with other wastes and the rest of the carbon dioxid in the liquid part of the blood4 ,in the lungs the carbon dioxid is exchanged for the free oxygen we have just inhaled1 and we exhale the carbon dioxid4 ,a good deal of water is also breathed out1 as you can tell from the way the mist gathers on a window pane when you blow on it4 ,if there were only animals 7including people7 in the world1 all the free oxygen in the air would in time be combined by the animals with hydrogen to make water and with carbon to make carbon dioxid 7,,co#b74 ,as animals cannot breathe water and cannot get any good from carbon dioxid1 they would all smother4 ,but the plants1 as we have already said1 use carbon dioxid 7,,co#b7 and water 7,h#b,o7 to make food4 ,they do not need so much oxygen1 and so they set some of it free4 ,the countless plants in the world set the oxygen free as rapidly as the countless animals combine it with hydrogen to make water and with carbon to make carbon dioxid4 ,since the water and carbon dioxid are the main things a plant needs to make its food1 the animals really are as helpful to the plants as the plants are to the animals4 ,for the animals furnish the materials to the plants for making their food in exchange for the ready-made food furnished by the plant4 ,and both plants and animals would die if light stopped helping to bring about chemical change4 ,,application #gd4 ,explain why the heart of a cabbage is white instead of green like the outside leaves2 why a photographer works in a dark room with only a ruby light2 why you get freckled in the sun4 ,,inference ,,exercise ,explain the following3 #dfa4 ,if a pin is put through a lamp cord1 a fuse is likely to blow out4 #dfb4 ,the wall paper back of a picture is often darker than that on the rest of the wall4 #dfc4 ,if you wet an eraser1 it rubs through the paper4 #dfd4 ,clothes are hot after being ironed4 #dfe4 ,if you drop candle grease on your clothes1 you can remove the grease by placing a blotter over it and pressing the blotter with a warm iron4 #dff4 ,milliners cover hats that are on display in windows where the sun shines in on the hats4 #dfg4 ,you pull down on a rope when you try to climb it4 #dfh4 ,in taking a picture1 you expose the sensitive film or plate to the light for a short time4 #dfi4 ,good cameras have an adjustable front part so that the lens may be moved nearer to the plate or film1 or farther from it1 according to the distance of the object to be photographed4 #dgj4 ,a pencil has to be resharpened frequently when it is much used4 ,,section #ej4 ,chemical change caused by electricity4 ,how are storage batteries charged8 ,how is silver plating done by electricity8 ,you have already done an experiment showing that electricity can start chemical change1 for you changed water into hydrogen and oxygen by passing a current of electricity through the water4 ,the plating of metals is made possible by the fact that electricity helps chemical change4 ,you can nickel plate a piece of copper in the following manner3 ,,experiment #ajc4 ,dissolve a few green crystals of double nickel salts in water1 until the water is a clear green4 ,the water should be about #b or #c inches deep in a glass or china bowl that is not less than #e inches across4 ,lay two bare copper wires across the bowl1 about #c inches apart1 as shown in ,figure #agg4 ,connect the positive wire from a storage battery1 or the wire from the carbon of a battery of three or four cells1 to an end of one bare wire4 ,connect the negative wire from the storage or the negative wire from the zinc of the other battery to an end of the second bare wire4 ,now fasten a fine bare wire #e or #f inches long around a small piece of copper1 and another like it around a piece of nickel1 as shown in ,figure #agf4 ,then put the piece of copper in the bottom of an evaporating dish1 with the wire hanging out1 as in ,figure #agg4 ,illustration3 ,,fig4 #agf4 ,the copper and the nickel cube ready to hang in the cleansing solution4 ,illustration3 ,,fig4 #agg4 ,cleaning the copper in acids4 ,pour over the piece of copper enough of the cleansing solution to cover it4#i ,the cleansing solution contains strong acids4 ,if you get any on your skin or clothes1 wash it off immediately with ammonia or soda4 ,as soon as the copper is bright and clean1 take it out of the cleansing solution and suspend it by the negative wire in the green nickel solution4 ,you can tell if you have it on the negative wire1 for in that case bubbles will rise from it during the experiment4 ,the copper should be entirely covered by the nickel solution1 but should not touch the bottom or sides of the bowl4 ,pour the cleansing solution from the evaporating dish back into the bottle4 ,suspend the nickel1 in the same way as the copper1 from the positive wire crossing the bowl4 ,when set up1 the apparatus should appear as shown in ,figure #agh4 ,footnote #i3 ,the formula for making the cleansing solution is as follows3 #a cup water4 #a cup concentrated sulfuric acid4 #a cup concentrated nitric acid4 #a teaspoonful concentrated hydrochloric acid4 ,the sulfuric and nitric acids must be measured in glass or china cups1 and the hydrochloric acid must be measured in a silver-plated spoon or in glass--not in tin4 ,illustration3 ,,fig4 #agh4 ,plating the copper by electricity4 ,turn on the electricity4 ,if the copper becomes black instead of silvery1 clean it again in the cleansing solution1 and move the two bare wires much farther apart1--practically the full width of the bowl4 ,if the copper still turns black1 it means that too much electricity is flowing4 ,in that case use fewer batteries4 ,the electricity has started two chemical changes4 ,it has made part of the piece of nickel combine with part of the solution of nickel salt to form more nickel salt1 and it has made some of the nickel salt around the copper change into metallic nickel4 ,then the negative electricity in the copper has attracted the positive bits of nickel metal made from the nickel salt1 and made them cling to the copper4 ,if there is no dirt or grease on the copper1 the particles of nickel get so close to it that they stick by adhesion1 even after the electric attraction has ceased4 ,this leaves the copper nickel-plated1 but to make it shiny the nickel plating must be polished4 ,silver plating and gold plating are done substantially in the way that you have done the nickel plating1 only gold salt or silver salt is used instead of nickel salt4 ,just as electricity helps chemical changes in plating1 it helps changes in a storage battery4 ,but in the storage battery the new compounds formed by charging the battery change back again and generate electricity when the poles of the battery are connected with each other by a good conductor4 ,,application #ge4 ,explain how spoons can be silver plated2 how water can be changed into hydrogen and oxygen4 ,,inference ,,exercise ,explain the following3 #dga4 ,clothes dry best in the sun and wind4 #dgb4 ,proofs of photographs that have not been thoroughly fixed fade if left out of their envelope4 #dgc4 ,blowing a match puts it out1 yet a good draft is necessary for a hot fire4 #dgd4 ,a cup does not naturally fall apart1 yet after it is broken it falls apart even if you fit the pieces together again4 #dge4 ,crayon leaves marks on a blackboard4 #dgf4 ,a baked potato tastes very different from a raw one4 #dgg4 ,an air-filled automobile tire is harder at noon than in the early morning4 #dgh4 ,when a live trolley wire breaks and falls to the street1 it becomes so hot that it burns4 #dgi4 ,glass jars of fruit should be kept in a fairly dark place4 #dhj4 ,you wash dishes in hot water4 ,,section #ea4 ,chemical change releases energy4 ,why is fire hot8 ,what makes glowworms glow8 ,why does cold quicklime boil when you pour cold water on it8 ,if no energy were released by chemical change1 we should run down like clocks1 and could never be wound up again4 ,we could breathe1 but to do so would do us no more good than it would if oxygen could not combine with things4 ,oxidation would go on in our bodies1 but it would neither keep us warm nor help us to move4 ,a few spasmodic jerks of our hearts1 a few gasps with our lungs1 and they would stop1 as the muscles would have no energy to keep them going4 ,the sunlight might continue to warm the earth1 as we are not sure that the sun gets any of its heat from chemical change4 ,but fires1 while they would burn for an instant1 would be absolutely cold2 no energy would be given out by the fuel combining with oxygen4 ,but the fires could not burn long1 because there would be nothing to keep the gases and fuel hot enough to make them combine with the oxygen4 ,even during the instant that a fire lasted it would be invisible1 for it would give off no light if no energy were released by the chemical change4 ,only electric lights and heaters would continue to work1 and even some of these would fail4 ,the electric motors in submarines and electric automobiles would instantly stop2 battery flashlights would go out as quickly as the fire2 no doorbells would ring4 ,in short1 all forms of electric batteries would stop sending currents of electricity out through their wires1 and everything depending upon batteries would stop running4 ,a fire gives out heat and light2 both are kinds of energy4 ,and it is the electric energy caused by the chemical change in batteries that runs submarines1 electric automobiles1 flashlights1 and doorbells4 ,since burning 7oxidation7 is simply a form of chemical change1 it is not difficult to realize that chemical change releases energy4 ,,why ,,glowworms ,,glow4 ,when a glowworm glows at night1 or when the head of a match glows as you rub it on your wet hand in the dark1 we call the light phosphorescence4 ,the name phosphorus means light-bearing1 and anything like the element phosphorus1 that glows without actively burning1 is said to be phosphorescent4 ,match heads have phosphorus in them4 ,phosphorescence is almost always caused by chemical change4 ,the energy released is a dim light1 not heat or electricity4 ,sometimes millions of microscopic sea animals make the sea water in warm regions phosphorescent4 ,they1 like fireflies1 glowworms1 and will-o'-the-wisps1 have in them some substance that is slowly changing chemically1 and energy is released in the form of dim light as the change takes place4 ,most luminous paint is phosphorescent for the same reason1--there is a chemical change going on that releases energy in the form of light4 ,when you poured the hydrochloric acid on the zinc to make hydrogen1 the flask became warm2 the chemical change going on in the flask released heat energy4 ,,application #gf4 ,explain why pouring cold water on cold quicklime makes the slaked lime that results boiling hot2 why a cat's eyes shine in the dark2 why a piece of carbon and a piece of zinc placed in a solution of sal ammoniac will make electricity run through the wire that connects them2 why fire is hot4 ,,inference ,,exercise ,explain the following3 #dha4 ,a baking potato sometimes bursts in the oven4 #dhb4 ,turpentine is used in mixing paint4 #dhc4 ,sodium is a metal2 chlorine is a poisonous gas2 yet salt1 which is made up of these two1 is a harmless food4 #dhd4 ,when bricklayers mix water with cement and lime1 the resulting mortar boils and steams4 #dhe4 ,green plants will not grow in the dark4 #dhf4 ,parts of the body are constantly uniting with oxygen4 ,this keeps the body warm4 #dhg4 ,water will not always put out a kerosene fire4 #dhh4 ,delicately colored fabrics should be hung in the shade to dry4 #dhi4 ,a match glows when you rub it in the dark4 #dij4 ,candy hardens when it cools4 ,,section #eb4 ,explosions4 ,what makes a gun shoot8 ,what makes an automobile go8 ,usually we think of explosions as harmful1 and they often are1 of course4 ,yet without them we could no longer run automobiles2 gasoline launches would stop at once2 motorcycles would no longer run2 gasoline engines for pumping water or running machinery would not be of any use2 and all aviation would immediately cease4 ,tunneling through mountains1 building roads in rocky places1 taking up tree stumps1 and preparing hard ground for crops would all be made very much more difficult4 ,war would have to be carried on much as it was during the ,middle ,ages2 soldiers would use spears and bows and arrows2 battleships would be almost useless in attacking2 modern forts would be of little value2 cannon1 guns1 rifles1 howitzers1 mortars1 and revolvers would all be so much junk4 ,illustration3 ,,fig4 #agi4 ,the explosion of #ge pounds of dynamite4 ,a still from a motion-picture film4 ,illustration3 ,,fig4 #ahj4 ,diagram of the cylinder of an engine4 ,the piston is driven forward by the explosion of the gasoline in the cylinder4 ,,what ,,makes ,,an ,,automobile ,,go4 ,in all the above cases the explosions are caused by chemical action4 ,when gasoline mixed with air is sprayed into the cylinder of an automobile1 an electric spark makes the gasoline combine with the oxygen of the air2 the gasoline suddenly burns and changes to steam and carbon dioxid4 ,as you already know1 when a liquid like gasoline turns to gases such as steam and carbon dioxid1 the gases take much more room4 ,but that is not all that happens4 ,much heat is released by the burning of the gasoline spray1 and heat causes expansion4 ,so the gases formed by the burning gasoline are still further expanded by the heat released by the burning4 ,therefore they need a great deal more room2 but they are shut up in a small place in the top of a cylinder4 ,the only thing to hold them up in this small space1 however1 is a piston 7,fig4 #ahj71 and the suddenly expanding gases shove this piston down and escape4 ,the piston is attached to the drive wheel of the automobile1 and when the piston is pushed down it gives the automobile a push forward4 ,if it were not for the expansion of a gas in the cylinder1 this gas being confined to a small space1 the piston would not be pushed down4 ,an explosion is simply the sudden pushing of a confined gas expanding on its way to freedom4 ,the gasoline vapor and air were the confined gas4 ,their chemical combining made them expand2 by pushing the piston out of its way the newly formed gas suddenly freed itself4 ,this was an explosion1 and it gave the automobile one forward push4 ,but the automobile engine is so arranged that the piston goes up into the cylinder again1 and is pulled down again1 drawing a spray of gasoline and air into the cylinder after it4 ,then it goes up a second time1 an electric spark explodes the gasoline1 the piston is forced down violently once more1 and so it goes on4 ,there are several cylinders1 of course1 and the explosions take place within them one after the other so as to keep the automobile going steadily4 ,,how ,a ,,gun ,,shoots4 ,pulling a trigger makes a gun shoot by causing an explosion4 ,there is a spring on the hammer of a gun4 ,this drives the hammer down suddenly when you release the spring by pulling the trigger4 ,the hammer jars the chemicals in the cap and causes them to explode4 ,the heat and flame then cause the oxygen in the gunpowder to combine with some of the other elements in the powder to make a gas4 ,the gas requires more room than the powder and is further expanded by the heat released by the chemical change4 ,the expanding gas frees itself by pushing the bullet out of its way4 ,the bullet gets such a push through the exploding of the gunpowder that it may fly to a mark and pierce it4 ,illustration3 ,,fig4 #aha4 ,the most powerful explosions on earth occur in connection with volcanic activity4 ,the photograph shows ,mt4 ,lassen1 ,california1 the only active volcano in the ,united ,states4 ,there is a slight explosion even when you shoot an air gun4 ,first you compress some air in the upper part of the barrel of the air gun2 then you suddenly release it4 ,the only thing in the way of the expanding air is the bullet2 so the air pushes this out in front of it4 ,in ,experiment #cf1 where you stoppered a test tube containing a little water and then held the tube over a flame until the cork flew out1 you were causing an explosion4 ,as the water changed to steam1 the steam was an expanding gas4 ,it was at first confined to the test tube by the cork4 ,then there was an explosion2 the gas freed itself by blowing out the cork4 ,steam boilers have safety valves to prevent explosions4 ,these are valves so arranged that when the steam expands and presses hard enough to endanger the boiler1 the steam will open the valves and escape instead of bursting the boiler to get free4 ,,explosives4 ,dynamite1 gunpowder1 and most explosives are mixtures of solids or liquids that will combine easily and will form gases that expand greatly as a result of the combination4 ,one of the essentials in explosives is some compound of oxygen 7such as the manganese dioxid or potassium chlorate you used to make oxygen in ,experiment #ic7 which will easily set its oxygen free4 ,this oxygen combines very swiftly with something else in the explosive1 releasing heat and forming a gas that takes much more room4 ,in its effort to free itself1 this expanding gas will blast rocks out of the way1 shoot cannon balls1 or do any similar work4 ,but if gunpowder does not have to push anything of much importance out of its way to expand1 there is no explosion4 ,that is why a firecracker merely fizzes when you break it in two and light the powder4 ,the cardboard no longer confines the expanding gas2 so there is nothing to burst or to push violently out of the way4 ,useful explosions are generally caused by a chemical action which suddenly releases a great deal of heat and combines solid things into expanding gases4 ,but the bursting of a steam boiler1 or the blow out of an automobile tire1 or the bursting of a potato in the oven1 although not caused by chemical action1 still are real explosions4 ,an explosion is the sudden release of a confined gas4 ,,application #gg4 ,explain how gasoline makes a motorcycle go1 and why it goes pop1 pop1 pop4 ,explain why a paper bag will burst with a bang1 when you blow it up and then clap it between your hands2 why a ,fourth-of-,july torpedo goes off when you throw it on the pavement4 ,,inference ,,exercise ,explain the following3 #dia4 ,the engine of an automobile is cooled by the water that passes over it from the radiator4 #dib4 ,when you light a firecracker1 the flame travels down the wick until it reaches the gunpowder1 and then the firecracker bursts with a bang4 #dic4 ,if you light a small pile of gunpowder in the open1 as you do when you make a squib by breaking the firecracker in two1 you merely have a blaze4 #did4 ,air-filled tires make bicycles ride much more evenly than solid tires would4 #die4 ,when clay has once been baked into brick1 you can never change it back to clay4 #dif4 ,a photographic negative turns black all over if it is exposed to the light before it is fixed4 #dig4 ,the outside of a window shade fades4 #dih4 ,a vacuum electric lamp globe feels hot instantly when turned on1 but if turned off again at once1 it immediately feels cold4 #dii4 ,coal gas is made by heating coal very hot in an air-tight chamber4 #ejj4 ,white straw turns yellow when it is long exposed to the sunlight4 ,,chapter ,,eleven ,,solution ,,and ,,chemical ,,action ,,section #ec4 ,chemical change helped by solution4 ,why does iron have to get wet to rust8 ,is it good to drink water with your meals8 ,when iron rusts1 it is really slowly burning 7combining with oxygen74 ,if your house is on fire1 you throw water on it to stop the burning4 ,yet if you throw water on iron it rusts1 or burns1 better than if you leave it dry4 ,what do you suppose is the reason for this8 ,the answer is not difficult4 ,you know perfectly well that iron does not burn easily2 we could not make fire grates and stoves out of iron if it did4 ,but when iron is wet1 a little of it dissolves in the water that wets it4 ,there is also a little oxygen dissolved in the water1 as we know from the fact that fish can breathe under the water4 ,this dissolved oxygen can easily combine with the dissolved iron2 the solution helps the chemical change to take place4 ,the chemical change that results is oxidation1--the iron combining with oxygen1--which is a slow kind of burning2 and in iron this is usually called rusting4#aj ,but when we pour water on burning wood1 the wood stops burning1 for there is not nearly enough oxygen dissolved in water to combine rapidly with burning wood2 and the water shuts off the outside air from burning wood and therefore puts the fire out4 ,footnote #aj3 ,the rusting of iron is not quite as simple as this1 as it probably undergoes two or three changes before finally combining with oxygen4 ,but the solution helps all these changes4 ,another chemical change1 greatly helped by solution1 is the combining of the two things that baking powder is made of1 and the setting free of the carbon dioxid 7,,co#b7 that is in one of them4 ,try this experiment3 ,,experiment #ajd4 ,put half a teaspoonful of baking powder in the bottom of a cup and add a little water4 ,what happens8 ,the chemical action which takes place in the baking powder and releases the gas in bubbles--the gas is carbon dioxid 7,,co#b7--will not take place while the baking powder is dry2 but when it is dissolved1 the chemical change takes place in the solution4 ,if you ate your food entirely dry1 you would have a hard time digesting it2 and this would be for the same reason that baking powder will not work without water4 ,perhaps you can drink too much water with a meal and dilute the digestive juices too much2 certainly you should not use water to wash down your food and take the place of the saliva1 for the saliva is important in the digestion of starch4 ,but you need also partly to dissolve the food to have it digest well4 ,crackers and milk are usually more easily digested than are plain crackers1 for the milk partly dissolves the crackers1 and drinking one or two glasses of water with a meal hastens the digestion of the food4 ,,application #gh4 ,explain why paint preserves wood2 why iron will rust more quickly in a wet place than it will either under water or in a dry place2 why silver salts must be dissolved in order to plate a spoon by electricity4 ,,inference ,,exercise ,explain the following3 #eja4 ,there is dew on the grass early in the morning4 #ejb4 ,cold cream makes your hands and face soft4 #ejc4 ,glowworms and fireflies can be seen on the darkest nights4 #ejd4 ,a lake looks gray on a cloudy day and blue on a clear day4 #eje4 ,dried fruit will keep much longer than fresh fruit4 #ejf4 ,if you scratch a varnished surface1 you can rub the scratch out completely by using a cloth wet with alcohol4 #ejg4 ,soda is usually dissolved in a little water before it is added to a sour-milk batter4 #ejh4 ,iron rusts when it gets wet4 #eji4 ,peroxide is usually kept in brown bottles4 #eaj4 ,dry lye may be kept in tin cans1 but if the lye is moistened it will eat the can4 ,,section #ed4 ,acids4 ,why are lemons sour8 ,how do acids act8 ,some acids are very powerful4 ,there is one1 called hydrofluoric acid1 that will eat through glass and has to be kept in wax bottles2 and all acids tend to eat or corrode metals4 ,you saw what hydrochloric acid did to the zinc shavings when you wanted to make a balloon2 or1 to be more accurate1 you saw what the zinc shavings did to the acid1 for the hydrogen gas that bubbled off was driven out of the acid by the zinc4 ,then the zinc combined with the rest of the acid to form what chemists call a salt4 ,if we were to let the soft metal1 sodium1 act on hydrochloric acid1 we should get hydrogen also2 but the salt that formed would be regular table salt 7,na,cl74 ,you cannot do this experiment1 however1 as the sodium does its work so violently that it is dangerous4 ,,experiment #aje4 ,to be done by the teacher before the class4 ,if acid spatters on any one's skin or clothes1 wash it of immediately with ammonia or a strong soda solution4 ,drop a little candle grease on a piece of copper about #c_/d inch wide and #b or #c inches long4 ,in the flame of a ,bunsen burner1 gently heat the end of the copper that has the candle grease 7paraffin7 on it1 so that the paraffin will spread out all over the end4 ,let it harden4 ,with a nail1 draw a design in the paraffin on the copper1 scratching through the thin coat of paraffin to the copper below4 ,pour a couple of drops of concentrated nitric acid on the paraffin-covered end of the piece of copper1 and spread the acid with a match so that it can get down into the scratches4 ,let it stand by an open window for #e or #aj minutes4 ,do not inhale the brown fumes that are given off4 ,they are harmless in small amounts1 but if breathed directly they are very irritating4 ,now wash off the acid by holding the copper under the hydrant1 and scrape off the paraffin4 ,illustration3 ,,fig4 #ahb4 ,etching copper with acid4 ,the nitric acid did to the copper in this experiment exactly what the hydrochloric acid did to the zinc shavings when you made the toy balloon4 ,the copper drove the hydrogen out of the nitric acid and incidentally broke down some of the nitric acid to make the brown gas1 and then the copper joined the rest of the nitric acid to make a salt called copper nitrate4 ,this salt is green1 and it dissolves in water4 ,when you washed the copper1 the green salt was washed away and a dent remained in the copper where the copper salt had been4 ,here is a more practical experiment showing the action of acid on metal3 ,,experiment #ajf4 ,use two knives1 one of bright steel and the other a silver-plated one4 ,if the steel knife is not bright1 scour it until it is4 ,drop a little lemon juice on each knife and let it stand for a few minutes1 while the teacher does the next experiment4 ,then rinse both knives and examine them4 ,what has the lemon juice done to the silver knife8 to the steel one8 ,the lemon juice acts in this way because it is acid4 ,acids act on the taste nerves in the tongue and give the taste of sourness2 everything sour is an acid4 ,the black stuff formed on the steel knife by the lemon juice is an iron salt4 ,the iron in the knife drove the hydrogen out of the lemon juice1 but there was not enough for you to see it coming off2 then the iron combined with the rest of the lemon juice to form an iron salt4 ,whenever an acid acts on a metal1 the metal drives off the hydrogen and forms a salt4 ,the salt is not always good to eat2 for instance1 the salt that tin forms with acids is poisonous4 ,,action ,,of ,,acids ,,on ,,other ,,substances4 ,acids do not act on metals only1 however4 ,watch the next experiment to see what a strong acid will do to cloth4 ,,experiment #ajg4 ,to be done by the teacher4 ,put a drop of concentrated nitric or sulfuric acid on a piece of colored wool cloth1 or on a piece of colored silk4 ,let it stand for a few minutes1 then rinse it thoroughly4 ,test the cloth where the acid has been to see whether or not it is as strong as the rest of the cloth4 ,how has the acid affected the color8 ,illustration3 ,,fig4 #ahc4 ,strong acids will eat holes like this in cloth4 ,,action ,,of ,,acids ,,on ,,the ,,nerves ,,of ,,taste4 ,acids act on the taste nerves in the tongue and give the taste of sourness2 everything sour is an acid4 ,lemon juice1 sour milk1 and sour fruits are all too weak acids to injure clothes or skin1 but their sour taste is a result of the acid in them acting on the nerves of taste4 ,,application #gi4 ,a girl wanted to make lemonade4 ,she did not know which of two knives to use1 a steel-bladed one or a silver-plated one4 ,which should she have used8 ,,application #hj4 ,a woman was going to put up some tomatoes4 ,she needed something large to cook them in4 ,she had a shiny new tin dish pan1 an older enamelware dish pan1 a galvanized iron water pail1 and an old-fashioned copper kettle4 ,which would have been best for her to use8 ,make a list of as many acids as you can think of4 ,,inference ,,exercise ,explain the following3 #eaa4 ,sugar dissolves readily in hot coffee4 #eab4 ,the sugar disappears1 yet the coffee flavor remains and so does the sweetness of the sugar4 #eac4 ,a tin spoon left overnight in apple sauce becomes black4 #ead4 ,if one's clothes are on fire1 rolling over on the ground is better than running4 #eae4 ,lemon juice bleaches straw hats4 #eaf4 ,will-o'-the-wisps glow at night1 deceiving travelers by their resemblance to moving lanterns4 #eag4 ,tomatoes should never be left in a tin can after it has been opened4 #eah4 ,boiled milk tastes different from ordinary milk4 #eai4 ,your hands become very cold after you have washed things in gasoline4 #ebj4 ,wood decays more quickly when wet than when dry4 ,,section #ee4 ,bases4 ,why does strong soap make your face sting8 ,how is soap made8 ,contains no free alkali1 ,will not injure the most delicate of fabrics1 #ii-dd_/ajj pure1--such phrases as these are used in advertising soaps4 ,what is meant by #ii-dd_/ajj pure8 ,what is free alkali8 ,why should any soap injure fabrics8 ,what makes a soap strong8 ,the answer to all these questions is that there are some substances called bases1 which are the opposites of acids1 and some of which are as powerful as acids4 ,lye1 ammonia1 caustic soda1 and baking and washing soda are common bases4 ,the strong bases1 like lye and caustic soda1 are also called alkalies4 ,if you want to see what a strong base--an alkali--will do to the most delicate of fabrics1 and to fabrics that are not so delicate1 for that matter1 try the following experiment3 ,,experiment #ajh4 ,to be done by the teacher4 ,if you get any alkali on your skin or clothes1 wash it off immediately with vinegar or lemon juice4 ,put half a teaspoonful of lye and a quarter of a cup of water into a beaker1 a small pan1 or an evaporating dish4 ,bring it to a gentle boil4 ,drop a small piece of woolen cloth and a small piece of silk cloth into it and let them boil gently for a couple of minutes4 ,what happens to them8 ,try a piece of plain cotton cloth1 and then a piece of cloth that is mixed wool and cotton or mixed silk and cotton4 ,what happens to them8 ,this is a very good test to determine whether any goods you buy are pure silk or wool1 or whether there is a cotton thread mixed with them4 ,drop one end of a long hair into the hot lye solution4 ,what happens to it8 ,drop a speck of meat or a piece of finger nail into it4 ,from this experiment you can readily see why lye will burn your skin and ruin your clothes4 ,you can also see how it softens the food that sticks to the bottom of the cooking pan and makes the pan easy to clean4 ,lye is one of the strongest bases or alkalies in the world4 ,illustration3 ,,fig4 #ahd4 ,the lye has changed the wool cloth to a jelly4 ,,how ,,soap ,,is ,,made4 ,when lye and grease are boiled together1 they form soap4 ,you cannot very well make soap in the laboratory now1 as the measurements must be exact and you need a good deal of strong lye to make it in a quantity large enough to use4 ,but the fact that soap is made with oil1 fat1 or grease boiled with lye1 or caustic soda1 which is almost the same thing1 shows why a soap must be #ii-dd_/ajj pure1 or something like that1 if it is not to injure the most delicate fabric4 ,if a little too much lye is used there will be free alkali in the soap1 and it will make your hands harsh and sore and spoil the clothes you are washing4 ,a pure soap is one with no free alkali in it4 ,a strong soap is one that does have some free alkali in it2 there is a little too much lye for the oil or fat1 so some lye is left uncombined when the soap is made4 ,this free alkali cleans things well1 but it injures hands and clothes4 ,when the drainpipe of a kitchen sink is stopped up1 you can often clear it by sprinkling lye down it1 and then adding boiling water4 ,if you ever do this1 stand well back so that no lye will spatter into your face2 it sputters when the boiling water strikes it4 ,the grease in the drainpipe combines with the lye when the hot water comes down2 then the soap that is formed is carried down the pipe1 partly dissolved by the hot water4 ,when you sponge a grease spot with ammonia1 the same sort of chemical action takes place4 ,the ammonia is a base2 it combines with the grease to form soap1 and this soap rinses out of the cloth4 ,,the ,,litmus ,,test4 ,to tell what things are bases and what are acids1 a piece of paper dyed with litmus is ordinarily used4 ,litmus is made from a plant 7lichen74 ,this paper is called litmus paper4 ,try the following experiment with litmus paper3 ,,experiment #aji4 ,pour a few drops of ammonia1 a base1 into a cup4 ,into another cup pour a few drops of vinegar1 an acid4 ,dip your litmus paper first into one1 then into the other1 and then back into the first4 ,what color does the vinegar turn it8 the ammonia8 ,try lemon juice2 diluted hydrochloric acid2 a very dilute lye solution4 ,this is called the litmus test4 ,all ordinary acids1 if not too strong1 will turn litmus pink4 ,all bases or alkalies will turn it blue4 ,if it is already pink when you put it into an acid1 it will stay pink1 of course2 if it is already blue when you put it into a base1 it will stay blue4 ,but if you put a piece of litmus paper into something that is neither an acid nor a base1 like sugar or salt1 it will still stay the same color4 ,so1 to test for a base1 use a piece of litmus paper that is pink and see if it turns blue1 or if you want to test for an acid1 use blue litmus paper4 ,do this experiment3 ,,experiment #aaj4 ,with pink and blue litmus paper1 test the different substances named below to see which are acids and which are bases4 ,make a list of all the acids and another list for all the bases4 ,do not put down anything that is neither acid or base4 ,you cannot be sure a thing is an acid unless it turns blue litmus pink4 ,a piece of pink litmus would stay pink in an acid1 but it would also stay pink in things that were neither acid nor base1 like salt or water4 ,in the same way you cannot be sure a thing is a base unless it turns pink litmus blue4 ,here is a list of things to try3 #a1 sugar2 #b1 orange2 #c1 dilute sulfuric acid2 #d1 baking soda in water2 #e1 alum in water2 #f1 washing soda in water2 #g1 ammonia2 #h1 dilute lye2 #i1 lemon juice2 #aj1 vinegar2 #aa1 washing powder in water2 #ab1 sour milk2 #ac1 cornstarch in water2 #ad1 wet kitchen soap2 #ae1 oil2 #af1 salt in water4 ,you may have to make the orange and sour milk test at home4 ,you may take two pieces of litmus paper home with you and test anything else that you may care to4 ,if you have a garden1 try the soil in it4 ,if it is acid it needs lime4 ,,application #ha4 ,a boy spilled some greasy soup on his best dark blue coat4 ,which of the following methods would have served to clean the coat8 to sponge it 7a7 with cold water2 7b7 with water 7hot7 and ammonia2 7c7 with hot water and vinegar2 7d7 with concentrated nitric acid2 to sprinkle lye on the spot and pour boiling water over it4 ,,application #hb4 ,a woman scorched the oatmeal she was cooking for breakfast4 ,when she wanted to wash the pan1 she found that the blackened cereal stuck fast to the bottom4 ,which of the following things would have served best to loosen the burned oatmeal from the pan3 lye and hot water1 ammonia1 vinegar1 salt water1 lemon juice8 ,,inference ,,exercise ,explain the following3 #eba4 ,after clothes have been washed with washing soda or strong soap1 they should be thoroughly rinsed4 ,otherwise they will be badly eaten as they dry4 #ebb4 ,carbon will burn2 oxygen will support combustion2 yet carbon dioxid 7,,co#b71 which is made of both these elements1 will neither burn nor support combustion4 #ebc4 ,you can clean silver by putting it in hot soda solution in contact with aluminum4 #ebd4 ,when you stub your toe while walking1 you tend to fall forward4 #ebe4 ,electric lamps glow when you turn on the switch4 #ebf4 ,if you use much ammonia in washing clothes or cleaning1 your hands become harsh and dry4 #ebg4 ,if a person swallows lye or caustic soda1 he should immediately drink as much vegetable oil or animal oil as possible4 #ebh4 ,water is made of hydrogen and oxygen2 air is made of nitrogen and oxygen2 yet while things will not burn in water1 they will burn easily in air4 #ebi4 ,the backs of books that have been kept in cases for several years are not as bright colored as the side covers4 #ecj4 ,if you try to burn a book or magazine in a grate1 only the outer pages and edges burn4 ,,section #ef4 ,neutralization4 ,when you put soda in vinegar1 what makes the vinegar less sour8 ,when we use sour milk for cooking1 why does the food not taste sour8 ,one of the most interesting and important facts about acids and bases is that if they are put together in the right proportions they turn to salt and water4 ,strong hydrochloric acid 7,h,cl71 for instance1 will attack the skin and clothes1 as you know2 if you should drink it1 it would kill you4 ,caustic soda 7,na,o,h71 a kind of lye1 is such a strong alkali that it would dissolve the skin of your mouth in the way that lye dissolved hair in ,experiment #ajh4 ,yet if you put these two strongly poisonous chemicals together1 they promptly turn to ordinary table salt 7,na,cl7 and water 7,h#b,o74 ,or1 as the chemists write it3 ,na,o,h,h,cl - ,na,cl,h#b,o4 ,you can make this happen yourself in the following experiment1 using the acid and base dilute enough so that they will not hurt you3 ,,experiment #aaa4 ,although strong hydrochloric acid and strong caustic soda are dangerous1 if they are diluted with enough water they are perfectly harmless4 ,you will find two bottles1 one labeled caustic soda 7,na,o,h7 diluted for tasting1 and the other labeled hydrochloric acid 7,h,cl7 diluted for tasting4 ,from one bottle take a little in the medicine dropper and let a drop fall on your tongue4 ,taste the contents of the other bottle in the same way4 ,it is not usually safe to taste things in the laboratory4 ,taste only those things which are marked for tasting4 ,now put a teaspoonful of the same hydrochloric acid into a clean evaporating dish4 ,lay a piece of litmus paper in the bottom of the dish4 ,with a medicine dropper gradually add the dilute caustic soda 7,na,o,h71 stirring as you add it4 ,watch the litmus paper4 ,when the litmus paper begins to turn blue1 add the dilute caustic soda drop by drop until the litmus paper stays blue when you stir the mixture4 ,now add a drop or two more of the acid until the litmus turns pink again4 ,taste the mixture4 ,put the evaporating dish on the wire gauze over a ,bunsen burner1 and bring the liquid to a boil4 ,boil it gently until it begins to sputter4 ,then take the ,bunsen burner in your hand and hold it under the dish for a couple of seconds2 remove it for a few seconds1 and then again hold it under the dish for a couple of seconds2 remove it once more1 and keep this up until the water has all evaporated and left dry white crystals and powder in the bottom of the dish4 ,as soon as the dish is cool1 taste the crystals and powder4 ,what are they8 ,is salt an acid or a base8 ,whenever you put acids and bases together1 you get some kind of salt and water4 ,thus the chlorine 7,cl7 of the hydrochloric acid 7,h,cl7 combines with the sodium 7,na7 of caustic soda 7,na,o,h7 to form ordinary table salt1 sodium chloride 7,na,cl71 while the hydrogen 7,h7 of the hydrochloric acid 7,h,cl7 combines with the oxygen and hydrogen 7,,oh7 of the caustic soda 7,na,o,h7 to form water 7,h#b,o74 ,chemists write this as follows3 ,na,o,h,h,cl - ,na,cl,h#b,o4 ,,why ,,sour ,,milk ,,pancakes ,,are ,,not ,,sour4 ,it is because bases neutralize acids that you put baking soda with sour milk when you make sour milk pancakes or muffins4 ,the soda is a weak base4 ,the sour milk is a weak acid4 ,the soda neutralizes the acid1 changing it into a kind of salt and plain water4 ,therefore the sour milk pancakes or muffins do not taste sour4 ,in the same way a little soda keeps tomatoes from curdling the milk when it is added to make cream of tomato soup4 ,it is the acid in the tomatoes that curdles milk4 ,if you neutralize the acid by adding a base1 there is no acid left to curdle the milk2 the acid and base turn to water and a kind of salt4 ,when you did an experiment with strong acid1 you were advised to have some ammonia at hand to wash off any acid that might get on your skin or clothes4 ,the ammonia1 being a base1 would immediately neutralize the acid and therefore keep it from doing any damage4 ,lye also would neutralize the acid1 but if you used the least bit too much1 the lye would do as much harm as the acid4 ,that is why you should use a weak base1 like ammonia or baking soda or washing soda1 to neutralize any acid that spills on you4 ,then if you get too much on1 it will not do any harm4 ,in the same way you were warned to have vinegar near at hand while you worked with lye4 ,strong nitric acid also would neutralize the lye1 but if you happened to use a drop too much1 the acid would be worse than the lye4 ,vinegar1 of course1 would not hurt you1 no matter how much you put on4 ,any acid will neutralize any base4 ,but it would take a great deal of a weak acid to neutralize a strong base or alkali2 you would have to use a great deal of vinegar to neutralize concentrated lye4 ,in the same way it would take a great deal of a weak base to neutralize a strong acid2 you would have to use a large amount of baking soda or ammonia to neutralize concentrated nitric acid4 ,,application #hc4 ,a woman was cleaning kettles with lye4 ,her little boy was playing near1 and some lye splashed on his hand4 ,she looked swiftly around and saw the following things3 soap1 oil1 lemon1 flour1 peroxide1 ammonia1 iodine1 baking soda1 essence of peppermint4 ,which should she have put on the boy's hand8 ,,application #hd4 ,a teacher spilled some nitric acid on her apron4 ,on the shelf there were3 hydrochloric acid1 vinegar1 lye1 caustic soda1 baking soda1 ammonia1 salt1 alcohol1 kerosene1 salad oil4 ,which should she have put on her apron8 ,,application #he4 ,a boy had sour stomach4 ,his sister said1 ,chew some gum4 ,his aunt said1 ,drink hot water with a little peppermint in it4 ,his mother told him to take a little baking soda in water4 ,his brother said1 ,try some hot lemonade4 ,which advice should he have followed8 ,,application #hf4 ,two women were bleaching a faded pair of curtains4 ,the ,javelle water which they had used was made of bleaching powder and washing soda4 ,before hanging the curtains out to dry1 one of them said that she was afraid the ,javelle water would become so strong as the water evaporated from the curtains that it would eat the curtains4 ,they decided they had better rinse them out with something that would counteract the soda and lime in the ,javelle water1 and in the laundry and pantry they found3 ammonia1 blueing1 starch1 washing powder1 soap1 vinegar1 and gasoline4 ,which of them1 if any1 would it have been well to put in the rinsing water8 ,,inference ,,exercise ,explain the following3 #eca4 ,solid pieces of washing soda disappear in hot water4 #ecb4 ,greasy clothes put into hot water with washing soda become clean4 #ecc4 ,if you hang these clothes up to dry without rinsing them1 the soda will weaken the cloth4 #ecd4 ,lemon juice in the rinsing water will prevent washing soda from injuring the clothes4 #ece4 ,if you hang them in the sun1 the color will fade4 #ecf4 ,a piece of soot blown against them will stick4 #ecg4 ,a drop of oil that may spatter against them will spread4 #ech4 ,the clothes will be easier to iron if dampened4 #eci4 ,the creases made in ironing the clothes will reappear even if you flatten the creases out with your hand4 #edj4 ,after they have been worn1 washed1 and ironed a number of times1 clothes are thinner than they were when they were new4 ,,section #eg4 ,effervescence4 ,what makes baking powder bubble8 ,what makes the foam on soda water8 ,did you ever make soda lemonade8 ,it is easy to make and is rather good4 ,try making it at home4 ,here are the directions3 ,,experiment #aab4 ,make a glass of ordinary lemonade 7half a lemon1 #a-a_/b teaspoonfuls of sugar2 fill the glass with water74 ,pour half of this lemonade into another cup or glass4 ,into the remaining half glass stir half a teaspoonful of soda4 ,drink it while it fizzes4 ,does it taste sour8 ,when anything fizzes or bubbles up like this1 we say that it effervesces4 ,effervescence is the bubbling up of a gas from a liquid4 ,the gas that bubbled up from your lemonade was carbon dioxid 7,,co#b71 and this is the gas that usually bubbles up out of things when they effervesce4 ,when you make bread1 the yeast turns the sugar into carbon dioxid 7,,co#b7 and alcohol4 ,the carbon dioxid tries to bubble up out of the dough1 and the bubbles make little holes all through the dough4 ,this makes the bread light4 ,when bread rises1 it really is slowly effervescing4 ,,how ,,soda ,,water ,,is ,,made4 ,certain firms make pure carbon dioxid 7commercially known as carbonic acid gas7 and compress it in iron tanks4 ,these iron tanks of carbon dioxid 7,,co#b7 are shipped to soda-water fountains and soda-bottling works4 ,here the compressed carbon dioxid is dissolved in water under pressure1--this is called charging the water4 ,when the charged water comes out of the faucet in the soda fountains1 or out of the spout of a seltzer siphon1 or out of a bottle of soda pop1 the carbon dioxid that was dissolved in the water under pressure bubbles up and escapes1--the soda water effervesces4 ,sometimes there is compressed carbon dioxid down in the ground4 ,this dissolves in the underground water1 and when the water bubbles up from the ground and the pressure is released1 the carbon dioxid foams out of the water2 it effervesces like the charged water at a soda fountain4 ,but the most useful and best-known effervescence is the kind you got when you stirred the baking soda in the lemonade4 ,baking soda is made of the same elements as caustic soda 7,na,o,h71 with carbon dioxid 7,,co#b7 combined with them4 ,the formula for baking soda could be written ,na,o,h,c,o#b1 but usually chemists put all of the ,o's together at the end and write it ,na,h,c,o#c4 ,whenever baking soda is mixed with any kind of acid1 the caustic soda part 7,na,o,h7 is used up in neutralizing the acid4 ,this leaves the carbon dioxid 7,,co#b7 part free1 so that it bubbles off and we have effervescence4 ,baking soda mixed with an acid always effervesces4 ,that is why sour milk muffins and pancakes are light as well as not sour4 ,the effervescing carbon dioxid makes bubbles all through the batter1 while the caustic soda 7,na,o,h7 in the baking soda neutralizes the acid of the sour milk4 ,illustration3 ,,fig4 #ahe4 ,making a glass of soda lemonade4 ,,effervescence ,,generally ,,due ,,to ,,the ,,freeing ,,of ,,carbon ,,dioxid4 ,since baking soda is so much used in the home for neutralizing acids1 people sometimes get the idea that whenever there is neutralization there is effervescence4 ,of course this is not true4 ,whenever you neutralize an acid with baking soda or washing soda1 the carbon dioxid in the soda bubbles up and you have effervescence4 ,but if you neutralize an acid with ammonia1 lye1 or plain caustic soda1 there is not a bit of effervescence4 ,ammonia1 lye1 and plain caustic soda have no carbon dioxid in them to bubble out4 ,baking powder is merely a mixture of baking soda and dry acid 7cream of tartar or phosphates in the better baking powders1 alum in the cheap ones74 ,these dry acids cannot act on the soda until they go into solution4 ,as long as the baking powder remains dry in the can1 there is no effervescence4 ,but when the baking powder is stirred into the moist biscuit dough or cake batter1 the baking powder dissolves2 so the acid in it can act on the baking soda and set free the carbon dioxid4 ,in most cases it is the freeing of carbon dioxid that constitutes effervescence1 but the freeing of any gas from liquid is effervescence4 ,when you made hydrogen by pouring hydrochloric acid 7,h,cl7 on zinc shavings1 the acid effervesced1--the hydrogen gas was set free and it bubbled up4 ,stirring or shaking helps effervescence1 just as it does crystallization4 ,as the little bubbles form1 the stirring or shaking brings them together and lets them join to form big bubbles that pass quickly up through the liquid4 ,that is why soda pop will foam so much if you shake it before you pour it1 or if you stir it in your glass4 ,,application #hg4 ,explain why we do not neutralize the acid in sour milk gingerbread with weak caustic soda instead of with baking soda2 why soda water which is drawn with considerable force from the fine opening at a soda fountain makes so much more foam than does the same charged water if it is drawn from a large opening1 from which it flows gently2 why there is always baking soda and dry acid in baking powder4 ,,application #hh4 ,a woman wanted to make gingerbread4 ,she had no baking powder and no sour milk1 but she had sweet milk and all the other articles necessary for making gingerbread4 ,she had also baking soda1 caustic soda1 lemons1 oranges1 vanilla1 salad oil1 vinegar1 and lye4 ,was there any way in which she might have made the gingerbread light without spoiling it8 ,,inference ,,exercise ,explain the following3 #eda4 ,harness is oiled to keep it flexible4 #edb4 ,when you pour nitric acid on copper filings1 there is a bubbling up of gas4 #edc4 ,the flask or dish in which the action takes place becomes very hot4 #edd4 ,the copper disappears and a clear green solution is left4 #ede4 ,in making cream of tomato soup1 soda is added to the tomatoes before the milk is1 so that the milk will not curdle ,how does the soda prevent curdling8 #edf4 ,the soda makes the soup froth up4 #edg4 ,a wagon squeaks when an axle needs greasing4 #edh4 ,seidlitz powders are mixed in only half a glass of water4 #edi4 ,the work of developing photographs is all done with a ruby light for illumination4 #eej4 ,coal slides forward off the shovel into a furnace when you stop the shovel at the furnace door4 ,,chapter ,,twelve ,,analysis ,,section #eh4 ,analysis4 ,how can people tell what things are made of8 ,if it were not for chemical analysis1 most of the big factories would have to shut down1 much of our agricultural experimentation would stop1 the ,pure ,food ,law would be impossible to enforce1 mining would be paralyzed1 and the science of chemistry would almost vanish4 ,analysis is finding out what things are made of4 ,in order to make steel from ore1 the ore has to be analyzed2 and factories could not run very well without steel4 ,in order to test soil1 to test cow's milk1 or to find the food value of different kinds of feed1 analysis is essential4 ,as to the ,pure ,food ,law1 how could the government find out that a firm was using artificial coloring matter or preservatives if there were no way of analyzing the food8 ,in mining1 the ore must be assayed2 that is1 it must be analyzed to show what part of it is gold1 for instance1 and what part consists of other minerals4 ,also1 the analysis must show what these substances are1 so that they can be treated properly4 ,and the science of chemistry is largely the science of analyzing--finding out what things are made of and how they will act on each other4 ,the subject of chemical analysis is extremely important4 ,but in this course it is impossible and unnecessary for you to learn to analyze everything2 the main thing is for you to know what analysis is and to have a general notion of how a chemist analyzes things4 ,illustration3 ,,fig4 #ahf4 ,the platinum loop used in making the borax bead test4 ,when you tested a number of substances with litmus paper to find out which of them were acids1 you were really doing some work in chemical analysis4 ,chemists actually use litmus paper in this way to find out whether a substance is an acid or a base4 ,,the ,,borax ,,bead ,,test4 ,this is another chemical test1 by which certain substances can be recognized3 ,,experiment #aac4 ,make a loop of wire about a quarter of an inch across1 using light-weight platinum wire 7about ,no4 #cj74 ,seal the straight end of the wire into the end of a piece of glass tubing by melting the end of the tube around the wire4 ,hold the loop of wire in the flame of a ,bunsen burner for a few seconds1 then dip the looped end in borax powder4 ,be careful not to get borax on the upper part of the wire or on the handle4 ,some of the borax will stick to the hot loop4 ,hold this in the flame until it melts into a glassy bead in the loop4 ,you may have to dip it into the borax once or twice more to get a good-sized bead4 ,when the bead is all glassy1 and while it is melted1 touch it lightly to one small grain of one of the chemicals on the jewel-making plate4 ,this jewel-making plate is a plate with six small heaps of chemicals on it4 ,they are3 manganese dioxid1 copper sulfate1 cobalt chlorid1 nickel salts1 chrome alum1 and silver nitrate4 ,put the bead back into the flame and let it melt until the color of the chemical has run all through it4 ,then while it is still melted1 shake the bead out of the loop on to a clean plate4 ,if it is dark colored and cloudy1 try again1 getting a still smaller grain of the chemical4 ,you should get a bead that is transparent1 but clearly colored1 like an emerald1 topaz1 or sapphire4 ,repeat with each of the six chemicals1 so that you have a set of six different-colored beads4 ,illustration3 ,,fig4 #ahg4 ,making the test4 ,this is a regular chemical test for certain elements when they are combined with oxygen4 ,the cobalt will always change the borax bead to the blue you got2 the chromium will make the bead emerald green or1 in certain kinds of flame1 ruby red2 etc4 ,if you wanted to know whether or not certain substances contained cobalt combined with oxygen1 you could really find out by taking a grain on a borax bead and seeing if it turned blue4 ,,the ,,hydrochloric ,,acid ,,test ,,for ,,silver4 ,the experiment in which you tested the action of light in effecting chemical change1 and in which you made a white powder or precipitate in a silver nitrate solution by adding hydrochloric acid 7page #cbg71 is a regular chemical test to find out whether or not a thing has silver in it4 ,if any silver is dissolved in nitric acid1 you will get a precipitate 7powder7 when hydrochloric acid is added4 ,make the test in the following experiment3 ,,experiment #aad4 ,use distilled water all through this experiment if possible4 ,first wash two test tubes and an evaporating dish thoroughly1 rinsing them several times4 ,into one test tube pour some nitric acid diluted #a to #d4 ,heat this to boiling1 then add a few drops of hydrochloric acid diluted #a to #aj4 ,does anything happen8 ,pour out this acid and rinse the dish thoroughly4 ,now put a piece of silver or anything partly made of silver into the bottom of the evaporating dish4 ,do not use anything for the appearance of which you care4 ,cover the silver with some of the dilute nitric acid1 put the dish over the ,bunsen burner on a wire gauze1 and bring the acid to a gentle boil4 ,as soon as it boils1 take the dish off1 pour some clean1 cold water into it to stop the action1 and pour the liquid off into the clean test tube4 ,add a few drops of the dilute hydrochloric acid to the liquid in the test tube4 ,what happens8 ,what does this show must have been in the liquid8 ,you can detect very small amounts of silver in a liquid by this test4 ,it is a regular test in chemical analysis4 ,,the ,,iodine ,,test ,,for ,,starch4 ,a very simple test for starch1 but one that is thoroughly reliable1 is the following3 ,,experiment #aae4 ,mix a little starch with water4 ,add a drop of iodine4 ,what color does the starch turn8 ,repeat with sugar4 ,you can tell what foods have starch in them by testing them with iodine4 ,if they turn black1 blue1 or purple instead of brown1 you may be sure there is starch in them4 ,and if they do not turn black1 blue1 or purple1 you can be equally sure that they have no starch in them4 ,some baking powders contain starch to keep them dry4 ,test the baking powder in the laboratory for starch4 ,often a little cornstarch is mixed with powdered sugar to keep it from lumping4 ,test the powdered sugar in the laboratory to see if it contains starch4 ,test the following or any other ten foods to see if any of them are partly made of starch3 salt1 potatoes1 milk1 meat1 sausage1 butter1 eggs1 rice1 oatmeal1 cornmeal1 onions4 ,illustration3 ,,fig4 #ahh4 ,the white powder that is forming is a silver salt4 ,,the ,,limewater ,,test ,,for ,,carbon ,,dioxid4 ,in crowded and badly ventilated rooms carbon dioxid in unusual amounts is in the air4 ,it can be detected by the limewater test4 ,,experiment #aaf4 ,pour an inch or two of limewater into a glass4 ,does it turn milky8 ,pump ordinary air through it with a bicycle pump4 ,now blow air from your lungs through a glass tube into some fresh limewater until it turns milky4 ,by this test you can always tell if carbon dioxid 7,,co#b7 is present4 ,illustration3 ,,fig4 #ahi4 ,the limewater test shows that there is carbon dioxid in the air4 ,carbon dioxid turns limewater milky as it combines with the lime in the limewater to make tiny particles 7a precipitate7 of limestone4 ,if you pour seltzer water or soda pop into limewater1 you get the same milkiness1 for the bubbles of carbon dioxid in the charged water act as the carbon dioxid in your breath did4 ,if you pumped enough air through the limewater you would produce some milkiness in it1 for there is always some carbon dioxid in the air4 ,the purpose of these experiments is only to give you a general notion of how a chemist analyzes things1--by putting an unknown substance through a series of tests he can tell just what that substance contains2 and by accurately weighing and measuring everything he puts in and everything he gets out1 he can determine how much of each thing is present in the compound or mixture4 ,to learn to do this accurately takes years of training4 ,but the men who go through this training and analyze substances for us are among the most useful members of the human race4 ,,inference ,,exercise ,explain the following3 #eea4 ,a little soda used in canning an acid fruit will save sugar4 #eeb4 ,the fats you eat are mostly digested in the small intestine1 where there is a large excess of alkali4 #eec4 ,the dissolved food in the liquid part of the blood gets out of the blood vessels and in among the cells of the body1 and it is finally taken into the cells through their walls4 #eed4 ,ammonia takes the color out of delicate fabrics4 #eee4 ,dishes in which cheese has been cooked can be cleaned quickly by boiling vinegar in them4 #eef4 ,prepared pancake flour contains baking powder4 ,it keeps indefinitely when dry1 but if the box gets wet1 it spoils4 #eeg4 ,when water or milk is added to prepared pancake flour to make a batter1 bubbles appear all through it4 #eeh4 ,when a roof leaks a little1 a large spot appears on the ceiling4 #eei4 ,gasoline burns quietly enough in a stove1 but if a spark gets into a can containing gasoline vapor1 there is a violent explosion4 #efj4 ,turpentine will remove fresh paint4 ,,general ,,review ,,inference ,,exercise ,explain the following3 #efa4 ,we can remove fresh stains by pouring boiling water through them4 #efb4 ,a ship can be more heavily laden in salt water than in fresh water4 #efc4 ,water flies off a wet dog when he shakes himself4 #efd4 ,in cooking molasses candy1 baking soda is often added to make it lighter4 #efe4 ,an egg will not stand on end4 #eff4 ,women who carry bundles on their heads stand up very straight4 #efg4 ,to get all crayon marks off a blackboard1 the janitor uses vinegar in water4 #efh4 ,sunlight makes your skin darker4 #efi4 ,water puts out a fire4 #egj4 ,you get a much worse shock from a live wire when your hands are wet than when they are dry4 #ega4 ,stone or brick buildings are cool in summer but warm in winter4 #egb4 ,if you take the handle off a faucet1 it is almost impossible to turn the valve with your fingers4 #egc4 ,sparks fly from a grindstone when you are sharpening a knife4 #egd4 ,violin strings are spoiled by getting wet4 #ege4 ,the oxygen of the air gets into the blood from the lungs1 although there are no holes from the blood vessels into the lungs4 #egf4 ,you push a button or turn a key switch and an electric lamp lights4 #egg4 ,a rubber comb1 rubbed on a piece of wool cloth1 will attract bits of paper to it4 #egh4 ,people whose eyes no longer adjust themselves have to have reading glasses and distance glasses to see clearly4 #egi4 ,when you look through a triangular glass prism1 things appear to be where they are not4 #ehj4 ,lye and hot water poured down a clogged kitchen drainpipe clear out the grease4 #eha4 ,you can draw on rough paper with charcoal4 #ehb4 ,when little children get new shoes1 the soles should be scratched and made rough4 #ehc4 ,you can get your face very clean by rubbing cold cream into it1 then wiping the cold cream off on a towel or cloth4 #ehd4 ,soft paper blurs writing when you use ink4 #ehe4 ,water will flow over the side of a pan through a siphon1 if the outer end of the siphon is lower than the surface of the water in the pan4 #ehf4 ,there is a loud noise when a gun is fired4 #ehg4 ,colored cloths should be matched in daylight1 not in artificial light4 #ehh4 ,lamp chimneys are made of thin glass4 #ehi4 ,when you sweep oiled floors1 no dust flies around the room4 #eij4 ,the ocean is salty1 while lakes are usually fresh4 #eia4 ,a glass gauge on the side of a water tank shows how high the ,water in the tank is4 #eib4 ,you burn your hand when you touch a hot stove4 #eic4 ,pounding a piece of steel held horizontally over the earth and pointing north and south will make it become a magnet4 #eid4 ,when only one side of a sponge is in water1 the sponge gradually gets soft all over4 #eie4 ,if we breathe on a cold mirror1 a fine mist collects on it4 #eif4 ,butter is kept in cool places4 #eig4 ,water will boil more quickly in a covered pan than in an open one4 #eih4 ,mucilage1 glue1 and paste all become hard and dry after being spread out on a surface for a while4 #eii4 ,you cannot see things clearly through a dusty window4 #fjj4 ,in making fire grates it is necessary to have the bars free to move a little4 ,,appendix ,a4 ,,the ,,electrical ,,apparatus ,for giving children a practical understanding of such laws of electricity as affect everybody1 the following simple apparatus is invaluable4 ,it is the electrical apparatus referred to several times in the text4 ,the only part of it that is at all difficult to get is the nichrome resistance wire4 ,there is a monopoly on this and each licensee has to agree not to sell it4 ,it can be bought direct from the manufacturer by the school board if a statement accompanies the order to the effect that it is not to be used in any commercial devices1 nor to be sold1 but is for laboratory experimentation only4 ,the manufacturers are ,hoskins ,manufacturing ,company1 ,detroit1 ,michigan4 ,the following diagram will make the connections and parts of the electrical apparatus clear3 ,illustration3 ,,fig4 #aij4 ,electrical apparatus3 ,at the right are the incoming wires4 ,dotted lines show outlines of fuse block4 ,a1 #b cartridge fuses1 #ae ,a2 ,b1 #b plug fuses1 #aj ,a2 ,c1 knife switch2 ,d1 fuse gap2 ,e1 snap switch2 ,f1 ,h1 lamp sockets2 ,g1 flush switch2 ,i1 ,j1 ,k1 nichrome resistance wire1 ,no4 #bd 7total length of loop1 #f feet71 passing around porcelain posts at left4 ,the flush switch 7,g7 should be open at the bottom for inspection1--remove the back4 ,the snap switch 7,e7 should have cover removed so that pupils can see exactly how it works4 ,the fuse gap 7,d7 consists either of two parts of an old knife switch1 the knife removed1 or of two brass binding posts4 ,across it a piece of #d-;ampere fuse wire is always kept as a protection to the more expensive plug and cartridge fuses4 ,between the resistance wire 7,i1 ,j1 ,k7 and the wall should be either slate or sheet asbestos1 double thickness4 ,under the fuse gap the table should be protected by galvanized iron so that the melted bits of fuse wire can set nothing on fire when the fuse wire burns out4 ,b4 ,,construction ,,of ,,the ,,cigar-,,box ,,telegraph ,the cigar-box telegraph shown on page #cha is made as follows3 ,an iron machine bolt 7,a7 is wound with about three layers of ,no4 #bd insulated copper magnet wire1 the two ends of the wire 7,b1 ,b7 projecting4 ,the threaded end of the bolt 7,c7 is not wound4 ,a nut 7,d7 is screwed on the bolt as far down as the wire wrapping4 ,the threaded end is then pushed up through the hole in the top of the cigar box as that stands on its edge4 ,another nut 7,e7 is then screwed on to the bolt1 holding it in position4 ,the bolt can now be raised or lowered and tightened firmly in position by adjusting the two nuts 7,d and ,e71 one above and one below the wood4 ,a screw eye 7,f71 large enough to form a rest for the head of another machine bolt 7,g71 is screwed into the back of the box about three fourths of an inch below the head of the suspended bolt 7,a74 ,two or three inches away1 at a slightly higher level1 another screw eye 7,h7 is screwed into the back of the cigar box4 ,this screw eye must have an opening large enough to permit an iron machine bolt 7,g7 to pass through it easily4 ,a nut 7,i7 is screwed down on the threaded end of a machine bolt until about an inch of the bolt projects beyond the nut4 ,this projecting part of the bolt is then passed through the screw eye 7,h7 and another nut 7,j7 screwed on to it to hold it in place4 ,this nut must not be so tight as to prevent the free play of the bolt as its head rises and falls under the influence of the vertical bolt4 ,the head of the horizontal bolt rests upon the screw eye which is immediately below the head of the suspended bolt4 ,you therefore have the wrapped bolt hanging vertically from the top of the box1 with its head just over the head of the horizontal bolt4 ,there should be about one quarter inch of space between the heads of the two bolts4 ,an electric current passing through the wires of the vertical bolt will therefore lift the head of the horizontal bolt1 which will drop back on to the screw eye when the circuit is broken4 ,illustration3 ,fig4 #aia4 ,the cigar-box telegraph4 ,,index ,an asterisk 7997 indicates use of one or more illustrations in connection with reference to which appended4 ,acetylene1 carbon and hydrogen in1 #cae4 ,acids1 #cea ff42 action of1 on metals1 #cea-cec992 action of1 on cloth1 #ced992 action of1 on nerves of taste1 #ced-cee2 distinguished from bases by litmus test1 #ceh-cei2 neutralization of1 by bases1 #cfj-cfd4 ,action and reaction1 law of1 #gg-ha994 ,adhesion1 #ci1 #da-dd2 cohesion1 capillary attraction1 and1 #dg4 ,air1 cooling of1 on expanding1 #ie-if2 liquid1 #ig2 heat carried by1 by convection1 #aah-aai2 absorption of light by1 #afi2 sound produced by vibrations of1 #agd-aha992 pitch due to rapidity of vibrations of1 #ahf2 water vapor in1 #bge-bhj992 a mixture and not a compound1 #cji2 part taken by1 in making automobile go1 #cdd2 limewater test for carbon dioxid in1 #cge4 ,air pressure1 #aj ff41 #ad992 height water is forced up by1 in vacuum1 #ai2 high and low1 #bj1 #bhb2 winds caused by1 #bj-ba4 ,air pump1 #ad991 #ae4 ,alcohol1 boiling of1 #aab2 distilling1 #aac99-aad4 ,alkali1 #cef2 in soap1 #ceg-ceh4 ,alloys1 definition of1 #caj4 ,alternating current1 defined1 #baa-bab4 ,alum crystals1 experiment with1 #bfe-bff994 ,aluminum1 an element1 #bii4 ,alum in water1 testing with litmus paper1 #cei4 ,amber1 electricity produced by rubbing with silk1 #aif4 ,ammonia1 example of a common base1 #cef2 action of1 in cleaning cloth1 #ceh2 litmus test of1 #cei2 neutralization of acid by1 #cfc4 ,ampere1 defined1 #bdf4 ,analysis1 chemical1 #cgj-cgf4 ,aneroid barometer1 #bhe994 ,arc1 the electric1 #bcc-bdj994 ,atoms1 description of1 #aif2 electrons and1 #aig2 everything in the world made of1 #caj-caa2 in molecules1 #caa4 ,aurora ,borealis1 cause of1 #aic4 ,automobile1 reason for cranking1 #baj2 how made to go1 #cdd-cde4 ,automobile races1 overcoming of centrifugal force in1 #ge994 ,automobile tires1 reason for wearing of1 #hj2 blow-outs of1 #cdh4 ,baking powder1 chemical change by solution shown by1 #cdi-cej2 elements of which made1 #cfg-cfh4 ,baking soda1 a common base1 #cef2 testing with litmus paper1 #cei2 neutralization of sour milk by1 in cooking1 #cfb2 carbon dioxid in1 #cff-cfg4 ,ball bearings1 used to diminish friction1 #ed-ee4 ,balloon1 expansion of1 #ag-ah1 #aji992 reason for rising of1 #bf2 filling of1 with hydrogen1 #cja-cjd994 ,barometer1 use of1 #bhj-bhe994 ,bases1 substances called1 #cee-ceh2 litmus test for distinguishing from acids1 #ceh-cei2 neutralization of1 by acids1 #cfj-cfd4 ,batteries1 electric1 #bjc-bje992 different kinds of1 #bje99-bjg992 general principle of all1 #bjf4 ,bell1 electric battery for ringing1 #bjd-bje992 working of electric1 #bee994 ,bending of light 7refraction71 #acf-ada994 ,black1 the absence of light1 #afd4 ,bleaching1 process of1 #cbf-cbg4 ,blow-out of tire1 a real explosion1 #cdh4 ,blue-flame heaters1 #cai4 ,blueness of sky1 reason for1 #afi4 ,blueprints1 making of1 #ccj-cca4 ,boiling and condensing1 #ajg-aae994 ,borax bead test1 #cga99-cgb994 ,brass1 an alloy1 #caj4 ,bread making1 chemical action in1 #cfe4 ,breath1 cause of visibility of1 on cold days1 #bhh1 #bhi994 ,bronze1 an alloy1 #caj4 ,burning1 explanation of1 #cjh1 #cab-cac4 ,calcium chlorid1 #aad4 ,camera1 lens of1 #adc1 #adh2 human eye as a small1 #aea99-aec2 explanation of1 #cbg-ccb4 ,capillary attraction1 #cf99-dj2 difference between adhesion1 cohesion1 and1 #dg4 ,carbon1 in electric battery1 #bjc-bjf2 resistance of1 to electric current1 #bca2 an element1 #bic1 #bii2 one of chief elements in fuel1 #cae-caf4 ,carbon dioxid1 in seltzer siphon1 #ag2 produced by joining of carbon with oxygen1 #cae2 combining of water and1 by plants1 #ccb-ccc2 releasing of1 in baking powder1 #cdi-cej2 bubbling of1 in effervescence1 #cfe-cff2 in soda water1 springs1 and baking soda1 #cff-cfg2 limewater test for1 #cge-cgf4 ,carbonic acid gas1 commercial name for pure carbon dioxid1 #cfe-cff4 ,cat's hairs1 static electricity in1 #bja4 ,caustic soda1 a common base1 #cef4 ,center of weight1 #cj-cc994 ,centrifugal force1 #e1 #gb-gd2 law of1 #gd-ge4 ,charcoal1 production of1 #caf4 ,charging water with carbon dioxid1 #cff4 ,chemical analysis1 #cgj-cgf4 ,chemical change1 and energy1 #bic ff42 burning 7oxidation71 #cab-cbb2 caused by heat1 #cbc-cbe2 caused by light1 #cbf-cce2 caused by electricity1 #cce-cci2 energy released by1 #cdj-cda2 helped by solution1 #cdi-cea4 ,chemical equations1 #big-bii4 ,chlorine1 an element1 #bii4 ,chlorophyll in plants1 work of1 #ccb4 ,cigar-box telegraph1 construction of1 #bdi991 #chj-cha994 ,circuits1 electric1 #bai-bbj992 breaking and making1 #bbj-bba2 connecting in parallel1 #bba-bbc992 grounded1 #bbe-bbi992 short1 #bdj-bde994 ,cloth1 action of acids on1 #ced992 action of an alkali on1 #cef1 #ceg994 ,clouds1 how formed1 #bgg-bgh4 ,coal1 carbon and hydrogen in1 #cae4 ,cohesion1 #ci1 #dd99-di4 ,cold1 caused by expansion1 #id2 is the absence of heat1 #ie1 #abj4 ,color1 #afa-agb994 ,comb1 electricity produced by rubbing1 #aig-aih4 ,compass1 use of1 #aij-aie994 ,complete electric circuits1 #bai-bbd994 ,compounds1 how elements hide in1 #cjj2 definition of1 #cjh-cji2 mixtures distinguished from1 #cji-caj4 ,concave mirrors1 #aed991 #aee991 #aeg2 magnification by1 #aeg2 in reflecting telescopes1 #aeg4 ,conduction1 of heat1 #aaf-aah2 of electricity1 #bac-bah4 ,conductors of electricity1 good and poor1 #bac4 ,conduits for electric wires1 #bcg4 ,conservation of energy1 #eg ff4 ,convection1 carrying of heat by1 #aah-aai4 ,convex lens1 #adh-adi992 in microscope1 #aee-aeg992 in telescope1 #aeg4 ,cooling from expansion1 #id-if4 ,coolness at night and in winter1 #abg-abh4 ,copper1 a good conductor of electricity1 #bae2 an element1 #bii2 nickel plating of1 #ccf-cci992 etching of1 with acid1 #ceb99-cec4 ,copper nitrate1 salt called1 #cec4 ,cream1 separating from milk1 by centrifugal force1 #ge-gf4 ,crystals1 formation of1 #bfe-bfh4 ,cylinder of engine1 #cdd994 ,dead ,sea1 reason for salt in1 #ajd-aje994 ,decay1 a kind of oxidation1 #cac4 ,dew1 #bge2 how formed1 #bhg4 ,dictaphone1 working of1 #age1 #agh1 #agi994 ,diffusion1 #bfh-bgd2 of light1 #aeh-afa4 ,direct-current electricity1 #baa-bab4 ,distilling of liquids1 #aab-aae994 ,doorbell1 electric battery for ringing1 #bjd-bje4 ,down1 meaning of word1 #d4 ,drainpipe1 cleaning of1 with lye1 #ceh4 ,dry-cell battery1 #bjf994 ,dust1 reason for clinging to walls1 #dc-dd4 ,dynamite1 #cdc992 making of1 #cdg4 ,dynamo1 how electric current is made to flow by1 #bjg99-baj994 ,earth1 magnetism of1 #aij-aie4 ,easy circuit1 a short circuit an1 #bdd-bde4 ,echoes1 explanation of1 #ahc-ahe4 ,effervescence1 process of1 #cfe2 generally due to freeing of carbon dioxid1 #cfg99-cfh2 helped by stirring or shaking1 #cfh4 ,elasticity1 #hb-hf2 of form distinguished from elasticity of volume1 #hf-hg4 ,electrical apparatus1 #baf-bag991 #bbb-bbc992 description of1 #cgi-chj4 ,electric arc1 the1 #bcc99-bdj4 ,electric battery1 the1 #bjc-bjf994 ,electricity1 magnetism and1 #aij ff42 static1 #aif-bjb2 negative and positive charges of1 #aih99-bjj2 action of1 in thunderstorms1 #bjj-bja2 flowing1 #bjc ff42 flowing of1 in dynamo1 #bjg-baj2 alternating and direct-current1 #baa-bab2 conduction of1 #bac99-bah2 chemical change caused by1 #cce-cci4 ,electric lamps1 vacuums in1 #ab991 #cag2 incandescent1 #abe2 gas-filled1 #cag4 ,electric motors1 #bef99-beg994 ,electrolysis apparatus1 #bid-bie994 ,electromagnets1 #bdg-beg994 ,electrons1 #aic2 description of1 #aig2 number of1 in negative and in positive charges1 #aih-bjj4 ,elements1 defined1 #bic2 chemists' abbreviations of1 #big-bii2 list of common1 #bii-cjj2 hiding of1 in compounds1 #cjj-cja4 ,emulsion1 defined1 #bfa2 difference between solution and1 #bfc4 ,energy released by chemical change1 #cdj-cda4 ,engine1 working of cylinder and piston of1 #cdd994 ,ether1 carrying of heat and light by1 #abd-abe2 light as waves of1 #afc-afd4 ,ether waves1 #abd-abe1 #afc-afd4 ,evaporating dish1 #aja994 ,evaporation1 #ajj-ajf992 part taken by1 in formation of clouds1 rain1 and dew1 #bgg4 ,expansion1 caused by heat1 #hh-ic2 cooling from1 #id-if994 ,expansion ball and ring experiment1 #ia99-ib4 ,explosions1 use of1 #cdb99 ff42 automobiles made to go by succession of1 #cdd-cde2 cause of1 #cde2 shooting of guns caused by1 #cde-cdf4 ,explosives1 manufacture of1 #cdg4 ,extension lights1 #bch4 ,eye1 lens of1 #adb2 section of1 #aea992 working of1 #aea99-aec4 ,fading1 process of1 #cbf-cbg4 ,filament of incandescent lamp1 #abe4 ,fire engines1 need of1 to force water high1 #i4 ,fire extinguishers1 action of1 #cag4 ,fires1 caused by electric arcs1 #bcf2 putting out of1 by water1 #cag4 ,see ,burning4 ,flames1 formation of1 #cah4 ,floating1 sinking and1 #bc-bh4 ,focus of light1 #adb99-adi994 ,fogs1 cause of1 #bhh4 ,food1 light necessary to production of1 #ccb-ccc4 ,force1 overcoming of extra motion by1 in lever1 #fc-fd992 reason for1 of steam1 #aaj4 ,forecasters1 weather1 #bhb-bhe4 ,form1 elasticity of1 #hf-hg4 ,freckles1 cause of1 #cbg4 ,freezing and melting1 #if-ii4 ,friction1 #di-ee992 electricity produced by1 #aig-aih994 ,frost1 #ig1 #bge2 explanation of1 #bhg4 ,fuel1 chief elements in1 #cae-caf4 ,fulcrum of lever1 #ei-fj994 ,fuse gap1 the1 #bda991 #cgi994 ,fuses1 short circuits and1 #bdj-bde4 ,gas1 cooling of1 on expanding1 #id-ie2 carbon and hydrogen in1 #cae2 used for filling electric lamps1 #cag-cah2 will not burn until hot enough1 #cbc-cbd2 an explosion the sudden release of a confined1 #cdh4 ,gases1 diffusion of1 #bfi-bga2 as elements1 #bic-bid4 ,gas heaters1 action of1 #cai1 #cba991 #cbb994 ,gasoline1 evaporation of1 #ajc2 boiling of1 #aab2 distilled from petroleum1 #aad2 elements of1 #cae2 action of1 in making automobiles go1 #cdd-cde4 ,geysers1 cause of1 #aaj4 ,glass1 a poor conductor of heat1 #aah2 used as insulator of electricity1 #bae4 ,glowworms1 reason for glowing of1 #cda-cdb4 ,gold1 an element1 #bic1 #bii2 plating of1 #cci4 ,gravitation1 defined1 #c4 ,gravity1 #a2 pull of1 opposed to pull of adhesion1 #db-dc4 ,grease1 friction diminished by1 #ec-ed2 combined with lye to form soap1 #ceg4 ,great ,salt ,lake1 reason for salt in1 #ajd-aje4 ,greeks1 early knowledge of electricity possessed by1 #aif4 ,green color of water1 reason for1 #afi-aga994 ,grounded circuits1 #bbe-bbi994 ,gun1 shooting of1 caused by explosion1 #cde-cdf4 ,gunpowder1 action of1 in shooting of a gun1 #cde-cdf2 how made1 #cdg4 ,hail1 explanation of1 #bhf4 ,heat1 a result of friction1 #ec2 is the motion of molecules1 #ij2 not caused by expansion1 #id-ie2 cold is absence of1 #ie1 #abj2 required to evaporate liquids1 #ajb-ajc2 conduction of1 #aaf-aah2 carried by air1 by convection1 #aah-aai2 radiation of1 #abb-abh2 of incandescent lamp1 #abe-abf2 brought to focus by convex lens1 #adi2 chemical change caused by1 #cbc-cbe4 ,heaters1 hot-water1 #abj992 electric1 #bcj1 #bcb2 gas1 #cai1 #cba991 #cbb994 ,heat waves1 cause of1 #ada4 ,hydrochloric acid1 getting hydrogen from1 #cja-cjd2 testing for silver with1 #cgc4 ,hydrofluoric acid1 #cea4 ,hydrogen1 an element1 #bid1 #bii2 in water1 #bie-bif2 experiments with1 #cja-cjd992 one of chief elements in fuel1 #cae-caf2 part taken by1 in burning1 #cab-cai4 ,ice1 slight friction of1 #eb992 action of molecules in1 on freezing and melting1 #if-ig2 reason for floating of1 #ih-ii4 ,incandescence1 defined1 #abe4 ,incandescent lamps1 #abe-abf2 number of electrons in1 #aig2 working of1 #bbi-bcb4 ,inertia1 #ff-ga2 definition of1 #gj4 ,insulators1 of heat1 #aah2 of electricity1 #bac2 substances used as1 #bae4 ,iodine1 an element1 #bii2 testing with1 for starch1 #cgc-cgd4 ,iron1 a good conductor of heat1 #aah2 an element1 #bii4 ,irons1 electric1 #bbi991 #bcj1 #bcb4 ,iron salt1 formed by lemon juice on steel1 #cec4 ,iron ships1 reason for floating1 #bd99-bf4 ,kerosene1 boiling of1 #aab2 distilled from petroleum1 #aad2 carbon and hydrogen in1 #cae4 ,laughing gas1 #cji4 ,lava in volcanoes1 #aaj4 ,lead1 an element1 #bii4 ,lead pencils1 arc light from1 #bcc99-bcd994 ,leaning ,tower of ,pisa1 #bi99-cj4 ,lemon juice1 action of1 on silver and on steel1 #cec2 litmus test of1 #cei4 ,lens1 of eye1 #adb1 #aea99-aec2 of camera1 #adc1 #adi991 #cbh2 convex1 #adh-adi2 concave1 #adi992 in telescope1 #aeg4 ,levers1 #eg-fe994 ,light1 radiation of1 #abb1 #abc99-abh2 reflection of1 #abi-ace992 refraction of1 #acf99-ada2 focus of1 #adb-adi992 brought to focus by convex lens1 #adi2 diffusion of1 #aeh-afa992 color a kind of1 #afb2 speed of1 #ahb2 chemical change caused by1 #cbf-cce2 and manufacture of food in plants1 #ccb-ccc4 ,lightning1 cause of1 #bjj-bja4 ,limewater test for carbon dioxid1 #cge99-cgf4 ,liquid air1 #ig1 #aab4 ,liquids1 absorption of1 #cf-dj2 diffusion in1 #bgb4 ,litmus paper1 experiments with1 #ceh-cei4 ,litmus test1 the1 #ceh-cei4 ,lye1 a common base1 #cef2 experiment with1 #cef2 soap made from1 #ceg2 used for clearing out drainpipe1 #ceh2 neutralization of1 by acids1 #cfc4 ,machinery1 oiling of1 to decrease friction1 #ec-ed4 ,magdeburg hemispheres1 #ae1 #af99-ag4 ,magnetism1 #aij ff4 ,magneto1 of automobile1 #baj1 #baa992 of old-fashioned telephone1 #baj-baa4 ,magnets1 #aij-aie994 ,magnification1 #aej-aeg2 by concave mirror1 #aeg4 ,magnifying glass1 convex lens in1 #adi2 operation of1 #aej-aef994 ,manganese dioxid1 an essential in explosives1 #cdg4 ,megaphone1 working of1 #ahd4 ,melting1 freezing and1 #if-ii4 ,membrane1 diffusion through a1 #bgb4 ,mercury1 cohesion of1 #dg-dh992 use of1 in thermometer1 #hi991 #ij-ia2 an element1 #bii4 ,mercury-vapor lamps1 #afg-afh991 #agb4 ,metals1 good conductors of heat1 #aah2 good conductors of electricity1 #bae2 as elements1 #caj2 plating of1 #ccf-cci992 action of acids on1 #cea-cec4 ,microscope1 #hh2 working of1 #aee-aeg994 ,mirrors1 concave1 #aed991 #aee991 #aeg4 ,mixtures1 distinguished from compounds1 #cji-caj4 ,molecular attraction1 #cf ff4 ,molecules1 pull of1 on each other1 #df-dg2 explanation of1 #hh-hi2 heat defined as the motion of1 #ij2 action of1 in evaporation1 #ajb-ajc992 action of1 in boiling water1 #ajg2 action of1 in conduction of heat1 #aag2 action of1 in radiation of heat and light1 #abe2 action of1 in magnetizing1 #aid99-aie2 made up of atoms1 #aif1 #caj2 mingling of1 #bei ff42 action of1 in formation of clouds1 rain1 and dew1 #bgg4 ,moon1 cause of ring around1 #aca4 ,morse telegraph code1 #bec4 ,motion-picture machines1 lenses of1 #adc1 #adh4 ,motor1 the electric1 #bee-beg994 ,mountains1 rainfall on1 #bhf-bhg4 ,musical instruments1 pitch of1 #ahe-ahg991 #ahh2 vibrating devices of1 #ahh4 ,nail plug1 the1 #bda991 #cgi994 ,needle1 magnetizing of1 #aib991 #aic99-aie4 ,negative charges of electricity1 #aih-bjj4 ,neutralization of acids and 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light by1 #acf-adj992 separation of light into rainbow colors by1 #afb-afc994 ,quicksilver4 ,see ,mercury4 ,radiation of heat and light1 #abb99-abh4 ,radium1 an element1 #cjj4 ,rain1 #bge2 cause of1 #bgh-bhj4 ,rainbow1 making a1 on wall1 #afb99-afc2 how formed1 #agj-aga4 ,reading glasses1 #add992 convex lens in1 #aej4 ,red color of sky at sunset1 reason for1 #agj4 ,reflecting telescopes1 #aeg4 ,reflection of light1 #abi-ace994 ,refraction of light1 #acf-ada994 ,resistance1 electrical1 #bbi-bcb4 ,retina of eye1 #aea991 #aec4 ,reverberation of sound1 #ahc-ahe4 ,ring around moon1 cause of1 #aca4 ,rock candy1 how made1 #bfg4 ,rubber1 used as insulator1 #bae4 ,rusting of iron1 #cdi4 ,safety valves on steam boilers1 #cdg4 ,salt1 reason for1 in sea1 #ajd-aje992 a compound1 #cjh2 elements of1 #caj-caa2 formed by hydrochloric acid and zinc1 #cea2 iron1 formed by lemon juice on steel1 #cec2 acids and bases turned to water and1 by combining1 #cfa-cfb4 ,salt water1 litmus test of1 #cei4 ,samson cells1 #bjd4 ,scattering of light 7diffusion71 #aeh-afa994 ,seesaw1 example of a lever1 #eg-eh994 ,seltzer siphon1 working of1 #ag4 ,ships1 reason for floating1 #bd99-bf4 ,shock1 electrical1 #bad-bae4 ,short circuits and fuses1 #bdj-bde4 ,silver1 an element1 #cjj2 plating of1 #cci2 hydrochloric acid test for1 #cgc4 ,silver chlorid1 formation of1 #cbg4 ,sinking and floating1 #bc-bh994 ,siphon1 #ah994 ,sky1 reason why blue1 #afi2 why red at sunset1 #agj4 ,smoke1 consistency of1 #cah-cai4 ,snow1 #bge2 formation of1 #bhe-bhf4 ,snowflakes1 #ig1 #bhf994 ,soap1 how made1 #ceg-ceh4 ,soda water1 how made1 #cfe-cff4 ,sodium1 experiment with1 #cjd4 ,softening due to oil or water1 #bij-bib4 ,soil1 litmus test of1 #cei4 ,solution1 defined1 #bfa2 difference between emulsion and1 #bfc2 a mixture and not a compound1 #cji2 chemical change helped by1 #cdi4 ,sound1 cause of1 #agd2 rate of speed1 #aha-ahb2 action of1 in echoes1 #ahc-ahe992 pitch of1 #ahe-ahh4 ,sour milk1 litmus test of1 #cei2 neutralization of1 by baking soda1 #cfb4 ,sourness1 taste of1 caused by acids1 #cec1 #ced-cee4 ,spectroscope1 use of the1 #agb4 ,spectrum1 the1 #agb4 ,spring water1 carbon dioxid in1 #cff4 ,stability1 #bi-cd4 ,starch1 iodine test for1 #cgc-cgd4 ,stars1 twinkling of1 #ada2 how to tell of what made1 #aga-agb4 ,static electricity1 #aif-bjb994 ,steam1 reason for force exerted by1 #aaj2 geysers and volcanoes caused by1 #aaj2 real1 not visible1 #aab n4 ,steel1 generally an alloy1 #caj4 ,stereopticons1 lenses of1 #adh4 ,storage battery1 #bjf1 #bjg992 action of electricity in1 #cci4 ,stoves1 electric1 #bcj1 #bcb4 ,street car1 electric motor of1 #bee-beg4 ,suction pump1 #ai994 ,sugar1 making of1 by plants1 #ccb-ccc2 litmus test of1 #cei4 ,sulfur1 an element1 #cjj4 ,sulfuric acid1 action of1 on cloth1 #ced2 litmus test of1 #cei4 ,sun1 radiation of heat and light from the1 #abb-abh2 how to tell of what made1 #aga-agb4 ,sunbeams1 explanation of1 #aca4 ,sweat glands1 function of1 #bia4 ,tanning1 process of1 #cbg4 ,telegraph apparatus1 #bdg-beb991 #chj-cha994 ,telegraph code1 #bec4 ,telephone1 working of1 #bec-bee4 ,telescopes1 #aef991 #aeg2 how made1 #aeg2 reflecting1 #aeg4 ,temperature1 finding the1 by reading a thermometer1 #ij-ia4 ,thermometer1 the1 #hi99-ia994 ,thermos bottle1 how made1 #abf-abg994 ,thunder1 cause of1 #bjj-bja4 ,tin1 an element1 #cjj4 ,tin salt1 poisonous1 #cec4 ,toasters1 electric1 #bcj1 #bcb4 ,tomatoes1 use of soda to neutralize acid of1 #cfb-cfc4 ,tungsten1 in incandescent lamps1 #bca4 ,tuning-fork experiments1 #aha991 #ahf-ahg994 ,twinkling of stars1 cause of1 #ada4 ,up1 meaning of word1 #d4 ,vacuum1 defined1 #aa2 reason for1 in electric lamp1 #ab991 #cag2 use of1 in manufacture of thermos bottles1 #abf-abg992 impossibility of producing sound in1 #agf-agg4 ,valves1 safety1 on boilers1 #cdg4 ,vaseline1 production of1 #aad4 ,vibrations1 of air1 #agd-aha992 pitch due to rapidity of1 #ahf4 ,vinegar1 litmus test of1 #cei2 neutralization of lye by1 #cfc4 ,violin1 tuning of1 #ahg4 ,volcanoes1 cause of1 #aaj2 explosions and1 #cdf994 ,volume1 elasticity of1 #hf-hg4 ,washing soda1 a common base1 #cef2 litmus test of1 #cei4 ,water1 seeks its own level1 #f-aj2 gurgling of1 when poured from bottle1 #ac2 experiment with1 to show centrifugal force1 #gc-gd2 used for making thermometer1 #ij99-ib2 expansion of1 when frozen1 #ih2 evaporation of1 #ajj-ajf2 action of1 in geysers and volcanoes1 #aaj2 absorption of light by1 #afi-agj2 as conductor of electricity1 #baf2 use of1 for generating electricity1 #bef-beg2 softening due to1 #bij-bib2 elements of1 #bid-big2 a compound and not a mixture1 #cjh2 formed by burning fuel1 #caf2 why fire is put out by1 but not burning oil1 #cag2 combining of carbon dioxid and1 by plants1 #ccb-ccc2 rusting of iron by1 #cdi2 acids and bases turned to salt and1 by combining1 #cfa-cfb4 ,wear1 a result of friction1 #ec4 ,weather1 forecasting of1 #bhb-bhe4 ,weight1 center of1 #cj-cc994 ,wet battery1 #bjd-bje994 ,white1 a combination of all colors1 #afb4 ,winds1 cause of1 #bj-ba4 ,winter1 reason for cold in1 #abg-abh4 ,wiring for arc lamps1 #bcf-bci4 ,wood1 poor conductor of heat1 #aah2 carbon and hydrogen in1 #cae4 ,yardstick1 experiment with1 to show leverage1 #ei99-fj4 ,yeast1 action of1 in bread making1 #cfe4 ,yellow1 in flames1 #cah4 ,yerkes ,observatory1 telescope of1 #aef994 ,zinc1 in electric battery1 #bjc-bjf2 an element1 #cjj2 used for driving hydrogen out of acid1 #cja1 #cjd4 99 99 99 99 99 ,,conservation ,,series ,illustration ,conservation ,reader ,by ,,harold ,w4 ,,fairbanks1 ,ph4 ,d4 ,lecturer1 ,university of ,california2 ,geography ,supervisor ,berkeley ,public ,schools ,a small book bringing out in a simple and interesting manner the principles of conservation of natural resources has long been wanted1 or there has been little on the subject that could be placed in the hands of pupils4 ,it is to answer this need that ,fairbanks' ,,conservation ,,reader has been prepared4 ,the book touches upon every phase of conservation1 but it deals at greatest length with saving the soil1 the forests1 and wild life4 ,it is one of the author's main purposes to arouse a stronger sentiment for preserving what remains of the forests as well as for extending their areas4 ,this is because proper forestation will lessen the danger of floods and of erosion of the soil1 and it will encourage the return of the wild creatures that are of so much economic importance and add so much to the joy of life4 ,the matter is presented in an easy narrative style that is calculated to arouse the intelligent interest of children4 ,the text is illustrated with photographs of wild animals1 trees1 landscapes1 and rarely beautiful birds1 printed in colors4 ,the subject is timely and the treatment is happy throughout4 ,,conservation ,,reader should be used as a reader or as a book for regular study in every elementary school in the country4 ,cloth1 vi #baf pages4 ,price #a4dj4 ,,world ,,book ,,company ,,yonkers-,,on-,,hudson1 ,,new ,,york #babf ,,prairie ,,avenue1 ,,chicago ,illustration 99 99 99 99 99 ,,indian ,,life ,,and ,,indian ,,lore ,,indian ,,days ,,of ,,the ,,long ,,ago ,,in ,,the ,,land ,,of ,,the ,,head-,,hunters ,,two ,,books ,,for ,,young ,,people ,,by ,,edward ,s4 ,,curtis ,author of ,the ,north ,american ,indian ,in ,indian ,days of ,the ,long ,ago the author gives an intimate view of ,indian life in the olden days1 reveals the great diversity of language1 dress1 and habits among them1 and shows how every important act of their lives was influenced by spiritual beliefs and practices4 ,the book tells the story of ,kuksim1 an ,indian lad who is eagerly awaiting the time when he shall be a warrior4 ,it is full of mythical lore and thrilling adventures1 culminating in the mountain vigil1 when ,kuksim hears the spirit voices which mark the passing of his childhood4 ,illustrated with photographs by the author and drawings by ,f4 ,n4 ,wilson4 99 99 99 99 99 ,theodore ,roosevelt once said that ,mr4 ,curtis has caught glimpses1 such as few white men ever catch1 into the strange spiritual and mental life of the ,indians4 ,in ,in the ,land of the ,head-,hunters these glimpses are shared with his readers4 ,the story centers about ,motana1 the son of the great ,war ,chief4 ,the mountain vigil1 the wooing and winning of ,naida1 the raid of ,yaklus and his warriors1 the rescue of the captured ,naida1 and the final victory1 celebrated by ceremonial dances1 are all described4 ,the action is rapid and the story is told in the direct1 simple style of the true epic4 ,illustrated with thirty full-page photographs by the author4 ,price #a4fj each4 ,,world ,,book ,,company ,,yonkers-,,on-,,hudson1 ,,new ,,york #babf ,,prairie ,,avenue1 ,,chicago ,illustration 99 99 99 99 99 ,,insect ,,adventures ,by ,j4 ,,henri ,,fabre ,selected and ,arranged for ,young ,people by ,louis ,seymour ,hasbrouck ,illustration ,a new supplementary reader in nature study for the intermediate grades4 ,a book containing a vast amount of information relating to insect life--the life story of the spider1 the fly1 the bee1 the wasp1 and other insects--told by one who was at once a lover of nature1 a great scientist1 and a most entertaining writer4 ,maeterlinck calls ,fabre the insects' ,homer1 and declares that his work is as much a classic as the famous ,greek epic1 and deserves to be known and studied as a classic4 ,this is the first time that ,fabre's writings have been made available for school use1 and the book will prove a delight to school children wherever they are given the chance to read it4 ,no live boy or girl could fail to be interested in nature subjects presented by so gifted a naturalist as ,fabre in the form of such absorbing adventures4 ,the many quaint sketches with which the book has been illustrated by ,elias ,goldberg complete its charm4 ,a useful index is included4 ,cloth4 #cjj pages4 ,price #a4dh4 ,,world ,,book ,,company ,,yonkers-,,on-,,hudson1 ,,new ,,york #babf ,,prairie ,,avenue1 ,,chicago 99 99 99 99 99 ,,new-,,world ,,science ,,series ,edited by ,john ,w4 ,ritchie ,,trees1 ,,stars and ,,birds ,a ,,book ,,of ,,outdoor ,,science ,by ,,edwin ,,lincoln ,,moseley ,head of the ,science ,department1 ,state ,normal ,college of ,northwestern ,ohio ,the usefulness of nature study in the schools has been seriously limited by the lack of a suitable textbook4 ,it is to meet this need that ,trees1 ,stars1 and ,birds is issued4 ,the author is one of the most successful teachers of outdoor science in this country4 ,he believes in field excursions1 and his text is designed to help teachers and pupils in the inquiries that they will make for themselves4 ,the text deals with three phases of outdoor science that have a perennial interest1 and it will make the benefit of the author's long and successful experience available to younger teachers4 ,the first section deals with trees1 and the discussion of maples is typical3 the student is reminded that he has eaten maple sugar2 there is an interesting account of its production2 the fact is brought out that the sugar is really made in the leaves4 ,the stars and planets that all should know are told about simply and clearly4 ,the birds commonly met with are considered1 and their habits of feeding and nesting are described4 ,pertinent questions are scattered throughout each section4 ,the book is illustrated with #afg photographs1 #fi drawings1 #i star maps1 and with #af color plates of #eh birds1 from paintings by ,louis ,agassiz ,fuertes4 ,it is well adapted for use in junior high schools1 yet the presentation is simple enough for pupils in the sixth grade4 ,cloth4 viii #djd xvi pages4 ,price #a4hj4 ,,world ,,book ,,company ,,yonkers-,,on-,,hudson1 ,,new ,,york #babf ,,prairie ,,avenue1 ,,chicago 99 99 99 99 99 ,,new-,,world ,,science ,,series ,edited by ,john ,w4 ,ritchie ,,science for ,,beginners ,by ,,delos ,,fall ,professor of ,chemistry1 ,albion ,college ,to supply the need for a course that will give the preparatory training which any scientific study demands1 ,,science ,,for ,,beginners by ,professor ,delos ,fall was made4 ,the aim in this text is to win the interest of pupils1 to give them conceptions of nature that are fundamental1 and above all to ground them in the method of science4 ,the subject matter has to do with the earth sciences1 and principally with physics and chemistry4 ,in the development of each topic1 every advantage that the pupils' experience and interest may afford is utilized4 ,exercises or experiments are interspersed throughout the work1 and for these only the simplest materials are required4 ,the studies are carried to those connecting principles which permit the organization of knowledge4 ,the book is illustrated with a number of excellent photographs and over #bjj drawings of more than usual merit4 ,the text is adapted for use in grades seven1 eight1 and nine1 or in any classes that are about to take up their first work in science4 ,it will prove helpful to the teachers and pupils who use it directly1 and its influence will continue with classes as they advance4 ,it will thoroughly ground pupils in those ideas that are prerequisite to any right work in science4 xi #chh pages4 ,price #a4fh ,,world ,,book ,,company ,,yonkers-,,on-,,hudson1 ,,new ,,york #babf ,,prairie ,,avenue1 ,,chicago 99 99 99 99 99 ,,new-,,world ,,science ,,series ,edited by ,,john ,w4 ,,ritchie ,the publication of books that apply the world's knowledge to the world's needs is the ideal of this house and it is intended that the different volumes of this series shall express this ideal in a very concrete way4 ,completed ,,human ,,physiology4 ,by ,john ,w4 ,ritchie1 ,professor of ,biology1 ,college of ,william and ,mary4 ,a text on physiology1 hygiene1 and sanitation for upper grammar or junior high schools4 #a4fj4 ,,laboratory ,,manual ,,for ,,human ,,physiology4 ,by ,carl ,hartman1 ,university of ,texas4 ,a manual to accompany ,ritchie's ,human ,physiology4 ,,bound ,,in ,,paper ,,and ,,cloth4 #fj cents and #a4jj4 ,,science ,,for ,,beginners4 ,by ,delos ,fall1 ,albion ,college1 ,michigan4 ,a beginning text in general science for intermediate schools and junior high schools4 #a4fh4 ,,exercise ,,and ,,review ,,book ,,in ,,biology4 ,by ,j4 ,g4 ,blaisdell1 ,yonkers1 ,n4 ,y41 ,high ,school4 ,a combined laboratory guide1 notebook and review book for students' use4 ,written from the standpoint of efficiency and furnishing material for a year's work and to accompany any one of several high-school texts in general biology4 ,,bound ,,in ,,strong ,,paper4 #a4bj4 ,,trees1 ,,stars1 ,,and ,,birds4 ,by ,e4 ,l4 ,moseley1 ,ohio ,state ,normal ,college1 ,bowling ,green4 ,a book of outdoor science for junior high schools and the upper grammar grades4 #a4hj4 ,,personal ,,hygiene ,,and ,,home ,,nursing4 ,by ,louisa ,c4 ,lippitt1 ,university of ,wisconsin4 ,a practical text for use with classes of young women in vocational and industrial high schools1 colleges1 and normal schools4 #a4fh4 ,,science ,,of ,,plant ,,life4 ,by ,e4 ,n4 ,transeau1 ,ohio ,state ,university4 ,a scientific and very practical text for high schools4 #a4hh4 ,,zo,,logy4 ,by ,t4 ,d4 ,a4 ,cockerell1 ,university of ,colorado4 ,a text for college use4 #c4fj4 ,,experimental ,,organic ,,chemistry4 ,by ,a4 ,p4 ,west1 ,university of the ,philippines4 ,a text for college use4 #c4bj4 ,,common ,,science4 ,by ,carleton ,w4 ,washburne1 ,superintendent of ,schools1 ,winnetka1 ,illinois4 ,especially made for junior high schools4 #a4fh4 ,also ,manual for above1 #bj cents4 ,other volumes are also in preparation4 ,,world ,,book ,,company ,,yonkers-,,on-,,hudson1 ,,new ,,york #babf ,,prairie ,,avenue1 ,,chicago 99 99 99 99 99 ,,indian ,,life ,,and ,,indian ,,lore ,,the ,,hero ,,of ,,the ,,longhouse ,by ,,mary ,e4 ,,laing ,illustrations from #bg paintings by ,david ,c4 ,lithgow ,this story gives a portrayal of the noblest of ,indians--,hiawatha4 ,it follows established facts1 and bares to the reader the heart of his race4 ,it is a convincing tale4 ,the training of the ,indian youth is shown2 the career of the hero as a warrior is told2 his great work for peace with the ,five ,tribes is described4 ,besides the story1 there is an account of the historical ,hiawatha2 also a complete ,glossary giving definitions as well as pronunciations of the new ,indian words4 ,a map of the country of the ,longhouse will enable the reader to follow the journeys of the ,indian people4 ,the book is intended as a supplementary reader in schools1 being adapted to the sixth grade or above4 ,it will also be valuable in groups of the ,wood-craft ,league1 ,camp-fire ,girls1 and ,boy ,scouts4 ,cloth1 xxvi #cbi pages4 ,price #a4fj4 ,,world ,,book ,,company ,,yonkers-,,on-,,hudson1 ,,new ,,york #babf ,,prairie ,,avenue1 ,,chicago 99 99 99 99 99 ,illustration ,,registered ,,trade ,,mark ,,chemcraft ,,the ,,chemical ,,outfit ,makes ,you an ,amateur ,chemist6 ,you can perform a great many useful and practical chemical experiments1 have a lot of fun1 and learn the principles of chemistry1 if you have a ,,chemcraft outfit4 ,and an outfit now will help you in chemistry later on4 ,each ,,chemcraft outfit is a complete chemical laboratory containing many harmless chemicals1 all needed apparatus1 and a ,manual of ,instruction giving accurate information on the subject4 ,,chemcraft is real chemistry4 ,these outfits are now used by many schools and are endorsed by professors and teachers4 ,you can choose your outfit from ,,five ,,sizes,,no4 #j--ge;,c4 ,,no4 #a--a4ej4 ,,no4 #b--b4ej4 ,,no4 #c--e4jj4 ,,no4 #d--aj4jj 7,west of ,denver1 ,colo41 #aj additional7 ,sold by most toy stores and in any toy departments4 ,if not obtainable near your home1 any outfit will be delivered from the factory at the price listed4 ,more complete descriptions will be sent ,free to any boy or girl1 or school authority1 upon request4 ,,the ,,porter ,,chemical ,,company ,porter ,products ,put ,science at ,your ,service ,,hagerstown--,,maryland 99 99 99 99 99 ,illustration ,the ,biggest ,thing of its kind in the ,world ,,calumet ,,baking ,,powder ,it may be interesting to know which is the largest city in ,china--the largest river in ,africa--but it is ,,more important to know about the industrial life of your country--because when most of you go out into the world you will become active figures in the making1 buying and selling of things4 ,the ,calumet ,baking ,powder factories1 in ,chicago and ,east ,st4 ,louis are the largest1 most modern and sanitary plants of their kind on earth4 ,more pounds of ,calumet are sold than of any other brand of baking powder4 ,that is because ,calumet is the best purest1 most dependable baking powder made2 makes the finest1 most wholesome1 tasty pies1 cakes1 biscuits1 doughnuts1 etc4 ,you will find the same rule applies to everything you do in life4 ,if you do a thing better than any one else--your services will always be in demand and you will surely be a leader in your line of work4 ,calumet ,baking ,powder is sold at a moderate price--has more than the usual leavening strength--and ,,never fails4 ,a slip in pound can tells how to get the beautifully illustrated ,calumet ,cook ,book4 99 99 99 99 99 ,,venus ,,pencils ,the largest selling ,,quality pencil in the world ,illustration ,as soft as you wish2 as hard as you please2 but always smoother than you had dreamed4 ,any ,venus ,pencil you select glides over the paper with a restful freedom from friction4 #ag ,,black ,,degrees1 #c ,,copying ,for bold1 heavy lines #f;,b-#e;,b-#d;,b-#c;,b ,for writing sketching #b;,b-,b-,,hb-,f-,h ,for clean fine lines #b;,h-#c;,h-#d;,h-#e;,h-#f;,h ,for delicate1 thin lines #g;,h-#h;,h-#i;,h ,,plain ,,ends1 ,,per ,,doz4 #a4jj ,,rubber ,,ends1 ,,per ,,doz4 #a4bj ,,venus ,,erasers #ab ,,sizes ,illustration ,of the same superb quality as the ,venus ,pencil ,send for free sample4 ,at all ,stationers and ,stores ,american ,lead ,pencil ,co4 #bbj ,fifth ,ave41 ,n4 ,y4 and ,london1 ,eng4 99 99 99 99 99 ,transcriber's ,notes3 page #bch3 changed diagramed to diagrammed 7,as there diagrammed1 the electricity passes out4447 page #bec3 the ,morse telegraph code is as in the original2 this is not the modern ,international ,morse code ,page #dab1 changed conrcete to concrete 7444 shall express this ideal in a very concrete way47 ,general3 variable spelling of iodin_/iodine in the original has been preserved ,general3 spelling of dioxid and chlorid in the original has been preserved